title:
Time-evolution of tripartite quantum discord and entanglement under
  local and non-local random telegraph noise

abstract:
  Few studies explored the dynamics of non-classical correlations besides
entanglement in open multipartite quantum systems. Here, we address the
time-evolution of quantum discord and entanglement in a model of three
non-interacting qubits subject to a classical random telegraph noise in common
and separated environments. Two initial entangled states of the system are
examined, namely the GHZ- and W-type states. The dynamics of quantum
correlations results to be strongly affected by the input configuration of the
qubits, the type of the system-environment interaction, and the memory
properties of the environmental noise. When the qubits are non-locally coupled
to the random telegraph noise, the GHZ-type states partially preserve, at long
times, both discord and entanglement, regardless the correlation time of the
environmental noise. The survived entangled states turn out to be also
detectable by means of suitable entanglement witnesses. On the other hand, in
the same conditions, the decohering effects suppress all the quantum
correlation of the W-type states which are thus less robust than the GHZ-type
ones. The long-time survival of tripartite discord and entanglement opens
interesting perspectives in the use of multipartite entangled states for
practical applications in quantum information science.


title: Gravitational Hopfions

abstract:
  The electromagnetic hopfion (EM hopfion) is a topologically nontrivial
solution to the vacuum Maxwell equations with the property that any two field
lines belonging to either the electric, magnetic, or Poynting vector fields
(EBS fields) are closed and linked exactly once. The most striking and
characteristic feature of this peculiar field configuration is the existence of
an exceptional constant-time hyperplane wherein the EBS fields are tangent to
three orthogonal Hopf fibrations. Using twistor methods we find the spin-$N$
generalization of the EM hopfion. Furthermore, we analyze the spin-2 solution
within the framework of gravito-electromagnetism and show that the topology is
manifest in the tendex and vortex lines. By decomposing the spin-2 field into
spatial gravito-electric and gravito-magnetic tensors, we characterize its
topological structure and evolution in terms of the EM hopfion.


title:
Energy momentum tensor correlators in hot Yang-Mills theory: holography
  confronts lattice and perturbation theory

abstract:
  We investigate the behavior of energy momentum tensor correlators in strongly
coupled large-N_c Yang-Mills theory at nonzero temperature, working within the
Improved Holographic QCD model. In particular, we determine the spectral
functions and corresponding imaginary time correlators in the bulk and shear
channels, and compare the results to recent perturbative and lattice
calculations where available. For the bulk channel imaginary time correlator,
for which all three results exist, lattice data is seen to favor the
holographic prediction over the perturbative one over a wide range of
temperatures.


title: Is the Free Vacuum Energy Infinite?

abstract:
  Considering the fundamental cutoff applied by the uncertainty relations'
limit on virtual particles' frequency in the quantum vacuum, it is shown that
the vacuum energy density is proportional to the inverse of the forth power of
the dimensional distance of the space under consideration and thus the
corresponding vacuum energy automatically regularized to zero value for an
infinitely large free space. This can be used in regularizing a number of
unwanted infinities happen in the Casimir effect, the cosmological constant
problem and so on without using already known mathematical (not so reasonable)
techniques and tricks.


title: Graph immersions with parallel cubic form

abstract:
  We consider non-degenerate graph immersions into affine space $\mathbb
A^{n+1}$ whose cubic form is parallel with respect to the Levi-Civita
connection of the affine metric. There exists a correspondence between such
graph immersions and pairs $(J,\gamma)$, where $J$ is an $n$-dimensional real
Jordan algebra and $\gamma$ is a non-degenerate trace form on $J$. Every graph
immersion with parallel cubic form can be extended to an affine complete
symmetric space covering the maximal connected component of zero in the set of
quasi-regular elements in the algebra $J$. It is an improper affine hypersphere
if and only if the corresponding Jordan algebra is nilpotent. In this case it
is an affine complete, Euclidean complete graph immersion, with a polynomial as
globally defining function. We classify all such hyperspheres up to dimension
5. As a special case we describe a connection between Cayley hypersurfaces and
polynomial quotient algebras. Our algebraic approach can be used to study also
other classes of hypersurfaces with parallel cubic form.


title: Local Dimensions of Measures on Infinitely Generated Self-Affine Sets

abstract:
  We show the existence of the local dimension of an invariant probability
measure on an infinitely generated self-affine set, for almost all
translations. This implies that an ergodic probability measure is exactly
dimensional. Furthermore the local dimension equals the minimum of the local
Lyapunov dimension and the dimension of the space. We also give an estimate,
that holds for all translation vectors, with only assuming the affine maps to
be contractive.


title:
Exact realization of Integer and Fractional Quantum Hall Phases in
  U(1)xU(1) models in (2+1)d

abstract:
  In this work we present a set of microscopic U(1)xU(1) models which realize
insulating phases with a quantized Hall conductivity \sigma_{xy}. The models
are defined in terms of physical degrees of freedom, and can be realized by
local Hamiltonians. For one set of these models, we find that \sigma_{xy} is
quantized to be an even integer. The origin of this effect is a condensation of
objects made up of bosons of one species bound to a single vortex of the other
species. For other models, the Hall conductivity can be quantized as a rational
number times two. For these systems, the condensed objects contain bosons of
one species bound to multiple vortices of the other species. These systems have
excitations carrying fractional charges and non-trivial mutual statistics. We
present sign-free reformulations of these models which can be studied in Monte
Carlo, and we use such reformulations to numerically detect a gapless boundary
between the quantum Hall and trivial insulator states. We also present the
broader phase diagrams of the models.


title:
Optimal Hubbard models for materials with nonlocal Coulomb interactions:
  graphene, silicene and benzene

abstract:
  To understand how nonlocal Coulomb interactions affect the phase diagram of
correlated electron materials, we report on a method to approximate a
correlated lattice model with nonlocal interactions by an effective Hubbard
model with on-site interactions U* only. The effective model is defined by the
Peierls-Feynman-Bogoliubov variational principle. We find that the local part
of the interaction U is reduced according to U*=U-V', where V' is a weighted
average of nonlocal interactions. For graphene, silicene and benzene we show
that the nonlocal Coulomb interaction can decrease the effective local
interaction by more than a factor of 2 in a wide doping range.


title:
Excited-State Dynamics in SO2: II. The Role of Triplet States in the
  Bound State Relaxation Studied by Surface-Hopping Simulations

abstract:
  The importance of triplet states in the photorelaxation dynamics of SO2 is
studied by mixed quantum-classical dynamics simulations. Using the Surface
Hopping including ARbitrary Couplings (Sharc) method, intersystem crossing
processes caused by spin-orbit coupling are found occuring on an ultrafast time
scale (few 100 fs) and thus competing with internal conversion. While in the
singlet-only dynamics only oscillatory population transfer between the 1B1 and
1A2 states is observed, in the dynamics including singlet and triplet states we
find additionally continuous ISC to the 3B2 state and to a smaller extent to
the 3B1/3A2 coupled states. The populations obtained from the dynamics are
discussed with respect to the overall nuclear motion and in the light of recent
TRPEPICO studies [Wilkinson et al., paper I].


title: Curve Counting \`a la G\"ottsche

abstract:
  Let n_\delta be the number of \delta-nodal curves lying in a suitably ample
complete linear system |L| and passing through appropriately many points on a
smooth projective complex algebraic surface. A major open problem is to
understand the behavior of n_\delta, specifically to finish off Lothar
G\"ottsche's mostly proved 1997 conjectures and then go on to treat the new
refinements by G\"ottsche and Vivek Shende. Five subproblems are explained, and
work on them is surveyed.


title: Five Statistical Questions about the Tree of Life

abstract:
  Stochastic modeling of phylogenies raises five questions that have received
varying levels of attention from quantitatively inclined biologists. 1) How
large do we expect (from the model) the ration of maximum historical diversity
to current diversity to be? 2) From a correct phylogeny of the extant species
of a clade, what can we deduce about past speciation and extinction rates? 3)
What proportion of extant species are in fact descendants of still-extant
ancestral species, and how does this compare with predictions od models? 4)
When one moves from trees on species to trees on sets of species (whether
traditional higher order taxa or clades from PhyloCode), does one expect trees
to become more unbiased as a purely logical consequence of tree structure,
without signifying any real biological phenomenon? 5) How do we expect that
fluctuation rates for counts of higher order taxa should compare with
fluctuation rates for number of species? WE present a mathematician's view
based on an oversimplified modeling framework in which all these questions can
be studied coherently.


title: Addendum to Uniqueness of certain polynomials constant on a line

abstract:
  The computer calculations in arXiv:0808.0284 to classify sharp polynomials
with nonegative coefficients constant on the line $x+y=1$ have been extended to
degrees 19 and 21. In degree 19 a surprisingly large number of 13 sharp
polynomials was found, while in degree 21 only the group invariant polynomial
exists.


title: Intensity contrast of solar network and faculae

abstract:
  This study aims at setting observational constraints on the continuum and
line core intensity contrast of network and faculae, specifically, their
relationship with magnetic field and disc position. Full-disc magnetograms and
intensity images by the HMI instrument onboard SDO were employed. Bright
magnetic features, representing network and faculae, were identified and the
relationship between their intensity contrast at continuum and line core with
magnetogram signal and heliocentric angle examined. Care was taken to minimize
the inclusion of the magnetic canopy and straylight from sunspots and pores as
network and faculae. In line with earlier studies, network features, on a per
unit magnetic flux basis, appeared brighter than facular features. Intensity
contrasts in the continuum and line core differ considerably, most notably,
they exhibit opposite centre-to-limb variations. We found this difference in
behaviour to likely be due to the different mechanisms of the formation of the
two spectral components. From a simple model based on bivariate polynomial fits
to the measured contrasts we confirmed spectral line changes to be a
significant driver of facular contribution to variation in solar irradiance.
The discrepancy between the continuum contrast reported here and in the
literature was shown to arise mainly from differences in spatial resolution and
treatment of magnetic signals adjacent to sunspots and pores. HMI is a source
of accurate contrasts and low-noise magnetograms covering the full solar disc.
For irradiance studies it is important to consider not just the contribution
from the continuum but also from the spectral lines. In order not to
underestimate long-term variations in solar irradiance, irradiance models
should take the greater contrast per unit magnetic flux associated with
magnetic features with low magnetic flux into account.


title:
Partial Regularity of solutions to the Four-Dimensional Navier-Stokes
  Equations

abstract:
  In this paper, we consider suitable weak solutions of incompressible
Navier--Stokes equations in four spatial dimensions. We prove that the
two-dimensional time-space Hausdorff measure of the set of singular points is
equal to zero.


title:
Observation of an anomalous density-dependent energy gap of the
  $\nu=5/2$ fractional quantum Hall state in the low density regime

abstract:
  We have studied the $\nu=5/2$ fractional quantum Hall state in a
density-tunable sample at extremely low electron densities. For the densities
accessed in our experiment, the Landau level mixing parameter $\kappa$ spans
the $2.52<\kappa<2.82$ range. In the vicinity of $5.8 \times 10^{10}$~cm$^{-2}$
or $\kappa = 2.6$ an anomalously large change in the density dependence of the
energy gap is observed. Possible origins of such an anomaly are discussed,
including a topological phase transition in the $\nu=5/2$ fractional quantum
Hall state.


title: A note on the torque anomaly

abstract:
  I reproduce, in the case of a conical geometry, the torque anomaly recently
noted by Fulling, Mera and Trendafilova for the wedge. The expected
conservation equation is obtained by a variational method and a mathematical
cancellation of the anomaly is exhibited, motivated by the process of
truncating the cone at some inner radius.


title: Stochastically-induced bistability in chemical reaction systems

abstract:
  We study a stochastic two-species chemical reaction system with two
mechanisms. One mechanism consists of chemical interactions which govern the
overall drift of species amounts in the system; the other mechanism consists of
resampling, branching or splitting which makes unbiased perturbative changes to
species amounts. Our results show that in a system with a large but bounded
capacity, certain combinations of these two types of interactions can lead to
stochastically-induced bistability. Depending on the relative magnitudes of the
rates of these two sets of interactions, bistability can occur in two distinct
ways with different dynamical signatures.


title: The Eos family halo

abstract:
  We study K-type asteroids in the broad surroundings of the Eos family because
they seem to be intimately related, according to their colours measured by the
Sloan Digital Sky Survey. Such `halos' of asteroid families have been rarely
used as constraints for dynamical studies to date. We explain its origin as
bodies escaping from the family `core' due to the Yarkovsky semimajor-axis
drift and interactions with gravitational resonances, mostly with the 9/4
mean-motion resonance with Jupiter at 3.03 AU. Our N-body dynamical model
allows us to independently estimate the age of the family 1.5 to 1.9 Gyr. This
is approximately in agreement with the previous age estimate by Vokrouhlick\'y
et al. (2006) based on a simplified model (which accounts only for changes of
semimajor axis). We can also constrain the geometry of the disruption event
which had to occur at the true anomaly f =~ 120 to 180 deg.


title:
Non-thermal fixed points: universality, topology, & turbulence in Bose
  gases

abstract:
  In these notes we discuss recent developments in the field of non-equilibrium
quantum dynamics. Specifically, we consider nearly coherent Bose gases brought
far out of equilibrium and study their behaviour in view of connections between
universal properties, (quasi-)topological field configurations and turbulent
dynamics. We demonstrate that the isolated Bose gas, on its way back to thermal
equilibrium, can approach metastable non-equilibrium configurations and spend a
long time in their vicinity. In such configurations, which have been termed
non-thermal fixed points, the system shows universal long-range properties
manifest through scaling, i.e., self-similar correlations. The spatial field
pattern, at the same time, is characterized by the appearance of defects and
domain formation whose geometry gives rise to the particular scaling laws seen
in the correlation functions. We obtain an overall picture which connects
well-known concepts for describing universal dynamics such as wave-turbulence,
superfluid turbulence, and (quasi-)topological excitations. This allows to
bring together a wide range of concepts and methods with a large spectrum of
applications.

categories: cond-mat.quant-gas cond-mat.stat-mech hep-ph physics.flu-dyn quant-ph


title: Quantum Excitations in Time-Dependent Backgrounds

abstract:
  We give a technique for calculating the occupation number of quantum fields
in time-dependent backgrounds by using the relation between one-dimensional
{\em quantum} oscillators and two-dimensional {\em classical} oscillators. We
illustrate our method by giving closed analytical results for the
time-dependent spectrum of occupation numbers during gravitational collapse in
3+1 dimensions.

categories: hep-th cond-mat.other gr-qc hep-ph math-ph math.MP


title:
Susceptibilities in the PNJL model with 8q interactions and comparison
  with lQCD

abstract:
  We present some results pertaining quantities which are regarded as good
indicators of the pseudo-critical temperatures for the deconfinement and
partial chiral restoration transitions using a polynomial form for the Polyakov
potential part and an extended version of the NJL model which includes 6 and 8
quark interaction terms. Some comparisons with results from the lattice
formulation of QCD (lQCD) are performed and results for the location of the
critical endoint in the phase diagram are also presented. It is shown that the
comparison with lQCD results favors a moderately strong OZI-violating 8 quark
interaction term.


title: Spans of special cycles of codimension less than 5

abstract:
  We show that the span of special cycles in the $r$th Chow group of a Shimura
variety of orthogonal type is finite dimensional, if $r < 5$. As our main tool,
we develop the theory of Jacobi forms with rational index $M \in \Mat{N}(\QQ)$.


title: Statistical properties of zeta functions' zeros

abstract:
  The paper reviews existing results about the statistical distribution of
zeros for the three main types of zeta functions: number-theoretical,
geometrical, and dynamical. It provides necessary background and some details
about the proofs of main results.


title: Steps in the exact time-dependent potential energy surface

abstract:
  We study the exact Time-Dependent Potential Energy Surface (TDPES) in the
presence of strong non-adiabatic coupling between the electronic and nuclear
motion. The concept of the TDPES emerges from the exact factorization of the
full electron-nuclear wave-function [A. Abedi, N. T. Maitra, and E. K. U.
Gross, Phys. Rev. Lett. \textbf{105}, 123002 (2010)]. Employing a 1D
model-system, we show that the TDPES exhibits a dynamical step that bridges
between piecewise adiabatic shapes. We analytically investigate the position of
the steps and the nature of the switching between the adiabatic pieces of the
TDPES.


title: On Linnik's conjecture: sums of squares and microsquares

abstract:
  We show that almost all natural numbers n not divisible by 4, and not
congruent to 7 modulo 8, are represented as the sum of three squares, one of
which is the square of an integer no larger than (log n)^{1+e} (any e>0). This
answers a conjecture of Linnik for almost all natural numbers, and sharpens a
conclusion of Bourgain, Rudnick and Sarnak concerning nearest neighbour
distances between normalised integral points on the sphere.


title: Modeling crosstalk in silicon photomultipliers

abstract:
  Optical crosstalk seriously limits the photon-counting resolution of silicon
photomultipliers. In this work, realistic analytical models to describe the
crosstalk effects on the response of these photodetectors are presented and
compared with experimental data. The proposed models are based on the
hypothesis that each pixel of the array has a finite number of available
neighboring pixels to excite via crosstalk. Dead-time effects and geometrical
aspects of the propagation of crosstalk between neighbors are taken into
account in the models for different neighborhood configurations. Simple
expressions to account for crosstalk effects on the pulse-height spectrum as
well as to evaluate the excess noise factor due to crosstalk are also given.
Dedicated measurements were carried out under both dark-count conditions and
pulsed illumination. Moreover, the influence of afterpulsing on the measured
pulse-height spectrum was studied, and a measurement of the recovery time of
pixels was reported. High-resolution pulse-height spectra were obtained by
means of a detailed waveform analysis, and the results have been used to
validate our crosstalk models.


title: Lead Nanopowder as Advanced Semi-Conductor, An Insight

abstract:
  This work reports aspect related to semi-conducting nature of nano-sized
particles of lead. This attempt finds its semiconducting behaviors elaborately
and such advanced insight has so far not been said in literatures. New findings
of Pb nanopowder (metal) by optical, fluorescence, cyclic voltammetry and four
probe studies are presented in this study. UV-Vis analysis confirms the nano
nature of the sample i.e. 5 nm and SPR peak confirms its metallic nature. The
successful calculations of band gap, temperature dependent resistance value
confirm its semi-conducting nature and explore its potential application in
various industries. This work throws some light on and helps further research.


title: Corrections for the Lutz-Kelker Bias for Galactic Masers

abstract:
  Based on published data, we have collected information about Galactic maser
sources with measured distances. In particular, 44 Galactic maser sources
located in star-forming regions have trigonometric parallaxes, proper motions,
and radial velocities. In addition, ten more radio sources with incomplete
information are known, but their parallaxes have been measured with a high
accuracy. For all 54 sources, we have calculated the corrections for the
well-known Lutz-Kelker bias. Based on a sample of 44 sources, we have refined
the parameters of the Galactic rotation curve. Thus, at R_0=8 kpc, the peculiar
velocity components for the Sun are (Uo,Vo,Wo)=(7.5,17.6,8.4)+\-(1.2,1.2,1.2)
km s^-1 and the angular velocity components are
  \omega_0=-28.7+\-0.5 km s^-1 kpc^-1,
  \omega'_0=+4.17+\-0.10 km s^-1 kpc^-2, and
  \omega''_0=-0.87+\-0.06 km s^-1 kpc^-3. The corresponding Oort constants are
A=16.7+\-0.6 km s^-1 kpc^-1 and B=-12.0+\-1.0 km s^-1 kpc^-1; the circular
rotation velocity of the solar neighborhood around the Galactic center is V_0 =
230+\-16 km s^-1. We have found that the corrections for the Lutz-Kelker bias
affect the determination of the angular velocity \omega_0 most strongly; their
effect on the remaining parameters is statistically insignificant. Within the
model of a two-armed spiral pattern, we have determined the pattern pitch angle
i=-6.5^\circ and the phase of the Sun in the spiral wave \chi_0=150^\circ.


title:
Convergence of the eigenvalue density for beta-Laguerre ensembles on
  short scales

abstract:
  In this note, we prove that the normalized trace of the resolvent of the
beta-Laguerre ensemble eigenvalues is close to the Stieltjes transform of the
Marchenko-Pastur (MP) distribution with very high probability, for values of
the imaginary part greater than m^{-1+\epsilon}. As an immediate corollary, we
obtain convergence of the one-point density to the MP law on short scales. The
proof serves to illustrate some simplifications of the method introduced in our
previous work to prove a local semi-circle law for Gaussian beta-ensembles.


title:
A Buffer-aided Successive Opportunistic Relay Selection Scheme with
  Power Adaptation and Inter-Relay Interference Cancellation for Cooperative
  Diversity Systems

abstract:
  In this paper we consider a simple cooperative network consisting of a
source, a destination and a cluster of decode-and-forward half-duplex relays.
At each time-slot, the source and (possibly) one of the relays transmit a
packet to another relay and the destination, respectively, resulting in
inter-relay interference (IRI). In this work, with the aid of buffers at the
relays, we mitigate the detrimental effect of IRI through interference
cancellation. More specifically, we propose the min-power scheme that minimizes
the total energy expenditure per time slot under an IRI cancellation scheme.
Apart from minimizing the energy expenditure, the min-power selection scheme,
also provides better throughput and lower outage probability than existing
works in the literature. It is the first time that interference cancellation is
combined with buffer-aided relays and power adaptation to mitigate the IRI and
minimize the energy expenditure. The new relay selection policy is analyzed in
terms of outage probability and diversity, by modeling the evolution of the
relay buffers as a Markov Chain (MC). We construct the state transition matrix
of the MC, and hence obtain the steady state with which we can characterize the
outage probability. The proposed scheme outperforms relevant state-of-the-art
relay selection schemes in terms of throughput, diversity and energy
efficiency, as demonstrated via examples.


title:
Statistical Analysis of Current Sheets in Three-Dimensional
  Magnetohydrodynamic Turbulence

abstract:
  We develop a framework for studying the statistical properties of current
sheets in numerical simulations of 3D magnetohydrodynamic (MHD) turbulence. We
describe an algorithm that identifies current sheets in a simulation snapshot
and then determines their geometrical properties (including length, width, and
thickness) and intensities (peak current density and total energy dissipation
rate). We then apply this procedure to simulations of reduced MHD turbulence
and perform a statistical analysis on the obtained population of current
sheets. We evaluate the role of reconnection by separately studying the
populations of current sheets which contain magnetic X-points and those which
do not. We find that the statistical properties of the two populations are
different in general. We compare the scaling of these properties to
phenomenological predictions obtained for the inertial range of MHD turbulence.
Finally, we test whether the reconnecting current sheets are consistent with
the Sweet-Parker model.


title: Stopping Criteria for Iterative Decoding based on Mutual Information

abstract:
  In this paper we investigate stopping criteria for iterative decoding from a
mutual information perspective. We introduce new iteration stopping rules based
on an approximation of the mutual information between encoded bits and decoder
soft output. The first type stopping rule sets a threshold value directly on
the approximated mutual information for terminating decoding. The threshold can
be adjusted according to the expected bit error rate. The second one adopts a
strategy similar to that of the well known cross-entropy stopping rule by
applying a fixed threshold on the ratio of a simple metric obtained after each
iteration over that of the first iteration. Compared with several well known
stopping rules, the new methods achieve higher efficiency.


title: SRB measures for hyperbolic polygonal billiards

abstract:
  We prove that polygonal billiards with contracting reflection laws exhibit
hyperbolic attractors with countably many ergodic SRB measures. These measures
are robust under small perturbations of the reflection law, and the tables for
which they exist form a generic set in the space of all polygons. Specific
polygonal tables are studied in detail.


title:
Total internal and external lengths of the Bolthausen-Sznitman
  coalescent

abstract:
  In this paper, we study a weak law of large numbers for the total internal
length of the Bolthausen-Szmitman coalescent. As a consequence, we obtain the
weak limit law of the centered and rescaled total external length. The latter
extends results obtained by Dhersin & M\"ohle \cite{DM12}. An application to
population genetics dealing with the total number of mutations in the
genealogical tree is also given.


title:
Nonisolated forms of rational triple point singularities of surfaces and
  their resolutions

abstract:
  The work is a detailed study of rational singularities of multiplicity 3
(RTP-singularities, for short). We give a list of nonisolated hypersurface
singularities of which normalisations are the RTP-singularities, and construct
their minimal resolution graphs by means of a subdivision of Newton polygons of
those -- a method introduced by M. Oka for isolated complete intersection
singularities. We show that nonisolated forms of RTP-singularities and their
normalisations are both Newton non-degenerate.


title: Coherence for invertible objects and multi-graded homotopy rings

abstract:
  We prove a coherence theorem for invertible objects in a symmetric monoidal
category. This is used to deduce associativity, skew-commutativity, and related
results for multi-graded morphism rings, generalizing the well-known versions
for stable homotopy groups.


title: Stellar Magnetic Fields as a Heating Source for Extrasolar Giant Planets

abstract:
  It has been observed that hot Jupiters located within 0.08 AU of their host
stars commonly display radii in excess of those expected based on models. A
number of theoretical explanations for this phenomenon have been suggested, but
the ability of any one mechanism to account for the full range of observations
remains to be rigorously proven. I identify an additional heating mechanism,
arising from the interaction of the interplanetary magnetic field and the
planetary magnetosphere, and show that this is capable of providing enough
energy to explain the observed planetary radii. Such a model predicts that the
degree of heating should be dependent on the stellar magnetic field, for which
stellar activity serves as a proxy. Accordingly, I examine populations of hot
Jupiters from the Kepler database and confirm that stellar activity (determined
using Kepler CDPP levels) is correlated with the presence of planetary radii
inflated beyond the basal level of R = 0.87 R_J identified by previous
researchers. I propose that the primary mechanism for transferring energy from
the magnetosphere to the planetary interior is Joule heating arising from
global electric circuits analogous to those seen in solar system objects.


title: Positivity and periodicity of $Q$-systems in the WZW fusion ring

abstract:
  We study properties of solutions of $Q$-systems in the WZW fusion ring
obtained by the Kirillov-Reshetikhin modules. We make a conjecture about their
positivity and periodicity and give a proof of it in some cases. We also
construct a positive solution of the level $k$ restricted $Q$-system of
classical types in the fusion rings. As an application, we prove some
conjectures of Kirillov and Kuniba-Nakanishi-Suzuki on the level $k$ restricted
$Q$-systems.


title:
Gap Symmetry and Stability Analysis in the Multi-Orbital Fe-Based
  Superconductors

abstract:
  The iron-based superconductors allow for a zoo of possible order parameters
due to their orbital degrees of freedom. These order parameters are often
written in an orbital basis, as this allows to distinguish their different
symmetry. Unlike in standard single-band superconductors, where electrons of
the same band - and hence, energy - are paired, a general order parameter in
such a multi-orbital system also contains pairing of electrons belonging to
different bands. As this corresponds to pairing of electrons of different
energy, such order parameters are energetically less stable. Here, we present a
simple criterion for a stability analysis of the orbital part of the gap
function based on the basic principle that electrons of equal energy are paired
in the superconducting state. This not only allows to find the most stable
states, but also to identify the terms in a (tight-binding) Hamiltonian
suppressing any given superconducting state. Our approach thus allows to
identify the minimal Hamiltonian necessary to compare competing instabilities.


title: Higher dimensional black holes as constrained systems

abstract:
  We construct a Lagrangian and Hamiltonian formulation for charged black holes
in a d-dimensional maximally symmetric spherical space. By considering first
new variables that give raise to an interesting dimensional reduction of the
problem, we show that the introduction of a charge term is compatible with
classical solutions to Einstein equations. In fact, we derive the well-known
solutions for charged black holes, specially in the case of d=4, where the
Reissner-Nordstr\"om solution holds, without reference to Einstein field
equations. We argue that our procedure may be of help for clarifying symmetries
and dynamics of black holes, as well as some quantum aspects.


title: Quantum criticality at the Chern-to-normal insulator transition

abstract:
  Using the non-commutative Kubo formula for aperiodic solids [1-3] and a
recently developed numerical implementation [4], we study the conductivity
$\sigma$ and resistivity $\rho$ tensors as functions of Fermi level and
temperature, for models of strongly disordered Chern insulators. The formalism
enabled us to converge the transport coefficients at temperatures low enough to
enter the quantum critical regime at the Chern-to-trivial insulator transition.
We find that the $\rho_{xx}$-curves at different temperatures intersect each
other at one single critical point, and that they obey a single-parameter
scaling law with an exponent close to the universally accepted value for the
unitary symmetry class. However, when compared with the established
experimental facts on the plateau-insulator transition in the Integer Quantum
Hall Effect, we find a universal critical conductance $\sigma_{xx}^c$ twice as
large, an ellipse rather than a semi-circle law, and absence of the quantized
Hall insulator phase.


title: Implication of possible observation of enhanced Bd0 --> mu+ mu- decay

abstract:
  The very rare Bd0 --> mu+ mu- decay may be the last chance for New Physics in
flavor sector at the LHC, before the 13 TeV run in 2015. Partially motivated by
the known tension in sin(2beta/phi_1), enhancement beyond (3-4) x 10^-10 would
likely imply the effect of a fourth generation of quarks. If observed at this
level, the 126 GeV boson may not be the actual Higgs boson, while the b --> d
quadrangle (modulo m_t') would jump out. The 2011-2012 data is likely not
sensitive to values below 3 x 10^-10, and the mode should continue to be
pursued with the 13 TeV run.


title: Meander knots and links

abstract:
  We introduced concept of meander knots, 2-component meander links and
multi-component meander links and derived different families of meander knots
and links from open meanders with at most 16 crossings. We also defined
semi-meander knots (or knots with ordered Gauss code) and their product.


title:
Constraint equations for 3 + 1 vacuum Einstein equations with a
  translational space-like Killing field in the asymptotically flat case

abstract:
  We solve the constraint equations for a vacuum space-time with a
translational space-like Killing field satisfying the vacuum Einstein
equations. Vacuum Einstein equations with a translational space-like Killing
field have been studied by Choquet-Bruhat and Moncrief in the compact case, and
by Ashtekar, Bicak and Schmidt in the case where an additional spherical
symmetry is added. In this paper we consider the asymptotically flat case. This
corresponds to solving a nonlinear elliptic system on R2. The main difficulty
in that case is due to the delicate inversion of the Laplacian on R2.


title:
The First Ground Level Enhancement Event of Solar Cycle 24: Direct
  Observation of Shock Formation and Particle Release Heights

abstract:
  We report on the 2012 May 17 Ground Level Enhancement (GLE) event, which is
the first of its kind in Solar Cycle 24. This is the first GLE event to be
fully observed close to the surface by the Solar Terrestrial Relations
Observatory (STEREO) mission. We determine the coronal mass ejection (CME)
height at the start of the associated metric type II radio burst (i.e., shock
formation height) as 1.38 Rs (from the Sun center). The CME height at the time
of GLE particle release was directly measured from a STEREO image as 2.32 Rs,
which agrees well with the estimation from CME kinematics. These heights are
consistent with those obtained for cycle-23 GLEs using back-extrapolation. By
contrasting the 2012 May 17 GLE with six other non-GLE eruptions from
well-connected regions with similar or larger flare size and CME speed, we find
that the latitudinal distance from the ecliptic is rather large for the non-GLE
events due to a combination of non-radial CME motion and unfavorable solar B0
angle, making the connectivity to Earth poorer. We also find that the coronal
environment may play a role in deciding the shock strength.


title: Accelerated Backpressure Algorithm

abstract:
  We develop an Accelerated Back Pressure (ABP) algorithm using Accelerated
Dual Descent (ADD), a distributed approximate Newton-like algorithm that only
uses local information. Our construction is based on writing the backpressure
algorithm as the solution to a network feasibility problem solved via
stochastic dual subgradient descent. We apply stochastic ADD in place of the
stochastic gradient descent algorithm. We prove that the ABP algorithm
guarantees stable queues. Our numerical experiments demonstrate a significant
improvement in convergence rate, especially when the packet arrival statistics
vary over time.


title: Core hole-electron correlation in coherently coupled molecules

abstract:
  We study the core hole-electron correlation in coherently coupled molecules
by energy dispersive near edge X-ray absorption fine-structure spectroscopy. In
a transient phase, which exists during the transition between two bulk
arrangements, 1,4,5,8-naphthalene-tetracarboxylicacid-dianhydride multilayer
films exhibit peculiar changes of the line shape and energy position of the
X-ray absorption signal at the C K-edge with respect to the bulk and gas phase
spectra. By a comparison to a theoretical model based on a coupling of
transition dipoles, which is established for optical absorption, we demonstrate
that the observed spectroscopic differences can be explained by an
intermolecular delocalized core hole-electron pair. By applying this model we
can furthermore quantify the coherence length of the delocalized core-exciton.


title: Arithmetic of abelian varieties with constrained torsion

abstract:
  Let $K$ be a number field. We present several new finiteness results for
isomorphism classes of abelian varieties over $K$ whose $\ell$-power torsion
fields are arithmetically constrained for some rational prime $\ell$. Such
arithmetic constraints are related to an unresolved question of Ihara regarding
the kernel of the canonical outer Galois representation on the pro-$\ell$
fundamental group of $P^1 - \{0,1,\infty\}$.
  Under GRH, we demonstrate the set of classes is finite for any fixed $K$ and
any fixed dimension. Without GRH, we prove a semistable version of the result.
In addition, several unconditional results are obtained when the degree of
$K/\Q$ and the dimension of abelian varieties are not too large, through a
careful analysis of the special fiber of such abelian varieties. In some cases,
the results (viewed as a bound on the possible values of $\ell$) are uniform in
the degree of the extension $K/\Q$.


title: Levy flights and nonlocal quantum dynamics

abstract:
  We develop a fully fledged theory of quantum dynamical patterns of behavior
that are nonlocally induced. To this end we generalize the standard
Laplacian-based framework of the Schr\"{o}dinger picture quantum evolution to
that employing nonlocal (pseudodifferential) operators. Special attention is
paid to the Salpeter (here, $m\geq 0$) quasirelativistic equation and the
evolution of various wave packets, in particular to their radial expansion in
3D. Foldy's synthesis of "covariant particle equations" is extended to
encompass free Maxwell theory, which however is devoid of any "particle"
content. Links with the photon wave mechanics are explored.

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


title:
Crazy Sequential Representation: Numbers from 0 to 11111 in terms of
  Increasing and Decreasing Orders of 1 to 9

abstract:
  Natural numbers from 0 to 11111 are written in terms of 1 to 9 in two
different ways. The first one in increasing order of 1 to 9, and the second one
in decreasing order. This is done by using the operations of addition,
multiplication, subtraction, potentiation, and division. In both the situations
there are no missing numbers, except one, i.e., 10958 in the increasing case.


title: Natural generalized invertibility and prescribed idempotents

abstract:
  We study the natural inverse introduced by X. Mary and show some connections
with the $(p,q)$-inverses of Djordjevic and Wei, where $p$ and $q$ are
prescribed idempotents. We deal first with rings with identity and then
specialize to the particular case of the algebra of bounded linear operators.
We give a characterization of the set of operators along which an operator is
natural invertible in terms of prescribed range and nullspace. Finally, the
special case when the prescribed idempotent is the spectral projection is
discussed.


title: Chiral f-wave Topological Superuid in Triangular Optical Lattices

abstract:
  We demonstrate that an exotically chiral f-wave topological superfluid can be
induced in coldfermionic-atom triangular optical lattices through the
laser-field-generated effective non-Abelian gauge field, controllable Zeeman
fields and s-wave Feshbach resonance. We find that the chiral f-wave
topological superfluid is characterized by three gapless Majorana edge states
located on the boundary of the system. More interestingly, these Majorana edge
states degenerate into one Majorana fermion bound to each vortex in the
superfluid. Our proposal enlarges topological superfluid family and specifies a
unique experimentally controllable system to study the Majorana fermion
physics.


title: Neutrino On The Possible New Time Structure

abstract:
  We continue to study the problems of discovering new temporal and spatial
properties of neutrinos from the point of the possible multi-dimensional
extension the D=(3+1)- special theory of relativity. It is neutrino that can
connect our Universe with new types of the matter, the new Universe. The
possible discovery with neutrino new structure of the Time can confirm these
ideas. However, the neutrino experiments aimed at new phenomena search can lead
us to paradoxes related with the limits of applicability of the theory of
relativity which demands special studies.
  This new phenomenon one can call by "Neutrino Paradoxes in Theories of
Relativity".
  As examples of such paradoxes one can illustrate on the neutrino experiments
MINOS,OPERA et al devoted to the measurements of neutrino velocity. As the
interpretation of their results are model-dependent, by our opinion, the main
goal of the observation a possible new time structure in these experiments is
not reached. As the solutions to this problem it seems to us the way of holding
cycle of long base neutrino experiments at high(super-high) energies which
requires further debate in the literature. In addition to our discussions one
can remark that the questions of neutrino physics ($M_S \rightarrow O(1-20\,
TeV- range)$) could be directly related to the collider physics at the LHC.


title: A broad-band laser-driven double Fano system - photoelectron spectra

abstract:
  Fano profiles, with their asymmetric character, have many potential
applications in technology. The design of Fano profiles into optical systems
may create new nonlinear and switchable metamaterials, high-quality optical
waveguides, ultrasensitive media for chemical or biosensing etc. In this paper,
we consider an external field-driven double Fano model, in which, instead of
one autoionizing state, there are two discrete states embedded in one
continuum. We assume further that the external electromagnetic field can be
decomposed into two parts: a deterministic (or coherent) part and a randomly
fluctuating chaotic component, which is a \delta-correlated, Gaussian, Markov
and stationary process (white noise). This assumption corresponds to the case
of the real multimode laser operating without any correlation between the
modes. We solve a set of coupled stochastic integro-differential equations
involving the Fano model with two discrete levels. We derive an exact formula
by determining the photoelectron spectrum and compare it with the results
obtained in our previous papers.


title:
Analytical and Numerical Characterizations of Shannon Ordering for
  Discrete Memoryless Channels

abstract:
  This paper studies several problems concerning channel inclusion, which is a
partial ordering between discrete memoryless channels (DMCs) proposed by
Shannon. Specifically, majorization-based conditions are derived for channel
inclusion between certain DMCs. Furthermore, under general conditions, channel
equivalence defined through Shannon ordering is shown to be the same as
permutation of input and output symbols. The determination of channel inclusion
is considered as a convex optimization problem, and the sparsity of the weights
related to the representation of the worse DMC in terms of the better one is
revealed when channel inclusion holds between two DMCs. For the exploitation of
this sparsity, an effective iterative algorithm is established based on
modifying the orthogonal matching pursuit algorithm.


title: The universality of the Carnot theorem

abstract:
  It is common in many thermodynamic textbooks to illustrate the Carnot theorem
through the usage of diverse state equations for gases, paramagnets, and other
simple thermodynamic systems. As it is well-known, the universality of the
Carnot efficiency is easily demonstrated in a temperature-entropy diagram,
which means that the Carnot efficiecy is independent of the working substance.
In this present work we remark that the universality of the Carnot theorem goes
beyond the conventional state equations, and it is fulfilled by gas state
equations that do not behave as ideal gas in the dilution limit when the volume
is infinite. Some of these unconventional state equations have certain
thermodynamic "anomalies" that nonetheless do not forbid them from obeying the
Carnot theorem. We discuss how this very general behaviour arises from the
Maxwell relations, which are connected with a geometrical property expressed
through preserving area transformations. A rule is proposed to calculate the
Maxwell relations associated with a thermodynamic system by using the
preserving area relationships. In this way it is possible to calculate the
number of possible preserving area mappings by giving the number of possible
Jacobian identities between all pairs of thermodynamic variables included in
the corresponding Gibbs equation. This work is intended for undergraduate and
specialists in thermodynamics and related areas.


title: Axionic Co-genesis of Baryon, Dark Matter and Dark Radiation

abstract:
  We argue that coherent oscillations of the axion field excited by the
misalignment mechanism and non-thermal leptogenesis by the saxion decay can
naturally explain the observed abundance of dark matter and baryon asymmetry,
thus providing a solution to the baryon-dark matter coincidence problem. The
successful axionic co-genesis requires a supersymmetry breaking scale of
O(10^{6-7}) GeV, which is consistent with the recently discovered
standard-model like Higgs boson of mass about 126 GeV. Although the saxion
generically decays into a pair of axions, their abundance sensitively depends
on the saxion stabilization mechanism as well as couplings with the Higgs
field. We discuss various ways to make the saxion dominantly decay into the
right-handed neutrinos rather than into axions, and show that the abundance of
axion dark radiation can be naturally as small as \Delta N_{\rm eff} \lesssim
{\cal O}(0.1), which is allowed by the Planck data.


title: "Super"-Dilatation Symmetry of the Top-Higgs System

abstract:
  The top-Higgs system, consisting of top quark (LH doublet, RH singlet) and
Higgs boson kinetic terms, with gauge fields set to zero, has an exact (modulo
total divergences) symmetry where both fermion and Higgs fields are shifted and
mixed in a supersymmetric fashion. The full Higgs-Yukawa interaction and
Higgs-potential, including additional \sim 1/\Lambda^2 NJL-like interactions,
also has this symmetry to O(1/\Lambda^4), up to null-operators. Thus the
interaction lagrangian can be viewed as a power series in 1/\Lambda^2. The
symmetry involves interplay of the Higgs quartic interaction with the
Higgs-Yukawa interaction and implies the relationship, \lambda = \half g^2
between the top--Yukawa coupling, g, and Higgs quartic coupling, \lambda, at a
high energy scale \Lambda >= few TeV. We interpret this to be a new physics
scale. The top quark is massless in the symmetric phase, satisfying the
Nambu-Goldstone theorem. The fermionic shift part of the current is \propto
(1-H^\dagger H/v^2), owing to the interplay of \lambda and g, and vanishes in
the broken phase. Hence the Nambu-Goldstone theorem is trivially evaded in the
broken phase and the top quark becomes heavy (it is not a Goldstino). We have
m_t=m_h, subject to radiative corrections that can in principle pull the Higgs
into concordance with experiment.


title: On Maximum Conservative Extensions

abstract:
  We investigate the set of Pi-1-2 sentences which are Pi-1-1 conservative over
the theories of reverse mathematics RCA0+ISigma_n and ACA0. We exhibit new
elements of these sets and conclude that the sets are Pi_2 complete. Along the
way, we show that, over the theory RCA, induction for Sigma-n formulas has
essentially no consequences for Delta-(n+1) formulas.


title: Multi-rate Sub-Nyquist Spectrum Sensing in Cognitive Radios

abstract:
  Wideband spectrum sensing is becoming increasingly important to cognitive
radio (CR) systems for exploiting spectral opportunities. This paper introduces
a novel multi-rate sub-Nyquist spectrum sensing (MS3) system that implements
cooperative wideband spectrum sensing in a CR network. MS3 can detect the
wideband spectrum using partial measurements without reconstructing the full
frequency spectrum. Sub-Nyquist sampling rates are adopted in sampling channels
for wrapping the frequency spectrum onto itself. This significantly reduces
sensing requirements of CR. The effects of sub-Nyquist sampling are considered,
and the performance of multi-channel sub-Nyquist samplings is analyzed. To
improve its detection performance, sub-Nyquist sampling rates are chosen to be
different such that the numbers of samples are consecutive prime numbers.
Furthermore, when the received signals at CRs are faded or shadowed, the
performance of MS3 is analytically evaluated. Numerical results show that the
proposed system can significantly enhance the wideband spectrum sensing
performance while requiring low computational and implementation complexities.


title:
Infinity of Geodesics in an Homogeneous and Isotropic Expanding
  Space-Time

abstract:
  In this paper we construct a discrete simulation of an expanding homogeneous
and isotropic space-time that expands via expansion of its basic elements to
figure out properties and characteristics of such a space-time and derive
conclusions. We prove that in such an expanding space-time, the geodesics are
curved and more precisely, they fluctuate on the boundaries of the expanding
basic elements. The non existence of privileged expansion direction leads to
the existence of an infinity of fluctuating geodesics between any two locations
in this space-time, that provides a prediction of polarization in geometric
optics, and a prediction of an earlier acceleration of the expansion as for the
cosmic inflation model. This simulation is a case study and an example of
space-time with variable topology using the principle of variation of topology
via a transformation that creates holes.


title: Schwarzschild-like metric and a quantum vacuum

abstract:
  A quantum vacuum, represented by a viscous fluid, is added to the Einstein
vacuum, surrounding a spherical distribution of mass. This gives as a solution,
in spherical coordinates, a Schwarzschild-like metric. The plot of g00 and g11
components of the metric, as a function of the radial coordinate, display the
same qualitative behavior as that of the Schwarzschild metric. However, the
temperature of the event horizon is equal to the Hawking temperature multiplied
by a factor of two, while the entropy is equal to half of the Bekenstein one.


title: Why could ice ages be unpredictable?

abstract:
  It is commonly accepted that the variations of Earth's orbit and obliquity
control the timing of Pleistocene glacial-interglacial cycles. Evidence comes
from power spectrum analysis of palaeoclimate records and from inspection of
the timing of glacial and deglacial transitions. However, we do not know how
tight this control is. Is it, for example, conceivable that random climatic
fluctuations could cause a delay in deglaciation, bad enough to skip a full
precession or obliquity cycle and subsequently modify the sequence of ice ages?
  To address this question, seven previously published conceptual models of ice
ages are analysed by reference to the notion of generalised synchronisation.
Insight is being gained by comparing the effects of the astronomical forcing
with idealised forcings composed of only one or two periodic components. In
general, the richness of the astronomical forcing allows for synchronisation
over a wider range of parameters, compared to periodic forcing. Hence, glacial
cycles may conceivably have remained paced by the astronomical forcing
throughout the Pleistocene.
  However, all the models examined here also show a range of parameters for
which the structural stability of the ice age dynamics is weak. This means that
small variations in parameters or random fluctuations may cause significant
shifts in the succession of ice ages if the system were effectively in that
parameter range. Whether or not the system has strong structural stability
depends on the amplitude of the effects associated with the astronomical
forcing, which significantly differ across the different models studied here.
The possibility of synchronisation on eccentricity is also discussed and it is
shown that a high Rayleigh number on eccentricity, as recently found in
observations, is no guarantee of reliable synchronisation.


title: ContentFlow: Mapping Content to Flows in Software Defined Networks

abstract:
  Information-Centric Networks place content as the narrow waist of the network
architecture. This allows to route based upon the content name, and not based
upon the locations of the content consumer and producer. However, current
Internet architecture does not support content routing at the network layer. We
present ContentFlow, an Information-Centric network architecture which supports
content routing by mapping the content name to an IP flow, and thus enables the
use of OpenFlow switches to achieve content routing over a legacy IP
architecture. ContentFlow is viewed as an evolutionary step between the current
IP networking architecture, and a full fledged ICN architecture. It supports
content management, content caching and content routing at the network layer,
while using a legacy OpenFlow infrastructure and a modified controller. In
particular, ContentFlow is transparent from the point of view of the client and
the server, and can be inserted in between with no modification at either end.
We have implemented ContentFlow and describe our implementation choices as well
as the overall architecture specification. We evaluate the performance of
ContentFlow in our testbed.


title: Bourgin-Yang versions of the Borsuk-Ulam theorem for $p$-toral groups

abstract:
  Let $V$ and $W$ be orthogonal representations of $G$ with $V^G= W^G=\{0\}$.
Let $S(V )$ be the sphere of $V$ and $f : S(V ) \to W$ be a $G$-equivariant
mapping. We give an estimate for the dimension of the set $Z_f=f^{-1}\{0\}$ in
terms of $ \dim V$ and $\dim W$, if $G$ is the torus $\mathbb T^k$, or the
$p$-torus $\mathbb Z_p^k$. This extends the classical Bourgin-Yang theorem onto
this class of groups. Finally, we show that for any $p$-toral group $G$ and a
$G$-map $f:S(V) \to W$, with $\dim V=\infty$ and $\dim W<\infty$, we have $\dim
Z_f= \infty$.


title: Generating target probability sequences and events

abstract:
  Cryptography and simulation of systems require that events of pre-defined
probability be generated. This paper presents methods to generate target
probability events based on the oblivious transfer protocol and target
probabilistic sequences using probability distribution functions.


title: Standard Model Higgs field and energy scale of gravity

abstract:
  The effective potential of the Higgs scalar field in the Standard Model may
have a second degenerate minimum at an ultrahigh vacuum expectation value. This
second minimum then determines, by radiative corrections, the values of the
top-quark and Higgs-boson masses at the standard minimum corresponding to the
electroweak energy scale. An argument is presented that this ultrahigh vacuum
expectation value is proportional to the energy scale of gravity, E_{Planck}
\equiv \sqrt{\hbar c^5/G_N}, considered to be characteristic of a spacetime
foam. In the context of a simple model, the existence of kink-type wormhole
solutions places a lower bound on the ultrahigh vacuum expectation value and
this lower bound is of the order of E_{Planck}.


title: Kinematics of Star Clusters in M101

abstract:
  We have identified a few thousand star clusters in the nearby, late-type
spiral galaxy M101, including approximately 90 candidate ancient globular
clusters (GCs), from multi-band Hubble Space Telescope (HST) images. We
obtained follow-up low-resolution (R approximately 2000) optical spectroscopy
from Gemini-GMOS for 43 total clusters, of which 18 are old GCs and 25 are
young massive clusters (YMCs). We measure radial velocities for these clusters
and find that, as expected, the YMCs rotate with the HI disk. The old GCs do
not show any obvious evidence for rotation and have a much higher velocity
dispersion than the YMCs, suggesting that the GCs in M101 are likely part of a
stellar halo or thick disk.


title:
"The Waters I am Entering No One yet Has Crossed": Alexander Friedman
  and the Origins of Modern Cosmology

abstract:
  Ninety years ago, in 1922, Alexander Friedman (1888-1925) demonstrated for
the first time that the General Relativity equations admit non-static solutions
and thus the Universe may expand, contract, collapse, and even be born. The
fundamental equations he derived still provide the basis for the current
cosmological theories of the Big Bang and the Accelerating Universe. Later, in
1924, he was the first to realize that General Relativity allows the Universe
to be infinite. Friedman's ideas initially met strong resistance from Einstein,
yet from 1931 he became their staunchest supporter. This essay connects
Friedman's cosmological ideas with the 1998-2004 results of the astronomical
observations that led to the 2011 Nobel Prize in Physics. It also describes
Friedman's little known topological ideas of how to check General Relativity in
practice and compares his contributions to those of Georges Lemaitre. Recently
discovered corpus of Friedman's writings in the Ehrenfest Archives at Leiden
University sheds some new light on the circumstances surrounding his 1922 work
and his relations with Paul Ehrenfest.


title: Ferromagnetic Kondo effect in a triple quantum dot system

abstract:
  We propose that a simple device of three laterally-coupled quantum dots, the
central one contacted by metal leads, can realize the ferromagnetic Kondo
model, which is characterized by interesting properties like a non-analytic
inverted zero-bias anomaly and an extreme sensitivity to a magnetic field.
Furthermore, by tuning the gate voltages of the lateral dots, this device may
allow to study the transition from ferromagnetic to antiferromagnetic Kondo
effect, a simple case of a Berezinskii-Kosterlitz-Thouless transition. We model
the device by three coupled Anderson impurities that we study by numerical
renormalization group. We calculate the single-particle spectral function of
the central dot, which at zero frequency is proportional to the zero-bias
conductance, across the transition, both in the absence and in the presence of
a magnetic field.


title: Exact test for Markov order

abstract:
  We describe an exact test of the null hypothesis that a Markov chain is nth
order versus the alternate hypothesis that it is $(n+1)$-th order. The
procedure does not rely on asymptotic properties, but instead builds up the
test statistic distribution via surrogate data and is valid for any sample
size. Surrogate data are generated using a novel algorithm that guarantees, per
shot, a uniform sampling from the set of sequences that exactly match the nth
order properties of the observed data.


title:
Terrestrial effects of possible astrophysical sources of an AD 774-775
  increase in 14C production

abstract:
  We examine possible sources of a substantial increase in tree ring 14C
measurements for the years AD 774-775. Contrary to claims regarding a coronal
mass ejection (CME), the required CME energy is not several orders of magnitude
greater than known solar events. We consider solar proton events (SPEs) with
three different fluences and two different spectra. The data may be explained
by an event with fluence about one order of magnitude beyond the October 1989
SPE. Two hard spectrum cases considered here result in moderate ozone
depletion, so no mass extinction is implied, though we do predict increases in
erythema and damage to plants from enhanced solar UV. We are able to rule out
an event with a very soft spectrum that causes severe ozone depletion and
subsequent biological impacts. Nitrate enhancements are consistent with their
apparent absence in ice core data. The modern technological implications of
such an event may be extreme, and considering recent confirmation of
superflares on solar-type stars, this issue merits attention.

categories: astro-ph.SR physics.ao-ph physics.geo-ph physics.space-ph q-bio.PE


title: The meson spectrum in large-N QCD

abstract:
  We present lattice results on the meson spectrum and decay constants in
large-N QCD. The results are obtained in the quenched approximation for N = 2,
3, 4, 5, 6, 7 and 17 and extrapolated to infinite N.


title: Dynamical symmetries of generalized Taub-NUT and multi-center metrics

abstract:
  Hidden symmetries of generalized Kaluza-Klein-type metrics are studied using
van Holten's systematic analysis \cite{vH} based on Killing tensors. Applied to
generalized Taub-NUT metrics, Kepler-type symmetries with associated
Runge-Lenz-type conserved quantities are constructed. In the multicenter case,
the subclass of two-center metrics gives rise to a conserved Runge-Lenz-type
scalar, while no Kepler-type constant of the motion does exist for non aligned
$(N\geq3)$-centers. We also investigated the diatomic molecule system of
Wilczek et al. where "truly" non-Abelian gauge fields mimicking monopole-like
fields arised. From the latter system we deduced a new conserved charge.


title: Bounding resonant Majorana neutrinos from four-body B and D decays

abstract:
  Searches of lepton-number violation in different processes are very useful to
constrain the parameter space of Majorana neutrinos. Here we use available
upper bounds on the branching fractions of B^- -> D^0pi^+mu^-mu^- and D^0 ->
(pi^-pi^-/K^-pi^-) mu^-mu^- decays to derive constraints on the mass and
mixings of Majorana neutrinos by assuming they are produced resonantly in these
four-body decays. While the excluded region obtained from B^- decays are
competitive with existing limits from three-body D^- and B^- decays, it is
shown that experimental improvements on D^0 decays offer a good potential to
provide similar results.


title:
Multivariate Difference-Differential Dimension Polynomials and New
  Invariants of Difference-Differential Field Extensions

abstract:
  In this paper we introduce a method of characteristic sets with respect to
several term orderings for difference-differential polynomials. Using this
technique, we obtain a method of computation of multivariate dimension
polynomials of finitely generated difference-differential field extensions.
Furthermore, we find new invariants of such extensions and show how the
computation of multivariate difference-differential polynomials is applied to
the equivalence problem for systems of algebraic difference-differential
equations.


title: Rate-Privacy in Wireless Sensor Networks

abstract:
  This paper introduces the concept of rate privacy in the context of wireless
sensor networks. Our discussion reveals that the concept indeed is of a great
importance for the privacy preservation of such networks. As a result, we
propose a buffering scheme to protect the rate from adversaries. Simulation
results verify the applicability of our approach.


title: Nonperturbative universal Chern-Simons theory

abstract:
  Closed simple integral representation through Vogel's universal parameters is
found both for perturbative and nonperturbative (which is inverse invariant
group volume) parts of free energy of Chern-Simons theory on $S^3$. This proves
the universality of that partition function. For classical groups it manifestly
satisfy N \rightarrow -N duality, in apparent contradiction with previously
used ones. For SU(N) we show that asymptotic of nonperturbative part of our
partition function coincides with that of Barnes G-function, recover
Chern-Simons/topological string duality in genus expansion and resolve
abovementioned contradiction. We discuss few possible directions of development
of these results: derivation of representation of free energy through
Gopakumar-Vafa invariants, possible appearance of non-perturbative additional
terms, 1/N expansion for exceptional groups, duality between string coupling
constant and K\"ahler parameters, etc.


title:
Improved AGN light curve analysis with the z-transformed discrete
  correlation function

abstract:
  The cross-correlation function (CCF) is commonly employed in the study of
AGN, where it is used to probe the structure of the broad line region by line
reverberation, to study the continuum emission mechanism by correlating
multi-waveband light curves and to seek correlations between the variability
and other AGN properties. The z -transformed discrete correlation function
(ZDCF) is a new method for estimating the CCF of sparse, unevenly sampled light
curves. Unlike the commonly used interpolation method, it does not assume that
the light curves are smooth and it does provide errors on its estimates. The
ZDCF corrects several biases of the discrete correlation function method of
Edelson & Krolik (1988) by using equal population binning and Fisher's z
-transform. These lead to a more robust and powerful method of estimating the
CCF of sparse light curves of as few as 12 points. Two examples of light curve
analysis with the ZDCF are presented. 1) The ZDCF estimate of the
auto-correlation function is used to uncover a correlation between AGN
magnitude and variability time scale in a small simulated sample of very sparse
and irregularly sampled light curves. 2) A maximum likelihood function for the
ZDCF peak location is used to estimate the time-lag between two light curves.
Fortran 77 and 95 code implementations of the ZDCF and the maximum likelihood
peak location (PLIKE) algorithms are freely available (see
http://www.weizmann.ac.il/weizsites/tal/research/software/).


title:
$0\nu\beta\beta$ and $2\nu\beta\beta$ nuclear matrix elements, QRPA, and
  isospin symmetry restoration

abstract:
  Within QRPA we achieve partial restoration of the isospin symmetry and hence
fulfillment of the requirement that the $2\nu\beta\beta$ Fermi matrix element
$M^{2\nu}_F$ vanishes, as it should, unlike in the previous version of the
method. This is accomplished by separating the renormalization parameter
$g_{pp}$ of the particle-particle proton-neutron interaction into the isovector
and isoscalar parts. The isovector parameter $g_{pp}^{T=1}$ need to be chosen
to be essentially equal to the pairing constant $g_{pair}$, so no new parameter
is needed. For the $0\nu\beta\beta$ decay the Fermi matrix element $M^{0\nu}_F$
is substantially reduced, while the full matrix element $M^{0\nu}$ is reduced
by $\approx$ 10%. We argue that this more consistent approach should be used
from now on in the proton-neutron QRPA and in analogous methods.


title: Multi-Dimensional Spatially-Coupled Codes

abstract:
  Spatially-coupled (SC) codes are constructed by coupling many regular
low-density parity-check codes in a chain. The decoding chain of SC codes stops
when facing burst erasures. This problem can not be overcome by increasing
coupling number. In this paper, we introduce multi-dimensional (MD) SC codes.
Numerical results show that 2D-SC codes are more robust to the burst erasures
than 1D-SC codes. Furthermore, we consider designing MD-SC codes with smaller
rateloss.


title: Spatially-Coupled Precoded Rateless Codes

abstract:
  Raptor codes are rateless codes that achieve the capacity on the binary
erasure channels. However the maximum degree of optimal output degree
distribution is unbounded. This leads to a computational complexity problem
both at encoders and decoders. Aref and Urbanke investigated the potential
advantage of universal achieving-capacity property of proposed
spatially-coupled (SC) low-density generator matrix (LDGM) codes. However the
decoding error probability of SC-LDGM codes is bounded away from 0. In this
paper, we investigate SC-LDGM codes concatenated with SC low-density
parity-check codes. The proposed codes can be regarded as SC Hsu-Anastasopoulos
rateless codes. We derive a lower bound of the asymptotic overhead from
stability analysis for successful decoding by density evolution. The numerical
calculation reveals that the lower bound is tight. We observe that with a
sufficiently large number of information bits, the asymptotic overhead and the
decoding error rate approach 0 with bounded maximum degree.


title: Efficient Termination of Spatially-Coupled Codes

abstract:
  Spatially-coupled low-density parity-check codes attract much attention due
to their capacity-achieving performance and a memory-efficient sliding-window
decoding algorithm. On the other hand, the encoder needs to solve large linear
equations to terminate the encoding process. In this paper, we propose modified
spatially-coupled codes. The modified $(\dl,\dr,L)$ codes have less rate-loss,
i.e., higher coding rate, and have the same threshold as $(\dl,\dr,L)$ codes
and are efficiently terminable by using an accumulator.


title: Exact final state integrals for strong field QED

abstract:
  This paper introduces the exact, analytic integration of all final state
variables for the process of nonlinear Compton scattering in an intense plane
wave laser pulse, improving upon a previously slow and challenging numerical
approach. Computationally simple and insightful formulae are derived for the
total scattering probability and mean energy-momentum of the emitted radiation.
The general form of the effective mass appears explicitely. We consider several
limiting cases, and present a quantum correction to Larmor's formula. Numerical
results are plotted and analysed in detail.


title:
Nanostructure determination from the pair distribution function: A
  parametric study of the INVERT approach

abstract:
  We present a detailed study of the mechanism by which the INVERT method
[Phys. Rev. Lett. 104, 125501] guides structure refinement of disordered
materials. We present a number of different possible implementations of the
central algorithm and explore the question of algorithm weighting. Our analysis
includes quantification of the relative contributions of variance and
fit-to-data terms during structure refinement, which leads us to study the
roles of density fluctuations and configurational jamming in the RMC fitting
process. We present a parametric study of the pair distribution function
solution space for C60, a-Si and a-SiO2, which serves to highlight the
difficulties faced in developing a transferable weighting scheme.


title: A Polynomial Time Algorithm for Lossy Population Recovery

abstract:
  We give a polynomial time algorithm for the lossy population recovery
problem. In this problem, the goal is to approximately learn an unknown
distribution on binary strings of length $n$ from lossy samples: for some
parameter $\mu$ each coordinate of the sample is preserved with probability
$\mu$ and otherwise is replaced by a `?'. The running time and number of
samples needed for our algorithm is polynomial in $n$ and $1/\varepsilon$ for
each fixed $\mu>0$. This improves on algorithm of Wigderson and Yehudayoff that
runs in quasi-polynomial time for any $\mu > 0$ and the polynomial time
algorithm of Dvir et al which was shown to work for $\mu \gtrapprox 0.30$ by
Batman et al. In fact, our algorithm also works in the more general framework
of Batman et al. in which there is no a priori bound on the size of the support
of the distribution. The algorithm we analyze is implicit in previous work; our
main contribution is to analyze the algorithm by showing (via linear
programming duality and connections to complex analysis) that a certain matrix
associated with the problem has a robust local inverse even though its
condition number is exponentially small. A corollary of our result is the first
polynomial time algorithm for learning DNFs in the restriction access model of
Dvir et al.


title: ABM11 PDFs and the cross section benchmarks in NNLO

abstract:
  We report an updated version of the ABKM09 NNLO PDF fit, which includes the
most recent HERA collider data on the inclusive cross sections and an improved
treatment of the heavy-quark contribution to deep-inelastic scattering using
advantages of the running-mass definition for the heavy quarks. The ABM11 PDFs
obtained from the updated fit are in a good agreement with the recent LHC data
on the W- and Z-production within the experimental and PDF uncertainties. We
also perform a determination of the strong coupling constant \alpha_s in a
variant of the ABM11 fit insensitive to the influence of the higher twist terms
and find the value of \alpha_s=0.1133(11) which is in good agreement with the
nominal ABM11 one and our earlier determination.


title: Constraining the initial entropy of directly-detected exoplanets

abstract:
  The post-formation, initial entropy S_i of a gas giant planet is a key
witness to its mass-assembly history and a crucial quantity for its early
evolution. However, formation models are not yet able to predict reliably S_i,
making unjustified the use solely of traditional, 'hot-start' cooling tracks to
interpret direct imaging results and calling for an observational determination
of initial entropies to guide formation scenarios. Using a grid of models in
mass and entropy, we show how to place joint constraints on the mass and
initial entropy of an object from its observed luminosity and age. This
generalises the usual estimate of only a lower bound on the real mass through
hot-start tracks. Moreover, we demonstrate that with mass information, e.g.
from dynamical stability analyses or radial velocity, tighter bounds can be set
on the initial entropy. We apply this procedure to 2M1207 b and find that its
initial entropy is at least 9.2 kB/baryon, assuming that it does not burn
deuterium. For the planets of the HR 8799 system, we infer that they must have
formed with S_i > 9.2 kB/baryon, independent of uncertainties about the age of
the star. Finally, a similar analysis for beta Pic b reveals that it must have
formed with S_i > 10.5 kB/baryon, using the radial-velocity mass upper limit.
These initial entropy values are respectively ca. 0.7, 0.5, and 1.5 kB/baryon
higher than the ones obtained from core accretion models by Marley et al.,
thereby quantitatively ruling out the coldest starts for these objects and
constraining warm starts, especially for beta Pic b.


title: Compact cold atom gravimeter for field applications

abstract:
  We present a cold atom gravimeter dedicated to field applications. Despite
the compactness of our gravimeter, we obtain performances (sensitivity 42
microGal/Hz^0.5, accuracy 25 microGal) close to the bestgravimeters. We report
gravity measurements in an elevator which led us to the determination of the
Earth's gravity gradient with a precision of 4 E. These measurements in a
non-laboratory environment demonstrate that our technology of gravimeter is
enough compact, reliable and robust for field applications. Finally, we report
gravity measurements in a moving elevator which open the way to absolute
gravity measurements in an aircraft or a boat.


title: Update Rules for Parameter Estimation in Bayesian Networks

abstract:
  This paper re-examines the problem of parameter estimation in Bayesian
networks with missing values and hidden variables from the perspective of
recent work in on-line learning [Kivinen & Warmuth, 1994]. We provide a unified
framework for parameter estimation that encompasses both on-line learning,
where the model is continuously adapted to new data cases as they arrive, and
the more traditional batch learning, where a pre-accumulated set of samples is
used in a one-time model selection process. In the batch case, our framework
encompasses both the gradient projection algorithm and the EM algorithm for
Bayesian networks. The framework also leads to new on-line and batch parameter
update schemes, including a parameterized version of EM. We provide both
empirical and theoretical results indicating that parameterized EM allows
faster convergence to the maximum likelihood parameters than does standard EM.


title: Bayes Networks for Sonar Sensor Fusion

abstract:
  Wide-angle sonar mapping of the environment by mobile robot is nontrivial due
to several sources of uncertainty: dropouts due to "specular" reflections,
obstacle location uncertainty due to the wide beam, and distance measurement
error. Earlier papers address the latter problems, but dropouts remain a
problem in many environments. We present an approach that lifts the
overoptimistic independence assumption used in earlier work, and use Bayes nets
to represent the dependencies between objects of the model. Objects of the
model consist of readings, and of regions in which "quasi location invariance"
of the (possible) obstacles exists, with respect to the readings. Simulation
supports the method's feasibility. The model is readily extensible to allow for
prior distributions, as well as other types of sensing operations.


title: Exploiting Uncertain and Temporal Information in Correlation

abstract:
  A modelling language is described which is suitable for the correlation of
information when the underlying functional model of the system is incomplete or
uncertain and the temporal dependencies are imprecise. An efficient and
incremental implementation is outlined which depends on cost functions
satisfying certain criteria. Possibilistic logic and probability theory (as it
is used in the applications targetted) satisfy these criteria.


title: Correlated Action Effects in Decision Theoretic Regression

abstract:
  Much recent research in decision theoretic planning has adopted Markov
decision processes (MDPs) as the model of choice, and has attempted to make
their solution more tractable by exploiting problem structure. One particular
algorithm, structured policy construction achieves this by means of a decision
theoretic analog of goal regression using action descriptions based on Bayesian
networks with tree-structured conditional probability tables. The algorithm as
presented is not able to deal with actions with correlated effects. We describe
a new decision theoretic regression operator that corrects this weakness. While
conceptually straightforward, this extension requires a somewhat more
complicated technical approach.


title: Corporate Evidential Decision Making in Performance Prediction Domains

abstract:
  Performance prediction or forecasting sporting outcomes involves a great deal
of insight into the particular area one is dealing with, and a considerable
amount of intuition about the factors that bear on such outcomes and
performances. The mathematical Theory of Evidence offers representation
formalisms which grant experts a high degree of freedom when expressing their
subjective beliefs in the context of decision-making situations like
performance prediction. Furthermore, this reasoning framework incorporates a
powerful mechanism to systematically pool the decisions made by individual
subject matter experts. The idea behind such a combination of knowledge is to
improve the competence (quality) of the overall decision-making process. This
paper reports on a performance prediction experiment carried out during the
European Football Championship in 1996. Relying on the knowledge of four
predictors, Evidence Theory was used to forecast the final scores of all 31
matches. The results of this empirical study are very encouraging.


title: Algorithms for Learning Decomposable Models and Chordal Graphs

abstract:
  Decomposable dependency models and their graphical counterparts, i.e.,
chordal graphs, possess a number of interesting and useful properties. On the
basis of two characterizations of decomposable models in terms of independence
relationships, we develop an exact algorithm for recovering the chordal
graphical representation of any given decomposable model. We also propose an
algorithm for learning chordal approximations of dependency models isomorphic
to general undirected graphs.


title:
Incremental Pruning: A Simple, Fast, Exact Method for Partially
  Observable Markov Decision Processes

abstract:
  Most exact algorithms for general partially observable Markov decision
processes (POMDPs) use a form of dynamic programming in which a
piecewise-linear and convex representation of one value function is transformed
into another. We examine variations of the "incremental pruning" method for
solving this problem and compare them to earlier algorithms from theoretical
and empirical perspectives. We find that incremental pruning is presently the
most efficient exact method for solving POMDPs.


title: Defining Explanation in Probabilistic Systems

abstract:
  As probabilistic systems gain popularity and are coming into wider use, the
need for a mechanism that explains the system's findings and recommendations
becomes more critical. The system will also need a mechanism for ordering
competing explanations. We examine two representative approaches to explanation
in the literature - one due to G\"ardenfors and one due to Pearl - and show
that both suffer from significant problems. We propose an approach to defining
a notion of "better explanation" that combines some of the features of both
together with more recent work by Pearl and others on causality.


title: Structured Arc Reversal and Simulation of Dynamic Probabilistic Networks

abstract:
  We present an algorithm for arc reversal in Bayesian networks with
tree-structured conditional probability tables, and consider some of its
advantages, especially for the simulation of dynamic probabilistic networks. In
particular, the method allows one to produce CPTs for nodes involved in the
reversal that exploit regularities in the conditional distributions. We argue
that this approach alleviates some of the overhead associated with arc
reversal, plays an important role in evidence integration and can be used to
restrict sampling of variables in DPNs. We also provide an algorithm that
detects the dynamic irrelevance of state variables in forward simulation. This
algorithm exploits the structured CPTs in a reversed network to determine, in a
time-independent fashion, the conditions under which a variable does or does
not need to be sampled.


title: A Bayesian Approach to Learning Bayesian Networks with Local Structure

abstract:
  Recently several researchers have investigated techniques for using data to
learn Bayesian networks containing compact representations for the conditional
probability distributions (CPDs) stored at each node. The majority of this work
has concentrated on using decision-tree representations for the CPDs. In
addition, researchers typically apply non-Bayesian (or asymptotically Bayesian)
scoring functions such as MDL to evaluate the goodness-of-fit of networks to
the data. In this paper we investigate a Bayesian approach to learning Bayesian
networks that contain the more general decision-graph representations of the
CPDs. First, we describe how to evaluate the posterior probability that is, the
Bayesian score of such a network, given a database of observed cases. Second,
we describe various search spaces that can be used, in conjunction with a
scoring function and a search procedure, to identify one or more high-scoring
networks. Finally, we present an experimental evaluation of the search spaces,
using a greedy algorithm and a Bayesian scoring function.


title: Exploring Parallelism in Learning Belief Networks

abstract:
  It has been shown that a class of probabilistic domain models cannot be
learned correctly by several existing algorithms which employ a single-link
look ahead search. When a multi-link look ahead search is used, the
computational complexity of the learning algorithm increases. We study how to
use parallelism to tackle the increased complexity in learning such models and
to speed up learning in large domains. An algorithm is proposed to decompose
the learning task for parallel processing. A further task decomposition is used
to balance load among processors and to increase the speed-up and efficiency.
For learning from very large datasets, we present a regrouping of the available
processors such that slow data access through file can be replaced by fast
memory access. Our implementation in a parallel computer demonstrates the
effectiveness of the algorithm.


title: Efficient Induction of Finite State Automata

abstract:
  This paper introduces a new algorithm for the induction if complex finite
state automata from samples of behavior. The algorithm is based on information
theoretic principles. The algorithm reduces the search space by many orders of
magnitude over what was previously thought possible. We compare the algorithm
with some existing induction techniques for finite state automata and show that
the algorithm is much superior in both run time and quality of inductions.


title:
Robustness Analysis of Bayesian Networks with Local Convex Sets of
  Distributions

abstract:
  Robust Bayesian inference is the calculation of posterior probability bounds
given perturbations in a probabilistic model. This paper focuses on
perturbations that can be expressed locally in Bayesian networks through convex
sets of distributions. Two approaches for combination of local models are
considered. The first approach takes the largest set of joint distributions
that is compatible with the local sets of distributions; we show how to reduce
this type of robust inference to a linear programming problem. The second
approach takes the convex hull of joint distributions generated from the local
sets of distributions; we demonstrate how to apply interior-point optimization
methods to generate posterior bounds and how to generate approximations that
are guaranteed to converge to correct posterior bounds. We also discuss
calculation of bounds for expected utilities and variances, and global
perturbation models.


title:
A Standard Approach for Optimizing Belief Network Inference using Query
  DAGs

abstract:
  This paper proposes a novel, algorithm-independent approach to optimizing
belief network inference. rather than designing optimizations on an algorithm
by algorithm basis, we argue that one should use an unoptimized algorithm to
generate a Q-DAG, a compiled graphical representation of the belief network,
and then optimize the Q-DAG and its evaluator instead. We present a set of
Q-DAG optimizations that supplant optimizations designed for traditional
inference algorithms, including zero compression, network pruning and caching.
We show that our Q-DAG optimizations require time linear in the Q-DAG size, and
significantly simplify the process of designing algorithms for optimizing
belief network inference.


title:
Model Reduction Techniques for Computing Approximately Optimal Solutions
  for Markov Decision Processes

abstract:
  We present a method for solving implicit (factored) Markov decision processes
(MDPs) with very large state spaces. We introduce a property of state space
partitions which we call epsilon-homogeneity. Intuitively, an
epsilon-homogeneous partition groups together states that behave approximately
the same under all or some subset of policies. Borrowing from recent work on
model minimization in computer-aided software verification, we present an
algorithm that takes a factored representation of an MDP and an 0<=epsilon<=1
and computes a factored epsilon-homogeneous partition of the state space. This
partition defines a family of related MDPs - those MDPs with state space equal
to the blocks of the partition, and transition probabilities "approximately"
like those of any (original MDP) state in the source block. To formally study
such families of MDPs, we introduce the new notion of a "bounded parameter MDP"
(BMDP), which is a family of (traditional) MDPs defined by specifying upper and
lower bounds on the transition probabilities and rewards. We describe
algorithms that operate on BMDPs to find policies that are approximately
optimal with respect to the original MDP. In combination, our method for
reducing a large implicit MDP to a possibly much smaller BMDP using an
epsilon-homogeneous partition, and our methods for selecting actions in BMDPs
constitute a new approach for analyzing large implicit MDPs. Among its
advantages, this new approach provides insight into existing algorithms to
solving implicit MDPs, provides useful connections to work in automata theory
and model minimization, and suggests methods, which involve varying epsilon, to
trade time and space (specifically in terms of the size of the corresponding
state space) for solution quality.


title: A Scheme for Approximating Probabilistic Inference

abstract:
  This paper describes a class of probabilistic approximation algorithms based
on bucket elimination which offer adjustable levels of accuracy and efficiency.
We analyze the approximation for several tasks: finding the most probable
explanation, belief updating and finding the maximum a posteriori hypothesis.
We identify regions of completeness and provide preliminary empirical
evaluation on randomly generated networks.


title: Myopic Value of Information in Influence Diagrams

abstract:
  We present a method for calculation of myopic value of information in
influence diagrams (Howard & Matheson, 1981) based on the strong junction tree
framework (Jensen, Jensen & Dittmer, 1994). The difference in instantiation
order in the influence diagrams is reflected in the corresponding junction
trees by the order in which the chance nodes are marginalized. This order of
marginalization can be changed by table expansion and in effect the same
junction tree with expanded tables may be used for calculating the expected
utility for scenarios with different instantiation order. We also compare our
method to the classic method of modeling different instantiation orders in the
same influence diagram.


title: Limitations of Skeptical Default Reasoning

abstract:
  Poole has shown that nonmonotonic logics do not handle the lottery paradox
correctly. In this paper we will show that Pollock's theory of defeasible
reasoning fails for the same reason: defeasible reasoning is incompatible with
the skeptical notion of derivability.


title: Decision-making Under Ordinal Preferences and Comparative Uncertainty

abstract:
  This paper investigates the problem of finding a preference relation on a set
of acts from the knowledge of an ordering on events (subsets of states of the
world) describing the decision-maker (DM)s uncertainty and an ordering of
consequences of acts, describing the DMs preferences. However, contrary to
classical approaches to decision theory, we try to do it without resorting to
any numerical representation of utility nor uncertainty, and without even using
any qualitative scale on which both uncertainty and preference could be mapped.
It is shown that although many axioms of Savage theory can be preserved and
despite the intuitive appeal of the method for constructing a preference over
acts, the approach is inconsistent with a probabilistic representation of
uncertainty, but leads to the kind of uncertainty theory encountered in
non-monotonic reasoning (especially preferential and rational inference),
closely related to possibility theory. Moreover the method turns out to be
either very little decisive or to lead to very risky decisions, although its
basic principles look sound. This paper raises the question of the very
possibility of purely symbolic approaches to Savage-like decision-making under
uncertainty and obtains preliminary negative results.


title: Sequential Update of Bayesian Network Structure

abstract:
  There is an obvious need for improving the performance and accuracy of a
Bayesian network as new data is observed. Because of errors in model
construction and changes in the dynamics of the domains, we cannot afford to
ignore the information in new data. While sequential update of parameters for a
fixed structure can be accomplished using standard techniques, sequential
update of network structure is still an open problem. In this paper, we
investigate sequential update of Bayesian networks were both parameters and
structure are expected to change. We introduce a new approach that allows for
the flexible manipulation of the tradeoff between the quality of the learned
networks and the amount of information that is maintained about past
observations. We formally describe our approach including the necessary
modifications to the scoring functions for learning Bayesian networks, evaluate
its effectiveness through an empirical study, and extend it to the case of
missing data.


title: Image Segmentation in Video Sequences: A Probabilistic Approach

abstract:
  "Background subtraction" is an old technique for finding moving objects in a
video sequence for example, cars driving on a freeway. The idea is that
subtracting the current image from a timeaveraged background image will leave
only nonstationary objects. It is, however, a crude approximation to the task
of classifying each pixel of the current image; it fails with slow-moving
objects and does not distinguish shadows from moving objects. The basic idea of
this paper is that we can classify each pixel using a model of how that pixel
looks when it is part of different classes. We learn a mixture-of-Gaussians
classification model for each pixel using an unsupervised technique- an
efficient, incremental version of EM. Unlike the standard image-averaging
approach, this automatically updates the mixture component for each class
according to likelihood of membership; hence slow-moving objects are handled
perfectly. Our approach also identifies and eliminates shadows much more
effectively than other techniques such as thresholding. Application of this
method as part of the Roadwatch traffic surveillance project is expected to
result in significant improvements in vehicle identification and tracking.


title: The Complexity of Plan Existence and Evaluation in Probabilistic Domains

abstract:
  We examine the computational complexity of testing and finding small plans in
probabilistic planning domains with succinct representations. We find that many
problems of interest are complete for a variety of complexity classes: NP,
co-NP, PP, NP^PP, co-NP^PP, and PSPACE. Of these, the probabilistic classes PP
and NP^PP are likely to be of special interest in the field of uncertainty in
artificial intelligence and are deserving of additional study. These results
suggest a fruitful direction of future algorithmic development.


title: Algorithm Portfolio Design: Theory vs. Practice

abstract:
  Stochastic algorithms are among the best for solving computationally hard
search and reasoning problems. The runtime of such procedures is characterized
by a random variable. Different algorithms give rise to different probability
distributions. One can take advantage of such differences by combining several
algorithms into a portfolio, and running them in parallel or interleaving them
on a single processor. We provide a detailed evaluation of the portfolio
approach on distributions of hard combinatorial search problems. We show under
what conditions the protfolio approach can have a dramatic computational
advantage over the best traditional methods.


title: Learning Bayesian Nets that Perform Well

abstract:
  A Bayesian net (BN) is more than a succinct way to encode a probabilistic
distribution; it also corresponds to a function used to answer queries. A BN
can therefore be evaluated by the accuracy of the answers it returns. Many
algorithms for learning BNs, however, attempt to optimize another criterion
(usually likelihood, possibly augmented with a regularizing term), which is
independent of the distribution of queries that are posed. This paper takes the
"performance criteria" seriously, and considers the challenge of computing the
BN whose performance - read "accuracy over the distribution of queries" - is
optimal. We show that many aspects of this learning task are more difficult
than the corresponding subtasks in the standard model.