title: Accurate weak lensing of standard candles. I. Flexible cosmological fits

abstract:
  With the availability of thousands of type Ia supernovae in the near future
the magnitude scatter induced by lensing will become a major issue as it
affects parameter estimation. Current N-body simulations are too time consuming
to be integrated in the likelihood analyses used for estimating the
cosmological parameters. In this paper we show that in the weak lensing regime
a statistical numerical approximation produces accurate results orders of
magnitude faster. We write down simple fits to the second, third and fourth
central moments of the lensing magnification probability distribution as a
function of redshift, of the power spectrum normalization and of the
present-day matter density. We also improve upon existing models of lensing
variance and show that a shifted lognormal distribution fits well the numerical
one. These fits can be easily employed in cosmological likelihood analyses.
Moreover, our theoretical predictions make it possible to invert the problem
and begin using supernovae lensing to constrain the cosmological parameters.


title:
The XMM Deep survey in the CDFS V. Iron K lines from active galactic
  nuclei in the distant Universe

abstract:
  X-ray spectroscopy of active galactic nuclei (AGN) offers the opportunity to
directly probe the inner regions of the accretion disk. We present the results
of our analysis of average AGN XMM-Newton X-ray spectra in the Chandra Deep
Field South observation (XMM CDFS). We computed the average spectrum of a
sample of 54 AGN with spectroscopic redshifts and signal-to-noise ratio S/N >
15 in the 2-12 keV rest-frame band in at least one EPIC camera. We have taken
the effects of combining spectra from sources at different redshifts and both
EPIC cameras into account, as well as their spectral resolution; we checked our
results using thorough simulations. We explored the Fe line components of
distant AGN focusing on the narrow core which arises from regions far from the
central engine and on the putative relativistic component (from the accretion
disk). The average spectrum shows a highly significant Fe feature. Our
model-independent estimates of the equivalent width (EW) suggest a higher EW in
a broader range. The line, modelled as an unresolved Gaussian, is significant
at 6.8 sigma and has an EW=95 eV (full sample). The current data can be fitted
equally well adding a relativistic profile to the narrow component (in the full
sample, EW=140 eV and 67 eV respectively for the relativistic and narrow
lines). Thanks to the high quality of the XMM CDFS spectra and to the detailed
modelling of the continuum and instrumental effects, we have shown that the
most distant AGN exhibit a highly significant Fe emission feature. It can be
modelled both with narrow and broad lines. We found tantalising evidence for
reflection by material both very close and far away from the central engine.
The EW of both features are similar to those observed in individual nearby AGN,
hence they must be a widespread characteristic of AGN, since otherwise the
average values would be smaller than observed.


title:
Sivers effect and the single spin asymmetry A_N in p(transv. pol.) p -->
  h X processes

abstract:
  The single spin asymmetry A_N, for large P_T single inclusive particle
production in p(transv. pol.) p collisions, is considered within a generalised
parton model and a transverse momentum dependent factorisation scheme. The
focus is on the Sivers effect and the study of its potential contribution to
A_N, based on a careful analysis of the Sivers functions extracted from
azimuthal asymmetries in semi-inclusive deep inelastic scattering processes. It
is found that such Sivers functions could explain most features of the A_N
data, including some recent STAR results which show the persistence of a non
zero A_N up to surprisingly large P_T values.


title: Low-temperature Raman spectra of L-histidine crystal

abstract:
  We present a Raman spectroscopy investigation of the vibrational properties
of L-histidine crystals at low temperatures. The temperature dependence of the
spectra show discontinuities at 165 K, which we identify with modifications in
the bonds associated to both the NH3+ and CO2- motifs indicative of a
conformational phase transition that changes the intermolecular bonds.
Additional evidence of such a phase transition was provided by differential
scanning calorimetry measurements, which identified an enthalpic anomaly at
~165 K.


title: The Beachcombers' Problem: Walking and Searching with Mobile Robots

abstract:
  We introduce and study a new problem concerning the exploration of a
geometric domain by mobile robots. Consider a line segment $[0,I]$ and a set of
$n$ mobile robots $r_1,r_2,..., r_n$ placed at one of its endpoints. Each robot
has a {\em searching speed} $s_i$ and a {\em walking speed} $w_i$, where $s_i
<w_i$. We assume that each robot is aware of the number of robots of the
collection and their corresponding speeds. At each time moment a robot $r_i$
either walks along a portion of the segment not exceeding its walking speed
$w_i$ or searches a portion of the segment with the speed not exceeding $s_i$.
A search of segment $[0,I]$ is completed at the time when each of its points
have been searched by at least one of the $n$ robots. We want to develop {\em
mobility schedules} (algorithms) for the robots which complete the search of
the segment as fast as possible. More exactly we want to maximize the {\em
speed} of the mobility schedule (equal to the ratio of the segment length
versus the time of the completion of the schedule).
  We analyze first the offline scenario when the robots know the length of the
segment that is to be searched. We give an algorithm producing a mobility
schedule for arbitrary walking and searching speeds and prove its optimality.
Then we propose an online algorithm, when the robots do not know in advance the
actual length of the segment to be searched. The speed $S$ of such algorithm is
defined as $S = \inf_{I_L} S(I_L)$ where $S(I_L)$ denotes the speed of
searching of segment $I_L=[0,L]$. We prove that the proposed online algorithm
is 2-competitive. The competitive ratio is shown to be better in the case when
the robots' walking speeds are all the same.


title: Convex risk minimization via proximal splitting methods

abstract:
  In this paper we investigate the applicability of a recently introduced
primal-dual splitting method in the context of solving portfolio optimization
problems which assume the minimization of risk measures associated to different
convex utility functions. We show that, due to the splitting characteristic of
the used primal-dual method, the main effort in implementing it constitutes in
the calculation of the proximal points of the utility functions, which assume
explicit expressions in a number of cases. When quantifying risk via the
meanwhile classical Conditional Value-at-Risk, an alternative approach relying
on the use of its dual representation is presented as well. The theoretical
results are finally illustrated via some numerical experiments on real and
synthetic data sets.


title:
Observation of a diffractive contribution to dijet production in
  proton-proton collisions at $\sqrt{s} = 7$ TeV

abstract:
  The differential cross section measurement for dijet production at
proton-proton collisions at $\sqrt{s}=7$ TeV is presented as a function of an
approximation for the fractional momentum loss of the scattered proton
($\tilde{\xi}$), an useful observable to distinguish model predictions of
diffractive and nondiffractive components. The data was collected by the CMS
detector at low instantaneous luminosity runs at LHC, corresponding to an
integrated luminosity of $2.7 {\rm nb}^{-1}$. This is the first observation of
single diffractive dijets at LHC.


title: Spectral asymptotics of a strong $\delta'$ interaction on a planar loop

abstract:
  We consider a generalized Schr\"odinger operator in $L^2(\R^2)$ with an
attractive strongly singular interaction of $\delta'$ type characterized by the
coupling parameter $\beta>0$ and supported by a $C^4$-smooth closed curve
$\Gamma$ of length $L$ without self-intersections. It is shown that in the
strong coupling limit, $\beta\to 0_+$, the number of eigenvalues behaves as
$\frac{2L}{\pi\beta} + \OO(|\ln\beta|)$, and furthermore, that the asymptotic
behaviour of the $j$-th eigenvalue in the same limit is $-\frac{4}{\beta^2}
+\mu_j+\OO(\beta|\ln\beta|)$, where $\mu_j$ is the $j$-th eigenvalue of the
Schr\"odinger operator on $L^2(0,L)$ with periodic boundary conditions and the
potential $-\frac14 \gamma^2$ where $\gamma$ is the signed curvature of
$\Gamma$.


title: Drifting, moding, and nulling: another look at pulsar B1918+19

abstract:
  Arecibo observations of the conal triple pulsar B1918+19 at 0.327- and
1.4-GHz are used to analyse its subpulse behaviour in detail. We confirm the
presence of three distinct drift modes (A,B,C) plus a disordered mode (N) and
show that they follow one another in specific cycles. Interpreting the pulsar's
profile as resulting from a sightline traverse which cuts across an outer cone
and tangentially grazes an inner cone, we demonstrate that the phase modulation
of the inner cone is locked to the amplitude modulation of the outer cone in
all the drift modes. The 9% nulls are found to be largely confined to the
dominant B and N modes, and, in the N mode, create alternating bunches of nulls
and emission in a quasi-periodic manner with an averaged fluctuation rate of
about 12 rotation periods ($P_1$). We explore the assumption that the apparent
drift is the first alias of a faster drift of subbeams equally spaced around
the cones. This is shown to imply that all modes A, B and C have a common
circulation time of 12 $P_1$ and differ only in the number of subbeams. This
timescale is on the same order as predicted by the classic {\bf E}$\times${\bf
B} drift and also coincides with the N-mode modulation. We therefore arrive at
a picture where the circulation speed remains roughly invariant while the
subbeams progressively diminish in number from modes A to B to C, and are then
re-established during the N mode. We suggest that aliasing combined with
subbeam loss may be responsible for apparently dramatic changes in drift rates
in other pulsars.


title:
Constraints on a possible dibaryon from combined analysis of the $pn \to
  d \pi^+ \pi^-$ and $pn \to pn \pi^+ \pi^-$ cross sections

abstract:
  We use recent data that show a narrow peak around $\sqrt{s}=2.37\ \text{GeV}$
in the $pn \to d \pi^+ \pi^-$ cross section, with about double strength at the
peak than in the analogous $pn \to d \pi^0 \pi^0$ reaction, and, assuming that
it is due to the excitation of a dibaryon resonance, we evaluate the cross
section for the $pn \to pn \pi^+ \pi^-$ reaction, with the final $pn$ unbound
but with the same quantum numbers as the deuteron. We use accurate techniques
to determine the final state interaction in the case of the $pn$ forming a
deuteron or a positive energy state, which allow us to get the $pn \to pn \pi^+
\pi^-$ cross section with $pn$ in I=0 and S=1, that turns out to be quite close
or saturates the experimental $pn \to pn \pi^+ \pi^-$ total cross section
around $\sqrt{s} = 2.37\ \text{GeV}$, depending on the angular momentum
assumed. We then parametrize a background with different methods, and the sum
of the resonant and background contributions is fitted to present data. The
resulting cross section exceeds the experimental results in the region of the
resonant peak, showing a problem in the dibaryon hypothesis. Yet, in view of
the dispersion of present experimental data, and the scarce information around
$\sqrt{s} = 2.37\ \text{GeV}$, a call is made for precise measurements of the
$pn \to pn\pi^+\pi^-$ reaction around this energy, to further clarify this
issue.


title:
Unified formalism for higher-order variational problems and its
  applications in optimal control

abstract:
  In this paper we consider an intrinsic point of view to describe the
equations of motion for higher-order variational problems with constraints on
higher-order trivial principal bundles. Our techniques are an adaptation of the
classical Skinner-Rusk approach for the case of Lagrangian dynamics with
higher-order constraints. We study a regular case where it is possible to
establish a symplectic framework and, as a consequence, to obtain a unique
vector field determining the dynamics. As an interesting application we deduce
the equations of motion for optimal control of underactuated mechanical systems
defined on principal bundles.


title:
Information-theoretic tools for parametrized coarse-graining of
  non-equilibrium extended systems

abstract:
  In this paper we focus on the development of new methods suitable for
efficient and reliable coarse-graining of {\it non-equilibrium} molecular
systems. In this context, we propose error estimation and controlled-fidelity
model reduction methods based on Path-Space Information Theory, and combine it
with statistical parametric estimation of rates for non-equilibrium stationary
processes. The approach we propose extends the applicability of existing
information-based methods for deriving parametrized coarse-grained models to
Non-Equilibrium systems with Stationary States (NESS). In the context of
coarse-graining it allows for constructing optimal parametrized Markovian
coarse-grained dynamics, by minimizing information loss (due to
coarse-graining) on the path space. Furthermore, the associated path-space
Fisher Information Matrix can provide confidence intervals for the
corresponding parameter estimators. We demonstrate the proposed coarse-graining
method in a non-equilibrium system with diffusing interacting particles, driven
by out-of-equilibrium boundary conditions.

categories: physics.comp-ph cs.IT math.IT physics.data-an


title: Dynamic Bowtie for Fan-beam CT

abstract:
  A bowtie is a filter used to shape an x-ray beam and equalize its flux
reaching different detector channels. For development of spectral CT with
energy-discriminative photon-counting (EDPC) detectors, here we propose and
evaluate a dynamic bowtie for performance optimization based on a patient model
or a scout scan. Our dynamic bowtie modifies an x-ray beam intensity profile by
mechanical rotation and adaptive adjustment of the x-ray source flux. First, a
mathematical model for dynamic bowtie filtering is established for an
elliptical section in fan-beam geometry, and the contour of the optimal bowtie
is derived. Then, numerical simulation is performed to compare the performance
of the dynamic bowtie in the cases of an ideal phantom and a realistic
cross-section relative to the counterparts without any bowtie and with a fixed
bowtie respectively. Our dynamic bowtie can equalize the expected numbers of
photons in the case of an ideal phantom. In practical cases, our dynamic bowtie
can effectively reduce the dynamic range of detected signals inside the field
of view. Although our design is optimized for an elliptical phantom, the
resultant dynamic bowtie can be applied to a real fan-beam scan if the
underlying cross-section can be approximated as an ellipse. Furthermore, our
design methodology can be applied to specify an optimized dynamic bowtie for
any cross-section of a patient, preferably using rapid prototyping technology.
This fan-beam dynamic bowtie work could be extended to the cone-beam geometry
in a follow-up study.


title: Localized defect modes in graphene

abstract:
  We study the properties of localized vibrational modes associated with
structural defects in a sheet of graphene. For the example of the Stone-Wales
defects, one- and two-atom vacancies, many-atom linear vacancies, and adatoms
in a honeycomb lattice, we demonstrate that the local defect modes are
characterized by stable oscillations with the frequencies lying outside the
linear frequency bands of an ideal graphene. In the frequency spectral density
of thermal oscillations, such localized defect modes lead to the additional
peaks from the right side of the frequency band of the ideal sheet of graphene.
Thus, the general structure of the frequency spectral density can provide a
fingerprint of its quality and the type of quantity of the structural defect a
graphene sheet may contain.


title:
Air pollution forecasting by coupled atmosphere-fire model WRF and SFIRE
  with WRF-Chem

abstract:
  Atmospheric pollution regulations have emerged as a dominant obstacle to
prescribed burns. Thus, forecasting the pollution caused by wildland fires has
acquired high importance. WRF and SFIRE model wildland fire spread in a two-way
interaction with the atmosphere. The surface heat flux from the fire causes
strong updrafts, which in turn change the winds and affect the fire spread.
Fire emissions, estimated from the burning organic matter, are inserted in
every time step into WRF-Chem tracers at the lowest atmospheric layer. The
buoyancy caused by the fire then naturally simulates plume dynamics, and the
chemical transport in WRF-Chem provides a forecast of the pollution spread. We
discuss the choice of wood burning models and compatible chemical transport
models in WRF-Chem, and demonstrate the results on case studies.


title:
Single impurities in a Bose-Einstein condensate can make two polaron
  flavors

abstract:
  Polarons, self-localized composite objects formed by the interaction of a
single impurity particle with a host medium, are a paradigm of strong
interaction many-body physics. We show that dilute gas Bose-Einstein
condensates (BEC's) are the first medium known to self-localize the same
impurity particles both in a Landau-Pekar polaron state akin to that of
self-localized electrons in a dielectric lattice, and in a bubble state akin to
that of electron bubbles in helium. We also show that the BEC-impurity system
is fully characterized by just two dimensionless coupling constants, and that
it can be adiabatically steered from the Landau-Pekar regime to the bubble
regime in a smooth crossover trajectory.


title: Computing higher homotopy groups is W[1]-hard

abstract:
  Recently it was shown that, for every fixed k>1, given a finite simply
connected simplicial complex X, the kth homotopy group \pi_k(X) can be computed
in time polynomial in the number n of simplices of X. We prove that this
problem is W[1]-hard w.r.t. the parameter k even for X of dimension 4, and thus
very unlikely to admit an algorithm with running time bound f(k)n^C for an
absolute constant C. We also simplify, by about 20 pages, a 1989 proof by Anick
that, with k part of input, the computation of the rank of \pi_k(X) is #P-hard.


title:
Lorentz-Violating Regulator Gauge Fields as the Origin of Dynamical
  Flavour Oscillations

abstract:
  We show how a mass mixing matrix can be generated dynamically, for two
massless fermion flavours coupled to a Lorentz invariance violating (LIV) gauge
field. The LIV features play the role of a regulator for the gap equations, and
the non-analytic dependence of the dynamical masses, as functions of the gauge
coupling, allows to consider the limit where the LIV gauge field eventually
decouples from the fermions. Lorentz invariance is then recovered, to describe
the oscillation between two free fermion flavours, and we check that the finite
dynamical masses are the only effects of the original LIV theory. We also
discuss briefly a connection of our results with the case of Majorana neutrinos
in both, the standard model, where only left-handed (active) neutrinos are
considered, and extensions thereof, with sterile right-handed neutrinos.


title: Precovering and preenveloping ideals

abstract:
  L. Salce introduced the notion of a cotorsion pair (F,C) in the category of
abelian groups. But his definitions and basic results carry over to more
general abelian categories and have proven useful in a variety of settings. A
significant result of cotorsion theory proven by Eklof and Trlifaj is that if a
pair (F,C) of classes of R-modules is cogenerated by a set, then it is
complete. Recently Herzog, Fu, Asensio and Torrecillas developed the ideal
approximation theory. In this article we look at a result motivated by the
Eklof-Trlifaj argument for an ideal I when it is generated by a set of
homomorphisms.


title: Bulk Synthesis of Iron-based Superconductors

abstract:
  Exploratory synthesis efforts for iron-based superconductors (FeSC) have been
driven by hopes of improving superconducting critical temperatures (TCs),
providing high-quality samples for in-depth studies of intrinsic properties,
and exploring potential superconductivity in similar families of materials.
This manuscript summarizes the synthesis routes that are used for producing
FeSC and their undoped parents, in single crystal and polycrystalline forms. A
few of the materials challenges are summarized.


title: A note on Gabor frames in finite dimensions

abstract:
  The purpose of this note is to present a proof of the existence of Gabor
frames in general linear position in all finite dimensions. The tools developed
in this note are also helpful towards an explicit construction of such a frame,
which is carried out in the last section. This result has applications in
signal recovery through erasure channels, operator identification, and
time-frequency analysis.


title:
Learning Geo-Temporal Non-Stationary Failure and Recovery of Power
  Distribution

abstract:
  Smart energy grid is an emerging area for new applications of machine
learning in a non-stationary environment. Such a non-stationary environment
emerges when large-scale failures occur at power distribution networks due to
external disturbances such as hurricanes and severe storms. Power distribution
networks lie at the edge of the grid, and are especially vulnerable to external
disruptions. Quantifiable approaches are lacking and needed to learn
non-stationary behaviors of large-scale failure and recovery of power
distribution. This work studies such non-stationary behaviors in three aspects.
First, a novel formulation is derived for an entire life cycle of large-scale
failure and recovery of power distribution. Second, spatial-temporal models of
failure and recovery of power distribution are developed as geo-location based
multivariate non-stationary GI(t)/G(t)/Infinity queues. Third, the
non-stationary spatial-temporal models identify a small number of parameters to
be learned. Learning is applied to two real-life examples of large-scale
disruptions. One is from Hurricane Ike, where data from an operational network
is exact on failures and recoveries. The other is from Hurricane Sandy, where
aggregated data is used for inferring failure and recovery processes at one of
the impacted areas. Model parameters are learned using real data. Two findings
emerge as results of learning: (a) Failure rates behave similarly at the two
different provider networks for two different hurricanes but differently at the
geographical regions. (b) Both rapid- and slow-recovery are present for
Hurricane Ike but only slow recovery is shown for a regional distribution
network from Hurricane Sandy.


title:
Substructures from weak interactions in light of possible threshold
  signals at LEP and LHC

abstract:
  We present indications of possible substructures from weak interactions, by
inspecting LEP and LHC date and inferring threshold effects due to the
production of pairs of composite heavy gauge bosons W+-, Z and their
hypothetical partners with different spin. Thus, we find possible evidence of
scalar or pseudoscalar partners of the W+- and the Z, viz. at 53 and 57 GeV,
respectively. Additionally, data may indicate excited states of the Z at 210
and 240 GeV.


title:
Guaranteed and Sharp a Posteriori Error Estimates in Isogeometric
  Analysis

abstract:
  We present functional-type a posteriori error estimates in isogeometric
analysis. These estimates, derived on functional grounds, provide guaranteed
and sharp upper bounds of the exact error in the energy norm. {Moreover, since
these estimates do not contain any unknown/generic constants, they are fully
computable, and thus provide quantitative information on the error.} By
exploiting the properties of non-uniform rational B-splines, we present
efficient computation of these error estimates. The numerical realization and
the quality of the computed error distribution are addressed. The potential and
the limitations of the proposed approach are illustrated using several
computational examples.


title:
Markovian models for one dimensional structure estimation on heavily
  noisy imagery

abstract:
  Radar (SAR) images often exhibit profound appearance variations due to a
variety of factors including clutter noise produced by the coherent nature of
the illumination. Ultrasound images and infrared images have similar cluttered
appearance, that make 1 dimensional structures, as edges and object boundaries
difficult to locate. Structure information is usually extracted in two steps:
first, building and edge strength mask classifying pixels as edge points by
hypothesis testing, and secondly estimating from that mask, pixel wide
connected edges. With constant false alarm rate (CFAR) edge strength detectors
for speckle clutter, the image needs to be scanned by a sliding window composed
of several differently oriented splitting sub-windows. The accuracy of edge
location for these ratio detectors depends strongly on the orientation of the
sub-windows. In this work we propose to transform the edge strength detection
problem into a binary segmentation problem in the undecimated wavelet domain,
solvable using parallel 1d Hidden Markov Models. For general dependency models,
exact estimation of the state map becomes computationally complex, but in our
model, exact MAP is feasible. The effectiveness of our approach is demonstrated
on simulated noisy real-life natural images with available ground truth, while
the strength of our output edge map is measured with Pratt's, Baddeley an Kappa
proficiency measures. Finally, analysis and experiments on three different
types of SAR images, with different polarizations, resolutions and textures,
illustrate that the proposed method can detect structure on SAR images
effectively, providing a very good start point for active contour methods.


title: Forcing With Copies of Countable Ordinals

abstract:
  Let \alpha be a countable ordinal and \P(\alpha) the collection of its
subsets isomorphic to \alpha. We show that the separative quotient of the set
\P (\alpha) ordered by the inclusion is isomorphic to a forcing product of
iterated reduced products of Boolean algebras of the form P(\omega
^\gamma)/I(\omega ^\gamma), where \gamma is a limit ordinal or 1 and I(\omega
^\gamma) the corresponding ordinal ideal. Moreover, the poset \P(\alpha) is
forcing equivalent to a two-step iteration P(\omega)/Fin * \pi, where \pi is an
\omega_1-closed separative pre-order in each extension by P(\omega)/Fin and, if
the distributivity number is equal to\omega_1, to P(\omega)/Fin. Also we
analyze the quotients over ordinal ideals P(\omega ^\delta)/I(\omega ^\delta)
and their distributivity and tower numbers.


title:
Slowing evolution is more effective than enhancing drug development for
  managing resistance

abstract:
  Drug resistance is a serious public health problem that threatens to thwart
our ability to treat many infectious diseases. Repeatedly, the introduction of
new drugs has been followed by the evolution of resistance. In principle there
are two ways to address this problem: (i) enhancing drug development, and (ii)
slowing drug resistance. We present data and a modeling approach based on
queueing theory that explores how interventions aimed at these two facets
affect the ability of the entire drug supply system to provide service.
Analytical and simulation-based results show that, all else equal, slowing the
evolution of drug resistance is more effective at ensuring an adequate supply
of effective drugs than is enhancing the rate at which new drugs are developed.
This lends support to the idea that evolution management is not only a
significant component of the solution to the problem of drug resistance, but
may in fact be the most important component.


title:
Night sky photometry and spectroscopy performed at the Vienna University
  Observatory

abstract:
  We present night sky brightness measurements performed at the Vienna
University Observatory and at the Leopold-Figl-Observatorium fuer Astrophysik,
which is located about 35km to the southwest of Vienna. The measurements have
been performed with Sky Quality Meters made by Unihedron. They cover a time
span of roughly one year and have been carried out every night, yielding a
night sky brightness value every 7 seconds and thus delivering a large amount
of data. In this paper, the level of light pollution at the Vienna University
Observatory, which ranges from 15 to 19.25 magnitudes per square arcsecond, is
presented for the very first time in a systematic way. We discuss the influence
of different environmental conditions on the night sky brightness and
implications for human vision. We show that the circalunar rhythm of night sky
brightness is extinguished at our observatory due to light pollution.
  Additionally, we present spectra of the night sky in Vienna, taken with a
0.8m telescope. The goal of these spectroscopic measurements was to identify
the main types of light sources and the spectral lines which cause the light
pollution in Vienna. It turned out that fluorescent lamps are responsible for
the strongest lines of the night sky above Vienna (e.g. lines at 546 nm and at
611 nm).


title: The Randomized Dependence Coefficient

abstract:
  We introduce the Randomized Dependence Coefficient (RDC), a measure of
non-linear dependence between random variables of arbitrary dimension based on
the Hirschfeld-Gebelein-R\'enyi Maximum Correlation Coefficient. RDC is defined
in terms of correlation of random non-linear copula projections; it is
invariant with respect to marginal distribution transformations, has low
computational cost and is easy to implement: just five lines of R code,
included at the end of the paper.


title: A Dynamic Axiomatic Approach to First-Price Auctions

abstract:
  The first-price auction is popular in practice for its simplicity and
transparency. Moreover, its potential virtues grow in complex settings where
incentive compatible auctions may generate little or no revenue. Unfortunately,
the first-price auction is poorly understood in theory because equilibrium is
not {\em a priori} a credible predictor of bidder behavior.
  We take a dynamic approach to studying first-price auctions: rather than
basing performance guarantees solely on static equilibria, we study the
repeated setting and show that robust performance guarantees may be derived
from simple axioms of bidder behavior. For example, as long as a loser raises
her bid quickly, a standard first-price auction will generate at least as much
revenue as a second-price auction. We generalize this dynamic technique to
complex pay-your-bid auction settings and show that progressively stronger
assumptions about bidder behavior imply progressively stronger guarantees about
the auction's performance.
  Along the way, we find that the auctioneer's choice of bidding language is
critical when generalizing beyond the single-item setting, and we propose a
specific construction called the {\em utility-target auction} that performs
well. The utility-target auction includes a bidder's final utility as an
additional parameter, identifying the single dimension along which she wishes
to compete. This auction is closely related to profit-target bidding in
first-price and ascending proxy package auctions and gives strong revenue
guarantees for a variety of complex auction environments. Of particular
interest, the guaranteed existence of a pure-strategy equilibrium in the
utility-target auction shows how Overture might have eliminated the cyclic
behavior in their generalized first-price sponsored search auction if bidders
could have placed more sophisticated bids.


title: On the Popov-Pommerening conjecture for linear algebraic groups

abstract:
  Let $G$ be a reductive group over an algebraically closed subfield $k$ of
$\mathbb{C}$ of characteristic zero, $H \subseteq G$ an observable subgroup
normalized by a maximal torus of $G$ and $X$ an affine $k$-variety acted on by
$G$. Popov and Pommerening conjectured in the late 70's that the invariant
algebra $k[X]^H$ is finitely generated. We prove the conjecture for 1)
subgroups of $\mathrm{SL}_n(k)$ closed under left (or right) Borel action and
for 2) a class of Borel regular subgroups of classical groups. We give a
partial affirmative answer to the conjecture for general regular subgroups of
$\mathrm{SL}_n(k)$.


title:
The distorted axi-planar superfluid phase of $^3$He in the "nematically
  ordered" aerogel

abstract:
  Stimulated by the results of NMR experiments with superfluid $^3$He in
"nematically ordered" aerogel [1] we report on the results of phenomenological
analysis of stability of different phases of superfluid $^3$He subjected to a
strong homogeneous uniaxial anisotropy. On a basis of this analysis we suggest
a form of the order parameter for the new ESP2 phase observed in the quoted
experiments. In the weak coupling limit the suggested order parameter
approaches that of the axi-planar phase. We discuss a possible experimental
check of the proposed identification of the new phase.


title: SOX: Short distance neutrino Oscillations with BoreXino

abstract:
  The very low radioactive background of the Borexino detector, its large size,
and the well proved capability to detect both low energy neutrino and
anti-neutrino make an ideal case for the study of short distance neutrino
oscillations with artificial sources at Gran Sasso. This paper describes the
possible layouts of 51Cr neutrino and 144Ce-144Pr anti-neutrino source
experiments in Borexino and shows the expected sensitivity for three possible
different phases of the experiment.


title:
Non-thermal X-rays and interstellar gas toward the \gamma-ray supernova
  remnant RX J1713.7-3946: Evidence for X-ray enhancement around CO and HI
  clumps

abstract:
  RX J1713.7-3946 is the most remarkable very-high-energy \gamma-ray supernova
remnant which emits synchrotron X-rays without thermal features. We made a
comparative study of CO, HI and X-rays in order to better understand the
relationship between the X-rays, and the molecular and atomic gas. The results
indicate that the X-rays are enhanced around the CO and HI clumps on a pc scale
but are decreased inside the clumps on a 0.1 pc scale. Magnetohydrodynamic
numerical simulations of the shock interaction with molecular and atomic gas
indicate that the interaction between the shock waves and the clumps excite
turbulence which amplifies the magnetic field around the clumps (Inoue et al.
2012). We suggest that the amplified magnetic field around the CO and HI clumps
enhances the synchrotron X-rays and possibly the acceleration of cosmic-ray
electrons.


title: Multi-matrix models at general coupling

abstract:
  The eigenvalue distribution of Hoppe's two matrix model is investigated in
detail as a function of the model's coupling. For small couplings it is a
perturbed Wigner semicircle, while for large couplings it is a parabolic
distribution which crosses over to a Wigner semicircle for eigenvalues within
approximatley an inverse coupling from the boundary of the distribution. The
model is approximately commuting at large couplings and we find the joint
eigenvalue distribution of the two matrices. We also study a related three
matrix model finding the corresponding three dimensional eigenvalue
distribution there also. The techniques developed here are more widely
applicable to other multi-matrix models.


title: The kinematics of the diffuse ionized gas in NGC 4666

abstract:
  The global properties of the interstellar medium with processes such as
infall and outflow of gas and a large scale circulation of matter and its
consequences for star formation and chemical enrichment are important for the
understanding of galaxy evolution. In this paper we studied the kinematics and
morphology of the diffuse ionized gas (DIG) in the disk and in the halo of the
star forming spiral galaxy NGC 4666 to derive information about its kinematical
properties. Especially, we searched for infalling and outflowing ionized gas.
We determined surface brightness, radial velocity, and velocity dispersion of
the warm ionized gas via high spectral resolution (R ~ 9000) Fabry-P\'erot
interferometry. This allows the determination of the global velocity field and
the detection of local deviations from this verlocity field. We calculated
models of the DIG distribution and its kinematics for comparison with the
measured data. In this way we determined fundamental parameters such as the
inclination and the scale height of NGC 4666, and established the need for an
additional gas component to fit our observed data. We found individual areas,
especially along the minor axis, with gas components reaching into the halo
which we interpret as an outflowing component of the diffuse ionized gas. As
the main result of our study, we were able to determine that the vertical
structure of the DIG distribution in NGC 4666 is best modeled with two
components of ionized gas, a thick and a thin disk with 0.8 kpc and 0.2 kpc
scale height, respectively. Therefore, the enhanced star formation in NGC 4666
drives an outflow and also maintains a thick ionized gas layer reminiscent of
the Reynold's layer in the Milky Way.


title: Spread of correlations in long-range interacting quantum systems

abstract:
  The non-equilibrium response of a quantum many-body system defines its
fundamental transport properties and how initially localized quantum
information spreads. However, for long-range-interacting quantum systems little
is known. We address this issue by analyzing a local quantum quench in the
long-range Ising model in a transverse field, where interactions decay as a
variable power-law with distance $\propto r^{-\alpha}$, $\alpha>0$. Using
complementary numerical and analytical techniques, we identify three dynamical
regimes: short-range-like with an emerging light cone for $\alpha>2$; weakly
long-range for $1<\alpha<2$ without a clear light cone but with a finite
propagation speed of almost all excitations; and fully non-local for $\alpha<1$
with instantaneous transmission of correlations. This last regime breaks
generalized Lieb--Robinson bounds and thus locality. Numerical calculation of
the entanglement spectrum demonstrates that the usual picture of propagating
quasi-particles remains valid, allowing an intuitive interpretation of our
findings via divergences of quasi-particle velocities. Our results may be
tested in state-of-the-art trapped-ion experiments.

categories: quant-ph cond-mat.quant-gas cond-mat.stat-mech cond-mat.str-el


title: Universal valued fields and lifting points in local tropical varieties

abstract:
  Let $k$ be a field with a real valuation $\nu$ and $R$ a $k$-algebra. We show
that there exist a $k$-algebra $K$ and a real valuation $\mu$ on $K$ extending
$\nu$ such that any real ring valuation of $R$ is induced by $\mu$ via some
homomorphism from $R$ to $K$; $K$ can be chosen to be a field. Then we study
the case when $\nu$ is trivial and $R$ a complete local Noetherian ring with
the residue field $k$. Let $K$ be the ring $\bar{k}[[t^\R]]$ of Hahn series
with its natural valuation $\mu$; $\bar{k}$ is an algebraic closure of $k$.
Despite $K$ is not universal in the strong sense defined above, it has the
following weak universality property: for any local valuation $v$ and a finite
set of elements $x_1,...,x_n$ of $R$ there exists a homomorphism $f\colon R\to
K$ such that $v(x_i)=\mu(f(x_i))$, $i=1,...,n$. If $R=k[[x_1,...,x_n]]/I$ for
an ideal $I$, this property implies that every point of the local tropical
variety of $I$ lifts to a $K$-point of $R$. Similarly, if $R=k[x_1,...,x_n]/I$
is a finitely generated algebra over $k$, lifting points in the tropical
variety of $I$ can be interpreted as the weak universality property of the
field $\bar{k}((t^\R))$ of Hahn series.


title: Distributed stochastic optimization via correlated scheduling

abstract:
  This paper considers a problem where multiple users make repeated decisions
based on their own observed events. The events and decisions at each time step
determine the values of a utility function and a collection of penalty
functions. The goal is to make distributed decisions over time to maximize time
average utility subject to time average constraints on the penalties. An
example is a collection of power constrained sensor nodes that repeatedly
report their own observations to a fusion center. Maximum time average utility
is fundamentally reduced because users do not know the events observed by
others. Optimality is characterized for this distributed context. It is shown
that optimality is achieved by correlating user decisions through a commonly
known pseudorandom sequence. An optimal algorithm is developed that chooses
pure strategies at each time step based on a set of time-varying weights.


title: Machine Translation Systems in India

abstract:
  Machine Translation is the translation of one natural language into another
using automated and computerized means. For a multilingual country like India,
with the huge amount of information exchanged between various regions and in
different languages in digitized format, it has become necessary to find an
automated process from one language to another. In this paper, we take a look
at the various Machine Translation System in India which is specifically built
for the purpose of translation between the Indian languages. We discuss the
various approaches taken for building the machine translation system and then
discuss some of the Machine Translation Systems in India along with their
features.


title:
Interlayer magnetoresistance in multilayer Dirac electron systems:
  motion and merging of Dirac cones

abstract:
  We theoretically study the effect of the motion and the merging of Dirac cone
on the interlayer magnetoresistance in multilayer graphene like systems. This
merging, which could be induced by a uniaxial strain, gives rise in monolayer
Dirac electron system to a topological transition from a semi-metallic phase to
an insulating phase where Dirac points disappear. Based on a universal
Hamiltonian proposed to describe the motion and the merging of Dirac points in
two dimensional Dirac electron crystals, we calculate the interlayer
conductivity of a stack of deformed graphene like layers using Kubo formula in
the quantum limit where only the contribution of the $n=0$ Landau level is
relevant. A crossover from a negative to a positive interlayer
magnetoresistance is found to take place as the merging is approached. This
sign change of the magnetoresistance could also result from a coupling between
the Dirac valleys which is enhanced as the magnetic field amplitude increases.
Our results may describe the behavior of the magnetotransport in the organic
conductor $\alpha$-(BEDT)$_2$I$_3$ at high pressure where the merging of Dirac
cones could be observed.


title: GEMs and amplitude bounds in the colored Boulatov model

abstract:
  In this paper we construct a methodology for separating the divergencies due
to different topological manifolds dual to Feynman graphs in colored group
field theory. After having introduced the amplitude bounds using propagator
cuts, we show how Graph-Encoded-Manifolds (GEM) techniques can be used in order
to factorize divergencies related to different parts of the dual topologies of
the Feynman graphs in the general case. We show the potential of the formalism
in the case of 3-dimensional solid torii in the colored Boulatov model.


title:
High temperature Bose-Einstein condensation into an excited state at
  equilibrium

abstract:
  We describe Bose-Einstein condensation of strongly interacting particles into
a quantum state which is an excited single-particle state, but becomes the
ground state as density increases because it minimizes the interaction energy
compared to other states. Mean field calculations for a graphene potential just
wide enough for two closely interacting layers of molecular hydrogen show
condensation at temperatures up to 60 K. In the condensed state, molecules hop
between layers, increasing the first peak in the pair-correlation function just
past the hard core repulsion diameter.


title:
Interpretation of magnetoelectric phase states using the praphase
  concept and exchange symmetry

abstract:
  The majority of magnetoelectric crystals show complex temperature-magnetic
field or temperature-pressure phase diagrams with alternating antiferromagnetic
incommensurate, magnetoelectric, and commensurate phases. Such phase diagrams
occur as a result of successive magnetic instabilities with respect to
different order parameters, which usually transform according to different
irreducible representations (IR) of the space group of the crystal. Therefore,
in order to build a phenomenological theory of phase transitions in such
magnetoelectrics one has to employ several order parameters and assume the
proximity of various instabilities on the thermodynamic path. In this work we
analyze the magnetoelectrics MnWO4, CuO, NaFeSi2O6, NaFeGe2O6, Cu3Nb2O8,
alpha-CaCr2O4, and FeTe2O5Br using the praphase concept and the symmetry of the
exchange Hamiltonian. We find that in all the considered cases the appearing
magnetic structures are described by IR's entering into a single exchange
multiplet, whereas in the cases of MnWO4 and CuO by a single IR of the space
group of the praphase structure. Therefore, one can interpret the complex phase
diagrams of magnetoelectrics as induced by a single IR either of the praphase
or of the symmetry group of the exchange Hamiltonian. Detailed
temperature-magnetic field phase diagrams of MnWO4 and CuO for certain field
directions are obtained and the magnetic structures of the field-induced phases
are determined.


title: Functional-Friction Networks: New Insights on the Laboratory Earthquakes

abstract:
  We report some new applications of functional complex networks on acoustic
emission waveforms from frictional interfaces. Our results show that laboratory
faults undergo a sequence of generic phases as well as strengthening, weakening
or fast-slip and slow-slip leading to healing. Also, using functional networks,
we extend the dissipated energy due to acoustic emission signals in terms of
short-term and long-term features of events. We show that the transition from
regular to slow ruptures can have an additional production from the critical
rupture class similar to the direct observations of this phenomenon in the
transparent samples. Furthermore, we demonstrate detailed sub-micron evolution
of the interface due to the short-term evolution of rupture tip, which is
represented by phenomenological description of the modularity rates. In
addition, we found nucleation phase of each single event for most amplified
events follows a nearly constant time scale, corresponding to initial
strengthening of interfaces.


title: On the self-regulation of intense star-formation in galaxies at z=1-3

abstract:
  (abridged) We have analyzed the properties of the rest-frame optical emission
lines of a sample of 53 intensely star forming galaxies at z=1.3 to 2.7
observed with SINFONI on the ESO-VLT. We find large velocity dispersions in the
lines, sigma=30-250 km/s. Our data agree well with simulations where we applied
beam-smearing and assumed a scaling relation of the form: velocity dispersion
is proportional to the square root of the star-formation intensity
(star-formation rate per unit area). We conclude that the dispersions are
primarily driven by star formation. To explain the high surface brightness and
optical line ratios, high thermal pressures in the warm ionized medium, WIM,
are required (log P/k (K/cm^3)>~6-7). Such thermal pressures in the WIM are
similar to those observed in nearby starburst galaxies, but occur over much
larger physical scales. Moreover, the relatively low ionization parameters
necessary to fit the high surface brightnesses and optical line ratios suggest
that the gas is not only directly associated with regions of star formation,
but is wide spread throughout the general ISM. Thus the optical emission line
gas is a tracer of the large scale dynamics of the bulk of the ISM. We present
a simple model for the energy input from young stars in an accreting galaxy, to
argue that the intense star-formation is supporting high turbulent pressure,
which roughly balances the gravitational pressure and thus enables distant gas
accreting disks to maintain a Toomre disk instability parameter Q~1. For a star
formation efficiency of 3%, only 5-15% of the mechanical energy from young
stars that is deposited in the ISM is needed to support the level of turbulence
required for maintaining this balance. Since this balance is maintained by
energy injected into the ISM by the young stars themselves, this suggests that
star formation in high redshift galaxies is self-regulating.


title: Phase retrieval for imaging problems

abstract:
  We study convex relaxation algorithms for phase retrieval on imaging
problems. We show that structural assumptions on the signal and the
observations, such as sparsity, smoothness or positivity, can be exploited to
both speed-up convergence and improve recovery performance. We detail
experimental results in molecular imaging problems simulated from PDB data.


title: The supernova/gamma-ray burst/jet connection

abstract:
  The observed association between supernovae and gamma-ray bursts represents a
cornerstone in our understanding of the nature of gamma-ray bursts. The
collapsar model provides a theoretical framework for this connection. A key
element is the launch of a bi-polar jet (seen as a gamma-ray burst). The
resulting hot cocoon disrupts the star while the 56Ni produced gives rise to
radioactive heating of the ejecta, seen as a supernova. In this discussion
paper I summarise the observational status of the supernova/gamma-ray burst
connection in the context of the 'engine' picture of jet-driven supernovae and
highlight SN 2012bz/GRB 120422A -- with its luminous supernova but intermediate
high-energy luminosity -- as a possible transition object between
low-luminosity and jet gamma-ray bursts. The jet channel for supernova
explosions may provide new insight into supernova explosions in general.


title:
Shubnikov-de Haas effect in low electron density SrTiO3: Conduction band
  edge of SrTiO3 redux

abstract:
  The Shubnikov-de Haas effect is used to explore the conduction band edge of
high mobility SrTiO3 films doped with La. The results largely confirm the
earlier measurements by Uwe et al. [Jap. J. Appl. Phys. 24, Suppl. 24-2, 335
(1985)]. The band edge dispersion differs significantly from the predictions of
ab initio electronic structure theory.


title: Relating neutrino masses and mixings by discrete symmetries

abstract:
  Lepton mixing can originate from the breaking of a flavor symmetry in
different ways in the neutrino and the charged lepton sector. We propose an
extension of this framework which allows to connect the mixing parameters with
masses, and more precisely, with certain types of degeneracy of the neutrino
mass spectrum. We obtain relations between the mixing parameters for the cases
of partial degeneracy, m1 = m2, and complete degeneracy, m1 = m2 = m3. These
relations determine also the Majorana phases. It is shown that relatively small
corrections to these lowest order results can produce the required mass
splitting and modify the mixing without significant changes of the other
symmetry results.


title: Unconventional superconductivity on the triangular lattice Hubbard model

abstract:
  Using large-scale dynamical cluster quantum Monte Carlo simulations, we
explore the unconventional superconductivity in the hole-doped Hubbard model on
the triangular lattice. Due to the interplay of electronic correlations,
geometric frustration, and Fermi surface topology, we find a doubly degenerate
singlet pairing state at an interaction strength close to the bare bandwidth.
Such an unconventional superconducting state is mediated by antiferromagnetic
spin fluctuations along the $\Gamma$-$K$ direction, where the Fermi surface is
nested. An exact decomposition of the irreducible particle-particle vertex
further confirms the dominant component of the effective pairing interaction
comes from the spin channel. Our findings provide support for chiral $d +i d$
superconductivity in water-intercalated sodium cobaltates Na$_{x}$CoO$_{2}
\cdot y$H$_{2}$O, as well as insight into the superconducting phases of the
organic compounds $\kappa$-(ET)$_{2}$X and Pd(dmit)$_{2}$.


title:
The Mixed Spin 3 - Spin 3/2 Ferrimagnetic Ising Model on Cellular
  Automaton

abstract:
  The mixed spin 3- spin 3/2 Ising model has been simulated using cooling
algorithm on cellular automaton (CA). The simulations have been made in the
interval -6<=D<=6 for J=1 for the square lattices with periodic boundary
conditions. The ground state phase diagram of the model has different type
ferrimagnetic orderings. Through D/J=2 line, compensation points occurs at
kT/J=0. The values of the critical exponents ( {\nu}, {\alpha}, {\beta} and
{\gamma}) are estimated within the framework of the finite-size scaling theory
and power law relations for selected D/J values (-2, 0, 1, 2 and 4). The
estimated critical exponent values are in a good agreement with their universal
values of the two dimensional Ising model.


title:
Measurement of the Parity-Violating Asymmetry in Electron-Deuteron
  Scattering in the Nucleon Resonance Region

abstract:
  We report on parity-violating asymmetries in the nucleon resonance region
measured using $5 - 6$ GeV longitudinally polarized electrons scattering off an
unpolarized deuterium target. These results are the first parity-violating
asymmetry data in the resonance region beyond the $\Delta(1232)$, and provide a
verification of quark-hadron duality in the nucleon electroweak $\gamma Z$
interference structure functions at the (10-15)% level. The results are of
particular interest to models relevant for calculating the $\gamma Z$
box-diagram corrections to elastic parity-violating electron scattering
measurements.


title: Heterotic non-Abelian orbifolds

abstract:
  We perform the first systematic analysis of particle spectra obtained from
heterotic string compactifications on non-Abelian toroidal orbifolds. After
developing a new technique to compute the particle spectrum in the case of
standard embedding based on higher dimensional supersymmetry, we compute the
Hodge numbers for all recently classified 331 non-Abelian orbifold geometries
which yield N=1 supersymmetry for heterotic compactifications. Surprisingly,
most Hodge numbers follow the empiric pattern h^(1,1) - h^(2,1) = 0 mod 6,
which might be related to the number of three standard model generations.
Furthermore, we study the fundamental groups in order to identify the
possibilities for non-local gauge symmetry breaking. Three examples are
discussed in detail: the simplest non-Abelian orbifold S_3 and two more
elaborate examples, T_7 and \Delta(27), which have only one untwisted Kaehler
and no untwisted complex structure modulus. Such models might be especially
interesting in the context of no-scale supergravity. Finally, we briefly
discuss the case of orbifolds with vanishing Euler numbers in the context of
enhanced (spontaneously broken) supersymmetry.


title: Dilaton Quantum Gravity

abstract:
  We propose a simple fixed point scenario in the renormalization flow of a
scalar dilaton coupled to gravity. This would render gravity non-perturbatively
renormalizable and thus constitute a viable theory of quantum gravity. On the
fixed point dilatation symmetry is exact and the quantum effective action takes
a very simple form. Realistic gravity with a nonzero Planck mass is obtained
through a nonzero expectation value for the scalar field, constituting a
spontaneous scale symmetry breaking. Furthermore, relevant couplings for the
flow away from the fixed point can be associated with a 'dilatation anomaly'
that is responsible for dynamical dark energy. For the proposed fixed point and
flow away from it the cosmological 'constant' vanishes for asymptotic time.


title:
Finite temperature phase diagram of the classical Kitaev-Heisenberg
  model

abstract:
  We investigate the finite-temperature phase diagram of the classical
Kitaev-Heisenberg model on the hexagonal lattice. Due to the anisotropy
introduced by the Kitaev interaction, the model is magnetically ordered at low
temperatures for all values of parameters at which the model has a discrete
symmetry. The ordered phase is stabilized entropically by an order by disorder
mechanism where thermal fluctuations of classical spins select collinear
magnetic orders in which magnetic moments point along one of the cubic
directions. We find that there is an intermediate phase between the
low-temperature ordered phase and the high-temperature disordered phase. We
show that the intermediate phase is a critical Kosterlitz-Thouless phase
exhibiting correlations of the order parameter that decay algebraically in
space. Using finite size scaling analysis, we determine the boundaries of the
critical phase with reasonable accuracy. We show that the Kitaev interaction
plays a crucial role in understanding the finite temperature properties of
A$_2$IrO$_3$ systems.


title:
On the Capacity of the Finite Field Counterparts of Wireless
  Interference Networks

abstract:
  This work explores how degrees of freedom (DoF) results from wireless
networks can be translated into capacity results for their finite field
counterparts that arise in network coding applications. The main insight is
that scalar (SISO) finite field channels over $\mathbb{F}_{p^n}$ are analogous
to n x n vector (MIMO) channels in the wireless setting, but with an important
distinction -- there is additional structure due to finite field arithmetic
which enforces commutativity of matrix multiplication and limits the channel
diversity to n, making these channels similar to diagonal channels in the
wireless setting. Within the limits imposed by the channel structure, the DoF
optimal precoding solutions for wireless networks can be translated into
capacity optimal solutions for their finite field counterparts. This is shown
through the study of the 2-user X channel and the 3-user interference channel.
Besides bringing the insights from wireless networks into network coding
applications, the study of finite field networks over $\mathbb{F}_{p^n}$ also
touches upon important open problems in wireless networks (finite SNR, finite
diversity scenarios) through interesting parallels between p and SNR, and n and
diversity.


title: Testing the spin-cutoff parameterization with shell-model calculations

abstract:
  The nuclear level density, an important input to Hauser-Feshbach
calculations, depends not only on excitation energy but also on angular
momentum J. The J-dependence of the level density at fixed excitation energy
E_x is usually parameterized via the spin-cutoff factor sigma. We carefully
test the statistical accuracy of this parameterization for a large number of
spectra computed using semi-realistic interactions in the interacting shell
model, with a nonlinear least-squares fit of sigma and finding the error bar in
sigma. The spin-cutoff parameterization works well as long as there are enough
states to be statistical. In turn, the spin-cutoff factor can be related to the
average value of J^2 at a fixed excitation energy, and we briefly investigate
extracting <J^2 (E_x)> from a thermal calculation such as one might do via
Monte Carlo.


title: Signatures of spin-preserving symmetries in two-dimensional hole gases

abstract:
  We investigate ramifications of the persistent spin helix symmetry in
two-dimensional hole gases in the conductance of disordered mesoscopic systems.
To this end we extend previous models by going beyond the axial approximation
for III-V semiconductors. For heavy-hole subbands we identify an exact
spin-preserving symmetry analogous to the electronic case by analyzing the
crossover from weak antilocalization to weak localization and spin transmission
as a function of extrinsic spin-orbit interaction strength.


title: Directional metric regularity of multifunctions

abstract:
  In this paper, we study relative metric regularity of set-valued mappings
with emphasis on directional metric regularity. We establish characterizations
of relative metric regularity without assuming the completeness of the image
spaces, by using the relative lower semicontinuous envelopes of the distance
functions to set-valued mappings. We then apply these characterizations to
establish a coderivative type criterion for directional metric regularity as
well as for the robustness of metric regularity.


title:
Transmutation techniques and observability for time-discrete
  approximation schemes of conservative systems

abstract:
  In this article, we consider abstract linear conservative systems and their
time-discrete counterparts. Our main result is a representation formula
expressing solutions of the continuous model through the solution of the
corresponding time-discrete one. As an application, we show how observability
properties for the time continuous model yield uniform (with respect to the
time-step) observability results for its time-discrete approximation
counterparts, provided the initial data are suitably filtered. The main output
of this approach is the estimate on the time under which we can guarantee
uniform observability for the time-discrete models. Besides, using a reverse
representation formula, we also prove that this estimate on the time of uniform
observability for the time-discrete models is sharp. We then conclude with some
general comments and open problems.


title: The $abc$-problem for Gabor systems

abstract:
  A Gabor system generated by a window function $\phi$ and a rectangular
lattice $a \Z\times \Z/b$ is given by $${\mathcal G}(\phi, a \Z\times
\Z/b):=\{e^{-2\pi i n t/b} \phi(t- m a):\ (m, n)\in \Z\times \Z\}.$$ One of
fundamental problems in Gabor analysis is to identify window functions $\phi$
and time-frequency shift lattices $a \Z\times \Z/b$ such that the corresponding
Gabor system ${\mathcal G}(\phi, a \Z\times \Z/b)$ is a Gabor frame for
$L^2(\R)$, the space of all square-integrable functions on the real line $\R$.
In this paper, we provide a full classification of triples $(a,b,c)$ for which
the Gabor system ${\mathcal G}(\chi_I, a \Z\times \Z/b)$ generated by the ideal
window function $\chi_I$ on an interval $I$ of length $c$ is a Gabor frame for
$L^2(\R)$. For the classification of such triples $(a, b, c)$ (i.e., the
$abc$-problem for Gabor systems), we introduce maximal invariant sets of some
piecewise linear transformations and establish the equivalence between Gabor
frame property and triviality of maximal invariant sets. We then study dynamic
system associated with the piecewise linear transformations and explore various
properties of their maximal invariant sets. By performing holes-removal surgery
for maximal invariant sets to shrink and augmentation operation for a line with
marks to expand, we finally parameterize those triples $(a, b, c)$ for which
maximal invariant sets are trivial. The novel techniques involving
non-ergodicity of dynamical systems associated with some novel non-contractive
and non-measure-preserving transformations lead to our arduous answer to the
$abc$-problem for Gabor systems.


title: On the Minimax Capacity Loss under Sub-Nyquist Universal Sampling

abstract:
  This paper investigates the information rate loss in analog channels when the
sampler is designed to operate independent of the instantaneous channel
occupancy. Specifically, a multiband linear time-invariant Gaussian channel
under universal sub-Nyquist sampling is considered. The entire channel
bandwidth is divided into $n$ subbands of equal bandwidth. At each time only
$k$ constant-gain subbands are active, where the instantaneous subband
occupancy is not known at the receiver and the sampler. We study the
information loss through a capacity loss metric, that is, the capacity gap
caused by the lack of instantaneous subband occupancy information. We
characterize the minimax capacity loss for the entire sub-Nyquist rate regime,
provided that the number $n$ of subbands and the SNR are both large. The
minimax limits depend almost solely on the band sparsity factor and the
undersampling factor, modulo some residual terms that vanish as $n$ and SNR
grow. Our results highlight the power of randomized sampling methods (i.e. the
samplers that consist of random periodic modulation and low-pass filters),
which are able to approach the minimax capacity loss with exponentially high
probability.


title:
Conserved Charge Fluctuations and Susceptibilities in Strongly
  Interacting Matter

abstract:
  We study the conserved charge fluctuations, as quantified by the
corresponding susceptibilities, in strongly interacting matter as motived by
the quark-gluon plasma. Using the gauge-gravity correspondence approach, we
study the patterns of conserved charge fluctuations in two types of holographic
models for QCD, the D4/D8 and the D3/D7 models. We compute and compare the
quark number susceptibilities in both models and find an interesting common
feature of the two: at very strong coupling higher order susceptibilities are
suppressed and the conserved charge fluctuations become purely Guassian. In
light of the state-of-the-art lattice QCD results we also discuss what we can
learn from these susceptibilities about the underlying degrees of freedom in
the $1\sim 2T_c$ quark-gluon plasma and examine the viability of different
ideas such as holography, quasi-particles, as well as bound states. From
analyzes of second order susceptibilities we conclude that the bound states
exist and are important in the $1\sim 2T_c$ region. We further construct and
make predictions for several ratios of fourth-order susceptibilities that can
sensitively reveal such bound states.


title: Invariants and divergences in half-maximal supergravity theories

abstract:
  The invariants in half-maximal supergravity theories in D=4,5 are discussed
in detail up to dimension eight (e.g. R^4). In D=4, owing to the anomaly in the
rigid SL(2,R) duality symmetry, the restrictions on divergences need careful
treatment. In pure N=4 supergravity, this anomalous symmetry still implies
duality invariance of candidate counterterms at three loops. Provided one makes
the additional assumption that there exists a full 16-supercharge off-shell
formulation of the theory, counterterms at L>1 loops would also have to be
writable as full-superspace integrals. At the three-loop order such a
duality-invariant full-superspace integral candidate counterterm exists, but
its duality invariance is marginal in the sense that the full-superspace
counter-Lagrangian is not itself duality-invariant. We show that such marginal
invariants are not allowable as counterterms in a 16-supercharge off-shell
formalism. It is not possible to draw the same conclusion when vector
multiplets are present because of the appearance of F^4 terms in the SL(2,R)
anomaly. In D=5 there is no one-loop anomaly in the shift invariance of the
dilaton, and we argue that this implies finiteness at two loops, again subject
to the assumption that 16 supercharges can be preserved off-shell.


title:
Picosecond opto-acoustic interferometry and polarimetry in high-index
  GaAs

abstract:
  By means of a metal opto-acoustic transducer we generate quasi-longitudinal
and quasi-transverse picosecond strain pulses in a (311)-GaAs substrate and
monitor their propagation by picosecond acoustic interferometry. By probing at
the sample side opposite to the transducer the signals related to the
compressive and shear strain pulses can be separated in time. In addition to
conventional monitoring of the reflected probe light intensity we monitor also
the polarization rotation of the optical probe beam. This polarimetric
technique results in improved sensitivity of detection and provides
comprehensive information about the elasto-optical anisotropy. The experimental
observations are in a good agreement with a theoretical analysis.


title: Majorization entropic uncertainty relations

abstract:
  Entropic uncertainty relations in a finite dimensional Hilbert space are
investigated. Making use of the majorization technique we derive explicit lower
bounds for the sum of R\'enyi entropies describing probability distributions
associated with a given pure state expanded in eigenbases of two observables.
Obtained bounds are expressed in terms of the largest singular values of
submatrices of the unitary rotation matrix. Numerical simulations show that for
a generic unitary matrix of size N = 5 our bound is stronger than the well
known result of Maassen and Uffink (MU) with a probability larger than 98%. We
also show that the bounds investigated are invariant under the dephasing and
permutation operations. Finally, we derive a classical analogue of the MU
uncertainty relation, which is formulated for stochastic transition matrices.


title: The multiplicity of \phi\ Phe revisited

abstract:
  The chemically peculiar B star $\phi$ Phe was, until very recently,
considered a triple system, even though the data were not conclusive and the
orbits rather uncertain. Very recent results by Korhonen et al. (2013) provided
a revised orbit, different from the then available astrometric Hipparcos orbit.
  Additional spectroscopic data, obtained with the BESO spectrograph at Cerro
Armazones, confirm the newly found orbit, even though the resulting radial
velocities do not allow to improve on the recent orbit. We combine the latter
with the Hipparcos measurements to secure the astrometric orbit, and derive the
inclination of the system. Using evolutionary tracks, we can finally constrain
all the parameters of the two components in this system.
  We confirm the mass of the primary, 3 M$_\odot$, and find that the companion
has a mass of 0.9 M$_\odot$. The inclination of the system is $i=93^{\circ} \pm
4.7^{\circ}$, and is potentially eclipsing; we predict the time of the next
conjunction. Given that the eccentricity of the orbit and the exact value of
the semi-amplitude of the radial velocity relies on just one set of points, we
also urge observers to measure radial velocities at the next periastron passage
in April 2015.


title: Inert Doublet Model with a 125 GeV Higgs

abstract:
  A 125 GeV Higgs-like particle discovered at the LHC in 2012 has properties
expected for it in the Standard Model (SM), with a possible enhancement in the
two-photon channel. Such SM-like Higgs scenario can be realized within the
Inert Doublet Model (IDM) - a version of the Two Higgs Doublet Model with an
exact discrete D (Z_2-type) symmetry. In this model one SU(2) doublet plays the
role of the SM Higgs doublet with one SM-like Higgs boson. The second doublet
has no vacuum expectation value and does not interact with fermions. Among four
scalars constituting this D-odd doublet the lightest one is stable, being if
neutral a good DM candidate with the right relic density. In this paper an
analysis of the two-photon Higgs decay rate in IDM, respecting theoretical and
other experimental constraints, is presented. The enhancement in the two-photon
channel is possible only if invisible channels are closed, with the enhancement
R_{\gamma \gamma}>1.2 for masses of DM and charged scalars below 154 GeV. The
temperature evolution of the Universe to the Inert phase (described by the IDM)
in T^2 approximation is presented and all possible sequences of phase
transitions in one, two and three steps are analyzed. Going beyond this
approximation by using an effective potential approach with one-loop T=0
Weinberg-Coleman term and temperature dependent effective potential at T\not =0
we address the question, whether the strong first-order phase transition needed
for baryogenesis can be realized in IDM. A region with a good DM relic density
and a strong first-order phase transition is established, and discussed in the
light of the XENON-100 data.


title: Proving the CEP with compact stars?

abstract:
  We present a model for hybrid compact stars composed of a quark core and a
hadronic mantle with an abrupt first order phase transition at the interface
and in accordance with the latest astrophysical measurements of two 2 M_sun
pulsars. We demonstrate the possibility of a disconnected mass-radius sequence
(third family) of high-mass pulsars as a distinct feature due to a large jump
$\Delta \epsilon$ in the energy density of the first order phase transition
setting in at $\epsilon_{\rm crit}\approx 500$ MeV/fm$^3$ and fulfilling
$\Delta \epsilon/\epsilon_{\rm crit} > 0.6$. We conclude that the measurement
of so called \textit{twin} compact stars at high mass (~ 2 M_sun) would support
the existence of a first order phase transition in symmetric matter at zero
temperature entailing the existence of a critical end point (CEP) in the QCD
phase diagram.


title:
Another proof of Scurry's characterization of a two weight norm
  inequality for a sequence-valued positive dyadic operator

abstract:
  In this note we prove Scurry's testing conditions for the boundedness of a
sequence-valued averaging positive dyadic operator from a weighted Lp space to
a sequence-valued weighted Lp space by using parallel stopping cubes.


title: Implications of conformal invariance in momentum space

abstract:
  We present a comprehensive analysis of the implications of conformal
invariance for 3-point functions of the stress-energy tensor, conserved
currents and scalar operators in general dimension and in momentum space. Our
starting point is a novel and very effective decomposition of tensor
correlators which reduces their computation to that of a number of scalar form
factors. For example, the most general 3-point function of a conserved and
traceless stress-energy tensor is determined by only five form factors.
Dilatations and special conformal Ward identities then impose additional
conditions on these form factors. The special conformal Ward identities become
a set of first and second order differential equations, whose general solution
is given in terms of integrals involving a product of three Bessel functions
(`triple-K integrals'). All in all, the correlators are completely determined
up to a number of constants, in agreement with well-known position space
results. We develop systematic methods for explicitly evaluating the triple-K
integrals. In odd dimensions they are given in terms of elementary functions
while in even dimensions the results involve dilogarithms. In some cases, the
triple-K integrals diverge and subtractions are necessary and we show how such
subtractions are related to conformal anomalies.
  This paper contains two parts that can be read independently of each other.
In the first part, we explain the method that leads to the solution for the
correlators in terms of triple-K integrals and how to evaluate these integrals,
while the second part contains a self-contained presentation of all results.
Readers interested only in results may directly consult the second part of the
paper.


title:
Quantum critical behavior in three dimensional lattice Gross-Neveu
  models

abstract:
  We study quantum critical behavior in three dimensional lattice Gross-Neveu
models containing two massless Dirac fermions. We focus on two models with
SU(2) flavor symmetry and either a $Z_2$ or a U(1) chiral symmetry. Both models
could not be studied earlier due to sign problems. We use the fermion bag
approach which is free of sign problems and compute critical exponents at the
phase transitions. We estimate $\nu = 0.83(1)$, $\eta = 0.62(1)$, $\eta_\psi =
0.38(1)$ in the $Z_2$ and $\nu = 0.849(8)$, $\eta = 0.633(8)$, $\eta_\psi =
0.373(3)$ in the U(1) model.


title: Coevolution (Or Not) of Supermassive Black Holes and Host Galaxies

abstract:
  We review the observed demographics and inferred evolution of supermassive
black holes (BHs) found by dynamical modeling of spatially resolved kinematics.
Most influential was the discovery of a tight correlation between BH mass and
the velocity dispersion of the host-galaxy bulge. It and other correlations led
to the belief that BHs and bulges coevolve by regulating each other's growth.
New results are now replacing this simple story with a richer and more
plausible picture in which BHs correlate differently with different galaxy
components. BHs are found in pure-disk galaxies, so classical
(elliptical-galaxy-like) bulges are not necessary to grow BHs. But BHs do not
correlate with galaxy disks. And any correlations with disk-grown pseudobulges
or halo dark matter are so weak as to imply no close coevolution. We suggest
that there are four regimes of BH feedback. 1- Local, stochastic feeding of
small BHs in mainly bulgeless galaxies involves too little energy to result in
coevolution. 2- Global feeding in major, wet galaxy mergers grows giant BHs in
short, quasar-like "AGN" events whose feedback does affect galaxies. This makes
classical bulges and coreless-rotating ellipticals. 3- At the highest BH
masses, maintenance-mode feedback into X-ray gas has the negative effect of
helping to keep baryons locked up in hot gas. This happens in giant,
core-nonrotating ellipticals. They inherit coevolution magic from smaller
progenitors. 4- Independent of any feedback physics, the averaging that results
from successive mergers helps to engineer tight BH correlations.


title: Smooth Loops and Thomas Precession

abstract:
  Fundamentals of the local smooth loops due to Sabinin are concisely outlined
together with the corresponding infinitesimal objects, so-called
\nu-hyperalgebras, and the analogue of the Lie groups theory. We apply here
this theory to to formulation of a new concept of loop of boosts. A
quaternionic model of the three-parametric loop of boosts is obtained and a
remarkable connection with geodesic loops of Lobachevskii space is found. A
description of Thomas precession in the light of general theory of smooth loops
is given.


title:
On the role of transition region on the Alfven wave phase mixing in
  solar spicules

abstract:
  Alfvenic waves are thought to play an important role in coronal heating and
solar wind acceleration. Here we investigate the dissipation of standing Alfven
waves due to phase mixing at the presence of steady flow and sheared magnetic
field in the stratified atmosphere of solar spicules. The transition region
between chromosphere and corona has also been considered. The initial flow is
assumed to be directed along spicule axis, and the equilibrium magnetic field
is taken 2-dimensional and divergence-free. It is determined that in contrast
to propagating Alfven waves, standing Alfven waves dissipate in time rather
than in space. Density gradients and sheared magnetic fields can enhance
damping due to phase mixing. Damping times deduced from our numerical
calculations are in good agreement with spicule lifetimes. Since spicules are
short living and transient structures, such a fast dissipation mechanism is
needed to transport their energy to the corona.


title:
Collapse of a relativistic self-gravitating star with radial heat flux:
  Impact of anisotropic stresses

abstract:
  We develop a simple model for a self-gravitating spherically symmetric
relativistic star which begins to collapse from an initially static
configuration by dissipating energy in the form of radial heat flow. We utilize
the model to show how local anisotropy effects the collapse rate and thermal
behaviour of gravitationally evolving systems.


title: Space-Time-Matter

abstract:
  This essay examines our fundamental conceptions of time, spacetime, the
asymmetry of time, and the motion of a quantum mechanical particle. The concept
of time has multiple meanings and these are often confused in the literature
and must be distinguished if any light is to be thrown on this age-old issue.
The asymmetry of time also has different meanings that depend on
context-although the fundamental time asymmetry is associated with the
expansion of the universe. These and related issues are discussed in both
classical and quantum mechanical contexts.


title:
Ubah?: Voting pattern in a sectarianized post-information-monopoly
  population I. predictions from a simple projection model

abstract:
  We predict the results of the upcoming elections in Malaysia using a
projective model for a sectarianized post-information-monopoly population.


title:
Submillimeter Quasi-Periodic Oscillations in Magnetically Choked
  Accretion Flows Models of Sgr A*

abstract:
  High-frequency quasi-periodic oscillations (QPOs) appear in
general-relativistic magnetohydrodynamic simulations of magnetically choked
accretion flows around rapidly rotating black holes (BHs). We perform polarized
radiative transfer calculations with ASTRORAY code to explore the
manifestations of these QPOs for SgrA*. We construct a simulation-based model
of a radiatively inefficient accretion flow and find model parameters by
fitting the mean polarized source spectrum. The simulated QPOs have a total
sub-mm flux amplitude up to 5% and a linearly polarized flux amplitude up to
2%. The oscillations reach high levels of significance 10-30\sigma and high
quality factors Q~5. The oscillation period T~100M~35min corresponds to the
rotation period of the BH magnetosphere that produces a trailing spiral in
resolved disk images. The total flux signal is significant over noise for all
tested frequencies 87GHz, 230GHz, and 857GHz and inclination angles 10deg,
37deg, and 80deg. The non-detection in the 230GHz Sub-Millimeter Array light
curve is consistent with a low signal level and a low sampling rate. The
presence of sub-mm QPOs in SgrA* will be better tested with the Atacama Large
Millimeter Array.


title:
The Stellar Initial Mass Function of Ultra-Faint Dwarf Galaxies:
  Evidence for IMF Variations with Galactic Environment

abstract:
  We present constraints on the stellar initial mass function (IMF) in two
ultra-faint dwarf (UFD) galaxies, Hercules and Leo IV, based on deep HST/ACS
imaging. The Hercules and Leo IV galaxies are extremely low luminosity (M_V =
-6.2, -5.5), metal-poor (<[Fe/H]>= -2.4, -2.5) systems that have old stellar
populations (> 11 Gyr). Because they have long relaxation times, we can
directly measure the low-mass stellar IMF by counting stars below the
main-sequence turnoff without correcting for dynamical evolution. Over the
stellar mass range probed by our data, 0.52 - 0.77 Msun, the IMF is best fit by
a power-law slope of alpha = 1.2^{+0.4}_{-0.5} for Hercules and alpha = 1.3 +/-
0.8 for Leo IV. For Hercules, the IMF slope is more shallow than a Salpeter IMF
(alpha=2.35) at the 5.8-sigma level, and a Kroupa IMF (alpha=2.3 above 0.5
Msun) at 5.4-sigma level. We simultaneously fit for the binary fraction,
finding f_binary = 0.47^{+0.16}_{-0.14} for Hercules, and 0.47^{+0.37}_{-0.17}
for Leo IV. The UFD binary fractions are consistent with that inferred for
Milky Way stars in the same mass range, despite very different metallicities.
In contrast, the IMF slopes in the UFDs are shallower than other galactic
environments. In the mass range 0.5 - 0.8 Msun, we see a trend across the
handful of galaxies with directly measured IMFs such that the power-law slopes
become shallower (more bottom-light) with decreasing galactic velocity
dispersion and metallicity. This trend is qualitatively consistent with results
in elliptical galaxies inferred via indirect methods and is direct evidence for
IMF variations with galactic environment.


title:
A Herschel [CII] Galactic plane survey I: the global distribution of ISM
  gas components

abstract:
  [Abridged] The [CII] 158um line is an important tool for understanding the
life cycle of interstellar matter. Ionized carbon is present in a variety of
phases of the interstellar medium, including the diffuse ionized medium, warm
and cold atomic clouds, clouds in transition from atomic to molecular, and
dense and warm photon dominated regions (PDRs). The Galactic Observations of
Terahertz C+ (GOTC+) project surveys the [CII] line over the entire Galactic
disk with velocity-resolved observations using the Herschel/HIFI instrument. We
present the first longitude-velocity maps of the [CII] emission for Galactic
latitudes b=0deg, +-0.5deg, and +-1.0deg. [CII] emission is mostly associated
with spiral arms, mainly emerging from Galactocentric distances between 4 and
10 kpc. We estimate that most of the observed [CII] emission is produced by
dense PDRs (47%), with smaller contributions from CO-dark H2 gas (28%), cold
atomic gas (21%), and ionized gas (4%). Atomic gas inside the Solar radius is
mostly in the form of cold neutral medium (CNM), while the warm neutral medium
(WNM) gas dominates the outer galaxy. The average fraction of CNM relative to
total atomic gas is 43%. We find that the warm and diffuse CO-dark H2 is
distributed over a larger range of Galactocentric distances (4-11 kpc) than the
cold and dense H2 gas traced by 12CO and 13CO (4-8kpc). The fraction of CO-dark
H2 to total H2 increases with Galactocentric distance, ranging from 20% at 4
kpc to 80% at 10 kpc. On average, CO-dark H2 accounts for 30% of the molecular
mass of the Milky Way. When the CO-dark H2 component is included, the radial
distribution of the CO-to-H2 conversion factor is steeper than that when only
molecular gas traced by CO is considered. Most of the observed [CII] emission
emerging from dense PDRs is associated with modest far-ultraviolet fields in
the range chi0~1-30.


title: Molecular gas mass functions of normal star forming galaxies since z~3

abstract:
  We use deep far-infrared data from the PEP/GOODS-Herschel surveys and rest
frame ultraviolet photometry to study the evolution of the molecular gas mass
function of normal star forming galaxies. Computing the molecular gas mass,
M(mol), by scaling star formation rates (SFR) through depletion timescales, or
combining IR luminosity and obscuration properties as in Nordon et al., we
obtain M(mol) for roughly 700, z=0.2-3.0 galaxies near the star forming "main
sequence". The number density of galaxies follows a Schechter function of
M(mol). The characteristic mass M* is found to strongly evolve up to z~1, and
then to flatten at earlier epochs, resembling the infrared luminosity evolution
of similar objects. At z~1, our result is supported by an estimate based on the
stellar mass function of star forming galaxies and gas fraction scalings from
the PHIBSS survey. We compare our measurements to results from current models,
finding better agreement with those that are treating star formation laws
directly rather than in post-processing. Integrating the mass function, we
study the evolution of the M(mol) density and its density parameter Omega(mol).


title: Self-Dual Conformal Gravity

abstract:
  We find necessary and sufficient conditions for a Riemannian four-dimensional
manifold $(M, g)$ with anti-self-dual Weyl tensor to be locally conformal to a
Ricci--flat manifold. These conditions are expressed as the vanishing of scalar
and tensor conformal invariants. The invariants obstruct the existence of
parallel sections of a certain connection on a complex rank-four vector bundle
over $M$. They provide a natural generalisation of the Bach tensor which
vanishes identically for anti-self-dual conformal structures. We use the
obstructions to demonstrate that LeBrun's anti-self-dual metrics on connected
sums of $\CP^2$s are not conformally Ricci-flat on any open set.
  We analyze both Riemannian and neutral signature metrics. In the latter case
we find all anti-self-dual metrics with a parallel real spinor which are
locally conformal to Einstein metrics with non-zero cosmological constant.
These metrics admit a hyper-surface orthogonal null Killing vector and thus
give rise to projective structures on the space of $\beta$-surfaces.


title:
How Fluids Bend: the Elastic Expansion for Higher-Dimensional Black
  Holes

abstract:
  Hydrodynamics can be consistently formulated on surfaces of arbitrary
co-dimension in a background space-time, providing the effective theory
describing long-wavelength perturbations of black branes. When the co-dimension
is non-zero, the system acquires fluid-elastic properties and constitutes what
is called a fluid brane. Applying an effective action approach, the most
general form of the free energy quadratic in the extrinsic curvature and
extrinsic twist potential of stationary fluid brane configurations is
constructed to second order in a derivative expansion. This construction
generalizes the Helfrich-Canham bending energy for fluid membranes studied in
theoretical biology to the case in which the fluid is rotating. It is found
that stationary fluid brane configurations are characterized by a set of 3
elastic response coefficients, 3 hydrodynamic response coefficients and 1 spin
response coefficient for co-dimension greater than one. Moreover, the elastic
degrees of freedom present in the system are coupled to the hydrodynamic
degrees of freedom. For co-dimension-1 surfaces we find a 8 independent
parameter family of stationary fluid branes. It is further shown that elastic
and spin corrections to (non)-extremal brane effective actions can be accounted
for by a multipole expansion of the stress-energy tensor, therefore
establishing a relation between the different formalisms of Carter,
Capovilla-Guven and Vasilic-Vojinovic and between gravity and the effective
description of stationary fluid branes. Finally, it is shown that the Young
modulus found in the literature for black branes falls into the class predicted
by this approach - a relation which is then used to make a proposal for the
second order effective action of stationary blackfolds and to find the
corrected horizon angular velocity of thin black rings.


title: On universality of charge transport in AdS/CFT

abstract:
  We develop the holographic formulation of transport in strongly coupled
two-layer systems. We identify a dc conductivity, sigma^dc, that is finite even
in a translationally invariant setup, and universal for CFTs with a gravity
dual. The thermoelectric conductivity and heat conductivity are fully
determined by the electrical conductivity matrix, as a consequence of Ward
identities. We use the memory-matrix approach for double-layer systems,
together with Ward identities, to show that sigma^dc - extended to finite
frequency - has no Drude peak and, similarly, that its universal value is
unaffected if translation invariance is softly broken.


title: Theoretical results for top quark production

abstract:
  I discuss and compare several approaches to higher-order calculations of top
quark production. I study the relative effectiveness of the approaches in
approximating the exact NNLO results for the top-pair total cross section and
highlight the theoretical and numerical differences between them. I show that
the results from my soft-gluon resummation method are nearly identical to the
exact NNLO cross section at all LHC and Tevatron energies. This agreement has
important consequences for the validity of existing approximate NNLO
differential distributions, for further refinements of the predictions, and for
applications to other processes such as single-top production. I also compare
approximate NNLO top quark transverse momentum and rapidity distributions with
recent LHC measurements.


title: Lifshitz as a deformation of Anti-de Sitter

abstract:
  We consider holography for Lifshitz spacetimes with dynamical exponent
z=1+epsilon^2, where epsilon is small. We show that the holographically dual
field theory is a specific deformation of the relativistic CFT, corresponding
to the z=1 theory. Treating epsilon as a small expansion parameter we set up
the holographic dictionary for Einstein-Proca models up to order epsilon^2 in
three and four bulk dimensions. We explain how renormalization turns the
relativistic conformal invariance into non-relativistic Lifshitz invariance
with dynamical exponent z=1+epsilon^2. We compute the two-point function of the
conserved spin two current for the dual two-dimensional field theory and verify
that it is Lifshitz invariant. Using only QFT arguments, we show that a
particular class of deformations of CFTs generically leads to Lifshitz scaling
invariance and we construct examples of such deformations.


title:
Young Stellar Objects in Lynds 1641: Disks, Accretion, and Star
  Formation History

abstract:
  We investigate the young stellar objects (YSOs) in the Lynds~1641 (L1641)
cloud using multi-wavelength data including Spitzer, WISE, 2MASS, and XMM
covering ~1390 YSOs across a range of evolutionary stages. In addition, we
targeted a sub-sample of YSOs for optical spectroscopy. We use this data, along
with archival photometric data, to derive spectral types, extinction values,
masses, ages, as well as accretion rates. We obtain a disk fraction of ~50% in
L1641. The disk frequency is almost constant as a function of stellar mass with
a slight peak at log(M_*/M_sun)\approx-0.25. The analysis of multi-epoch
spectroscopic data indicates that the accretion variability of YSOs cannot
explain the two orders of magnitude of scatter for YSOs with similar masses.
Forty-six new transition disk (TD) objects are confirmed in this work, and we
find that the fraction of accreting TDs is lower than for optically thick disks
(40--45% vs. 77--79% respectively). We confirm our previous result that the
accreting TDs have a similar median accretion rate to normal optically thick
disks. We confirm that two star formation modes (isolated vs. clustered) exist
in L1641. We find that the diskless YSOs are statistically older than the YSOs
with optically-thick disks and the transition disk objects have a median age
which is intermediate between the two populations. We tentatively study the
star formation history in L1641 based on the age distribution and find that
star formation started to be active 2--3 Myr ago.


title:
The massive end of the luminosity and stellar mass functions: Dependence
  on the fit to the light profile

abstract:
  In addition to the large systematic differences arising from assumptions
about the stellar mass-to-light ratio, the massive end of the stellar mass
function is rather sensitive to how one fits the light profiles of the most
luminous galaxies. We quantify this by comparing the luminosity and stellar
mass functions based on SDSS cmodel magnitudes, and PyMorph single-Sersic and
Sersic-Exponential fits to the surface brightness profiles of galaxies in the
SDSS. The PyMorph fits return more light, so that the predicted masses are
larger than when cmodel magnitudes are used. As a result, the total stellar
mass density at z~0.1 is about 1.2x larger than in our previous analysis of the
SDSS. The differences are most pronounced at the massive end, where the
measured number density of objects having M* > 6 x 10^{11} Msun is ~5x larger.
Alternatively, at number densities of 10^{-6} Mpc^{-3}, the limiting stellar
mass is 2x larger. The differences with respect to fits by other authors,
typically based on Petrosian-like magnitudes, are even more dramatic, although
some of these differences are due to sky-subtraction problems, and are
sometimes masked by large differences in the assumed $M_*/L$ (even after
scaling to the same IMF). Our results impact studies of the growth and assembly
of stellar mass in galaxies, and of the relation between stellar and halo mass,
so we provide simple analytic fits to these new luminosity and stellar mass
functions and quantify how they depend on morphology, as well as the binned
counts in electronic format.


title: Probing Dark Matter at the LHC using Vector Boson Fusion Processes

abstract:
  Vector boson fusion (VBF) processes at the Large Hadron Collider (LHC)
provide a unique opportunity to search for new physics with electroweak
couplings. A feasibility study for the search of supersymmetric dark matter in
the final state of two VBF jets and large missing transverse energy is
presented at 14 TeV. Prospects for determining the dark matter relic density
are studied for the cases of Wino and Bino-Higgsino dark matter. The LHC could
probe Wino dark matter with mass up to approximately 600 GeV with a luminosity
of 1000 fb$^{-1}$.


title:
Chandra identification of 26 new black hole candidates in the central
  region of M31

abstract:
  We have previously identified 10 M31 black hole candidates (BHCs) in M31,
from their X-ray properties alone. They exhibit "hard state" emission spectra
that are seen at luminosities < ~10% Eddington in X-ray binaries (XBs)
containing a neutron star (NS) or black hole (BH), at luminosities that
significantly exceed the NS threshold. Nine of these are associated with
globular clusters (GCs); hence, these are most likely low mass X-ray binaries
(LMXBs); eight are included in this survey. We have recently discovered that
analysis of the long term 0.5--4.5 keV variability of XBs via structure
functions allows us to separate XBs from AGN, even though the emission spectra
are often similar; this has enabled us to search for BHCs outside of GCs. We
have identified 26 new BHCs (12 strong, 14 plausible) within 20' of the M31
nucleus (M31*), using 152 Chandra observations spaced over ~13 years; some of
our classifications were enhanced with XMM-Newton observations. Of these, 7
appear within 100" of M31*; this supports the theory suggesting that this
region experiences enhanced XB production via dynamical processes similar to
those seen in GCs. We have found a parameter space where our black hole
candidates are separated from Galactic neutron star binaries: we show that
modelling a simulated hard state spectrum with a disk blackbody + blackbody
model yields parameters that lie outside the space occupied by neutron star
binaries that are modeled this way. The probability that our BHCs all lie
within the NS parameter space is ~3E-29.


title: On-chip low loss heralded source of pure single photons

abstract:
  A key obstacle to the experimental realization of many photonic
quantum-enhanced technologies is the lack of low-loss sources of single photons
in pure quantum states. We demonstrate a promising solution: generation of
heralded single photons in a silica photonic chip by spontaneous four-wave
mixing. A heralding efficiency of 40%, corresponding to a preparation
efficiency of 80% accounting for detector performance, is achieved due to
efficient coupling of the low-loss source to optical fibers. A single photon
purity of 0.86 is measured from the source number statistics without filtering,
and confirmed by direct measurement of the joint spectral intensity. We
calculate that similar high-heralded-purity output can be obtained from visible
to telecom spectral regions using this approach. On-chip silica sources can
have immediate application in a wide range of single-photon quantum optics
applications which employ silica photonics.