title: Symmetry in Auxiliary-Field Quantum Monte Carlo Calculations

abstract:
  We show how symmetry properties can be used to greatly increase the accuracy
and efficiency in auxiliary-field quantum Monte Carlo (AFQMC) calculations of
electronic systems. With the Hubbard model as an example, we study symmetry
preservation in two aspects of ground-state AFQMC calculations, the
Hubbard-Straonovich transformation and the form of the trial wave function. It
is shown that significant improvement over state-of-the-art calculations can be
achieved. In unconstrained calculations, the implementation of symmetry often
leads to shorter convergence time and much smaller statistical errors, thereby
a substantial reduction of the sign problem. Moreover, certain excited states
become possible to calculate which are otherwise beyond reach. In calculations
with constraints, the use of symmetry can reduce the systematic error from the
constraint. It also allows release-constraint calculations, leading to
essentially exact results in many cases. Detailed comparisons are made with
exact diagonalization results. Accurate ground-state energies are then
presented for larger system sizes in the two-dimensional repulsive Hubbard
model.


title: Equilibrium and non-equilibrium Ising models by means of PCA

abstract:
  We propose a unified approach to reversible and irreversible PCA dynamics,
and we show that in the case of 1D and 2D nearest neighbour Ising systems with
periodic boundary conditions we are able to compute the stationary measure of
the dynamics also when the latter is irreversible. We also show how, according
to [DPSS12], the stationary measure is very close to the Gibbs for a suitable
choice of the parameters of the PCA dynamics, both in the reversible and in the
irreversible cases. We discuss some numerical aspects regarding this topic,
including a possible parallel implementation.


title: Heavy Quarks, Origin of Mass, and CP Violation for Universe

abstract:
  A scale-invariant "Gap Equation" is constructed for chiral quark $Q$ by
Goldstone, or $V_L$, exchange, where massless input is guaranteed by gauge
invariance. A numerical solution is found for Yukawa coupling $\sim 4\pi$. In
turn, because this gap equation is scale invariant, the strong coupling
solution is compatible with a 126 GeV dilaton, which would be a true messenger
from higher energies. Some possible phenomena pertaining to heavy chiral quarks
at few TeV scale is offered. Adding this heavy quark sector may provide enough
CP violation for generating the matter dominance of the Universe.


title: Transmodal Analysis of Neural Signals

abstract:
  Localizing neuronal activity in the brain, both in time and in space, is a
central challenge to advance the understanding of brain function. Because of
the inability of any single neuroimaging techniques to cover all aspects at
once, there is a growing interest to combine signals from multiple modalities
in order to benefit from the advantages of each acquisition method. Due to the
complexity and unknown parameterization of any suggested complete model of BOLD
response in functional magnetic resonance imaging (fMRI), the development of a
reliable ultimate fusion approach remains difficult. But besides the primary
goal of superior temporal and spatial resolution, conjoint analysis of data
from multiple imaging modalities can alternatively be used to segregate neural
information from physiological and acquisition noise. In this paper we suggest
a novel methodology which relies on constructing a quantifiable mapping of data
from one modality (electroencephalography; EEG) into another (fMRI), called
transmodal analysis of neural signals (TRANSfusion). TRANSfusion attempts to
map neural data embedded within the EEG signal into its reflection in fMRI
data. Assessing the mapping performance on unseen data allows to localize brain
areas where a significant portion of the signal could be reliably
reconstructed, hence the areas neural activity of which is reflected in both
EEG and fMRI data. Consecutive analysis of the learnt model allows to localize
areas associated with specific frequency bands of EEG, or areas functionally
related (connected or coherent) to any given EEG sensor. We demonstrate the
performance of TRANSfusion on artificial and real data from an auditory
experiment. We further speculate on possible alternative uses: cross-modal data
filtering and EEG-driven interpolation of fMRI signals to obtain arbitrarily
high temporal sampling of BOLD.


title: Superfluid theory of a gas of polarized dipolar Fermi molecules

abstract:
  We present a superfluid theory of a polarized dipolar Fermi gas. For two
dipolar molecules each of which consists of two atoms with positive charge and
negative charge, we derive an effective dipole-dipole pairing interaction.
Using this pairing interaction, we show that the resulting BCS gap equation is
not suffered from the well-known ultraviolet divergence, so that one can
quantitatively predict superfluid properties of a dipolar Fermi gas. Using this
cutoff-free superfluid theory, we examine the symmetry of the superfluid order
parameter at T=0. We also discuss the deformation of the Fermi surface,
originating from the anisotropy of the dipole-dipole interaction.


title:
A new construction of Lagrangians in the complex Euclidean plane in
  terms of planar curves

abstract:
  We introduce a new method to construct a large family of Lagrangian surfaces
in complex Euclidean plane by means of two planar curves making use of their
usual product as complex functions and integrating the Hermitian product of
their position and tangent vectors.
  Among this family, we characterize minimal, constant mean curvature,
Hamiltonian stationary, solitons for mean curvature flow and Willmore surfaces
in terms of simple properties of the curvatures of the generating curves. As an
application, we provide explicitly conformal parametrizations of known and new
examples of these classes of Lagrangians in complex Euclidean plane.


title: Cosmological Magnetic Fields

abstract:
  Magnetic fields are observed on nearly all scales in the universe, from stars
and galaxies upto galaxy clusters and even beyond. The origin of cosmic
magnetic fields is still an open question, however a large class of models puts
its origin in the very early universe. A magnetic dynamo amplifying an initial
seed magnetic field could explain the present day strength of the galactic
magnetic field. However, it is still an open problem how and when this initial
magnetic field was created. Observations of the cosmic microwave background
(CMB) provide a window to the early universe and might therefore be able to
tell us whether cosmic magnetic fields are of primordial, cosmological origin
and at the same time constrain its parameters. We will give an overview of the
observational evidence of large scale magnetic fields, describe generation
mechanisms of primordial magnetic fields and possible imprints in the CMB.


title:
Hybrid low-diffusion approximate Riemann solvers for Reynolds-stress
  transport

abstract:
  The paper investigates the use of low-diffusion
(contact-discontinuity-resolving [Liou M.S.: {\em J. Comp. Phys.} {\bf 160}
(2000) 623--648]) approximate Riemann solvers for the convective part of the
Reynolds-averaged Navier-Stokes (\tsn{RANS}) equations with Reynolds-stress
model (\tsn{RSM}) closure. Different equivalent forms of the \tsn{RSM-RANS}
system are discussed and classification of the complex terms introduced by
advanced turbulence closures is attempted. Computational examples are
presented, which indicate that the use of contact-discontinuity-resolving
convective numerical fluxes, along with a passive-scalar approach for the
Reynolds-stresses, may lead to unphysical oscillations of the solution. To
determine the source of these instabilities, theoretical analysis of the
Riemann problem for a simplified Reynolds-stress transport model-system, which
incorporates the divergence of the Reynolds-stress tensor in the convective
part of the mean-flow equations, and includes only those nonconservative
products which are computable (do not require modelling), was undertaken,
highlighting the differences in wave-structure compared to the passive-scalar
case. A hybrid solution, allowing the combination of any low-diffusion
approximate Riemann solver with the complex tensorial representations used in
advanced models, is proposed, combining low-diffusion fluxes for the mean-flow
equations with a more dissipative massflux for Reynolds-stress-transport.
Several computational examples are presented to assess the performance of this
approach.


title: Riemannian Curl in Contact Geometry

abstract:
  We consider a contact manifold with a pseudo-Riemannian metric and define a
contact vector field intrinsically associated to this pair of structures. We
call this new differential invariant the contact Riemannian curl. On a
Riemannian manifold, Killing vector fields are those that annihilate the
metric; a Killing $1$-form is obtained from a Killing vector field by lowering
indices. We show that the contact Riemannian curl vanishes if the metric is of
constant curvature and the contact structure is defined by a Killing $1$-form.
We also show that the contact Riemannian curl has a strong similarity with the
Schwarzian derivative since it depends only on the projective equivalence class
of the metric. For the Laplace-Beltrami operator on a contact manifold, the
contact Riemannian curl is proportional to the subsymbol defined in
arXiv:1205.6562. We also show that the contact Riemannian curl vanishes on the
(co)tangent bundle over a Riemannian manifold. This implies that the
corresponding subsymbol of the Laplace-Beltrami operator is identically zero.


title: Recent Advances in Nanostructured Thermoelectric Half-Heusler Compounds

abstract:
  Half-Heusler (HH) alloys have attracted considerable interest as promising
thermoelectric (TE) materials in the temperature range around 700 K and above,
which is close to the temperature range of most industrial waste heat sources.
The past few years have seen nanostructuing play an important role in
significantly enhancing the TE performance of several HH alloys. In this
article, we briefly review the recent progress and advances in these HH
nanocomposites. We begin by presenting the structure of HH alloys and the
different strategies that have been utilized for improving the TE properties of
HH alloys. Next, we review the details of HH nanocomposites as obtained by
different techniques. Finally, the review closes by highlighting several
promising strategies for further research directions in these very promising TE
materials.


title:
A diffusion limit for a test particle in a random distribution of
  scatterers

abstract:
  We consider a point particle moving in a random distribution of obstacles
described by a potential barrier. We show that, in a weak-coupling regime,
under a diffusion limit suggested by the potential itself, the probability
distribution of the particle converges to the solution of the heat equation.
The diffusion coefficient is given by the Green-Kubo formula associated to the
generator of the diffusion process dictated by the linear Landau equation.


title:
PeV neutrinos from interactions of cosmic rays with the interstellar
  medium in the Galaxy

abstract:
  We present a self-consistent interpretation of the of very-high-energy
neutrino signal from the direction of the inner Galaxy, which is a part of the
astronomical neutrino signal reported by IceCube. We demonstrate that an
estimate of the neutrino flux in the E>100 TeV energy range lies at the
high-energy power-law extrapolation of the spectrum of diffuse gamma-ray
emission from the Galactic Ridge, as observed by Fermi telescope. This suggests
that IceCube neutrino and Fermi/LAT gamma-ray fluxes are both produced in
interactions of cosmic rays with the interstellar medium in the Norma arm
and/or in the Galactic Bar. Cosmic rays responsible for the gamma-ray and
neutrino flux are characterised by hard spectrum with the slope harder than
-2.4 and cut-off energy higher than 10 PeV.


title: A note on the discrepancy of matrices with bounded row and column sums

abstract:
  A folklore result uses the Lovasz local lemma to analyze the discrepancy of
hypergraphs with bounded degree and edge size. We generalize this result to the
context of real matrices with bounded row and column sums.


title:
Significant ZT Enhancement in p-type Ti(Co,Fe)Sb-InSb Nanocomposites via
  a Synergistic High Mobility Electron Injection Energy filtering and Boundary
  Scattering Approach

abstract:
  It has been demonstrated that InSb nanoinclusions, which are formed in situ,
can simultaneously improve all three individual thermoelectric properties of
the n-type half Heusler compound (Ti,Zr,Hf)(Co,Ni)Sb [Xie et al., Acta Mater.
58, 4795 (2010)]. In the work presented herein, we have adopted the same
approach to the p-type half Heusler compound Ti(Co,Fe)Sb. The results of
resistivity, Seebeck coefficient, thermal conductivity, and Hall coefficient
measurements indicate that the combined high mobility electron injection, low
energy electron filtering, and boundary scattering, again, lead to a
simultaneous improvement of all three individual thermoelectric properties:
enhanced Seebeck coefficient and electrical conductivity as well as reduced
lattice thermal conductivity. A figure of merit of ZT=0.33 was attained at 900
K for the sample containing 1 atomic percent InSb nanoinclusions, a 450 percent
improvement over the nanoinclusion-free sample. This represents a rare case
that the same nanostructuring approach successfully works for both p-type and
n-type thermoelectric materials of the same class, hence pointing to a
promising materials design route for higher performance half-Heusler materials
in the future and hopefully will realize similar improvement in TE devices
based on such half Heusler alloys.


title: Structure of the rational monoid algebra for Boolean matrices of order 3

abstract:
  We use computer algebra to study the 512-dimensional associative algebra Q
B_3, the rational monoid algebra of 3 x 3 Boolean matrices. We obtain a basis
for the radical in bijection with the 42 non-regular elements of B_3. The
center of the 470-dimensional semisimple quotient has dimension 14; we use a
splitting algorithm to find a basis of orthogonal primitive idempotents. We
show that the semisimple quotient is the direct sum of simple two-sided ideals
isomorphic to d x d rational matrix algebras for d = 1, 1, 1, 2, 3, 3, 3, 3, 6,
6, 7, 9, 9, 12. We construct the irreducible representations of B_3 over Q by
calculating the representation matrices for a minimal set of generators.


title:
Searching for a hidden charm $h_1$ state in the $X(4660) \to \eta h_1$
  and $X(4660) \to \eta D^* \bar D^*$ decays

abstract:
  We explore the possibility of experimentally detecting a predicted $h_1
~[I^G(J^{PC})=0^-(1^{+-})]$ state of hidden charm made out from the $D^* \bar
D^*$ interaction. The method consists in measuring the decay of X(4660) into
$\eta D^* \bar D^*$, determining the binding energy with respect to the $D^*
\bar D^*$ threshold from the shape of the $D^* \bar D^*$ invariant mass
distribution. A complementary method consists in looking at the inclusive
$X(4660) \to \eta X$ decay, searching for a peak in the $X$ invariant mass
distribution given by the missing X(4660), $\eta$ mass. We make calculations to
determine the partial decay width of $X(4660) \to \eta h_1$ from the measured
$X(4660) \to \eta D^* \bar D^*$ distribution. This estimation should serve in
an experiment to foresee the possibility of detecting the $h_1$ state on top of
the background of inclusive events.


title: Visual boundaries of Diestel-Leader graphs

abstract:
  Diestel-Leader graphs are neither hyperbolic nor CAT(0), so their visual
boundaries may be pathological. Indeed, we show that for $d>2$,
$\partial\text{DL}_d(q)$ carries the indiscrete topology. On the other hand,
$\partial\text{DL}_2(q)$, while not Hausdorff, is $T_1$, totally disconnected,
and compact. Since $\text{DL}_2(q)$ is a Cayley graph of the lamplighter group
$L_q$, we also obtain a nice description of $\partial\text{DL}_2(q)$ in terms
of the lamp stand model of $L_q$ and discuss the dynamics of the action.


title: Efficiently determining Convergence in Polynomial Recurrence Sequences

abstract:
  We derive the necessary and sufficient condition, for a given Polynomial
Recurrence Sequence to converge to a given target rational K. By converge, we
mean that the Nth term of the sequence, is equal to K, as N tends to positive
infinity. The basic idea of our approach is to construct a univariate
polynomial equation in x, whose coefficients correspond to the terms of the
Sequence. The approach then obtains the condition by analyzing five cases that
cover all possible real values of x. The condition can be evaluated within time
that is a polynomial function of the size of the description of the Polynomial
Recurrence Sequence, hence convergence or non-convergence can be efficiently
determined.


title: Solar Energetic Particle drifts in the Parker spiral

abstract:
  Drifts in the Parker spiral interplanetary magnetic field are known to be an
important component in the propagation of galactic cosmic rays, while they are
thought to be negligible for Solar Energetic Particles (SEPs). As a result they
have so far been ignored in SEP propagation modelling and data analysis. We
examine drift velocities in the Parker spiral within single particle
first-order adiabatic theory, in a local coordinate system with an axis
parallel to the magnetic field. We show that, in the presence of scattering in
interplanetary space, protons at the high end of the SEP energy range
experience significant gradient and curvature drift. In the scatter-free case,
drift due to magnetic field curvature is present. The magnitude of drift
velocity increases by more than an order of magnitude at high heliographic
latitudes compared to near the ecliptic; it has a strong dependence on radial
distance r from the Sun, reaching a maximum at r~1 AU at low heliolatitudes and
r~10 AU at high heliolatitudes. Due to the mass over charge dependence of drift
velocities, the effect of drift for partially ionised SEP heavy ions is
stronger than for protons. Drift is therefore likely to be a considerable
source of cross field transport for high energy SEPs.


title:
Revealing the evolution, the stability and the escapes of families of
  resonant periodic orbits in Hamiltonian systems

abstract:
  We investigate the evolution of families of periodic orbits in a
bisymmetrical potential made up of a two-dimensional harmonic oscillator with
only one quartic perturbing term, in a number of resonant cases. Our main
objective is to compute sufficiently and accurately the position and the period
of the periodic orbits. For the derivation of the above quantities (position
and period) we deploy in each resonance case semi-numerical methods. The
comparison of our semi-numerical results with those obtained by the numerical
integration of the equations of motion indicates that, in every case the
relative error is always less than 1% and therefore, the agreement is more than
sufficient. Thus, we claim that semi-numerical methods are very effective tools
for computing periodic orbits. We also study in detail, the case when the
energy of the orbits is larger than the escape energy. In this case, the
periodic orbits in almost all resonance families become unstable and eventually
escape from the system. Our target is to calculate the escape period and the
escape position of the periodic orbits and also monitor their evolution with
respect to the value of the energy.


title: The Cauchy problem and Hadamard's example in the ring

abstract:
  Integral representation for harmonic function in the ring is constructed in
this work.
  We prove the existence and uniqueness of solutions of the Cauchy problem for
the Laplace equation in the ring. Integral representation for the solution of
the Cauchy problem was found.


title: Searches for new physics with leptons and jets at CMS

abstract:
  A variety of models of physics beyond the standard model predict new
particles that decay to leptons, jets, or both together. These models include
axigluons, colorons, diquarks, excited quarks, heavy long-lived charged
particles, leptoquarks, Randall-Sundrum gravitons, string resonances, and new
vector bosons (right-handed W and Z'). Using the data collected in 2011 and
2012 at center-of-mass energies of 7 and 8 TeV, the CMS collaboration has
performed searches for these new particles in channels with leptons and jets.
The results of these searches will be presented. No evidence of new physics has
been observed, and these results set new limits on the parameters of these
models.


title: Random Market Models with an H-Theorem

abstract:
  In this communication, some economic models given by functional mappings are
addressed. These are models for random markets where agents trade by pairs and
exchange their money in a random and conservative way. They display the
exponential wealth distribution as asymptotic equilibrium, independently of the
effectiveness of the transactions and of the limitation of the total wealth.
The entropy increases with time in these models and the existence of an
H-theorem is computationally checked. Also, it is shown that any small
perturbation of the models equations make them to lose the exponential
distribution as an equilibrium solution.


title: New phase transition in random planar diagrams and RNA-type matching

abstract:
  We study the planar matching problem, defined by a symmetric random matrix
with independent identically distributed entries, taking values 0 and 1. We
show that the existence of a perfect planar matching structure is possible only
above a certain critical density, $p_{c}$, of allowed contacts (i.e. of '1').
Using a formulation of the problem in terms of Dyck paths and a matrix model of
planar contact structures, we provide an analytical estimation for the value of
the transition point, $p_{c}$, in the thermodynamic limit. This estimation is
close to the critical value, $p_{c} \approx 0.379$, obtained in numerical
simulations based on an exact dynamical programming algorithm. We characterize
the corresponding critical behavior of the model and discuss the relation of
the perfect-imperfect matching transition to the known molten-glass transition
in the context of random RNA secondary structure's formation. In particular, we
provide strong evidence supporting the conjecture that the molten-glass
transition at T=0 occurs at $p_{c}$.


title: Sylvester's law of inertia for quadratic forms on vector bundles

abstract:
  This paper presents a generalisation of Sylvester's law of inertia to real
non-degenerate quadratic forms on a fixed real vector bundle over a connected
locally connected paracompact Hausdorff space. By interpreting the classical
inertia as a complete discrete invariant for the natural action of the general
linear group on quadratic forms, the simplest generalisation consists in
substituting such group with the group of gauge transformations of the bundle.
Contrary to the classical law of inertia, here the full action and its
restriction to the identity path component typically have different orbits,
leading to two invariants: a complete invariant for the full action is given by
the isomorphism class of the orthonormal frame bundle associated to a quadratic
form, while a complete invariant for the restricted action is the homotopy
class of any maximal positive-definite subbundle associated to a quadratic
form. The latter invariant is finer than the former, which in turn is finer
than inertia. Moreover, the orbit structure thus obtained might be used to shed
light on the topology of the space of non-degenerate quadratic forms on a
vector bundle.


title:
Partition Function of Chiral Boson on 2-Torus from Floreanini-Jackiw
  Lagrangian

abstract:
  We revisit the problem of quantizing a chiral boson on a torus. The
conventional approach is to extract the partition function of a chiral boson
from the path integral of a non-chiral boson. Instead we compute it directly
from the chiral boson Lagrangian of Floreanini and Jackiw modified by
topological terms involving auxiliary fields. A careful analysis of the
gauge-fixing condition for the extra gauge symmetry reproduces the correct
results for the free chiral boson, and has the advantage of being applicable to
a wider class of interacting chiral boson theories.


title:
A Search for l-C3H+ and l-C3H in Sgr B2(N), Sgr B2(OH), and the Dark
  Cloud TMC-1

abstract:
  Pety et al. (2012) recently reported the detection of several transitions of
an unknown carrier in the Horsehead PDR and attribute them to l-C3H+. Here, we
have tested the predictive power of their fit by searching for, and
identifying, the previously unobserved J=1-0 and J=2-1 transitions of the
unknown carrier (B11244) towards Sgr B2(N) in data from the publicly available
PRIMOS project. Also presented here are observations of the J=6-5 and J=7-6
transitions towards Sgr B2(N) and Sgr B2(OH) using the Barry E. Turner Legacy
Survey and results from the Kaifu et al. (2004) survey of TMC-1. We calculate
an excitation temperature and column density of B11244 of ~10 K and ~10^13 cm-2
in Sgr B2(N) and ~79 K with an upper limit of < 1.5 x 10^13 cm-2 in Sgr B2(OH)
and find trace evidence for the cation's presence in TMC-1. Finally, we present
spectra of the neutral species in both Sgr B2(N) and TMC-1, and comment on the
robustness of the assignment of the detected signals to l-C3H+.


title:
Microdosimetry spectra and RBE of H-1, He-4, Li-7 and C-12 nuclei in
  water studied with Geant4

abstract:
  A Geant4-based Monte Carlo model for Heavy-Ion Therapy (MCHIT) is used to
study radiation fields of H-1, He-4, Li-7 and C-12 beams with similar ranges
(~160-180 mm) in water. Microdosimetry spectra are simulated for wall-less and
walled Tissue Equivalent Proportional Counters (TEPCs) placed outside or inside
a phantom, as in experiments performed, respectively, at NIRS, Japan and GSI,
Germany. The impact of fragmentation reactions on microdosimetry spectra is
investigated for He-4, Li-7 and C-12, and contributions from nuclear fragments
of different charge are evaluated for various TEPC positions in the phantom.
The microdosimetry spectra measured on the beam axis are well described by
MCHIT, in particular, in the vicinity of the Bragg peak. However, the simulated
spectra for the walled TEPC far from the beam axis are underestimated. Relative
Biological Effectiveness (RBE) of the considered beams is estimated using a
modified microdosimetric-kinetic model. Calculations show a similar rise of the
RBE up to 2.2-2.9 close to the Bragg peak for helium, lithium and carbon beams
compared to the modest values of 1-1.2 at the plateau region. Our results
suggest that helium and lithium beams are also promising options for cancer
therapy.


title: Finite groups whose prime graphs are regular

abstract:
  Let G be a finite group and let Irr(G) be the set of all irreducible complex
characters of G. Let cd(G) be the set of all character degrees of G and denote
by \rho(G) the set of primes which divide some character degrees of G. The
prime graph \Delta(G) associated to G is a graph whose vertex set is \rho(G)
and there is an edge between two distinct primes p and q if and only if the
product pq divides some character degree of G. In this paper, we show that the
prime graph \Delta(G) of a finite group G is 3-regular if and only if it is a
complete graph with four vertices.


title:
Cost overruns in Large-Scale Transportation Infrastructure Projects:
  Explanations and Their Theoretical Embeddedness

abstract:
  Managing large-scale transportation infrastructure projects is difficult due
to frequent misinformation about the costs which results in large cost overruns
that often threaten the overall project viability. This paper investigates the
explanations for cost overruns that are given in the literature. Overall, four
categories of explanations can be distinguished: technical, economic,
psychological, and political. Political explanations have been seen to be the
most dominant explanations for cost overruns. Agency theory is considered the
most interesting for political explanations and an eclectic theory is also
considered possible. Nonpolitical explanations are diverse in character,
therefore a range of different theories (including rational choice theory and
prospect theory), depending on the kind of explanation is considered more
appropriate than one all-embracing theory.


title:
Lock-in and Its Influence on the Project Performance of Large-Scale
  Transportation Infrastructure Projects. Investigating the Way in Which
  Lock-in Can Emerge and Affect Cost Overruns

abstract:
  Lock-in, the escalating commitment of decision-makers to an ineffective
course of action, has the potential to explain the large cost overruns in large
scale transportation infrastructure projects. Lock-in can occur both at the
decision-making level (before the decision to build) and at the project level
(after the decision to build) and can influence the extent of overruns in two
ways. The first involves the methodology of calculating cost overruns according
to the formal decision to build. Due to lock-in, however, the real decision to
build is made much earlier in the decision-making process and the costs
estimated at that stage are often much lower than those that are estimated at a
later stage in the decision-making process, thus increasing cost overruns. The
second way that lock-in can affect cost overruns is through practice. Although
decisions about the project (design and implementation) need to be made,
lock-in can lead to inefficient decisions that involve higher costs. Sunk costs
(in terms of both time and money), the need for justification, escalating
commitment, and inflexibility and the closure of alternatives are indicators of
lock-in. In this paper, two case studies, of the Betuweroute and the HSL-South
projects in the Netherlands, demonstrate the presence of lock-in and its
influence on the extent of cost overruns at both the decision-making and
project levels. This suggests that recognition of lock-in as an explanation for
cost overruns significantly contributes to the understanding of the inadequate
planning process of projects and allows development of more appropriate means.


title:
Characteristics of Cost Overruns for Dutch Transport Infrastructure
  Projects and the Importance of the Decision to Build and Project Phases

abstract:
  Using a methodology similar to that used the in the worldwide research, the
cost performance of Dutch large-scale transport infrastructure projects is
determined. In the Netherlands, cost overruns are as common as cost underruns
but because cost overruns are larger than cost underruns projects on average
have a cost overrun of 16.5%. The focus on one country further enabled to
consider cost overruns during different project development phases. It turned
out that in the Netherlands the majority of the cost overrun occurs in the
pre-construction phase (the period between the formal decision to build and the
start of construction). The frequency as well as the magnitude of
pre-construction cost overrun is significantly higher than in the construction
phase. The used methodology of calculating cost overruns does however not take
lock-in into account. This phenomenon shows that the real decision to build was
taken much earlier in the decision-making process. Since estimated costs are
usually lower during these earlier stages, the cost overruns based on this real
decision to build are likely to be much higher. Cost overruns presented in
studies are therefore often underestimated and the problem of cost overruns is
much larger than we think.


title:
Different Cost Performance: Different Determinants? The Case of Cost
  Overruns in Dutch Transportation Infrastructure Projects

abstract:
  This paper examines three independent explanatory variables and their
relation with cost overrun in order to decide whether this is different for
Dutch infrastructure projects compared to worldwide findings. The three
independent variables are project type (road, rail, and fixed link projects),
project size (measured in terms of estimated costs) and the length of the
project implementation phase. For Dutch projects, average cost overrun is 10.6%
for rail, 18.6% for roads and 21.7% for fixed links. For project size, small
Dutch projects have the largest average percentage cost overruns but in terms
of total overrun, large projects have a larger share. The length of the
implementation phase and especially the length of the pre-construction phase
are important determinants of cost overruns in the Netherlands. With each
additional year of pre-construction, percentage cost overrun increases by five
percentage points. In contrast, the length of the construction phase has hardly
any influence on cost overruns. This is an important contribution to current
knowledge about cost overruns, because the period in which projects are most
prone to cost overruns is narrowed down considerably, at least in the
Netherlands. This means that period can be focused on to determine the causes
and cures of overruns.


title:
Explaining Cost Overruns of Large-Scale Transportation Infrastructure
  Projects using a Signalling Game

abstract:
  Strategic behaviour is one of the main explanations for cost overruns. It can
theoretically be supported by agency theory, in which strategic behaviour is
the result of asymmetric information between the principal and agent. This
paper gives a formal account of this relation by a signalling game. This is a
game with incomplete information which considers the way in which parties
anticipate upon other parties' behaviour in choosing a course of action. The
game shows how cost overruns are the result of an inappropriate signal. This
makes it impossible for the principal to distinguish between the types of
agents, and hence, allows for strategic behaviour. It is illustrated how cost
overruns can be avoided by means of two policy measures, e.g. an accountability
structure and benchmarking.


title:
Geographical Variation in Project Cost Performance: The Netherlands
  versus Worldwide

abstract:
  Cost overruns in transport infrastructure projects know no geographical
limits, overruns are a global phenomenon. Nevertheless, the size of cost
overruns varies with location. In the Netherlands, cost overruns appear to be
smaller compared to the rest of the world. This paper tests whether Dutch
projects perform significantly better in terms of cost overruns than other
geographical areas. It is concluded that for road and tunnel projects, the
Netherlands performs similarly to the rest of the world. For rail projects,
Dutch projects perform considerably better, with projects having significantly
lower percentage cost overruns in real terms (11%) compared to projects in
other North West European countries (27%) and in other geographical areas
(44%). Bridge projects also have considerably smaller cost overruns: 7% in the
Netherlands compared with 45% in other NW European countries and 27% in other
geographical areas. In explaining cost overruns, geography should therefore
clearly be taken into consideration.


title:
Fitting isochrones to open cluster photometric data III. Estimating
  metallicities from UBV photometry

abstract:
  The metallicity is a critical parameter that affects the correct
determination fundamental characteristics stellar cluster and has important
implications in Galactic and Stellar evolution research. Fewer than 10 % of the
2174 currently catalog open clusters have their metallicity determined in the
literature. In this work we present a method for estimating the metallicity of
open clusters via non-subjective isochrone fitting using the cross-entropy
global optimization algorithm applied to UBV photometric data. The free
parameters distance, reddening, age, and metallicity simultaneously determined
by the fitting method. The fitting procedure uses weights for the observational
data based on the estimation of membership likelihood for each star, which
considers the observational magnitude limit, the density profile of stars as a
function of radius from the center of the cluster, and the density of stars in
multi-dimensional magnitude space. We present results of [Fe/H] for nine
well-studied open clusters based on 15 distinct UBV data sets. The [Fe/H]
values obtained in the ten cases for which spectroscopic determinations were
available in the literature agree, indicating that our method provides a good
alternative to determining [Fe/H] by using an objective isochrone fitting. Our
results show that the typical precision is about 0.1 dex.


title: Compact Clifford-Klein forms -- geometry, topology and dynamics

abstract:
  We survey results on compact Clifford-Klein forms of homogeneous spaces, with
a focus on recent contributions and organized around approaches via topology,
geometry and dynamics. In addition, we survey results on moduli spaces of
compact forms.


title:
Functional renormalization group study of the two-flavor linear sigma
  model in the presence of the axial anomaly

abstract:
  The $SU(2)_A \times U(2)_V$-symmetric chiral linear sigma model in the
presence of the axial anomaly is studied in the local-potential approximation
of the Functional Renormalization Group (FRG). The renormalization group (RG)
flow is investigated in a truncation which reproduces recent results for the
$U(2)_A \times U(2)_V$-symmetric model in the limit of vanishing axial anomaly
strength. We search for the conjectured O(4) fixed point in the presence of the
$U(1)_A$ anomaly and analyze its stability properties.


title: Novel techniques to search for neutron radioactivity

abstract:
  Two new methods to observe neutron radioactivity are presented. Both methods
rely on the production and decay of the parent nucleus in flight. The relative
velocity measured between the neutron and the fragment is sensitive to
half-lives between ~1 and ~100 ps for the Decay in Target (DiT) method. The
transverse position measurement of the neutron in the Decay in a Magnetic Field
(DiMF) method is sensitive to half-lives between 10 ps and 1 ns.


title:
Compression of unitary rank--structured matrices to CMV-like shape with
  an application to polynomial rootfinding

abstract:
  This paper is concerned with the reduction of a unitary matrix U to CMV-like
shape. A Lanczos--type algorithm is presented which carries out the reduction
by computing the block tridiagonal form of the Hermitian part of U, i.e., of
the matrix U+U^H. By elaborating on the Lanczos approach we also propose an
alternative algorithm using elementary matrices which is numerically stable. If
U is rank--structured then the same property holds for its Hermitian part and,
therefore, the block tridiagonalization process can be performed using the
rank--structured matrix technology with reduced complexity. Our interest in the
CMV-like reduction is motivated by the unitary and almost unitary eigenvalue
problem. In this respect, finally, we discuss the application of the CMV-like
reduction for the design of fast companion eigensolvers based on the customary
QR iteration.


title:
Everything you always wanted to know about the parameterized complexity
  of Subgraph Isomorphism (but were afraid to ask)

abstract:
  Given two graphs $H$ and $G$, the Subgraph Isomorphism problem asks if $H$ is
isomorphic to a subgraph of $G$. While NP-hard in general, algorithms exist for
various parameterized versions of the problem: for example, the problem can be
solved (1) in time $2^{O(|V(H)|)}\cdot n^{O(\tw(H))}$ using the color-coding
technique of Alon, Yuster, and Zwick; (2) in time $f(|V(H)|,\tw(G))\cdot n$
using Courcelle's Theorem; (3) in time $f(|V(H)|,\genus(G))\cdot n$ using a
result on first-order model checking by Frick and Grohe; or (4) in time
$f(\maxdeg(H))\cdot n^{O(\tw(G)})$ for connected $H$ using the algorithm of
Matou\v{s}ek and Thomas. Already this small sample of results shows that the
way an algorithm can depend on the parameters is highly nontrivial and subtle.
  We develop a framework involving 10 relevant parameters for each of $H$ and
$G$ (such as treewidth, pathwidth, genus, maximum degree, number of vertices,
number of components, etc.), and ask if an algorithm with running time \[
f_1(p_1,p_2,..., p_\ell)\cdot n^{f_2(p_{\ell+1},..., p_k)} \] exist, where each
of $p_1,..., p_k$ is one of the 10 parameters depending only on $H$ or $G$. We
show that {\em all} the questions arising in this framework are answered by a
set of 11 maximal positive results (algorithms) and a set of 17 maximal
negative results (hardness proofs); some of these results already appear in the
literature, while others are new in this paper.
  On the algorithmic side, our study reveals for example that an unexpected
combination of bounded degree, genus, and feedback vertex set number of $G$
gives rise to a highly nontrivial algorithm for Subgraph Isomorphism. On the
hardness side, we present W[1]-hardness proofs under extremely restricted
conditions, such as when $H$ is a bounded-degree tree of constant pathwidth and
$G$ is a planar graph of bounded pathwidth.


title:
Tests of the Quark-Gluon Plasma Coupling Strength at Early Times with
  Heavy Quarks

abstract:
  The redistribution in momentum space of heavy quarks via their interactions
in the quark-gluon plasma is an excellent probe of the heavy quark coupling
strength to the medium. We utilize a Monte Carlo Langevin calculation for
tracking heavy quark - antiquark pairs embedded in a viscous hydrodynamic
space-time evolution. We find that the nuclear modification factor ($R_{AA}$)
for charm quarks is relatively insensitive to the coupling to the quark-gluon
plasma at early times where the highest temperatures are acheived. In contrast
the azimuthal angular correlation of charm and anticharm quarks is extremely
sensitive to the early time evolution. For beauty quarks the situation is
reversed in terms of sensitivity. Future measurements of heavy quarks have the
potential to map out the temperature dependence of the shear viscosity to
entropy density ratio ({\eta}/s).


title: On the Topology of the Facebook Page Network

abstract:
  The Facebook Page Network (FPN) is a platform for Businesses, Public Figures
and Organizations (BPOs) to connect with individuals and other BPOs in the
digital space. For over a decade scale-free networks have most appropriately
described a variety of seemingly disparate physical, biological and social
real-world systems unified by similar network properties such as
scale-invariance, growth via a preferential attachment mechanism, and a power
law degree distribution P(k) = ck^-{\lambda} where typically 2<{\lambda}<3. In
this paper we show that both the Facebook Page Network and its BPO-BPO
subnetwork suggest power law and scale-free characteristics. We argue that
social media analysts must consider the logarithmic and non-linear properties
of social media audiences of scale.


title: A good leaf order on simplicial trees

abstract:
  Using the existence of a good leaf in every simplicial tree, we order the
facets of a simplicial tree in order to find combinatorial information about
the Betti numbers of its facet ideal. Applications include an Eliahou-Kervaire
splitting of the ideal, as well as a refinement of a recursive formula of H\`a
and Van Tuyl for computing the graded Betti numbers of simplicial trees.


title: A Knowledge-based Treatment of Human-Automation Systems

abstract:
  In a supervisory control system the human agent knowledge of past, current,
and future system behavior is critical for system performance. Being able to
reason about that knowledge in a precise and structured manner is central to
effective system design. In this paper we introduce the application of a
well-established formal approach to reasoning about knowledge to the modeling
and analysis of complex human-automation systems. An intuitive notion of
knowledge in human-automation systems is sketched and then cast as a formal
model. We present a case study in which the approach is used to model and
reason about a classic problem from the human-automation systems literature;
the results of our analysis provide evidence for the validity and value of
reasoning about complex systems in terms of the knowledge of the system agents.
To conclude, we discuss research directions that will extend this approach, and
note several systems in the aviation and human-robot team domains that are of
particular interest.


title: Fibred product of commutative algebras: generators and relations

abstract:
  The method of direct computation of universal (fibred) product in the
category of commutative associative algebras of finite type with unity over a
field is given and proven. The field of coefficients is not supposed to be
algebraically closed and can be of any characteristic. Formation of fibred
product of commutative associative algebras is an algebraic counterpart of
gluing algebraic schemes by means of some equivalence relation in algebraic
geometry. If initial algebras are finite-dimensional vector spaces the
dimension of their product obeys Grassmann-like formula. Finite-dimensional
case means geometrically the strict version of adding two collections of points
containing some common part.
  The method involves description of algebras by generators and relations on
input and returns similar description of the product algebra. It is
"ready-to-eat" even for computer realization. The product algebra is
well-defined: taking another descriptions of the same algebras leads to
isomorphic product algebra. Also it is proven that the product algebra enjoys
universal property, i.e. it is indeed fibred product. The input data is a
triple of algebras and a pair of homomorphisms $A_1\stackrel{f_1}{\to}A_0
\stackrel{f_2}{\leftarrow}A_2$. Algebras and homomorphisms can be described in
any fashion. We prove that for computing the fibred product it is enough to
restrict to the case when $f_i,i=1,2,$ are surjective and describe how to
reduce to surjective case. Also the way to choose generators and relations for
input algebras is considered.


title:
I. Inverse Compton origin of pulsar \gamma-ray emission. II.
  Reconnection model of Crab flares

abstract:
  I. There is growing evidence that pulsars' high energy emission is generated
via Inverse Compton mechanism.
  II. The particles producing Crab flares, and possibly most of the Crab
Nebula's high energy emission, are accelerated via reconnection events, and not
at shock via Fermi mechanisms.


title:
On the mechanical stability of asymptotically flat black holes with
  minimally coupled scalar hair

abstract:
  We show that the asymptotically flat hairy black holes, solutions of the
Einstein field equations minimally coupled to a scalar field, previously
discovered by one of us, present mode instability against linear radial
perturbations. It is also shown that the number of unstable modes is finite and
their frequencies can be made arbitrarily small.


title: The cluster value problem for Banach spaces

abstract:
  The main result is that the cluster value problem in separable Banach spaces,
for the Banach algebras $A_u$ and $H^{\infty}$, can be reduced to the cluster
value problem in those spaces which are $\ell_1$ sums of a sequence of finite
dimensional spaces.


title:
Neural Dust: An Ultrasonic, Low Power Solution for Chronic Brain-Machine
  Interfaces

abstract:
  A major hurdle in brain-machine interfaces (BMI) is the lack of an
implantable neural interface system that remains viable for a lifetime. This
paper explores the fundamental system design trade-offs and ultimate size,
power, and bandwidth scaling limits of neural recording systems built from
low-power CMOS circuitry coupled with ultrasonic power delivery and backscatter
communication. In particular, we propose an ultra-miniature as well as
extremely compliant system that enables massive scaling in the number of neural
recordings from the brain while providing a path towards truly chronic BMI.
These goals are achieved via two fundamental technology innovations: 1)
thousands of 10 - 100 \mu m scale, free-floating, independent sensor nodes, or
neural dust, that detect and report local extracellular electrophysiological
data, and 2) a sub-cranial interrogator that establishes power and
communication links with the neural dust.


title:
Tailored conversion of synthetic graphite into rotationally misoriented
  few-layer graphene by a cold thermal shock

abstract:
  Following the discovery of graphene, keen attentions have been paid in
comprehending the noticeably superior electromagnetic, optical and absorptive
properties of few layer graphene (FLG) with rotational-stacking-faults. With
achieving intense fundamental interests, the demands to synthesize such FLG are
rapidly increasing. However, the potential applications of such FLG, especially
in composite science and energy storage devices, are practically hindered
because of non-fulfillment of required production rate. Additionally, synthesis
of such FLG with controlled layer-numbers still remains an unsolved challenge.
Further breakthroughs in this direction are thus highly desirable. The present
article is a step ahead in this direction and is possibly the first of its
kind. Here we show how such FLG, with precisely controlled number of layers,
can readily be obtained from an isostatically compacted synthetic graphite, by
controlled dynamic fracture, with microbranching instability, induced by
cold-thermal-shock and discovered the mechanism behind such transformation by a
theoretical modeling.


title: Zero forcing for sign patterns

abstract:
  We introduce a new variant of zero forcing - signed zero forcing. The
classical zero forcing number provides an upper bound on the maximum nullity of
a matrix with a given graph (i.e. zero-nonzero pattern). Our new variant
provides an analo- gous bound for the maximum nullity of a matrix with a given
sign pattern. This allows us to compute, for instance, the maximum nullity of a
Z-matrix whose graph is L(K_{n}), the line graph of a clique.


title: Scattering of Massless Particles in Arbitrary Dimension

abstract:
  We present a compact formula for the complete tree-level S-matrix of pure
Yang-Mills and gravity theories in arbitrary spacetime dimension. The new
formula for the scattering of n particles is given by an integral over the
position of n points on a sphere restricted to satisfy a dimension-independent
set of equations. The integrand is constructed using the reduced Pfaffian of a
2n by 2n matrix that depends on momenta and polarization vectors. In its
simplest form, the gravity integrand is a reduced determinant which is the
square of the Pfaffian in the Yang-Mills integrand. Gauge invariance is
completely manifest as it follows from a simple property of the Pfaffian.


title: Inconsistency and Accuracy of Heuristics with A* Search

abstract:
  Many studies in heuristic search suggest that the accuracy of the heuristic
used has a positive impact on improving the performance of the search. In
another direction, historical research perceives that the performance of
heuristic search algorithms, such as A* and IDA*, can be improved by requiring
the heuristics to be consistent -- a property satisfied by any perfect
heuristic. However, a few recent studies show that inconsistent heuristics can
also be used to achieve a large improvement in these heuristic search
algorithms. These results leave us a natural question: which property of
heuristics, accuracy or consistency/inconsistency, should we focus on when
building heuristics? While there are studies on the heuristic accuracy with the
assumption of consistency, no studies on both the inconsistency and the
accuracy of heuristics are known to our knowledge.
  In this study, we investigate the relationship between the inconsistency and
the accuracy of heuristics with A* search. Our analytical result reveals a
correlation between these two properties. We then run experiments on the domain
for the Knapsack problem with a family of practical heuristics. Our empirical
results show that in many cases, the more accurate heuristics also have higher
level of inconsistency and result in fewer node expansions by A*.


title:
The origin of fermion families and the value of the fine structure
  constant

abstract:
  This paper is concerned with a way of thinking about the standard model that
explains the existence of three fermion families and the value of the fine
structure constant. The main idea is that the ultraviolet divergences that we
encounter in the quantum field theories of the standard model, when interpreted
appropriately, have a deep physical significance that leads to new
relationships between the physical and bare masses quarks and leptons. This
interpretation is based on the assumption of a quantum gravity induced
ultraviolet cutoff at the Planck scale and a novel approach to mass
renormalization in which the usual perturbation series for the self-mass of a
quark or lepton is rearranged and formally summed. Perturbing around the
formally summed expression leads to self-consistency equations for the physical
quark and lepton masses with multiple solutions that lie outside the reach of
conventional perturbation theory. When applied to the standard model at the
lowest level of approximation, this approach explains how three generations of
charged leptons with a mass spectrum and a value of the fine structure constant
in rough agreement with experiment can emerge from a universal bare mass and
bare electromagnetic charge. This approach also explains how three generations
of physical quark doublets (six flavors) can emerge from a universal bare
doublet and bare color charge. Finally, it explains the origin of mixing (and
CP violation) and the absence of flavor-changing neutral currents.


title: TDOA assisted RSSD based localization using UWB and directional antennas

abstract:
  This paper studies the use of directional antennas for received signal
strength difference (RSSD) based localization using ultra-wideband and
demonstrates the achievable accuracy with this localization method applied to
UWB. As introduced in our previous work the RSSD localization is assisted with
one Time Difference of Arrival (TDOA) estimation. The use of directional
receiving antennas and an omni-directional transmitting antenna is assumed.
Localization is performed in 2D. Two localization approaches are considered:
RSSD using statistical channel model and fingerprinting approach. In the case
of statistical channel model simulations are performed using Matlab. In the
case of fingerprinting approach localization is done based on real
indoor-measurements.


title: Self-organization versus top-down planning in the evolution of a city

abstract:
  Interventions of central, top-down planning are serious limitations to the
possibility of modelling the dynamics of cities. An example is the city of
Paris (France), which during the 19th century experienced large modifications
supervised by a central authority, the `Haussmann period'. In this article, we
report an empirical analysis of more than 200 years (1789-2010) of the
evolution of the street network of Paris. We show that the usual network
measures display a smooth behavior and that the most important quantitative
signatures of central planning is the spatial reorganization of centrality and
the modification of the block shape distribution. Such effects can only be
obtained by structural modifications at a large-scale level, with the creation
of new roads not constrained by the existing geometry. The evolution of a city
thus seems to result from the superimposition of continuous, local growth
processes and punctual changes operating at large spatial scales.

categories: physics.soc-ph cond-mat.dis-nn cs.SI nlin.AO


title: Integral traces of weak Maass forms of genus zero odd prime level

abstract:
  Duke and the second author defined a family of linear maps from spaces of
weakly holomorphic modular forms of negative integral weight and level 1 into
spaces of weakly holomorphic modular forms of half integral weight and level 4
and showed that these lifts preserve the integrality of Fourier coefficients.
We show that the generalization of these lifts to modular forms of genus 0 odd
prime level also preserves the integrality of Fourier coefficients.


title:
Navigating Central Path with Electrical Flows: from Flows to Matchings,
  and Back

abstract:
  We present an $\tilde{O}(m^{10/7})=\tilde{O}(m^{1.43})$-time algorithm for
the maximum s-t flow and the minimum s-t cut problems in directed graphs with
unit capacities. This is the first improvement over the sparse-graph case of
the long-standing $O(m \min(\sqrt{m},n^{2/3}))$ time bound due to Even and
Tarjan [EvenT75]. By well-known reductions, this also establishes an
$\tilde{O}(m^{10/7})$-time algorithm for the maximum-cardinality bipartite
matching problem. That, in turn, gives an improvement over the celebrated
celebrated $O(m \sqrt{n})$ time bound of Hopcroft and Karp [HK73] whenever the
input graph is sufficiently sparse.


title: Multi-Sommerfeld enhancement in dark sector

abstract:
  We study the multi-Sommerfeld enhancement in the case where $V(r)$ is
composed of different kinds of potentials. We show that there are special
properties of the multi-Sommerfeld enhancement. The physical content of the
multi-Sommerfeld mechanism is carefully demonstrated. The multi-Sommerfeld
enhancement might play a role in dark matter annihilation.


title:
Hierarchical exchangeability of pure states in mean field spin glass
  models

abstract:
  The main result in this paper is motivated by the M\'ezard-Parisi ansatz
which predicts a very special structure for the distribution of spins in
diluted mean field spin glass models, such as the random K-sat model. Using the
fact that one can safely assume the validity of the Ghirlanda-Guerra identities
in these models, we prove hierarchical exchangeability of pure states for the
asymptotic Gibbs measures, which allows us to apply a representation result for
hierarchically exchangeable arrays recently proved in arXiv:1301.1259.
Comparing this representation with the predictions of the M\'ezard-Parisi
ansatz, one can see that the key property still missing is that the
multi-overlaps between pure states depend only on their overlaps.


title: Maxwell's Refrigerator: An Exactly Solvable Model

abstract:
  We describe a simple and solvable model of a device that -- like the
"neat-fingered being" in Maxwell's famous thought experiment -- transfers
energy from a cold system to a hot system by rectifying thermal fluctuations.
In order to accomplish this task, our device requires a memory register to
which it can write information: the increase in the Shannon entropy of the
memory compensates the decrease in the thermodynamic entropy arising from the
flow of heat against a thermal gradient. We construct the nonequilibrium phase
diagram for this device, and find that it can alternatively act as an eraser of
information. We discuss our model in the context of the second law of
thermodynamics.


title: A comparison of period finding algorithms

abstract:
  This paper presents a comparison of popular period finding algorithms applied
to the light curves of variable stars from the Catalina Real-time Transient
Survey (CRTS), MACHO and ASAS data sets. We analyze the accuracy of the methods
against magnitude, sampling rates, quoted period, quality measures
(signal-to-noise and number of observations), variability, and object classes.
We find that measure of dispersion-based techniques - analysis-of-variance with
harmonics and conditional entropy - consistently give the best results but
there are clear dependencies on object class and light curve quality. Period
aliasing and identifying a period harmonic also remain significant issues. We
consider the performance of the algorithms and show that a new conditional
entropy-based algorithm is the most optimal in terms of completeness and speed.
We also consider a simple ensemble approach and find that it performs no better
than individual algorithms.


title: Derivations preserving quasinilpotent elements

abstract:
  We consider a Banach algebra $A$ with the property that, roughly speaking,
sufficiently many irreducible representations of $A$ on nontrivial Banach
spaces do not vanish on all square zero elements. The class of Banach algebras
with this property turns out to be quite large -- it includes $C^*$-algebras,
group algebras on arbitrary locally compact groups, commutative algebras,
$L(X)$ for any Banach space $X$, and various other examples. Our main result
states that every derivation of $A$ that preserves the set of quasinilpotent
elements has its range in the radical of $A$.


title: Optimal arbitrarily accurate composite pulse sequences

abstract:
  Implementing a single qubit unitary is often hampered by imperfect control.
Systematic amplitude errors $\epsilon$, caused by incorrect duration or
strength of a pulse, are an especially common problem. But a sequence of
imperfect pulses can provide a better implementation of a desired operation, as
compared to a single primitive pulse. We find optimal pulse sequences
consisting of $L$ primitive $\pi$ or $2\pi$ rotations that suppress such errors
to arbitrary order $\mathcal{O}(\epsilon^{n})$ on arbitrary initial states.
Optimality is demonstrated by proving an $L=\mathcal{O}(n)$ lower bound and
saturating it with $L=2n$ solutions. Closed-form solutions for arbitrary
rotation angles are given for $n=1,2,3,4$. Perturbative solutions for any $n$
are proven for small angles, while arbitrary angle solutions are obtained by
analytic continuation up to $n=12$. The derivation proceeds by a novel
algebraic and non-recursive approach, in which finding amplitude error
correcting sequences can be reduced to solving polynomial equations.


title: Evolution of Magnetism in Single-Crystal Honeycomb Iridates

abstract:
  We report the successful synthesis of single-crystals of the layered iridate,
(Na$_{1-x}$Li$_{x}$)$_2$IrO$_3$, $0\leq x \leq 0.9$, and a thorough study of
its structural, magnetic, thermal and transport properties. The new compound
allows a controlled interpolation between Na$_2$IrO$_3$ and Li$_2$IrO$_3$,
while maintaing the novel quantum magnetism of the honeycomb Ir$^{4+}$ planes.
The measured phase diagram demonstrates a dramatic suppression of the N\'eel
temperature, $T_N$, at intermediate $x$ suggesting that the magnetic order in
Na$_2$IrO$_3$ and Li$_2$IrO$_3$ are distinct, and that at $x\approx 0.7$, the
compound is close to a magnetically disordered phase that has been sought after
in Na$_2$IrO$_3$ and Li$_2$IrO$_3$. By analyzing our magnetic data with a
simple theoretical model we also show that the trigonal splitting, on the
Ir$^{4+}$ ions changes sign from Na$_2$IrO$_3$ and Li$_2$IrO$_3$, and the
honeycomb iridates are in the strong spin-orbit coupling regime, controlled by
$\jeff=1/2$ moments.


title:
Note on black hole no hair theorems for massive forms and spin-1/2
  fields

abstract:
  We give a proof of the non-perturbative no hair theorems for a massive 2-form
field with 3-form field strength for general stationary axisymmetric and static
(anti)-de Sitter or asymptotically flat black hole spacetimes with some
suitable geometrical properties. The generalization of this result for higher
form fields is discussed. Next, we discuss the perturbative no hair theorems
for massive spin-1/2 fields for general static backgrounds with electric or
magnetic charge. Some generalization of this result for stationary axisymmetric
spacetimes are also discussed. All calculations are done in arbitrary spacetime
dimensions.


title: Pressure isotropization in high energy heavy ion collisions

abstract:
  The early stages of high energy heavy ion collisions are studied in the Color
Glass Condensate framework, with a real-time classical lattice simulation. When
increasing the coupling constant, we observe a rapid increase of the ratio of
longitudinal to transverse pressure. The transient regime that precedes this
behavior is of the order of 1 fm/c.


title:
Dispersion theory of nucleon polarizabilities and outlook on chiral
  effective field theory

abstract:
  Based on Compton scattering and meson photoproduction data the
polarizabilities of the nucleon are precisely studied and well understood due
to recent experimental and theoretical work based on nonsubtracted dispersion
relations. The {\it recommended} experimental values are $\alpha_p=12.0\pm
0.6$, $(12.0)$, $\beta_p=1.9\mp 0.6$, $(1.9)$, $\alpha_n=12.5\pm 1.7$,
$(12.7\pm 0.9)$, $\beta_n=2.7\mp 1.8$, $(2.5\mp 0.9)$ in units of
$10^{-4}$fm$^3$ and $\gamma^{(p)}_\pi=-36.4\pm 1.5$, $(-36.6)$,
$\gamma^{(n)}_\pi=+58.6\pm 4.0$, $(58.3)$, $(\gamma^{(p)}_0=-0.58\pm 0.20)$,
$\gamma^{(n)}_0=0.38\pm 0.22)$ in units of $10^{-4}$fm$^4$ [1]. The numbers
given in parentheses are predicted values. It is shown that all versions of
chiral effective field theories applied in analyses of nucleon polarizabilities
and Compton scattering ignore essential effects of $\omega$, $\rho$ and
$\sigma$ exchanges and of pseudoscalar $\pi$N coupling.


title: Cabling procedure for the colored HOMFLY polynomials

abstract:
  In the present paper we discuss the cabling procedure for the colored HOMFLY
polynomial. We describe how it can be used and how one can find all the
quantities such as projectors and $\mathcal{R}$-matrices, which are needed in
this procedure. The constructed matrix forms of the projectors and the
fundamental $\mathcal{R}$-matrices allow one in principle (neglecting the
computational difficulties) to find the HOMFLY polynomial in any representation
for any knot. We also discuss the group theory explanation of the cabling
procedure. This leads to the explanations of the form of the fundamental
$\mathcal{R}$-matrices and illuminates several conjectures proposed in previous
papers.


title: Estimation of the parameters of a stochastic logistic growth model

abstract:
  We consider a stochastic logistic growth model involving both birth and death
rates in the drift and diffusion coefficients for which extinction eventually
occurs almost surely. The associated complete Fokker-Planck equation describing
the law of the process is established and studied. We then use its solution to
build a likelihood function for the unknown model parameters, when discretely
sampled data is available. The existing estimation methods need adaptation in
order to deal with the extinction problem. We propose such adaptations, based
on the particular form of the Fokker-Planck equation, and we evaluate their
performances with numerical simulations. In the same time, we explore the
identifiability of the parameters which is a crucial problem for the
corresponding deterministic (noise free) model.


title: Importance sampling for jump processes and applications to finance

abstract:
  Adaptive importance sampling techniques are widely known for the Gaussian
setting of Brownian driven diffusions. In this work, we want to extend them to
jump processes. Our approach relies on a change of the jump intensity combined
with the standard exponential tilting for the Brownian motion. The free
parameters of our framework are optimized using sample average approximation
techniques. We illustrate the efficiency of our method on the valuation of
financial derivatives in several jump models.


title:
Time decay estimates for the wave equation with potential in dimension
  two

abstract:
  We study the wave equation with potential $u_{tt}-\Delta u+Vu=0$ in two
spatial dimensions, with $V$ a real-valued, decaying potential. With
$H=-\Delta+V$, we study a variety of mapping estimates of the solution
operators, $\cos(t\sqrt{H})$ and $\frac{\sin(t\sqrt{H})}{\sqrt{H}}$ under the
assumption that zero is a regular point of the spectrum of $H$. We prove a
dispersive estimate with a time decay rate of $|t|^{-\frac{1}{2}}$, a
polynomially weighted dispersive estimate which attains a faster decay rate of
$|t|^{-1}(\log |t|)^{-2}$ for $|t|>2$. Finally, we prove dispersive estimates
if zero is not a regular point of the spectrum of $H$.


title: Internal control of the Schr\"odinger equation

abstract:
  In this paper, we intend to present some already known results about the
internal controllability of the linear and nonlinear Schr\"odinger equation.
After presenting the basic properties of the equation, we give a self contained
proof of the controllability in dimension 1 using some propagation results. We
then discuss how to obtain some similar results on a compact manifold where the
zone of control satisfies the Geometric Control Condition. We also discuss some
known results and open questions when this condition is not satisfied. Then, we
present the links between the controllability and some resolvent estimates.
Finally, we discuss the new difficulties when we consider the Nonlinear
Schr\"odinger equation.


title: Probing higher spin black holes from CFT

abstract:
  In a class of 2D CFTs with higher spin symmetry, we compute thermal two-point
functions of certain scalar primary operators in the presence of nonzero
chemical potential for higher spin charge. These are shown to agree with the
same quantity calculated holographically using scalar fields propagating in a
charged black hole background of 3D higher spin gravity. This match serves as
further evidence for the duality between W_N minimal models at large central
charge and 3D higher spin gravity. It also supports a recent prescription for
computing boundary correlators of multi-trace scalar primary operators in
higher spin theories.


title:
On Three-Algebra and Bi-Fundamental Matter Amplitudes and Integrability
  of Supergravity

abstract:
  We explore tree-level amplitude relations for SU(N)xSU(M) bi-fundamental
matter theories. Embedding the group-theory structure in a Lie three-algebra,
we derive Kleiss-Kuijf-like relations for bi-fundamental matter theories in
general dimension. We investigate the three-algebra color-kinematics duality
for these theories. Unlike the Yang-Mills two-algebra case, the three-algebra
Bern-Carrasco-Johansson relations depend on the spacetime dimension and on the
detailed symmetry properties of the structure constants. We find the presence
of such relations in three and two dimensions, and absence in D>3.
Surprisingly, beyond six point, such relations are absent in the
Aharony-Bergman-Jafferis-Maldacena theory for general gauge group, while the
Bagger-Lambert-Gustavsson theory, and its supersymmetry truncations, obey the
color-kinematics duality like clockwork. At four and six points the relevant
partial amplitudes of the two theories are bijectively related, explaining
previous results in the literature. In D=2 the color-kinematics duality gives
results consistent with integrability of two-dimensional $\mathcal{N}=16$
supergravity: The four-point amplitude satisfies a Yang-Baxter equation; the
six- and eight-point amplitudes vanish for certain kinematics away from
factorization channels, as expected from integrability.


title:
A Bayesian approach for global sensitivity analysis of (multi-fidelity)
  computer codes

abstract:
  Complex computer codes are widely used in science and engineering to model
physical phenomena. Furthermore, it is common that they have a large number of
input parameters. Global sensitivity analysis aims to identify those which have
the most important impact on the output. Sobol indices are a popular tool to
perform such analysis. However, their estimations require an important number
of simulations and often cannot be processed under reasonable time constraint.
To handle this problem, a Gaussian process regression model is built to
surrogate the computer code and the Sobol indices are estimated through it. The
aim of this paper is to provide a methodology to estimate the Sobol indices
through a surrogate model taking into account both the estimation errors and
the surrogate model errors. In particular, it allows us to derive
non-asymptotic confidence intervals for the Sobol index estimations.
Furthermore, we extend the suggested strategy to the case of multi-fidelity
computer codes which can be run at different levels of accuracy. For such
simulators, we use an extension of Gaussian process regression models for
multivariate outputs.


title:
A Note on Lipschitz Continuity of Solutions of Poisson Equations in
  Metric Measure Spaces

abstract:
  In this note we show how to adjust some proofs of Koskela et. al 2003 and
Jiang 2011 in order to show that in certain spaces $(X,d,\mu)$, like
$RCD(K,N)$-spaces, every Sobolev function with local $L^{p}$-Laplacian and
$p>\dim\mu$ is locally Lipschitz continuous.


title: An Algorithmic Framework for Strategic Fair Division

abstract:
  We study the paradigmatic fair division problem of allocating a divisible
good among agents with heterogeneous preferences, commonly known as cake
cutting. Classical cake cutting protocols are susceptible to manipulation. Do
their strategic outcomes still guarantee fairness?
  To address this question we adopt a novel algorithmic approach, by designing
a concrete computational framework for fair division---the class of Generalized
Cut and Choose (GCC) protocols}---and reasoning about the game-theoretic
properties of algorithms that operate in this model. The class of GCC protocols
includes the most important discrete cake cutting protocols, and turns out to
be compatible with the study of fair division among strategic agents. In
particular, GCC protocols are guaranteed to have approximate subgame perfect
Nash equilibria, or even exact equilibria if the protocol's tie-breaking rule
is flexible. We further observe that the (approximate) equilibria of
proportional GCC protocols---which guarantee each of the $n$ agents a
$1/n$-fraction of the cake---must be (approximately) proportional. Finally, we
design a protocol in this framework with the property that its Nash equilibrium
allocations coincide with the set of (contiguous) envy-free allocations.


title:
Symmetry breaking of extremals for the Caffarelli-Kohn-Nirenberg
  inequalities in a non-Hilbertian setting

abstract:
  We provide an explicit necessary condition to have that no extremal for the
best constant in the Caffarelli-Kohn-Nirenberg inequality is radially
symmetric.


title: The two faces of Hawking radiation

abstract:
  What happens when Alice falls into a black hole? In spite of recent
challenges by Almheiri et al. -- the ""firewall" hypothesis -- the consensus on
this question tends to remain "nothing special". Here I argue that something
rather special can happen near the horizon, already at the semiclassical level:
besides the standard Hawking outgoing modes, Alice can records a quasi-thermal
spectrum of ingoing modes, whose temperature and intensity diverges as Alice's
Killing energy $E$ goes to zero. I suggest that this effect can be thought of
in terms a "horizon-infinity duality", which relates the perception of
near-horizon and asymptotic geodesic observers -- the two faces of Hawking
radiation.


title:
The MacWilliams identity for $m$-spotty weight enumerator over
  $\mathbb{F}_2+u\mathbb{F}_2+\cdots+u^{m-1}\mathbb{F}_2$

abstract:
  Past few years have seen an extensive use of RAM chips with wide I/O data
(e.g. 16, 32, 64 bits) in computer memory systems. These chips are highly
vulnerable to a special type of byte error, called an $m$-spotty byte error,
which can be effectively detected or corrected using byte error-control codes.
The MacWilliams identity provides the relationship between the weight
distribution of a code and that of its dual. The main purpose of this paper is
to present a version of the MacWilliams identity for $m$-spotty weight
enumerators over
$\mathbbm{F}_{2}+u\mathbbm{F}_{2}+\cdots+u^{m-1}\mathbbm{F}_{2}$ (shortly
$R_{u, m, 2}$).


title: Weyl-Cartan-Weitzenb\"ock gravity through Lagrange multiplier

abstract:
  We consider an extension of the Weyl-Cartan-Weitzenb\"{o}ck (WCW) and
teleparallel gravity, in which the Weitzenb\"{o}ck condition of the exact
cancellation of curvature and torsion in a Weyl-Cartan geometry is inserted
into the gravitational action via a Lagrange multiplier. In the standard metric
formulation of the WCW model, the flatness of the space-time is removed by
imposing the Weitzenb\"{o}ck condition in the Weyl-Cartan geometry, where the
dynamical variables are the space-time metric, the Weyl vector and the torsion
tensor, respectively. However, once the Weitzenb\"{o}ck condition is imposed on
the Weyl-Cartan space-time, the metric is not dynamical, and the gravitational
dynamics and evolution is completely determined by the torsion tensor. We show
how to resolve this difficulty, and generalize the WCW model, by imposing the
Weitzenb\"{o}ck condition on the action of the gravitational field through a
Lagrange multiplier. The gravitational field equations are obtained from the
variational principle, and they explicitly depend on the Lagrange multiplier.
As a particular model we consider the case of the Riemann-Cartan space-times
with zero non-metricity, which mimics the teleparallel theory of gravity. The
Newtonian limit of the model is investigated, and a generalized Poisson
equation is obtained, with the weak field gravitational potential explicitly
depending on the Lagrange multiplier and on the Weyl vector. The cosmological
implications of the theory are also studied, and three classes of exact
cosmological models are considered.


title: A new dielectric effect in viscous liquids

abstract:
  An accurate experimental and theoretical study has been performed about a
phenomenon, not previously reported in the literature, occurring in highly
viscous liquids: the formation of a definite pipe structure induced by the
passage of a heavy body, this structure lasting for quite a long time. A very
rich phenomenology (including mechanical, optical and structural effects)
associated with the formation of the pipe has been observed in different
liquids. Actually, the peculiar dynamical evolution of that structure does not
appear as a trivial manifestation of standard relaxation or spurious effects.
In particular we have revealed different time scales during the evolution of
the pipe and a non-monotonous decrease of the persistence time with decreasing
viscosity (with the appearance of at least two different maxima). We put
forward a microscopic model, consistent with the experimental data, where the
pipe behaves as a "dielectric shell" whose time evolution is described through
a simple thermodynamical approach, predicting several properties effectively
observed.


title: Peculiar points in the phase diagram of the water-alcohol solutions

abstract:
  The work is devoted to the investigation of nontrivial behavior of dilute
water-alcohol solutions. The temperature and concentration dependencies of the
contraction for aqueous solutions of ethanol and methanol are analyzed. The
existence of a specific point, the so-called peculiar point, was established.
It is shown that water-alcohol solutions of different types obey the principle
of corresponding states if temperature and volume fraction are used as
principal coordinates. In this case, the concentration of the peculiar point
for different solutions is close to x_{\nu}=0.28. Several predictions are made.


title:
CTA contributions to the 33rd International Cosmic Ray Conference
  (ICRC2013)

abstract:
  Compilation of CTA contributions to the proceedings of the 33rd International
Cosmic Ray Conference (ICRC2013), which took place in 2-9 July, 2013, in Rio de
Janeiro, Brazil


title:
The [O III] Nebula of the Merger Remnant NGC 7252: A Likely Faint
  Ionization Echo

abstract:
  We present images and spectra of a ~10 kpc-sized emission-line nebulosity
discovered in the prototypical merger remnant NGC 7252 and dubbed the `[O III]
nebula' because of its dominant [O III]_5007 line. This nebula seems to yield
the first sign of episodic AGN activity still occurring in the remnant, ~220
Myr after the coalescence of two gas-rich galaxies. Its location and kinematics
suggest it belongs to a stream of tidal-tail gas falling back into the remnant.
Its integrated [O III]_5007 luminosity is 1.4x10^40 erg/s, and its spectrum
features some high-excitation lines, including He II_4686. In diagnostic line-
ratio diagrams, the nebula lies in the domain of Seyfert galaxies, suggesting
that it is photoionized by a source with a power-law spectrum. Yet, a search
for AGN activity in NGC 7252 from X-rays to radio wavelengths yields no
detection, with the most stringent upper limit set by X-ray observations. The
upper luminosity limit of L_{2-10 keV,0} < 5x10^39 erg/s estimated for the
nucleus is ~10^3 times lower than the minimum ionizing luminosity of >5x10^42
erg/s necessary to excite the nebula. This large discrepancy suggests that the
nebula is a faint ionization echo excited by a mildly active nucleus that has
declined by ~3 orders of magnitude over the past 20,000-200,000 years. In many
ways this nebula resembles the prototypical `Hanny's Voorwerp' near IC 2497,
but its size is 3x smaller and its [O III] luminosity ~100x lower. We propose
that it be classified as an extended emission-line region (EELR). The [O III]
nebula is then the lowest-luminosity ionization echo and EELR discovered so
far, indicative of recent, probably sputtering AGN activity of Seyfert-like
intensity in NGC 7252.


title: Chiral and Gravitational Anomalies on Fermi Surfaces

abstract:
  A Fermi surface threaded by a Berry phase can be described by the
Wess-Zumino-Witten (WZW) term. After gauging, it produces a five-dimensional
Chern-Simons term in the action. We show how this Chern-Simons term captures
the essence of the Abelian, non-Abelian, and mixed gravitational anomalies in
describing both in- and off-equilibrium phenomena. In particular we derive a
novel contribution to the Chiral Vortical Effect that arises when a temperature
gradient is present. We also discuss the issue of universality of the anomalous
currents.


title: The Influence of Environment on the Circumgalactic Medium

abstract:
  The effect of environment on the circumgalactic medium (CGM) is investigated
through a comparison of Lya absorption line data in the Virgo Cluster and the
field. This Letter uses the first systematic survey of background QSOs in and
around the Virgo Cluster and large existing surveys of galaxies at low
redshift. While previous studies found denser gas (higher equivalent width)
closer to a galaxy (lower impact parameter), this correlation disappears in the
Virgo environment. In addition, the covering fraction of the CGM is lower in
the cluster environment than in the circumcluster environment and field. The
results indicate that the CGM is suppressed for cluster galaxies while galaxies
in the circumcluster environment have abundant CGM. The truncation of the CGM
may result in the quenching of star formation through starvation. Our results
also show that CGM surveys must consider the role of environment.


title:
A Megacam Survey of Outer Halo Satellites. II. Blue Stragglers in the
  Lowest Stellar Density Systems

abstract:
  We present a homogeneous study of blue straggler stars across ten outer halo
globular clusters, three classical dwarf spheroidal and nine ultra-faint
galaxies based on deep and wide-field photometric data taken with MegaCam on
the Canada-France-Hawaii Telescope. We find blue straggler stars to be
ubiquitous among these Milky Way satellites. Based on these data, we can test
the importance of primordial binaries or multiple systems on blue straggler
star formation in low density environments. For the outer halo globular
clusters we find an anti-correlation between the specific frequency of blue
straggler and absolute magnitude, similar to that previously observed for inner
halo clusters. When plotted against density and encounter rate, the frequency
of blue stragglers are well fitted by single trends with smooth transitions
between dwarf galaxies and globular clusters, which points to a common origin
for their blue stragglers. The fraction of blue stragglers stays constant and
high in the low encounter rate regime spanned by our dwarf galaxies, and
decreases with density and encounter rate in the range spanned by our globular
clusters. We find that young stars can mimic blue stragglers in dwarf galaxies
only if their ages are 2.5+/-0.5 Gyr and they represent ~1-7% of the total
number of stars, which we deem highly unlikely. These results point to
mass-transfer or mergers of primordial binaries or multiple systems as the
dominant blue straggler formation mechanism in low density systems.


title:
Planets Around Low-Mass Stars (PALMS). III. A Young Dusty L Dwarf
  Companion at the Deuterium-Burning Limit

abstract:
  We report the discovery of an L-type companion to the young M3.5V star 2MASS
J01225093-2439505 at a projected separation of 1.45" (~52 AU) as part of our
adaptive optics imaging search for extrasolar giant planets around young
low-mass stars. 2MASS 0122-2439 B has very red near-infrared colors similar to
the HR 8799 planets and the reddest known young/dusty L dwarfs in the field.
Moderate-resolution (R~3800) 1.5-2.4 $\mu$m spectroscopy reveals a
near-infrared spectral type of L4-L6 and an angular H-band shape, confirming
its cool temperature and young age. The kinematics of 2MASS 0122-2439 AB are
marginally consistent with members of the ~120 Myr AB Dor young moving group
based on the photometric distance to the primary (36 +/- 4 pc) and our radial
velocity measurement of 2MASS 0122-2439 A from Keck/HIRES. We adopt the AB Dor
group age for the system, but the high energy emission, lack of Li I
$\lambda$6707 absorption, and spectral shape of 2MASS 0122-2439 B suggest a
range of ~10-120 Myr is possible. The age and luminosity of 2MASS 0122-2439 B
fall in a strip where "hot-start" evolutionary model mass tracks overlap as a
result of deuterium burning. The implied mass of 2MASS 0122-2439 B is ~12-13
Mjup or ~22-27 Mjup if it is an AB Dor member, or possibly as low as 11 Mjup if
the wider age range is adopted. Evolutionary models predict an effective
temperature for 2MASS 0122-2439 B that corresponds to spectral types near the
L/T transition (~1300-1500 K) for field objects. However, we find a mid-L
near-infrared spectral type, indicating that 2MASS 0122-2439 B represents
another case of photospheric dust being retained to cooler temperatures at low
surface gravities, as seen in the spectra of young (8-30 Myr) planetary
companions. [Abridged]


title: Review on the determination of alpha_s from the QCD static energy

abstract:
  We review the determination of the strong coupling alpha_s from the
comparison of the perturbative expression for the Quantum Chromodynamics static
energy with lattice data. We collect here all the perturbative expressions
needed to evaluate the static energy at the currently known accuracy.


title: The Chemical Imprint of Silicate Dust on the Most Metal-Poor Stars

abstract:
  We investigate the impact of dust-induced gas fragmentation on the formation
of the first low-mass, metal-poor stars (< 1Msun) in the early universe.
Previous work has shown the existence of a critical dust-to-gas ratio, below
which dust thermal cooling cannot cause gas fragmentation. Assuming the first
dust is silicon-based, we compute critical dust-to-gas ratios and associated
critical silicon abundances ([Si/H]crit). At the density and temperature
associated with protostellar disks, we find that a standard Milky Way grain
size distribution gives [Si/H]crit = -4.5 +/- 0.1, while smaller grain sizes
created in a supernova reverse shock give [Si/H]crit = -5.3 +/- 0.1. Other
environments are not dense enough to be influenced by dust cooling. We test the
silicate dust cooling theory by comparing to silicon abundances observed in the
most iron-poor stars ([Fe/H] < -4.0). Several stars have silicon abundances low
enough to rule out dust-induced gas fragmentation with a standard grain size
distribution. Moreover, two of these stars have such low silicon abundances
that even dust with a shocked grain size distribution cannot explain their
formation. Adding small amounts of carbon dust does not significantly change
these conclusions. Additionally, we find that these stars exhibit either high
carbon with low silicon abundances or the reverse. A silicate dust scenario
thus suggests that the earliest low-mass star formation in the most metal-poor
regime may have proceeded through two distinct cooling pathways: fine structure
line cooling and dust cooling. This naturally explains both the carbon-rich and
carbon-normal stars at extremely low [Fe/H].


title: Testing protoplanetary disc dispersal with radio emission

abstract:
  We consider continuum free-free radio emission from the upper atmosphere of
protoplanetary discs as a probe of the ionized luminosity impinging upon the
disc. Making use of previously computed hydrodynamic models of disc
photoevaporation within the framework of EUV and X-ray irradiation, we use
radiative transfer post-processing techniques to predict the expected free-free
emission from protoplanetary discs. In general, the free-free luminosity scales
roughly linearly with ionizing luminosity in both EUV and X-ray driven
scenarios, where the emission dominates over the dust tail of the disc and is
partial optically thin at cm wavelengths. We perform a test observation of GM
Aur at 14-18 Ghz and detect an excess of radio emission above the dust tail to
a very high level of confidence. The observed flux density and spectral index
are consistent with free-free emission from the ionized disc in either the EUV
or X-ray driven scenario. Finally, we suggest a possible route to testing the
EUV and X-ray driven dispersal model of protoplanetary discs, by combining
observed free-free flux densities with measurements of mass-accretion rates. On
the point of disc dispersal one would expect to find a M_dot^2 scaling with
free-free flux in the case of EUV driven disc dispersal or a M_dot scaling in
the case of X-ray driven disc dispersal.


title: Leptogenesis with Lepton-Number-Violating Dirac Neutrinos

abstract:
  Dirac neutrinos with lepton-number-violating interactions can give rise to a
new leptogenesis mechanism. In its simplest renormalizable realization, based
on a gauged B-L symmetry spontaneously broken by four units, the decay of a new
scalar creates an asymmetry in the right-handed neutrinos. A neutrinophilic
two-Higgs-doublet model converts this asymmetry to the baryons, provides a
natural explanation of the small neutrino masses, and can lead to an effective
number of relativistic degrees of freedom of N(eff) = 3.29 due to the
entropy-suppressed contribution of the right-handed neutrinos.


title: d_{xy}-Density wave in fermion-fermion cold atom mixtures

abstract:
  We study density wave instabilities in a doubly-degenerate Fermi-Fermi
mixture with $SU(2)\times SU(2)$ symmetry on a square lattice. For sufficiently
large on-site inter-species repulsion, when the two species of fermions are
both at half-filling, two conventional ($s$-wave) number density waves are
formed with a $\pi$-phase difference between them to minimize the inter-species
repulsion. Upon moving one species away from half-filling, an unconventional
density wave with $d_{xy}$-wave symmetry emerges. When both species are away
from the vicinity of half-filling, superconducting instabilities dominate. We
present results of a functional renormalization-group calculation that maps out
the phase diagram at weak couplings. Also, we provide a simple explanation for
the emergence of the $d_{xy}$-density wave phase based on a four-patch model.
We find a robust and general mechanism for $d_{xy}$-density-wave formation that
is related to the shape and size of the Fermi surfaces. The density imbalance
between the two species of fermions in the vicinity of half-filling leads to
phase-space discrepancy for different inter-species Umklapp couplings. Using a
phase space argument for leading corrections in the one-loop renormalization
group approach to fermions, we show that the phase-space discrepancy in our
system causes opposite flows for the two leading intra-species Umklapp
couplings and that this triggers the $d_{xy}$-density-wave instability.


title: A Multiplicity Census of Intermediate-Mass Stars in Scorpius-Centaurus

abstract:
  Stellar multiplicity properties have been studied for much of the range from
the lowest to the highest stellar masses, but intermediate-mass stars from
F-type to late A-type have received relatively little attention. Here we report
on a Gemini/NICI snapshot imaging survey of 138 such stars in the young
Scorpius-Centaurus (Sco-Cen) region, for the purpose of studying multiplicity
with sensitivity down to planetary masses at wide separations. In addition to
two brown dwarfs and a companion straddling the hydrogen burning limit we
reported previously, here we present 26 new stellar companions and determine a
multiplicity fraction within 0.1"--5.0" of 21+/-4%. Depending on the adopted
semi-major axis distribution, our results imply a total multiplicity in the
range of ~60--80%, which further supports the known trend of a smoothly
continuous increase in the multiplicity fraction as a function of primary
stellar mass. A surprising feature in the sample is a distinct lack of nearly
equal-mass binaries, for which we discuss possible reasons. The survey yielded
no additional companions below or near the deuterium-burning limit, implying
that their frequency at >200 AU separations is not quite as high as might be
inferred from previous detections of such objects within the Sco-Cen region.


title:
Bringing Simulation and Observation Together to Better Understand the
  Intergalactic Medium

abstract:
  The methods by which one characterizes the distribution of matter in
cosmological simulations is intrinsically different from how one performs the
same task observationally. In this paper, we make substantial steps towards
comparing simulations and observations of the intergalactic medium (IGM) in a
more sensible way. We present a pipeline that generates and fits synthetic QSO
absorption spectra using sight lines cast through a cosmological simulation,
and simultaneously identifies structure by directly analyzing the variations in
HI and OVI number density. We compare synthetic absorption spectra with a less
observationally motivated, but more straightforward density threshold-based
method for finding absorbers. Our efforts focus on HI and OVI to better
characterize the warm/hot intergalactic medium, a subset of the IGM that is
challenging to conclusively identify observationally. We find that the two
methods trace roughly the same quantities of HI and OVI above observable column
density limits, but the synthetic spectra typically identify more substructure
in absorbers. We use both methods to characterize HI and OVI absorber
properties. We find that both integrated and differential column density
distributions from both methods generally agree with observations. The
distribution of Doppler parameters between the two methods are similar for Lya
and compare reasonably with observational results, but while the two methods
agree with each other with OVI systems, they both are systematically different
from observations. We find a strong correlation between OVI baryon fraction and
OVI column density. We also discuss a possible bimodality in the temperature
distribution of the gas traced by OVI.


title: On the Potential for General Relativity and its Geometry

abstract:
  The unique ghost-free mass and nonlinear potential terms for general
relativity are presented in a diffeomorphism and local Lorentz invariant
vierbein formalism. This construction requires an additional two-index
Stuckelberg field, beyond the four scalar fields used in the metric
formulation, and unveils a new local SL(4) symmetry group of the mass and
potential terms, not shared by the Einstein-Hilbert term. The new field is
auxiliary but transforms as a vector under two different Lorentz groups, one of
them the group of local Lorentz transformations, the other an additional global
group. This formulation enables a geometric interpretation of the mass and
potential terms for gravity in terms of certain volume forms. Furthermore, we
find that the decoupling limit is much simpler to extract in this approach; in
particular, we are able to derive expressions for the interactions of the
vector modes. We also note that it is possible to extend the theory by
promoting the two-index auxiliary field into a Nambu-Goldstone boson
nonlinearly realizing a certain space-time symmetry, and show how it is "eaten
up" by the antisymmetric part of the vierbein.


title: Nebular spectroscopy of the nearby type IIb supernova 2011dh

abstract:
  We present nebular spectra of the nearby Type IIb supernova (SN) 2011dh taken
between 201 and 678 days after core collapse. At these late times, SN 2011dh
exhibits strong emission lines including a very broad and persistent H{\alpha}
feature. New models of the nebular spectra confirm that the progenitor of SN
2011dh was a low-mass giant (M ~ 13 - 15 M_sun) that ejected ~0.07 M_sun of
56Ni and ~0.27 M_sun of oxygen at the time of explosion, consistent with the
recent disappearance of a candidate yellow supergiant progenitor. We show that
light from the SN location is dominated by the fading SN at very late times (~2
yr) and not, for example, by a binary companion or a background source. We
present evidence for interaction between the expanding SN blastwave and a
circumstellar medium at late times and show that the SN is likely powered by
positron deposition by ~1 yr after explosion. We also examine the geometry of
the ejecta and show that SN 2011dh's nebular line profiles indicate a globally
spherical explosion with aspherical components or clumps.