title: Testing Cosmic Homogeneity Using Galaxy Clusters

abstract:
  According to the cosmological principle, galaxy cluster sizes and cluster
densities, when averaged over sufficiently large volumes of space, are expected
to be constant everywhere, except for a slow variation with look-back time
(redshift). Thus, average cluster sizes or correlation lengths provide a means
of testing for homogeneity that is almost free of selection biases. Using ~10^6
galaxies from the SDSS DR7 survey, I show that regions of space separated by ~2
Gpc/h have the same average cluster size and density to 5 - 10 percent. I show
that the average cluster size, averaged over many galaxies, remains constant to
less than 10 percent from small redshifts out to redshifts of 0.25. The
evolution of the cluster sizes with increasing redshift gives fair agreement
when the same analysis is applied to the Millennium Simulation. However, the MS
does not replicate the increase in cluster amplitudes with redshift seen in the
SDSS data. This increase is shown to be caused by the changing composition of
the SDSS sample with increasing redshifts. There is no evidence to support a
model that attributes the SN Ia dimming to our happening to live in a large,
nearly spherical void.


title: Standardization of surface potential measurements of graphene domains

abstract:
  We compare the three most commonly used scanning probe techniques to obtain a
reliable value of the work function in graphene domains of different thickness.
The surface potential (SP) of graphene is directly measured in Hall bar
geometry via a combination of electrical functional microscopy and spectroscopy
techniques, which enables calibrated work function measurements of graphene
domains with values ~4.55+/-0.02 eV and ~4.44+/-0.02eV for single- and
bi-layer, respectively. We demonstrate that frequency-modulated Kelvin probe
force microscopy (FM-KPFM) provides more accurate measurement of the SP than
amplitude-modulated (AM)-KPFM. The discrepancy between experimental results
obtained by different techniques is discussed. In addition, we use FM-KPFM for
contactless measurements of the specific components of the device resistance.
We show a strong non-Ohmic behavior of the electrode-graphene contact
resistance and extract the graphene channel resistivity.


title:
On stability, convergence and accuracy of bES-FEM and bFS-FEM for nearly
  incompressible elasticity

abstract:
  We present in this paper a rigorous theoretical framework to show stability,
convergence and accuracy of improved edge-based and face-based smoothed finite
element methods (bESFEM and bFS-FEM) for nearly-incompressible elasticity
problems. The crucial idea is that the space of piecewise linear polynomials
used for the displacements is enriched with bubble functions on each element,
while the pressure is a piecewise constant function. The meshes of triangular
or tetrahedral elements required by these methods can be generated
automatically. The enrichment induces a softening in the bilinear form allowing
the weakened weak (W2)procedure to produce a high-quality solution, free from
locking and that does not oscillate. We prove theoretically that both methods
confirm the uniform inf-sup and convergence conditions. Four numerical examples
are given to validate the reliability of the bES-FEM and bFS-FEM.


title: On Topological Structure of Web Services Networks for Composition

abstract:
  In order to deal efficiently with the exponential growth of the Web services
landscape in composition life cycle activities, it is necessary to have a clear
view of its main features. As for many situations where there is a lot of
interacting entities, the complex networks paradigm is an appropriate approach
to analyze the interactions between the multitudes of Web services. In this
paper, we present and investigate the main interactions between semantic Web
services models from the complex network perspective. Results show that both
parameter and operation networks exhibit the main characteristics of typical
real-world complex networks such as the small-world property and an
inhomogeneous degree distribution. These results yield valuable insight in
order to develop composition search algorithms, to deal with security threat in
the composition process and on the phenomena which characterize its evolution.


title:
Stationary behaviour of observables after a quantum quench in the
  spin-1/2 Heisenberg XXZ chain

abstract:
  We consider a quantum quench in the spin-1/2 Heisenberg XXZ chain. At late
times after the quench it is believed that the expectation values of local
operators approach time-independent values, that are described by a generalized
Gibbs ensemble. Employing a quantum transfer matrix approach we show how to
determine short-range correlation functions in such generalized Gibbs ensembles
for a class of initial states.

categories: cond-mat.stat-mech math-ph math.MP quant-ph


title: CFTs on Riemann Surfaces of genus $g\geq 1$: Dependence on moduli

abstract:
  The dependence of the Virasoro-$N$-point function on the moduli of the
Riemann surface is investigated. We propose an algebraic geometric approach
that applies to any hyperelliptic Riemann surface.


title: Classification of symmetry groups for planar n-body choreographies

abstract:
  Since the foundational work of Chenciner and Montgomery in 2000 there has
been a great deal of interest in choreographic solutions of the n-body problem:
periodic motions where the n bodies all follow one another at regular intervals
along a closed path. The principal approach combines variational methods with
symmetry properties. In this paper, we give a systematic treatment of the
symmetry aspect. In the first part we classify all possible symmetry groups of
planar n-body, collision-free choreographies. These symmetry groups fall in to
2 infinite families and, if n is odd, three exceptional groups. In the second
part we develop the equivariant fundamental group and use it to determine the
topology of the space of loops with a given symmetry, which we show is related
to certain cosets of the pure braid group in the full braid group, and to
centralizers of elements of the corresponding coset. In particular, we refine
the symmetry classification by classifying the connected components of the set
of loops with any given symmetry. This leads to the existence of many new
choreographies in $n$-body systems governed by a strong force potential.


title: Community Structure in Interaction Web Service Networks

abstract:
  Many real-world complex systems such as social, biological, information as
well as technological systems results of a decentralized and unplanned
evolution which leads to a common structuration. Irrespective of their origin,
these so-called complex networks typically exhibit small-world and scale-free
properties. Another common feature is their organisation into communities. In
this paper, we introduce models of interaction networks based on the
composition process of syntactic and semantic Web services. An extensive
experimental study conducted on a benchmark of real Web services shows that
these networks possess the typical properties of complex networks (small-world,
scale-free). Unlike most social networks, they are not transitive. Using a
representative sample of community detection algorithms, a community
structuration is revealed. The comparative evaluation of the discovered
community structures shows that they are very similar in terms of content.
Furthermore, the analysis performed on the community structures and on the
communities themselves, leads us to conclude that their topological properties
are consistent.


title: Entropy and lowest eigenvalue on evolving manifolds

abstract:
  In this note we determine the first two derivatives of the classical
Boltzmann-Shannon entropy of the conjugate heat equation on general evolving
manifolds. Based on the second derivative of the Boltzmann-Shannon entropy, we
construct Perelman's F and W entropy in abstract geometric flows. Monotonicity
of the entropies holds when a technical condition is satisfied. This condition
is satisfied on static Riemannian manifolds with nonnegative Ricci curvature,
for Hamilton's Ricci flow, List's extended Ricci flow, M\"uller's Ricci flow
coupled with harmonic map flow and Lorentzian mean curvature flow when the
ambient space has nonnegative sectional curvature. Under the extra assumption
that the lowest eigenvalue is differentiable along time, we derive an explicit
formula for the evolution of the lowest eigenvalue of the Laplace-Beltrami
operator with potential in the abstract setting.


title:
S and Q Matrices Reloaded: applications to open, inhomogeneous, and
  complex cavities

abstract:
  We present a versatile numerical algorithm for computing resonances of open
dielectric cavities. The emphasis is on the generality of the system's
configuration, i.e. the geometry of the (main) cavity (and possible inclusions)
and the internal and external dielectric media (homogeneous and inhomogeneous).
The method is based on a scattering formalism to obtain the position and width
of the (quasi)-eigenmodes. The core of the method lies in the scattering
S-matrix and its associated delay Q-matrix which contain all the relevant
information of the corresponding scattering experiment. For instance, the
electromagnetic near- and far-fields are readily extracted. The flexibility of
the propagation method is displayed for a selected system.


title: Scaling attractors in interacting teleparallel dark energy

abstract:
  It has been proposed recently the existence of a non-minimal coupling between
a canonical scalar field (quintessence) and gravity in the framework of
teleparallel gravity, motivated by similar constructions in the context of
General Relativity. The dynamics of the model, known as teleparallel dark
energy, has been further developed, but no scaling attractor has been found.
Here we consider a model in which the non-minimal coupling is ruled by a
dynamically changing coefficient $\alpha\equiv f_{,\phi}/\sqrt{f}$, with
$f(\phi)$ an arbitrary function of the scalar field $\phi$. It is shown that in
this case the existence of scaling attractors is possible, which means that the
universe will eventually enter these scaling attractors, regardless of the
initial conditions. As a consequence, the cosmological coincidence problem
could be alleviated without fine-tunings.


title:
The Astrophysical Scales Set by the Cosmological Constant, Black-Hole
  Thermodynamics and Non-Linear Massive Gravity

abstract:
  We calculate explicitly the black-hole temperature for the Schwarzschild
de-Sitter solution inside massive gravity by defining the Killing-vector in the
direction of the St\"uckelberg function. We then consider the conditions which
an observer in massive gravity has to obey in order to agree with the standard
results of General Relativity.


title:
Mirror actively deformed and regulated for applications in space: design
  and performance

abstract:
  The need for both high quality images and lightweight structures is one of
the main drivers in space telescope design. An efficient wavefront control
system will become mandatory in future large observatories, retaining
performance while relaxing specifications in the global system's stability. We
present the mirror actively deformed and regulated for applications in space
project, which aims to demonstrate the applicability of active optics for
future space instrumentation. It has led to the development of a 24-actuator,
90-mm-diameter active mirror, able to compensate for large lightweight primary
mirror deformations in the telescope's exit pupil. The correcting system has
been designed for expected wavefront errors from 3-m-class lightweight primary
mirrors, while also taking into account constraints for space use. Finite
element analysis allowed an optimization of the system in order to achieve a
precision of correction better than 10 nm rms. A dedicated testbed has been
designed to fully characterize the integrated system performance in
representative operating conditions. It is composed of: a telescope simulator,
an active correction loop, a point spread function imager, and a Fizeau
interferometer. All conducted tests demonstrated the correcting mirror
performance and has improved this technology maturity to a TRL4.


title:
Quasistatic evolution models for thin plates arising as low energy
  Gamma-limits of finite plasticity

abstract:
  In this paper we deduce by {\Gamma}-convergence some partially and fully
linearized quasistatic evolution models for thin plates, in the framework of
finite plasticity. Denoting by {\epsilon} the thickness of the plate, we study
the case where the scaling factor of the elasto- plastic energy is of order
{\epsilon}^ (2{\alpha}-2), with {\alpha}>=3. We show that solutions to the
three- dimensional quasistatic evolution problems converge, as the thickness of
the plate tends to zero, to a quasistatic evolution associated to a suitable
reduced model depending on {\alpha}.


title: Hyperplane Sections, Groebner Bases, and Hough Transforms

abstract:
  The purpose of this paper is twofold. In the first part we concentrate on
hyperplane sections of algebraic schemes, and present results for determining
when Gr\"obner bases pass to the quotient and when they can be lifted. The main
difficulty to overcome is the fact that we deal with non-homogeneous ideals. As
a by-product we hint at a promising technique for computing implicitization
efficiently.
  In the second part of the paper we deal with families of algebraic schemes
and the Hough transforms, in particular we compute their dimension, and show
that in some interesting cases it is zero. Then we concentrate on their
hyperplane sections. Some results and examples hint at the possibility of
reconstructing external and internal surfaces of human organs from the parallel
cross-sections obtained by tomography.


title:
A robust tree method for pricing American options with CIR stochastic
  interest rate

abstract:
  We propose a robust and stable lattice method which permits to obtain very
accurate American option prices in presence of CIR stochastic interest rate
without any numerical restriction on its parameters. Numerical results show the
reliability and the accuracy of the proposed method.


title: Quasi-regular representations and property RD

abstract:
  We study \emph{property RD} in terms of rapid decay of matrix coefficients.
We give new formulations of property RD in terms of a $L^{1}$-integra\-bility
condition of a Banach representation. Combining this new definition with the
existence of cyclic subgroups of exponential growth in non-uniform lattices in
semisimple Lie groups, we deduce that there exist matrix coefficients
associated to several kinds of quasi-regular representations which satisfy a
"non-RD condition" for non-uniform lattices. We obtain also that such
coefficients can not satisfy \emph{the weak inequality} of Harish-Chandra.


title:
Linearized plastic plate models as Gamma-limits of 3D finite
  elastoplasticity

abstract:
  The subject of this paper is the rigorous derivation of reduced models for a
thin plate by means of {\Gamma}-convergence, in the framework of finite
plasticity. Denoting by {\epsilon} the thickness of the plate, we analyse the
case where the scaling factor of the elasto-plastic energy is of order
{\epsilon}^(2{\alpha}-2), with {\alpha}>=3. According to the value of {\alpha},
partially or fully linearized models are deduced, which correspond, in the
absence of plastic deformation, to the Von Karman plate theory and the
linearized plate theory.


title: Counting algebraic integers of fixed degree and bounded height

abstract:
  Let $k$ be a number field. For $\mathcal{H}\rightarrow \infty$, we give an
asymptotic formula for the number of algebraic integers of absolute Weil height
bounded by $\mathcal{H}$ and fixed degree over $k$.


title:
Feasibility Analysis of Low Cost Graphical Processing Units for
  Electromagnetic Field Simulations by Finite Difference Time Domain Method

abstract:
  Among several techniques available for solving Computational Electromagnetics
(CEM) problems, the Finite Difference Time Domain (FDTD) method is one of the
best suited approaches when a parallelized hardware platform is used. In this
paper we investigate the feasibility of implementing the FDTD method using the
NVIDIA GT 520, a low cost Graphical Processing Unit (GPU), for solving the
differential form of Maxwell's equation in time domain. Initially a generalized
benchmarking problem of bandwidth test and another benchmarking problem of
'matrix left division is discussed for understanding the correlation between
the problem size and the performance on the CPU and the GPU respectively. This
is further followed by the discussion of the FDTD method, again implemented on
both, the CPU and the GT520 GPU. For both of the above comparisons, the CPU
used is Intel E5300, a low cost dual core CPU.


title:
Chiral properties of bismuth ferrite (BiFeO3) inferred from resonant
  x-ray Bragg diffraction

abstract:
  A new chiral phase of ferric ions in bismuth ferrite, the only material known
to support multiferroic behaviour at room temperature, is inferred from
extensive sets of data gathered by resonant x-ray Bragg diffraction. Values of
all ferric multipoles participating in a minimal model of Fe electronic
structure are deduced from azimuthal-angle scans. Extensive sets of
azimuthal-angle data, gathered by resonant x-ray Bragg diffraction, yield
values of all ferric multipoles participating in a minimal model of Fe
electronic structure. Paramagnetic (700 K) and magnetically ordered (300 K)
phases of a single crystal of BiFeO3 have been studied with x-rays tuned near
to the iron K-edge (7.1135 keV). At both temperatures, intensities at a Bragg
spot forbidden in the nominal space-group, R3c, are consistent with a chiral
motif of ferric ions in a circular cycloid propagating along (1, 1, 0)H.
Templeton and Templeton scattering at 700 K is attributed in part to
charge-like quadrupoles in a cycloid. The contribution is not present in a
standard, simplified model of electronic states of the resonant ion with
trivial cylindrical symmetry.


title: Liouville theorems for $f$-harmonic maps into Hadamard spaces

abstract:
  In this paper, we study harmonic functions on weighted manifolds and harmonic
maps from weighted manifolds into Hadamard spaces introduced by Korevaar and
Schoen. We prove Liouville theorems for these harmonic maps with finite energy.


title:
Weight function approach to study a crack propagating along a bimaterial
  interface under asymmetric loading in anisotropic solids

abstract:
  This paper considers a steady-state crack propagating along an interface
between dissimilar orthotropic materials under an asymmetric load. Although
most of the known results so far deal with symmetric loading, it has been shown
recently that a significant asymmetry in the applied loading may lead to a
pronounced effect in terms of the values of the SIFs. The aim of the paper is
to extend these results from the static case to a moving crack. In particular,
we show the significance of the asymmetry of the loading for computing the
energy release rate.


title:
Charged Brownian Particles: Kramers and Smoluchowski Equations and the
  Hydrothermodynamical Picture

abstract:
  We consider a charged Brownian gas under the influence of external and non
uniform electric, magnetic and mechanical fields, immersed in a non uniform
bath temperature. With the collision time as an expansion parameter, we study
the solution to the associated Kramers equation, including a linear reactive
term. To first order we obtain the asymptotic (overdamped) regime, governed by
transport equations, namely: for the particle's density, a
Smoluchowski-reactive like equation; for the particle's momentum density, a
generalized Ohm's like equation; and for the particle's energy density, a
Maxwell-Cattaneo like equation. Defining a nonequilibrium temperature as the
mean kinetic energy density, and introducing Boltzmann's entropy density via
the one particle distribution function, we present a complete
thermohydrodynamical picture for a charged Brownian gas. We probe the validity
of the local equilibrium approximation, Onsager relations, variational
principles associated to the entropy production, and apply our results to:
carrier transport in semiconductors, hot carriers and Brownian motors. Finally,
we outline a method to incorporate non linear reactive kinetics and a mean
field approach to interacting Brownian particles.


title: Disorder-induced valley-orbit hybrid states in Si quantum dots

abstract:
  Quantum dots in silicon are promising candidates for implementation of
solid-state quantum information processing. It is important to understand the
effects of the multiple conduction band valleys of silicon on the properties of
these devices. Here we introduce a novel, systematic effective mass theory of
valley-orbit coupling in disordered silicon systems. This theory reveals
valley-orbit hybridization effects that are detrimental for storing quantum
information in the valley degree of freedom, including non-vanishing dipole
matrix elements between valley states and altered intervalley tunneling.


title:
An algorithm for determining the radii of convergence of algebraic power
  series

abstract:
  This paper describes an algorithm for determining radii of convergence of
power expansions for algebraic functions and the testing done to check it.
Since the current methods for computing these series are iterative, standard
methods for computing radii of convergence cannot in general, be used. However,
relying on geometric properties of algebraic functions, convergence radii of
these series can be determined precisely.


title:
An experimental evidence-based computational paradigm for new
  logic-gates in neuronal activity

abstract:
  We propose a new experimentally corroborated paradigm in which the
functionality of the brain's logic-gates depends on the history of their
activity, e.g. an OR-gate that turns into a XOR-gate over time. Our results are
based on an experimental procedure where conditioned stimulations were enforced
on circuits of neurons embedded within a large-scale network of cortical cells
in-vitro. The underlying biological mechanism is the unavoidable increase of
neuronal response latency to ongoing stimulations, which imposes a non-uniform
gradual stretching of network delays.


title:
Searches for long-lived charged particles in pp collisions at sqrt(s) =
  7 and 8 TeV

abstract:
  Results of searches for heavy stable charged particles produced in pp
collisions at sqrt(s) = 7 and 8 TeV are presented corresponding to an
integrated luminosity of 5.0 inverse femtobarns and 18.8 inverse femtobarns,
respectively. Data collected with the CMS detector are used to study the
momentum, energy deposition, and time-of-flight of signal candidates. Leptons
with an electric charge between e/3 and 8e, as well as bound states that can
undergo charge exchange with the detector material, are studied. Analysis
results are presented for various combinations of signatures in the inner
tracker only, inner tracker and muon detector, and muon detector only. Detector
signatures utilized are long time-of-flight to the outer muon system and
anomalously high (or low) energy deposition in the inner tracker. The data are
consistent with the expected background, and upper limits are set on the
production cross section of long-lived gluinos, scalar top quarks, and scalar
tau leptons, as well as pair produced long-lived leptons. Corresponding lower
mass limits, ranging up to 1322 GeV for gluinos, are the most stringent to
date.


title: Continuum percolation for Gibbs point processes

abstract:
  We consider percolation properties of the Boolean model generated by a Gibbs
point process and balls with deterministic radius. We show that for a large
class of Gibbs point processes there exists a critical activity, such that
percolation occurs a.s. above criticality. For locally stable Gibbs point
processes we show a converse result, i.e. they do not percolate a.s. at low
activity.


title: Excellence and uncountable categoricity of Zilber's exponential fields

abstract:
  We prove that Zilber's class of exponential fields is quasiminimal excellent
and hence uncountably categorical, filling two gaps in Zilber's original proof.


title:
Persistence of Metastable Vortex Lattice Domains in MgB2 in the Presence
  of Vortex Motion

abstract:
  Recently, extensive vortex lattice metastability was reported in MgB2 in
connection with a second-order rotational phase transition. However, the
mechanism responsible for these well-ordered metastable vortex lattice phases
is not well understood. Using small-angle neutron scattering, we studied the
vortex lattice in MgB2 as it was driven from a metastable to the ground state
through a series of small changes in the applied magnetic field. Our results
show that metastable vortex lattice domains persist in the presence of
substantial vortex motion and directly demonstrate that the metastability is
not due to vortex pinning. Instead, we propose that it is due to the jamming of
counterrotated vortex lattice domains which prevents a rotation to the ground
state orientation.


title:
Regular Hamiltonians for non-relativistic interacting quantum field
  theories

abstract:
  In the context of non-relativistic quantum field theory, a method is proposed
for multiplying field operators at the same spatial point and obtaining regular
(i.e. rigorously defined) interaction terms for the Hamiltonian. The basic idea
is to modify the Lebesgue measure of configuration space of many particles by
adding singular measures over the subspaces of configuration space in which the
positions of two or more particles coincide.


title: Modeling rotating stars in two dimensions

abstract:
  In this lecture I present the way stars can be modeled in two dimensions and
especially the fluid flows that are driven by rotation. I discuss some of the
various ways of taking into account turbulence and conclude this contribution
by a short presentation of some of the first results obtained with the ESTER
code on the modeling of interferometrically observed fast rotating early-type
stars.


title:
Ellipticity and prolaticity of the initial gravitational-shear field at
  the position of density maxima

abstract:
  Dark-matter haloes are supposed to form at the positions of maxima in the
initial matter density field. The gravitational-shear field's ellipticity and
prolaticity that serve as input for the ellipsoidal-collapse model, however,
are derived from a distribution that does not take the additional maximum
constraint into account. In this article, I quantify the variations of the most
probable and the expected values of the ellipticity and the prolaticity when
considering this additional constraint as well as the implications for the
ellipsoidal-collapse model. Based on the statistics of Gaussian random fields,
it is possible to set up a joint distribution for the eigenvalues of the
gravitational-shear tensor and the matter density that incorporates the maximum
constraint by invoking a vanishing first derivative and a negative definite
second derivative of the density field into the calculation. In the density
range relevant for cosmological structure formation, both the most probable and
the expected value of the ellipticity calculated from the standard distribution
used in the literature are about 3-8 per cent higher compared to the ones
calculated under the additional assumption of a density maximum. Additionally,
the analogous quantities for the prolaticity do not vanish but acquire slightly
positive values in the range of $10^{-3}$-$10^{-2}$. For large overdensities,
the predictions from both distributions converge. The values for
$\delta_\mathrm{c}$ and $\Delta_\mathrm{v}$ derived from the
ellipsoidal-collapse model using the standard distribution for the initial
ellipticity and prolaticity are up to 4 and 6 per cent higher, respectively,
than those obtained taking the additional maximum constraint into account in
the range of $10^{13}$-$10^{15}~h^{-1}~\mathrm{M}_\odot$ in mass and 0-2 in
redshift.


title: Dark energy as stimulated emission of gravitons from a background brane

abstract:
  The idea that dark energy is gravitational waves may explain its strength and
its time-evolution provided that the additional energy comes from a background.
A possible concept is that dark energy is the ensemble of coherent bursts
(solitons) of gravitational waves originally produced by stimulated emission
when the first generation of super-massive black holes was formed. These
solitons get their initial energy as well as keep up their energy density
throughout the evolution of the universe by stimulating emission from a
background brane. We model this process by working out this energy transfer in
a Boltzmann equation approach. The transit of these gravitational wave solitons
may be detectable. Key tests include pulsar timing, clock jitter and the radio
and neutrino backgrounds.


title: Superconformal quantum field theory in curved spacetime

abstract:
  By conformally coupling vector and hyper multiplets in Minkowski space, we
obtain a class of field theories with extended rigid conformal supersymmetry on
any Lorentzian four-manifold admitting twistor spinors. We construct the
conformal symmetry superalgebras which describe classical symmetries of these
theories and derive an appropriate BRST operator in curved spacetime. In the
process, we elucidate the general framework of cohomological algebra which
underpins the construction. We then consider the corresponding perturbative
quantum field theories. In particular, we examine the conditions necessary for
conformal supersymmetries to be preserved at the quantum level, i.e. when the
BRST operator commutes with the perturbatively defined S-matrix, which ensures
superconformal invariance of amplitudes. To this end, we prescribe a
renormalization scheme for time-ordered products that enter the perturbative
S-matrix and show that such products obey certain Ward identities in curved
spacetime. These identities allow us to recast the problem in terms of the
cohomology of the BRST operator. Through a careful analysis of this cohomology,
and of the renormalization group in curved spacetime, we establish precise
criteria which ensure that all conformal supersymmetries are preserved at the
quantum level. As a by-product, we provide a rigorous proof that the
beta-function for such theories is one-loop exact. We also briefly discuss the
construction of chiral rings and the role of non-perturbative effects in curved
spacetime.


title: Central differences, Euler numbers and symbolic methods

abstract:
  I relate some coefficients encountered when computing the functional
determinants on spheres to the central differentials of nothing. In doing this
I use some historic works, in particular transcribing the elegant symbolic
formalism of Jeffery (1861) into central difference form which has
computational advantages for Euler numbers, as discovered by Shovelton (1915).
I derive sum rules for these, and for the central differentials, the proof of
which involves an interesting expression for powers of sech x as multiple
derivatives. I present a more general, symbolic treatment of central difference
calculus which allows known, and unknown, things to be obtained in an elegant
and compact fashion gaining, at no cost, the expansion of the powers of the
inverse sinh, a basic central function. Systematic use is made of the operator
2 asinh(D/2). Umbral calculus is employed to compress the operator formalism.
For example the orthogonality/completeness of the factorial numbers, of the
first and second kinds, translates, umbrally, to T(t(x))=x. The classic
expansions of multiple angle cosh and sinh in terms of powers of sinh are
thence obtained with minimal effort.


title: Universal and ultrahomogeneous Polish metric structures

abstract:
  We use Fra\" iss\'e theoretic methods to construct several universal and
ultrahomogeneous Polish metric structures. Namely, universal and
ultrahomogeneous Polish metric space equipped with countably many closed
subsets of its powers, universal and ultrahomogeneous Polish metric space
equipped with a closed subset of the product of itself and some fixed compact
metric space, and universal and ultrahomogeneous Polish metric space equipped
with an L-Lipschitz function, for an arbitrary positive L, to some fixed Polish
metric space. These results are direct generalization of the classical result
of P. Urysohn. Possible applications are discussed.


title: Simple, Fast, and Scalable Reachability Oracle

abstract:
  A reachability oracle (or hop labeling) assigns each vertex v two sets of
vertices: Lout(v) and Lin(v), such that u reaches v iff Lout(u) \cap Lin(v)
\neq \emptyset. Despite their simplicity and elegance, reachability oracles
have failed to achieve efficiency in more than ten years since their
introduction: the main problem is high construction cost, which stems from a
set-cover framework and the need to materialize transitive closure. In this
paper, we present two simple and efficient labeling algorithms,
Hierarchical-Labeling and Distribution-Labeling, which can work onmassive
real-world graphs: their construction time is an order of magnitude faster than
the setcover based labeling approach, and transitive closure materialization is
not needed. On large graphs, their index sizes and their query performance can
now beat the state-of-the-art transitive closure compression and online search
approaches.


title:
Graph-Theoretic Characterization of The Feasibility of The
  Precoding-Based 3-Unicast Interference Alignment Scheme

abstract:
  A new precoding-based intersession network coding (NC) scheme has recently
been proposed, which applies the interference alignment technique, originally
devised for wireless interference channels, to the 3-unicast problem of
directed acyclic networks. The main result of this work is a graph-theoretic
characterization of the feasibility of the 3-unicast interference alignment
scheme. To that end, we first investigate several key relationships between the
point-to-point network channel gains and the underlying graph structure. Such
relationships turn out to be critical when characterizing graph-theoretically
the feasibility of precoding-based solutions.


title:
Real time evolution at finite temperatures with operator space matrix
  product states

abstract:
  We propose a method to simulate the real time evolution of one dimensional
quantum many-body systems at finite temperature by expressing both the density
matrices and the observables as matrix product states. This allows the
calculation of expectation values and correlation functions as scalar products
in operator space. The simulations of density matrices in inverse temperature
and the local operators in the Heisenberg picture are independent and result in
a grid of expectation values for all intermediate temperatures and times.
Simulations can be performed using real arithmetics with only polynomial growth
of computational resources in inverse temperature and time for integrable
systems. The method is illustrated for the XXZ model and the single impurity
Anderson model.


title: On k-visibility graphs

abstract:
  We examine several types of visibility graphs in which sightlines can pass
through $k$ objects. For $k \geq 1$ we bound the maximum thickness of semi-bar
$k$-visibility graphs between $\lceil \frac{2}{3} (k + 1) \rceil$ and $2k$. In
addition we show that the maximum number of edges in arc and circle
$k$-visibility graphs on $n$ vertices is at most $(k+1)(3n-k-2)$ for $n > 4k+4$
and ${n \choose 2}$ for $n \leq 4k+4$, while the maximum chromatic number is at
most $6k+6$. In semi-arc $k$-visibility graphs on $n$ vertices, we show that
the maximum number of edges is ${n \choose 2}$ for $n \leq 3k+3$ and at most
$(k+1)(2n-\frac{k+2}{2})$ for $n > 3k+3$, while the maximum chromatic number is
at most $4k+4$.


title: Quantum Simulation of Noncausal Kinematic Transformations

abstract:
  We propose the implementation of Galileo group symmetry operations or, in
general, linear coordinate transformations, in a quantum simulator. With an
appropriate encoding, unitary gates applied to our quantum system give rise to
Galilean boosts or spatial and time parity operations in the simulated
dynamics. This framework provides us with a flexible toolbox that enhances the
versatility of quantum simulation theory, allowing the direct access to
dynamical quantities that would otherwise require full tomography. Furthermore,
this method enables the study of noncausal kinematics and phenomena beyond
special relativity in a quantum controllable system.


title:
Hub-Accelerator: Fast and Exact Shortest Path Computation in Large
  Social Networks

abstract:
  Shortest path computation is one of the most fundamental operations for
managing and analyzing large social networks. Though existing techniques are
quite effective for finding the shortest path on large but sparse road
networks, social graphs have quite different characteristics: they are
generally non-spatial, non-weighted, scale-free, and they exhibit small-world
properties in addition to their massive size. In particular, the existence of
hubs, those vertices with a large number of connections, explodes the search
space, making the shortest path computation surprisingly challenging. In this
paper, we introduce a set of novel techniques centered around hubs,
collectively referred to as the Hub-Accelerator framework, to compute the
k-degree shortest path (finding the shortest path between two vertices if their
distance is within k). These techniques enable us to significantly reduce the
search space by either greatly limiting the expansion scope of hubs (using the
novel distance- preserving Hub-Network concept) or completely pruning away the
hubs in the online search (using the Hub2-Labeling approach). The
Hub-Accelerator approaches are more than two orders of magnitude faster than
BFS and the state-of-the-art approximate shortest path method Sketch for the
shortest path computation. The Hub- Network approach does not introduce
additional index cost with light pre-computation cost; the index size and index
construction cost of Hub2-Labeling are also moderate and better than or
comparable to the approximation indexing Sketch method.


title:
Poincare inequality and the uniqueness of solutions for the heat
  equation associated with subelliptic diffusion operators

abstract:
  In this paper we study global Poincare inequalities on balls in a large class
of sub-Riemannian manifolds satisfying the generalized curvature dimension
inequality introduced by F.Baudoin and N.Garofalo. As a corollary, we prove the
uniqueness of solutions for the subelliptic heat equation. Our results apply in
particular to CR Sasakian manifolds with Tanaka-Webster-Ricci curvature bounded
from below and Carnot groups of step two.


title:
The IVP for the Benjamin-Ono-Zakharov-Kuznetsov equation in weighted
  Sobolev spaces

abstract:
  In this paper we study the initial-value problem associated with the
Benjamin-Ono-Zakharov-Kuznetsov equation. We prove that the IVP for such
equation is locally well-posed in the usual Sobolev spaces $H^{s}(\R^2),$
$s>2$, and in the anisotropic spaces $H^{s_1,s_2}(\R^2)$, $s_2>2$, $s_1\geq
s_2$. We also study the persistence properties of the solution and local
well-posedness in the weighted Sobolev class $$
\mathcal{Z}_{s,r}=H^{s}(\R^{2})\cap L^{2}((1+x^{2} +y^{2})^rdxdy), $$ where
$s>2$, $r\geq 0$, and $s\geq 2r$. Unique continuation properties of the
solution are also established. These continuation principles show that our
persistence properties are sharp. Most of our arguments are accomplished taking
into account that ones for the Benjamin-Ono equation.


title: Probe and Adapt: Rate Adaptation for HTTP Video Streaming At Scale

abstract:
  Today, the technology for video streaming over the Internet is converging
towards a paradigm named HTTP-based adaptive streaming (HAS). HAS comes with
two unique flavors. First, by riding on top of HTTP/TCP, it leverages the
network-friendly TCP to achieve firewall/NATS traversal and bandwidth sharing.
Second, by pre-encoding and storing the video in a number of discrete bitrate
levels, it introduces video bitrate adaptivity in a scalable way that the video
encoding is excluded from the closed-loop adaptation. A conventional wisdom is
that the TCP throughput observed by a HAS client indicates the available
network bandwidth, thus can be used as a reliable reference for the video
bitrate selection.
  We argue that this no longer holds true when HAS becomes a substantial
fraction of the Internet traffic. We show that when multiple HAS clients
compete at a network bottleneck, the presence of competing clients and the
discrete nature of the video bitrates would together create confusion for a
client to correctly perceive its fair-share bandwidth. Through analysis and
real experiments, we demonstrate that this fundamental limitation would lead
to, for example, video rate oscillation that negatively impacts the video
watching experiences. We therefore argue that it is necessary to implement at
the application layer a "probe-and-adapt" mechanism for HAS video rate
adaptation, which is akin but orthogonal to the transport-layer network rate
adaptation achieved by TCP. We present PANDA -- a client-side rate adaptation
algorithm for HAS -- as an embodiment of this idea. Our testbed results show
that compared to conventional algorithms, PANDA is able to reduce the
instability of video rate by 60%, at a given risk of buffer underrun.


title:
A note on local well-posedness of generalized KdV type equations with
  dissipative perturbations

abstract:
  In this note we report local well-posedness results for the Cauchy problems
associated to generalized KdV type equations with dissipative perturbation for
given data in the low regularity $L^2$-based Sobolev spaces. The method of
proof is based on the {\em contraction mapping principle} employed in some
appropriate time weighted spaces.


title:
Fixed-Parameter and Approximation Algorithms for Maximum Agreement
  Forests of Multifurcating Trees

abstract:
  We present efficient algorithms for computing a maximum agreement forest
(MAF) of a pair of multifurcating (nonbinary) rooted trees. Our algorithms
match the running times of the currently best algorithms for the binary case.
The size of an MAF corresponds to the subtree prune-and-regraft (SPR) distance
of the two trees and is intimately connected to their hybridization number.
These distance measures are essential tools for understanding reticulate
evolution, such as lateral gene transfer, recombination, and hybridization.
Multifurcating trees arise naturally as a result of statistical uncertainty in
current tree construction methods.


title:
Limiting the Neighborhood: De-Small-World Network for Outbreak
  Prevention

abstract:
  In this work, we study a basic and practically important strategy to help
prevent and/or delay an outbreak in the context of network: limiting the
contact between individuals. In this paper, we introduce the average
neighborhood size as a new measure for the degree of being small-world and
utilize it to formally define the desmall- world network problem. We also prove
the NP-hardness of the general reachable pair cut problem and propose a greedy
edge betweenness based approach as the benchmark in selecting the candidate
edges for solving our problem. Furthermore, we transform the de-small-world
network problem as an OR-AND Boolean function maximization problem, which is
also an NP-hardness problem. In addition, we develop a numerical relaxation
approach to solve the Boolean function maximization and the de-small-world
problem. Also, we introduce the short-betweenness, which measures the edge
importance in terms of all short paths with distance no greater than a certain
threshold, and utilize it to speed up our numerical relaxation approach. The
experimental evaluation demonstrates the effectiveness and efficiency of our
approaches.


title: Pseudo-bosons for the $D_2$ type quantum Calogero model

abstract:
  In the first part of this paper we show how a simple system, a 2-dimensional
quantum harmonic oscillator, can be described in terms of pseudo-bosonic
variables. This apparently {\em strange} choice is useful when the {\em
natural} Hilbert space of the system, $L^2({\bf R}^2)$ in this case, is, for
some reason, not the most appropriate. This is exactly what happens for the
$D_2$ type quantum Calogero model considered in the second part of the paper,
where the Hilbert space $L^2({\bf R}^2)$ appears to be an unappropriate choice,
since the eigenvectors of the relevant hamiltonian are not square-integrable.
Then we discuss how a certain intertwining operator arising from the model can
be used to fix a different Hilbert space more {\em useful}.


title:
Can Stellar Mixing Explain the Lack of Type Ib Supernovae in
  Long-Duration GRBs?

abstract:
  The discovery of supernovae associated with long-duration gamma ray burst
observations is primary evidence that the progenitors of these outbursts are
massive stars. One of the principle mysteries in understanding these
progenitors has been the fact that all of these gamma-ray burst associated
supernovae are type Ic supernovae, with no evidence of helium in the stellar
atmosphere. Many studies have focused on whether or not this helium is simply
hidden from spectral analyses. In this paper, we show results from recent
stellar models using new convection algorithms based on our current
understanding of stellar mixing. We demonstrate that enhanced convection may
lead to severe depletion of stellar helium layers, suggesting that the helium
is not observed simply because it is not in the star. We also present
light-curves and spectra of these compact helium-depleted stars, compared to
models with more conventional helium layers.


title:
Deciding semantic finiteness of pushdown processes and first-order
  grammars w.r.t. bisimulation equivalence

abstract:
  The problem if a given configuration of a pushdown automaton (PDA) is
bisimilar with some (unspecified) finite-state process is shown to be
decidable. The decidability is proven in the framework of first-order grammars,
which are given by finite sets of labelled rules that rewrite roots of
first-order terms. The framework is equivalent to PDA where also deterministic
(i.e. alternative-free) epsilon-steps are allowed, i.e. to the model for which
S\'enizergues showed an involved procedure deciding bisimilarity (1998, 2005).
Such a procedure is here used as a black-box part of the algorithm. The result
extends the decidability of the regularity problem for deterministic PDA that
was shown by Stearns (1967), and later improved by Valiant (1975) regarding the
complexity. The decidability question for nondeterministic PDA, answered
positively here, had been open (as indicated, e.g., by Broadbent and G\"oller,
2012).


title: Non-simple genus minimizers in lens spaces

abstract:
  Given a one-dimensional homology class in a lens space, a question related to
the Berge conjecture on lens space surgeries is to determine all knots
realizing the minimal rational genus of all knots in this homology class. It is
known that simple knots are rational genus minimizers. In this paper, we
construct many non-simple genus minimizers. This negatively answers a question
of Rasmussen.


title:
Form factors in equilibrium and non-equilibrium mixed states of the
  Ising model

abstract:
  Using the "Liouville space'' (the space of operators) of the massive Ising
model of quantum field theory, there is a natural definition of form factors in
any mixed state. These generalize the usual form factors, and are building
blocks for mixed-state correlation functions. We study the cases of mixed
states that are diagonal in the asymptotic particle basis, and obtain exact
expressions for all mixed-state form factors of order and disorder fields. We
use novel techniques based on deriving and solving a system of nonlinear
functional differential equations. We then write down the full form factor
expansion for mixed-state correlation functions of these fields. Under weak
analytic conditions on the eigenvalues of the density matrix, this is an exact
large-distance expansion. The form factors agree with the known
finite-temperature form factors when the mixed state is specialized to a
thermal Gibbs ensemble. Our results can be used to analyze correlation
functions in generalized Gibbs ensembles (which occur after quantum quenches).
Applying this to the density matrix for non-equilibrium steady states with
energy flows, we observe that non-equilibrium form factors have branch cuts in
rapidity space. We verify that this is in agreement with a non-equilibrium
generalization of the KMS relations, and we conjecture that the leading
large-distance behavior of order and disorder non-equilibrium correlation
functions contains oscillations in the log of the distance between the fields.


title:
Charge-sensitive vibrational modes in the (EDT-TTF-OX)_2AsF_6 chiral
  molecular conductors

abstract:
  Infrared and Raman spectra of the three chiral molecular conductors
(EDT-TTF-OX)_2AsF_6, comprising two salts based on enantiopure EDT-TTF-OX donor
molecules and one based on their racemic mixture, have been measured as a
function of temperature. In the frequency range of the C=C stretching
vibrations of EDT-TTF-OX, charge-sensitive modes are identified based on
theoretical calculations for neutral and oxidized EDT-TTF-OX using density
functional theory (DFT) methods. The positions of the C=C stretching modes in
both Raman and infrared spectra of the (EDT-TTF-OX)_2AsF_6 materials are
analyzed assuming linear relationship between the frequency and charge on the
molecule. The charge density on the EDT-TTF-OX donor molecule is estimated to
be +0.5 in all the investigated materials and does not change with temperature.
Therefore it is suggested, that M-I transition observed in (EDT-TTF-X)_2AsF_6
chiral molecular conductors at low temperature is not related to the charge
ordering mechanism.


title: Terahertz Waveguiding in Silicon-Core Fibers

abstract:
  We propose the use of a silicon-core optical fiber for terahertz (THz)
waveguide applications. Finite-difference time-domain simulations have been
performed based on a cylindrical waveguide with a silicon core and silica
cladding. High-resistivity silicon has a flat dispersion over a 0.1 - 3 THz
range, making it viable for propagation of tunable narrowband CW THz and
possibly broadband picosecond pules of THz radiation. Simulations show the
propagation dynamics and the integrated intensity, from which transverse mode
profiles and absorption lengths are extraced. It is found that for 140 - 250
micron core diameters the mode is primarily confined to the core, such that the
overall absorbance is only slightly less than in bulk polycrystalline silicon.


title: Photonic molecules formed by coupled hybrid resonators

abstract:
  We describe a method that enables free-standing whispering-gallery-mode
microresonators, and report spectral tuning of photonic molecules formed by
coupled free and on-chip resonators with different geometries and materials. We
study direct coupling via evanescent fields of free silica microtoroids and
microspheres with on-chip polymer coated silica microtoroids. We demonstrate
thermal tuning of resonance modes to achieve maximal spectral overlap, mode
splitting induced by direct coupling, and the effects of distance between the
resonators on the splitting spectra.


title:
Geometric Description of the Preduals of Atomic Commutative von Neumann
  Algebras

abstract:
  Strongly facially symmetric spaces isometrically isomorphic to the predual
space of an atomic commutative von Neumann algebra are described


title:
Using spherical wavelets to search for magnetically-induced alignment in
  the arrival directions of ultra-high energy cosmic rays

abstract:
  Due to the action of the intervening cosmic magnetic fields, ultra-high
energy cosmic rays (UHECRs) can be deflected in such a way as to create
clustered energy-ordered filamentary structures in the arrival direction of
these particles, the so-called multiplets. In this work we propose a new method
based on the spherical wavelet transform to identify multiplets in sky maps
containing arrival directions of UHECRs. The method is illustrated in
simulations with a multiplet embedded in isotropic backgrounds with different
numbers of events. The efficiency of the algorithm is assessed through the
calculation of Type I and II errors.


title:
Evolution of intratumoral phenotypic heterogeneity: the role of trait
  inheritance

abstract:
  A tumor can be thought of as an ecosystem, which critically means that we
cannot just consider it as a collection of mutated cells but more as a complex
system of many interacting cellular and microenvironmental elements. At its
simplest, a growing tumor with increased proliferation capacity must compete
for space as a limited resource. Hypercellularity leads to a contact-inhibited
core with a competitive proliferating rim. Evolution and selection occurs, and
an individual cell's capacity to survive and propagate is determined by its
combination of traits and interaction with the environment. With heterogeneity
in phenotypes, the clone that will dominate is not always obvious as there are
both local interactions and global pressures. Several combinations of
phenotypes can coexist, changing the fitness of the whole.
  To understand some aspects of heterogeneity in a growing tumor we build an
off-lattice agent based model consisting of individual cells with assigned
trait values for proliferation and migration rates. We represent heterogeneity
in these traits with frequency distributions and combinations of traits with
density maps. How the distributions change over time is dependent on how traits
are passed on to progeny cells, which is our main inquiry. We bypass the
translation of genetics to behavior by focussing on the functional end result
of inheritance of the phenotype combined with the environmental influence of
limited space.


title:
Isocurvature and Curvaton Perturbations with Red Power Spectrum and
  Large Hemispherical Asymmetry

abstract:
  We calculate the power spectrum and hemispherical asymmetry of isocurvature
and curvaton perturbations due to a complex field \Phi which is evolving along
the tachyonic part of its potential. Using a semi-classical evolution of
initially sub-horizon quantum fluctuations, we compute the power spectrum, mean
field and hemispherical asymmetry as a function of the number of e-foldings of
tachyonic growth \Delta N and the tachyonic mass term cH^2. We find that a
large hemispherical asymmetry due to the modulation of |\Phi| can easily be
generated via the spatial modulation of |\Phi| across the horizon, with Delta
|\Phi|/|\Phi| > 0.5 when the observed Universe exits the horizon within 10-40
e-foldings of the beginning of tachyonic evolution and c is in the range 0.1-1.
The spectral index of the isocurvature and curvaton perturbations is generally
negative, corresponding to a red power spectrum. Dark matter isocurvature
perturbations due to an axion-like curvaton with a large hemispherical
asymmetry may be able to explain the hemispherical asymmetry observed by WMAP
and Planck. In this case, the red spectrum can additionally suppress the
hemispherical asymmetry at small scales, which should make it easier to satisfy
scale-dependence requirements on the asymmetry from quasar number counts.


title: Matrix Inversion Is As Easy As Exponentiation

abstract:
  We prove that the inverse of a positive-definite matrix can be approximated
by a weighted-sum of a small number of matrix exponentials. Combining this with
a previous result [OSV12], we establish an equivalence between matrix inversion
and exponentiation up to polylogarithmic factors. In particular, this
connection justifies the use of Laplacian solvers for designing fast
semi-definite programming based algorithms for certain graph problems. The
proof relies on the Euler-Maclaurin formula and certain bounds derived from the
Riemann zeta function.


title: A Mechanism for Hadron Molecule Production in p pbar(p) Collisions

abstract:
  We propose a mechanism allowing the formation of loosely bound molecules of
charmed mesons in high energy proton-(anti)proton collisions.


title: Energetics and diffusion of gold in bismuth telluride

abstract:
  We have coupled electron microscopy and energy dispersive spectroscopy
experiments with \textit{ab-initio} modeling to study the solubility and
diffusion of Au in Bi$_2$Te$_3$. We found that thermal annealing of Au films
results in Au concentrations in Bi$_2$Te$_3$ above the previously reported
solubility limit. The time scale of Au diffusion into Bi$_2$Te$_3$ is also much
greater than expected. To explain our observations, we calculate defect
formation energies and diffusion barriers within DFT. We identify an
interstitial mechanism consistent with the previously observed low solubility
and (rapid) anisotropic diffusion. However, the lower formation energies of
substitutional defects suggest that they may be active in our experiments and
explain the high observed concentrations.


title: Proximate fixed property and operations

abstract:
  Klee introduced the proximate fixed point property for compacta which is
stronger than fixed point property. We consider relations between proximate
fixed point property of spaces being result of application of different
operations to continua. As an application we show this property for products,
cones, suspensions and joins of span 0 continua.


title:
Weak observability estimates for 1-D wave equations with rough
  coefficients

abstract:
  In this paper we prove observability estimates for 1-dimensional wave
equations with non-Lipschitz coefficients. For coefficients in the Zygmund
class we prove a "classical" observability estimate, which extends the
well-known observability results in the energy space for $BV$ regularity. When
the coefficients are instead log-Lipschitz or log-Zygmund, we prove
observability estimates "with loss of derivatives": in order to estimate the
total energy of the solutions, we need measurements on some higher order
Sobolev norms at the boundary. This last result represents the intermediate
step between the Lipschitz (or Zygmund) case, when observability estimates hold
in the energy space, and the H\"older one, when they fail at any finite order
(as proved in \cite{Castro-Z}) due to an infinite loss of derivatives. We also
establish a sharp relation between the modulus of continuity of the
coefficients and the loss of derivatives in the observability estimates. In
particular, we will show that under any condition which is weaker than the
log-Lipschitz one (not only H\"older, for instance), observability estimates
fail in general, while in the intermediate instance between the Lipschitz and
the log-Lipschitz ones they can hold only admitting a loss of a finite number
of derivatives. This classification has an exact counterpart when considering
also the second variation of the coefficients.


title:
Optimisation of CMOS pixel sensors for high performance vertexing and
  tracking

abstract:
  CMOS Pixel Sensors tend to become relevant for a growing spectrum of charged
particle detection instruments. This comes mainly from their high granularity
and low material budget. However, several potential applications require a
higher read-out speed and radiation tolerance than those achieved with
available devices based on a 0.35 micrometers feature size technology. This
paper shows preliminary test results of new prototype sensors manufactured in a
0.18 micrometers process based on a high resistivity epitaxial layer of
sizeable thickness. Grounded on these observed performances, we discuss a
development strategy over the coming years to reach a full scale sensor
matching the specifications of the upgraded version of the Inner Tracking
System (ITS) of the ALICE experiment at CERN, for which a sensitive area of up
to about 10 square meters may be equipped with pixel sensors.


title:
Exponential asymptotics for line solitons in two-dimensional periodic
  potentials

abstract:
  As a first step toward a fully two-dimensional asymptotic theory for the
bifurcation of solitons from infinitesimal continuous waves, an analytical
theory is presented for line solitons, whose envelope varies only along one
direction, in general two-dimensional periodic potentials. For this
two-dimensional problem, it is no longer viable to rely on a certain recurrence
relation for going beyond all orders of the usual multi-scale perturbation
expansion, a key step of the exponential asymptotics procedure previously used
for solitons in one-dimensional problems. Instead, we propose a more direct
treatment which not only overcomes the recurrence-relation limitation, but also
simplifies the exponential asymptotics process. Using this modified technique,
we show that line solitons with any rational line slopes bifurcate out from
every Bloch-band edge; and for each rational slope, two line-soliton families
exist. Furthermore, line solitons can bifurcate from interior points of Bloch
bands as well, but such line solitons exist only for a couple of special line
angles due to resonance with the Bloch bands. In addition, we show that a
countable set of multi-line-soliton bound states can be constructed
analytically. The analytical predictions are compared with numerical results
for both symmetric and asymmetric potentials, and good agreement is obtained.


title:
Elliptic genera of two-dimensional N=2 gauge theories with rank-one
  gauge groups

abstract:
  We compute the elliptic genera of two-dimensional N=(2,2) and N=(0,2) gauged
linear sigma models via supersymmetric localization, for rank-one gauge groups.
The elliptic genus is expressed as a sum over residues of a meromorphic
function whose argument is the holonomy of the gauge field along both the
spatial and the temporal directions of the torus. We illustrate our formulas by
a few examples including the quintic Calabi-Yau, N=(2,2) SU(2) and O(2) gauge
theories coupled to N fundamental chiral multiplets, and a geometric N=(0,2)
model.


title: On the Ratio of Revenue to Welfare in Single-Parameter Mechanism Design

abstract:
  What fraction of the potential social surplus in an environment can be
extracted by a revenue-maximizing monopolist? We investigate this problem in
Bayesian single-parameter environments with independent private values. The
precise answer to the question obviously depends on the particulars of the
environment: the feasibility constraint and the distributions from which the
bidders' private values are sampled. Rather than solving the problem in
particular special cases, our work aims to provide universal lower bounds on
the revenue-to-welfare ratio that hold under the most general hypotheses that
allow for non-trivial such bounds.
  Our results can be summarized as follows. For general feasibility
constraints, the revenue-to-welfare ratio is at least a constant times the
inverse-square-root of the number of agents, and this is tight up to constant
factors. For downward-closed feasibility constraints, the revenue-to-welfare
ratio is bounded below by a constant. Both results require the bidders'
distributions to satisfy hypotheses somewhat stronger than regularity; we show
that the latter result cannot avoid this requirement.


title:
Existence and uniqueness of minimizers of general least gradient
  problems

abstract:
  Motivated by problems arising in conductivity imaging, we prove existence,
uniqueness, and comparison theorems - under certain sharp conditions - for
minimizers of the general least gradient problem \[\inf_{u\in BV_f(\Omega)}
\int_{\Omega}\varphi(x,Du),\] where $f:\partial \Omega\to \R$ is continuous, \[
BV_f(\Omega):=\{v\in BV(\Omega): \ \ \forall x\in \partial \Omega, \ \
\lim_{r\to 0} \ \esssup_{y\in \Omega, |x-y|<r} |f(x) - v(y)| = 0 \ \}
%BV_f(\Omega)=\{u\in BV(\Omega): {0.1cm} u|_{\partial \Omega}=f {0.1cm}
\hbox{and} {0.1cm} {0.1cm} u {0.1cm} \hbox{is continuous at} {0.1cm} \partial
\Omega \}. \] and $\varphi(x,\xi)$ is a function that, among other properties,
is convex and homogeneous of degree 1 with respect to the $\xi$ variable. In
particular we prove that if $a\in C^{1,1}(\Omega)$ is bounded away from zero,
then minimizers of the weighted least gradient problem $\inf_{u \in
BV_f}\int_{\Omega} a|Du|$ are unique in $BV_f(\Omega)$. We construct
counterexamples to show that the regularity assumption $a\in C^{1,1}$ is sharp,
in the sense that it can not be replaced by $a\in C^{1,\alpha}(\Omega)$ with
any $\alpha<1$.


title:
On the probability distribution of the gcd and lcm of $r$-tuples of
  integers

abstract:
  This paper is devoted to the study of statistical properties of the greatest
common divisor and the least common multiple of random samples of positive
integers.


title: Birational geometry of hypersurfaces in products of projective spaces

abstract:
  We study the birational properties of hypersurfaces in products of projective
spaces. In the case of hypersurfaces in P^m x P^n, we describe their nef,
movable and effective cones and determine when they are Mori dream spaces.
Using these results, we give new simple examples of non-Mori dream spaces and
analogues of Mumford's example of a strictly nef line bundle which is not
ample.


title:
A Companion of "Relating Strong Behavioral Equivalences for Processes
  with Nondeterminism and Probabilities"

abstract:
  In the paper "Relating Strong Behavioral Equivalences for Processes with
Nondeterminism and Probabilities" to appear in TCS, we present a comparison of
behavioral equivalences for nondeterministic and probabilistic processes. In
particular, we consider strong trace, failure, testing, and bisimulation
equivalences. For each of these groups of equivalences, we examine the
discriminating power of three variants stemming from three approaches that
differ for the way probabilities of events are compared when nondeterministic
choices are resolved via deterministic schedulers. The established
relationships are summarized in a so-called spectrum. However, the equivalences
we consider in that paper are only a small subset of those considered in the
original spectrum of equivalences for nondeterministic systems introduced by
Rob van Glabbeek. In this companion paper we we enlarge the spectrum by
considering variants of trace equivalences (completed-trace equivalences),
additional decorated-trace equivalences (failure-trace, readiness, and
ready-trace equivalences), and variants of bisimulation equivalences (kernels
of simulation, completed-simulation, failure-simulation, and ready-simulation
preorders). Moreover, we study how the spectrum changes when randomized
schedulers are used instead of deterministic ones.


title: Tensors of Nonnegative Rank Two

abstract:
  A nonnegative tensor has nonnegative rank at most 2 if and only if it is
supermodular and has flattening rank at most 2. We prove this result, then
explore the semialgebraic geometry of the general Markov model on phylogenetic
trees with binary states, and comment on possible extensions to tensors of
higher rank.


title: Privacy Preserving Recommendation System Based on Groups

abstract:
  Recommendation systems have received considerable attention in the recent
decades. Yet with the development of information technology and social media,
the risk in revealing private data to service providers has been a growing
concern to more and more users. Trade-offs between quality and privacy in
recommendation systems naturally arise. In this paper, we present a privacy
preserving recommendation framework based on groups. The main idea is to use
groups as a natural middleware to preserve users' privacy. A distributed
preference exchange algorithm is proposed to ensure the anonymity of data,
wherein the effective size of the anonymity set asymptotically approaches the
group size with time. We construct a hybrid collaborative filtering model based
on Markov random walks to provide recommendations and predictions to group
members. Experimental results on the MovieLens and Epinions datasets show that
our proposed methods outperform the baseline methods, L+ and ItemRank, two
state-of-the-art personalized recommendation algorithms, for both
recommendation precision and hit rate despite the absence of personal
preference information.


title:
Quantum Hydrodynamics Approach to The Research of Quantum Effects and
  Vorticity Evolution in Spin Quantum Plasmas

abstract:
  In this paper we explicate a method of magneto quantum hydrodynamics (MQHD)
for the study of the quantum evolution of a system of spinning fermions in an
external electromagnetic field. The fundamental equations of microscopic
quantum hydrodynamics (the momentum balance equation and the magnetic moment
density equation) were derived from the many-particle microscopic Schroodinger
equation with $Spin-Spin and Coulomb modified Hamiltonian. Using the developed
approach the extended vorticity evolution equation for the quantum spinning
plasma were derived. The effects of new spin forces and spin-spin interaction
contributions on the motion of fermions, evolution of the magnetic moment
density and vorticity generation were predicted. The influence of the intrinsic
spin of electrons in the nonlinear whistler mode turbulence was investigated.
This results can be used for the theoretical studies of spinning many-particle
systems, especially dense quantum plasmas in compact astrophysical objects,
plasmas in semiconductors and micro-mechanical systems, in quantum x-ray
free-electron lasers.


title: Observed Properties of Extrasolar Planets

abstract:
  Observational surveys for extrasolar planets probe the diverse outcomes of
planet formation and evolution. These surveys measure the frequency of planets
with different masses, sizes, orbital characteristics, and host star
properties. Small planets between the sizes of Earth and Neptune substantially
outnumber Jupiter-sized planets. The survey measurements support the core
accretion model in which planets form by the accumulation of solids and then
gas in protoplanetary disks. The diversity of exoplanetary characteristics
demonstrates that most of the gross features of the Solar system are one
outcome in a continuum of possibilities. The most common class of planetary
system detectable today consists of one or more planets approximately one to
three times Earth's size orbiting within a fraction of the Earth-Sun distance.


title: Burstiness and spreading on temporal networks

abstract:
  We discuss how spreading processes on temporal networks are impacted by the
shape of their inter-event time distributions. Through simple mathematical
arguments and toy examples, we find that the key factor is the ordering in
which events take place, a property that tends to be affected by the bulk of
the distributions and not only by their tail, as usually considered in the
literature. We show that a detailed modeling of the temporal patterns observed
in complex networks can change dramatically the properties of a spreading
process, such as the ergodicity of a random walk process or the persistence of
an epidemic.


title: The openness conjecture for projective manifolds

abstract:
  We give a proof of the openness conjecture of Demailly and Koll\'ar for
positively curved singular metrics on ample line bundles over projective
varieties. As a corollary it follows that the openness conjecture for
plurisubharmonic functions with isolated sigularities holds.


title: Magnetic contribution to dilepton production in heavy-ion collisions

abstract:
  We calculate a novel "magnetic contribution" to the dilepton spectrum in
heavy-ion collisions arising from interaction of relativistic quarks with
intense magnetic field. Synchrotron radiation by quarks, which can be
approximated by the equivalent photon flux, is followed by dilepton decay of
photons in intense magnetic field. We argue that "magnetic contribution"
dominates the dilepton spectrum at low lepton energies, whereas a conventional
photon dilepton decay dominates at higher lepton energies.


title: Adaptive Primal-Dual Hybrid Gradient Methods for Saddle-Point Problems

abstract:
  The Primal-Dual hybrid gradient (PDHG) method is a powerful optimization
scheme that breaks complex problems into simple sub-steps. Unfortunately, PDHG
methods require the user to choose stepsize parameters, and the speed of
convergence is highly sensitive to this choice. We introduce new adaptive PDHG
schemes that automatically tune the stepsize parameters for fast convergence
without user inputs. We prove rigorous convergence results for our methods, and
identify the conditions required for convergence. We also develop practical
implementations of adaptive schemes that formally satisfy the convergence
requirements. Numerical experiments show that adaptive PDHG methods have
advantages over non-adaptive implementations in terms of both efficiency and
simplicity for the user.


title: On Achievable Rates for Channels with Mismatched Decoding

abstract:
  The problem of mismatched decoding for discrete memoryless channels is
addressed. A mismatched cognitive multiple-access channel is introduced, and an
inner bound on its capacity region is derived using two alternative encoding
methods: superposition coding and random binning. The inner bounds are derived
by analyzing the average error probability of the code ensemble for both
methods and by a tight characterization of the resulting error exponents.
Random coding converse theorems are also derived. A comparison of the
achievable regions shows that in the matched case, random binning performs as
well as superposition coding, i.e., the region achievable by random binning is
equal to the capacity region. The achievability results are further specialized
to obtain a lower bound on the mismatch capacity of the single-user channel by
investigating a cognitive multiple access channel whose achievable sum-rate
serves as a lower bound on the single-user channel's capacity. In certain
cases, for given auxiliary random variables this bound strictly improves on the
achievable rate derived by Lapidoth.


title: Length-based attacks in polycyclic groups

abstract:
  After the Anshel-Anshel-Goldfeld (AAG) key-exchange protocol was introduced
in 1999, it was implemented and studied with braid groups and with the Thompson
group as its underlying platforms. The length-based attack, introduced by
Hughes and Tannenbaum, has been used to extensively study AAG with the braid
group as the underlying platform. Meanwhile, a new platform, using polycyclic
groups, was proposed by Eick and Kahrobaei.
  In this paper, we show that with a high enough Hirsch length, the polycyclic
group as an underlying platform for AAG is resistant to the length-based
attack. In particular, polycyclic groups could provide a secure platform for
any cryptosystem based on conjugacy search problem such as non-commutative
Diffie-Hellman, ElGamal and Cramer-Shoup key exchange protocols.


title:
Symmetries of charged particle motion under time-independent
  electromagnetic fields

abstract:
  A symmetry analysis is presented for the three-dimensional nonrelativistic
motion of charged particles in arbitrary stationary electromagnetic fields. The
general form of the Lie point symmetries is found along with the fields that
respect them, considering non-trivial cases of physical interest. The
restrictions placed upon the electromagnetic field yield five classes of
solutions, expressed in terms of the vector and scalar potential. The Noether
type symmetries are also investigated and their corresponding invariants are
found. A second integral of motion, besides the Hamiltonian, results in three
general cases. Finally, a relation between the symmetries of the charged
particle motion and the symmetries of the magnetic field lines is established.


title: Calibration and Performance of the ATLAS Tile Calorimeter

abstract:
  The Tile Calorimeter (TileCal) is the hadronic calorimeter covering the most
central region of the ATLAS experiment at the LHC. It is a key detector for the
measurement of hadrons, jets, tau leptons and missing transverse energy. The
TileCal calibration system comprises radioactive source, laser and charge
injection elements and it allows to monitor and equalize the calorimeter
response at each stage of the signal production, from scintillation light to
digitization. This contribution presents a brief description of the different
TileCal calibration systems as well as the latest results on their performance
in terms of calibration factors, linearity and stability. The performance of
the Tile Calorimeter with the cosmic muons and collision data is also
presented, including the absolute energy scale, time resolution and associated
stabilities.


title:
On the Remote Detection of Suprathermal Ions in the Solar Corona and
  their Role as Seeds for Solar Energetic Particle Production

abstract:
  Forecasting large Solar Energetic Particle (SEP) events associated with
shocks driven by fast coronal mass ejections (CME) pose a major difficulty in
the field of Space Weather. Besides issues associated with CME initiation, the
SEP intensities are difficult to predict, spanning 3 orders of magnitude at any
given CME speed. Many lines of indirect evidence point to the pre-existence of
suprathermal seed particles for injection into the acceleration process as a
key ingredient limiting the SEP intensity of a given event. This paper outlines
the observational and theoretical basis for the inference that a suprathermal
particle population is present prior to large SEP events, explores various
scenarios for generating seed particles and their observational signatures, and
explains how such suprathermals could be detected through measuring the wings
of the H I Ly-alpha line.


title: Self-organization of progress across the century of physics

abstract:
  We make use of information provided in the titles and abstracts of over half
a million publications that were published by the American Physical Society
during the past 119 years. By identifying all unique words and phrases and
determining their monthly usage patterns, we obtain quantifiable insights into
the trends of physics discovery from the end of the 19th century to today. We
show that the magnitudes of upward and downward trends yield heavy-tailed
distributions, and that their emergence is due to the Matthew effect. This
indicates that both the rise and fall of scientific paradigms is driven by
robust principles of self-organization. Data also confirm that periods of war
decelerate scientific progress, and that the later is very much subject to
globalization.

categories: physics.soc-ph cs.DL cs.SI physics.data-an


title: On the gauge symmetries of the spinning particle

abstract:
  We reconsider the gauge symmetries of the spinning particle by a direct
examination of the Lagrangian using a systematic procedure based on the Noether
identities. It proves possible to find a set of local Bosonic and Fermionic
gauge transformations that have a simple gauge group structure, which is a true
Lie algebra, both for the massless and massive case. This new Fermionic gauge
transformation of the "position" and "spin" variables in the action decouples
from that of the "einbein" and "gravitino".
  It is also possible to redefine the fields so that this simple algebra of
commutators of the gauge transformations can be derived directly starting from
the Lagrangian written in these new variables.
  We discuss a possible extension of our analysis of this simple model to more
complicated cases.


title:
Density of states of disordered topological superconductor-semiconductor
  hybrid nanowires

abstract:
  Using Bogoliubov-de Gennes (BdG) equations we numerically calculate the
disorder averaged density of states of disordered semiconductor nanowires
driven into a putative topological p-wave superconducting phase by spin-orbit
coupling, Zeeman spin splitting and s-wave superconducting proximity effect
induced by a nearby superconductor. Comparing with the corresponding
theoretical self-consistent Born approximation (SCBA) results treating disorder
effects, we comment on the topological phase diagram of the system in the
presence of increasing disorder. Although disorder strongly suppresses the
zero-bias peak (ZBP) associated with the Majorana zero mode, we find some clear
remnant of a ZBP even when the topological gap has essentially vanished in the
SCBA theory because of disorder. We explicitly compare effects of disorder on
the numerical density of states in the topological and trivial phases.


title:
Finite element simulation of a perturbed axial-symmetric
  whispering-gallery mode and its use for intensity enhancement with a
  nanoparticle coupled to a microtoroid

abstract:
  We present an optical mode solver for a whispering gallery resonator coupled
to an adjacent arbitrary shaped nano-particle that breaks the axial symmetry of
the resonator. Such a hybrid resonator-nanoparticle is similar to what was
recently used for bio-detection and for field enhancement. We demonstrate our
solver by parametrically studying a toroid-nanoplasmonic device and get the
optimal nano-plasmonic size for maximal enhancement. We investigate cases near
a plasmonic resonance as well as far from a plasmonic resonance. Unlike common
plasmons that typically benefit from working near their resonance, here working
far from plasmonic resonance provides comparable performance. This is because
the plasmonic resonance enhancement is accompanied by cavity quality
degradation through plasmonic absorption.


title:
A quantum teleportation inspired algorithm produces sentence meaning
  from word meaning and grammatical structure

abstract:
  We discuss an algorithm which produces the meaning of a sentence given
meanings of its words, and its resemblance to quantum teleportation. In fact,
this protocol was the main source of inspiration for this algorithm which has
many applications in the area of Natural Language Processing.


title:
A general procedure for thermomechanical calibration of
  nano/micro-mechanical resonators

abstract:
  We provide a detailed description of a general procedure by which a
nano/micro-mechanical resonator can be calibrated using its thermal motion. A
brief introduction to the equations of motion for such a resonator is
presented, followed by a detailed derivation of the corresponding power
spectral density (PSD) function. The effective masses for a number of different
resonator geometries are determined using both finite element method (FEM)
modeling and analytical calculations.


title:
Gas surface density, star formation rate surface density, and the
  maximum mass of young star clusters in a disk galaxy. II. The grand-design
  galaxy M51

abstract:
  We analyze the relationship between maximum cluster mass, and surface
densities of total gas (Sigma_gas), molecular gas (Sigma_H_2), neutral gas
(Sigma_HI) and star formation rate (Sigma_SFR) in the grand design galaxy M51,
using published gas data and a catalog of masses, ages, and reddenings of more
than 1800 star clusters in its disk, of which 223 are above the cluster mass
distribution function completeness limit. We find for clusters older than 25
Myr that M_3rd, the median of the 5 most massive clusters, is proportional to
Sigma_HI^0.4. There is no correlation with Sigma_gas, Sigma_H2, or Sigma_SFR.
For clusters younger than 10 Myr, M_3rd is proportional to Sigma_HI^0.6, M_3rd
is proportional to Sigma_gas^0.5; there is no correlation with either Sigma_H_2
or Sigma_SFR. The results could hardly be more different than those found for
clusters younger than 25 Myr in M33. For the flocculent galaxy M33, there is no
correlation between maximum cluster mass and neutral gas, but M_3rd is
proportional to Sigma_gas^3.8; M_3rd is proportional to Sigma_H_2^1.2; M_3rd
proportional to Sigma_SFR^0.9. For the older sample in M51, the lack of tight
correlations is probably due to the combination of the strong azimuthal
variations in the surface densities of gas and star formation rate, and the
cluster ages. These two facts mean that neither the azimuthal average of the
surface densities at a given radius, nor the surface densities at the
present-day location of a stellar cluster represent the true surface densities
at the place and time of cluster formation. In the case of the younger sample,
even if the clusters have not yet traveled too far from their birthsites, the
poor resolution of the radio data compared to the physical sizes of the
clusters results in measured Sigmas that are likely quite diluted compared to
the actual densities relevant for the formation of the clusters.


title: Effective models for strong electronic correlations at graphene edges

abstract:
  We describe a method for deriving effective low-energy theories of electronic
interactions at graphene edges. Our method is applicable to general edges of
honeycomb lattices (zigzag, chiral, and even disordered) as long as localized
low-energy states (edge states) are present. The central characteristic of the
effective theories is a dramatically reduced number of degrees of freedom. As a
consequence, the solution of the effective theory by exact diagonalization is
feasible for reasonably large ribbon sizes. The quality of the involved
approximations is critically assessed by comparing the correlation functions
obtained from the effective theory with numerically exact quantum Monte-Carlo
calculations. We discuss effective theories of two levels: a relatively
complicated fermionic edge state theory and a further reduced Heisenberg spin
model. The latter theory paves the way to an efficient description of the
magnetic features in long and structurally disordered graphene edges beyond the
mean-field approximation.


title:
On the stark difference in satellite distributions around the Milky Way
  and Andromeda

abstract:
  We compare spherically-averaged radial number counts of bright (> 10^5 Lsun)
dwarf satellite galaxies within 400 kpc of the Milky Way (MW) and M31 and find
that the MW satellites are much more centrally concentrated. Remarkably, the
two satellite systems are almost identical within the central 100 kpc, while
M31 satellites outnumber MW satellites by about a factor of four at deprojected
distances spanning 100 - 400 kpc. We compare the observed distributions to
those predicted for LCDM suhbalos using a suite of 44 high-resolution ~10^12
halo zoom simulations, 22 of which are in pairs like the MW and M31. We find
that the radial distribution of satellites around M31 is fairly typical of
those predicted for subhalos, while the Milky Way's distribution is more
centrally concentrated that any of our simulated LCDM halos. One possible
explanation is that our census is bright (> 10^5 Lsun) MW dwarf galaxies is
significantly incomplete beyond ~ 100 kpc of the Sun. If there were ~8 - 20
more bright dwarfs orbiting undetected at 100 - 400 kpc, then the Milky Way's
radial distribution would fall within the range expected from subhalo
distributions and alos look very much like the known M31 system. We use our
simulations to demonstrate that there is enough area left unexplored by the
Sloan Digital Sky Survey and its extensions that the discovery of ~10 new
bright dwarfs is not implausible given the expected range of angular anisotropy
of subhalos in the sky.


title: Preheating with Non-Minimal Kinetic Terms

abstract:
  We present the first 3+1-dimensional numerical simulations of scalar fields
with non-minimal kinetic terms. As an example, we examine the existence and
stability of preheating in the presence of a Dirac-Born-Infeld (DBI) inflaton
coupled to a canonical matter field. The simulations represent the full
non-linear theory in the presence of an expanding Universe. We show that
parametric resonance in the matter field, along with self-resonance in the
inflaton, repopulate the Universe with matter particles as efficiently as in
traditional preheating.


title:
Nurturing Lyman Break Galaxies: Observed link between environment and
  spectroscopic features

abstract:
  We examine the effects of magnitude, colour, and Ly-alpha equivalent width
(EW) on the spatial distribution of z~3 Lyman break galaxies (LBGs) and report
significant differences in their auto-correlation functions (ACFs). The results
are obtained using samples of ~10,000-57,000 LBGs from the Canada-France-Hawaii
Telescope Legacy Survey. We find that magnitude has a larger effect on the ACF
amplitude on small scales (<~1 Mpc) and that colour is more influential on
large scales (>~1 Mpc). We find the most significant differences between ACFs
for LBGs with dominant net Ly-alpha EW in absorption (aLBGs) and dominant net
Ly-alpha EW in emission (eLBGs) determined from >~95% pure samples of each
population using a photometric technique calibrated from ~1000 spectra. The
aLBG ACF one-halo term departs from a power law fit near ~1 Mpc, corresponding
to the virial radii of M_DM ~10^13 M_solar haloes, and shows a strong two-halo
term amplitude. In contrast, the eLBG ACF one-halo term departs at ~0.12 Mpc,
suggesting parent haloes of M_DM ~10^11 M_solar, and a two-halo term that
exhibits a `hump' on intermediate scales that we localize to the faintest,
bluest members. We find that the `hump' can be well fit with a model in which a
significant fraction of eLBGs reside on shells. The auto- and cross-correlation
functions indicate that aLBGs are found in massive, group-like haloes and that
eLBGs are found largely on group outskirts and in the field. Ly-alpha is a
tracer of several intrinsic LBG properties, including morphology, implying that
the mechanisms behind the morphology-density relation are in place at z~3 and
that Ly-alpha EW may be a key environment diagnostic. Finally, our results show
that the mass of LBGs has been underestimated because the LBG ACF amplitude is
lower than the true average as a result of the spatial anti-correlation of the
spectral sub-types (abridged).


title: Anisotropic Halo Model

abstract:
  In the present work, we extend the classic halo model for the large-scale
matter distribution including a triaxial model for the halo profiles and their
alignments. In particular, we derive general expressions for the halo-matter
cross correlation function. In addition, by numerical integration, we obtain
instances of the cross-correlation function depending on the directions given
by halo shape axes. These functions are called anisotropic cross-correlations.
With the aim of comparing our theoretical results with the simulations, we
compute averaged anisotropic correlations in cones with their symmetry axis
along each shape direction of the centre halo. From these comparisons we
characterise and quantify the alignment of dark matter haloes on the
$\Lambda$CDM context by means of the presented anisotropic halo model. As our
model requires multidimensional integral computation we implement a Monte Carlo
method on GPU hardware which allows us to increase the precision of the results
whereas it improves the performance of the computation.


title:
Studying the relationship between X-ray emission and accretion in AGNs
  using the XMM-Newton Bright Serendipitous Survey

abstract:
  We study the link between the X-ray emission in radio-quiet AGNs and the
accretion rate on the central Supermassive Black Hole using a statistically
well-defined and representative sample of 71 type 1 AGNs extracted from the
XMM-Newton Bright Serendipitous Survey. We search and quantify the statistical
correlations between some fundamental parameters that characterize the X-ray
emission, i.e. the X-ray spectral slope, and the X-ray "loudness", and the
accretion rate, both absolute and normalized to the Eddington luminosity
(Eddington ratio). We parametrize the X-ray loudness using three different
quantities: the bolometric correction, the two-point spectral index and the
disk/corona luminosity ratio. We find that the X-ray spectral index depends on
the normalized accretion rate while the "X-ray loudness" depends on both the
normalized and the absolute accretion rate. The dependence on the Eddington
ratio, in particular, is probably induced by the X-ray spectral slope-Eddington
ratio correlation. The two proxies usually adopted in the literature to
quantify the X-ray loudness of an AGN, i.e. the bolometric correction and the
two-point spectral index, behave differently, with the bolometric correction
being more sensitive to the Eddington ratio and the two-point spectral index
having a stronger dependence with the absolute accretion. The explanation of
this result is likely related to the different sensitivity of the two
parameters to the X-ray spectral index.


title:
A minor merger scenario for the ultraluminous X-ray source ESO 243-49
  HLX-1 - II. Constraints from photometry

abstract:
  The point-like X-ray source HLX-1, close to the S0 galaxy ESO 243-49, is the
brightest known ultraluminous X-ray source and one the strongest
intermediate-mass black hole candidates. We argue that the counterpart of HLX-1
may be the nucleus of a satellite galaxy, undergoing minor merger with the S0
galaxy. We investigate this scenario by running a set of N-body/smoothed
particle hydrodynamics simulations of the minor merger between a S0 galaxy and
a gas-rich bulgy satellite galaxy, and by comparing the results with the
available photometric Hubble Space Telescope (HST) data of ESO 243-49 and of
the HLX-1 counterpart. In particular, we derive synthetic surface brightness
profiles for the simulated counterpart of HLX-1 in six HST filters, ranging
from far ultraviolet (FUV) to infrared wavelengths. Such synthetic profiles
include a contribution from the stellar population associated with the
simulated disrupted satellite and a contribution from an irradiated disc model.
These are in reasonable agreement with the observed surface brightness profiles
of the HLX-1 counterpart, provided that the merger is at sufficiently late
stage (>~2.5 Gyr since the first pericentre passage). The main difference
between models and observations is in the FUV band, where the HST image shows a
fuzzy and extended emission. We show that the spectral energy distribution of
the bulge of ESO 243-49 cannot be explained with a single old stellar
population, but requires the existence of a younger stellar component. This is
in good agreement with the star formation history derived from our N-body
simulations, and is a further hint for the minor merger scenario.


title: Lessons from an Extended Heterotic Mini-Landscape

abstract:
  We consider the key ingredients which made the Z_6II Mini-Landscape a
successful ground for model building. There one observes a preferred
distribution for the fields of the standard model which has direct implications
on the phenomenology, since it favors a heavy top quark and a plausible
solution to the $\mu$-problem. We extend the exploration to the Z_2xZ_4
orbifold, where a similar pattern is identified. To illustrate our findings we
present an explicit Z_2xZ_4 model that exhibits the MSSM spectrum plus
vector-like exotics at the orbifold point. We take this construction as an
example of a larger class of orbifold models which were anticipated at the GUT
level. Furthermore we comment on VEV configurations to decouple the exotics
while maintaining a meaningful R-symmetry which could forbid the mu-term.


title: Azimuthal Density Variations Around the Rim of Tycho's Supernova Remnant

abstract:
  {\it Spitzer} images of Tycho's supernova remnant in the mid-infrared reveal
limb-brightened emission from the entire periphery of the shell and faint
filamentary structures in the interior. As with other young remnants, this
emission is produced by dust grains, warmed to $\sim 100$ K in the post-shock
environment by collisions with energetic electrons and ions. The ratio of the
70 to 24 $\mu$m fluxes is a diagnostic of the dust temperature, which in turn
is a sensitive function of the plasma density. We find significant variations
in the 70/24 flux ratio around the periphery of Tycho's forward shock, implying
order-of-magnitude variations in density. While some of these are likely
localized interactions with dense clumps of the interstellar medium, we find an
overall gradient in the ambient density surrounding Tycho, with densities 3-10
times higher in the NE than in the SW. This large density gradient is
qualitatively consistent with the variations in the proper motion of the shock
observed in radio and X-ray studies. Overall, the mean ISM density around Tycho
is quite low ($\sim 0.1-0.2$ cm$^{-3}$), consistent with the lack of thermal
X-ray emission observed at the forward shock. We perform two-dimensional
hydrodynamic simulations of a Type Ia SN expanding into a density gradient in
the ISM, and find that the overall round shape of the remnant is still easily
acheivable, even for explosions into significant gradients. However, this leads
to an offset of the center of the explosion from the geometric center of the
remnant of up to 20%, although lower values of 10% are preferred. The best
match with hydrodynamical simulations is achieved if Tycho is located at a
large (3-4 kpc) distance in a medium with a mean preshock density of $\sim 0.2$
cm$^{-3}$. Such preshock densities are obtained for highly ($\ga 50$%) porous
ISM grains.


title:
Classifying and measuring the geometry of the quantum ground state
  manifold

abstract:
  From the Aharonov-Bohm effect to general relativity, geometry plays a central
role in modern physics. In quantum mechanics many physical processes depend on
the Berry curvature. However, recent advances in quantum information theory
have highlighted the role of its symmetric counterpart, the quantum metric
tensor. In this paper, we perform a detailed analysis of the ground state
Riemannian geometry induced by the metric tensor, using the quantum XY chain in
a transverse field as our primary example. We focus on a particular geometric
invariant -- the Gaussian curvature -- and show how both integrals of the
curvature within a given phase and singularities of the curvature near phase
transitions are protected by critical scaling theory. For cases where the
curvature is integrable, we show that the integrated curvature provides a new
geometric invariant, which like the Chern number characterizes individual
phases of matter. For cases where the curvature is singular, we classify three
types -- integrable, conical, and curvature singularities -- and detail
situations where each type of singularity should arise. Finally, to connect
this abstract geometry to experiment, we discuss three different methods for
measuring the metric tensor, namely via integrating a properly weighted noise
spectral function and by using leading order responses of the work distribution
to ramps and quenches in quantum many-body systems.