title: Incremental Probabilistic Inference

abstract:
  Propositional representation services such as truth maintenance systems offer
powerful support for incremental, interleaved, problem-model construction and
evaluation. Probabilistic inference systems, in contrast, have lagged behind in
supporting this incrementality typically demanded by problem solvers. The
problem, we argue, is that the basic task of probabilistic inference is
typically formulated at too large a grain-size. We show how a system built
around a smaller grain-size inference task can have the desired incrementality
and serve as the basis for a low-level (propositional) probabilistic
representation service.


title: Deliberation Scheduling for Time-Critical Sequential Decision Making

abstract:
  We describe a method for time-critical decision making involving sequential
tasks and stochastic processes. The method employs several iterative refinement
routines for solving different aspects of the decision making problem. This
paper concentrates on the meta-level control problem of deliberation
scheduling, allocating computational resources to these routines. We provide
different models corresponding to optimization problems that capture the
different circumstances and computational strategies for decision making under
time constraints. We consider precursor models in which all decision making is
performed prior to execution and recurrent models in which decision making is
performed in parallel with execution, accounting for the states observed during
execution and anticipating future states. We describe algorithms for precursor
and recurrent models and provide the results of our empirical investigations to
date.


title: Intercausal Reasoning with Uninstantiated Ancestor Nodes

abstract:
  Intercausal reasoning is a common inference pattern involving probabilistic
dependence of causes of an observed common effect. The sign of this dependence
is captured by a qualitative property called product synergy. The current
definition of product synergy is insufficient for intercausal reasoning where
there are additional uninstantiated causes of the common effect. We propose a
new definition of product synergy and prove its adequacy for intercausal
reasoning with direct and indirect evidence for the common effect. The new
definition is based on a new property matrix half positive semi-definiteness, a
weakened form of matrix positive semi-definiteness.


title: Inference Algorithms for Similarity Networks

abstract:
  We examine two types of similarity networks each based on a distinct notion
of relevance. For both types of similarity networks we present an efficient
inference algorithm that works under the assumption that every event has a
nonzero probability of occurrence. Another inference algorithm is developed for
type 1 similarity networks that works under no restriction, albeit less
efficiently.


title: Two Procedures for Compiling Influence Diagrams

abstract:
  Two algorithms are presented for "compiling" influence diagrams into a set of
simple decision rules. These decision rules define simple-to-execute, complete,
consistent, and near-optimal decision procedures. These compilation algorithms
can be used to derive decision procedures for human teams solving time
constrained decision problems.


title: An efficient approach for finding the MPE in belief networks

abstract:
  Given a belief network with evidence, the task of finding the I most probable
explanations (MPE) in the belief network is that of identifying and ordering
the I most probable instantiations of the non-evidence nodes of the belief
network. Although many approaches have been proposed for solving this problem,
most work only for restricted topologies (i.e., singly connected belief
networks). In this paper, we will present a new approach for finding I MPEs in
an arbitrary belief network. First, we will present an algorithm for finding
the MPE in a belief network. Then, we will present a linear time algorithm for
finding the next MPE after finding the first MPE. And finally, we will discuss
the problem of finding the MPE for a subset of variables of a belief network,
and show that the problem can be efficiently solved by this approach.


title: A Method for Planning Given Uncertain and Incomplete Information

abstract:
  This paper describes ongoing research into planning in an uncertain
environment. In particular, it introduces U-Plan, a planning system that
constructs quantitatively ranked plans given an incomplete description of the
state of the world. U-Plan uses a DempsterShafer interval to characterise
uncertain and incomplete information about the state of the world. The planner
takes as input what is known about the world, and constructs a number of
possible initial states with representations at different abstraction levels. A
plan is constructed for the initial state with the greatest support, and this
plan is tested to see if it will work for other possible initial states. All,
part, or none of the existing plans may be used in the generation of the plans
for the remaining possible worlds. Planning takes place in an abstraction
hierarchy where strategic decisions are made before tactical decisions. A
super-plan is then constructed, based on merging the set of plans and the
appropriately timed acquisition of essential knowledge, which is used to decide
between plan alternatives. U-Plan usually produces a super-plan in less time
than a classical planner would take to produce a set of plans, one for each
possible world.


title: The use of conflicts in searching Bayesian networks

abstract:
  This paper discusses how conflicts (as used by the consistency-based
diagnosis community) can be adapted to be used in a search-based algorithm for
computing prior and posterior probabilities in discrete Bayesian Networks. This
is an "anytime" algorithm, that at any stage can estimate the probabilities and
give an error bound. Whereas the most popular Bayesian net algorithms exploit
the structure of the network for efficiency, we exploit probability
distributions for efficiency; this algorithm is most suited to the case with
extreme probabilities. This paper presents a solution to the inefficiencies
found in naive algorithms, and shows how the tools of the consistency-based
diagnosis community (namely conflicts) can be used effectively to improve the
efficiency. Empirical results with networks having tens of thousands of nodes
are presented.


title:
GALGO: A Genetic ALGOrithm Decision Support Tool for Complex Uncertain
  Systems Modeled with Bayesian Belief Networks

abstract:
  Bayesian belief networks can be used to represent and to reason about complex
systems with uncertain, incomplete and conflicting information. Belief networks
are graphs encoding and quantifying probabilistic dependence and conditional
independence among variables. One type of reasoning of interest in diagnosis is
called abductive inference (determination of the global most probable system
description given the values of any partial subset of variables). In some
cases, abductive inference can be performed with exact algorithms using
distributed network computations but it is an NP-hard problem and complexity
increases drastically with the presence of undirected cycles, number of
discrete states per variable, and number of variables in the network. This
paper describes an approximate method based on genetic algorithms to perform
abductive inference in large, multiply connected networks for which complexity
is a concern when using most exact methods and for which systematic search
methods are not feasible. The theoretical adequacy of the method is discussed
and preliminary experimental results are presented.


title: Using Tree-Decomposable Structures to Approximate Belief Networks

abstract:
  Tree structures have been shown to provide an efficient framework for
propagating beliefs [Pearl,1986]. This paper studies the problem of finding an
optimal approximating tree. The star decomposition scheme for sets of three
binary variables [Lazarsfeld,1966; Pearl,1986] is shown to enhance the class of
probability distributions that can support tree structures; such structures are
called tree-decomposable structures. The logarithm scoring rule is found to be
an appropriate optimality criterion to evaluate different tree-decomposable
structures. Characteristics of such structures closest to the actual belief
network are identified using the logarithm rule, and greedy and exact
techniques are developed to find the optimal approximation.


title:
Using Potential Influence Diagrams for Probabilistic Inference and
  Decision Making

abstract:
  The potential influence diagram is a generalization of the standard
"conditional" influence diagram, a directed network representation for
probabilistic inference and decision analysis [Ndilikilikesha, 1991]. It allows
efficient inference calculations corresponding exactly to those on undirected
graphs. In this paper, we explore the relationship between potential and
conditional influence diagrams and provide insight into the properties of the
potential influence diagram. In particular, we show how to convert a potential
influence diagram into a conditional influence diagram, and how to view the
potential influence diagram operations in terms of the conditional influence
diagram.


title: Deciding Morality of Graphs is NP-complete

abstract:
  In order to find a causal explanation for data presented in the form of
covariance and concentration matrices it is necessary to decide if the graph
formed by such associations is a projection of a directed acyclic graph (dag).
We show that the general problem of deciding whether such a dag exists is
NP-complete.


title:
Incremental computation of the value of perfect information in
  stepwise-decomposable influence diagrams

abstract:
  To determine the value of perfect information in an influence diagram, one
needs first to modify the diagram to reflect the change in information
availability, and then to compute the optimal expected values of both the
original diagram and the modified diagram. The value of perfect information is
the difference between the two optimal expected values. This paper is about how
to speed up the computation of the optimal expected value of the modified
diagram by making use of the intermediate computation results obtained when
computing the optimal expected value of the original diagram.


title: Argumentative inference in uncertain and inconsistent knowledge bases

abstract:
  This paper presents and discusses several methods for reasoning from
inconsistent knowledge bases. A so-called argumentative-consequence relation
taking into account the existence of consistent arguments in favor of a
conclusion and the absence of consistent arguments in favor of its contrary, is
particularly investigated. Flat knowledge bases, i.e. without any priority
between their elements, as well as prioritized ones where some elements are
considered as more strongly entrenched than others are studied under different
consequence relations. Lastly a paraconsistent-like treatment of prioritized
knowledge bases is proposed, where both the level of entrenchment and the level
of paraconsistency attached to a formula are propagated. The priority levels
are handled in the framework of possibility theory.


title: Argument Calculus and Networks

abstract:
  A major reason behind the success of probability calculus is that it
possesses a number of valuable tools, which are based on the notion of
probabilistic independence. In this paper, I identify a notion of logical
independence that makes some of these tools available to a class of
propositional databases, called argument databases. Specifically, I suggest a
graphical representation of argument databases, called argument networks, which
resemble Bayesian networks. I also suggest an algorithm for reasoning with
argument networks, which resembles a basic algorithm for reasoning with
Bayesian networks. Finally, I show that argument networks have several
applications: Nonmonotonic reasoning, truth maintenance, and diagnosis.


title: Argumentation as a General Framework for Uncertain Reasoning

abstract:
  Argumentation is the process of constructing arguments about propositions,
and the assignment of statements of confidence to those propositions based on
the nature and relative strength of their supporting arguments. The process is
modelled as a labelled deductive system, in which propositions are doubly
labelled with the grounds on which they are based and a representation of the
confidence attached to the argument. Argument construction is captured by a
generalized argument consequence relation based on the ^,--fragment of minimal
logic. Arguments can be aggregated by a variety of numeric and symbolic
flattening functions. This approach appears to shed light on the common logical
structure of a variety of quantitative, qualitative and defeasible uncertainty
calculi.


title: On reasoning in networks with qualitative uncertainty

abstract:
  In this paper some initial work towards a new approach to qualitative
reasoning under uncertainty is presented. This method is not only applicable to
qualitative probabilistic reasoning, as is the case with other methods, but
also allows the qualitative propagation within networks of values based upon
possibility theory and Dempster-Shafer evidence theory. The method is applied
to two simple networks from which a large class of directed graphs may be
constructed. The results of this analysis are used to compare the qualitative
behaviour of the three major quantitative uncertainty handling formalisms, and
to demonstrate that the qualitative integration of the formalisms is possible
under certain assumptions.


title: Qualitative Measures of Ambiguity

abstract:
  This paper introduces a qualitative measure of ambiguity and analyses its
relationship with other measures of uncertainty. Probability measures relative
likelihoods, while ambiguity measures vagueness surrounding those judgments.
Ambiguity is an important representation of uncertain knowledge. It deals with
a different, type of uncertainty modeled by subjective probability or belief.


title:
A Bayesian Variant of Shafer's Commonalities For Modelling Unforeseen
  Events

abstract:
  Shafer's theory of belief and the Bayesian theory of probability are two
alternative and mutually inconsistent approaches toward modelling uncertainty
in artificial intelligence. To help reduce the conflict between these two
approaches, this paper reexamines expected utility theory-from which Bayesian
probability theory is derived. Expected utility theory requires the decision
maker to assign a utility to each decision conditioned on every possible event
that might occur. But frequently the decision maker cannot foresee all the
events that might occur, i.e., one of the possible events is the occurrence of
an unforeseen event. So once we acknowledge the existence of unforeseen events,
we need to develop some way of assigning utilities to decisions conditioned on
unforeseen events. The commonsensical solution to this problem is to assign
similar utilities to events which are similar. Implementing this commonsensical
solution is equivalent to replacing Bayesian subjective probabilities over the
space of foreseen and unforeseen events by random set theory probabilities over
the space of foreseen events. This leads to an expected utility principle in
which normalized variants of Shafer's commonalities play the role of subjective
probabilities. Hence allowing for unforeseen events in decision analysis causes
Bayesian probability theory to become much more similar to Shaferian theory.


title: The Probability of a Possibility: Adding Uncertainty to Default Rules

abstract:
  We present a semantics for adding uncertainty to conditional logics for
default reasoning and belief revision. We are able to treat conditional
sentences as statements of conditional probability, and express rules for
revision such as "If A were believed, then B would be believed to degree p."
This method of revision extends conditionalization by allowing meaningful
revision by sentences whose probability is zero. This is achieved through the
use of counterfactual probabilities. Thus, our system accounts for the best
properties of qualitative methods of update (in particular, the AGM theory of
revision) and probabilistic methods. We also show how our system can be viewed
as a unification of probability theory and possibility theory, highlighting
their orthogonality and providing a means for expressing the probability of a
possibility. We also demonstrate the connection to Lewis's method of imaging.


title: Possibilistic decreasing persistence

abstract:
  A key issue in the handling of temporal data is the treatment of persistence;
in most approaches it consists in inferring defeasible confusions by
extrapolating from the actual knowledge of the history of the world; we propose
here a gradual modelling of persistence, following the idea that persistence is
decreasing (the further we are from the last time point where a fluent is known
to be true, the less certainly true the fluent is); it is based on possibility
theory, which has strong relations with other well-known ordering-based
approaches to nonmonotonic reasoning. We compare our approach with Dean and
Kanazawa's probabilistic projection. We give a formal modelling of the
decreasing persistence problem. Lastly, we show how to infer nonmonotonic
conclusions using the principle of decreasing persistence.


title: Discounting and Combination Operations in Evidential Reasoning

abstract:
  Evidential reasoning is now a leading topic in Artificial Intelligence.
Evidence is represented by a variety of evidential functions. Evidential
reasoning is carried out by certain kinds of fundamental operation on these
functions. This paper discusses two of the basic operations on evidential
functions, the discount operation and the well-known orthogonal sum operation.
We show that the discount operation is not commutative with the orthogonal sum
operation, and derive expressions for the two operations applied to the various
evidential function.


title: Probabilistic Assumption-Based Reasoning

abstract:
  The classical propositional assumption-based model is extended to incorporate
probabilities for the assumptions. Then it is placed into the framework of
evidence theory. Several authors like Laskey, Lehner (1989) and Provan (1990)
already proposed a similar point of view, but the first paper is not as much
concerned with mathematical foundations, and Provan's paper develops into a
different direction. Here we thoroughly develop and present the mathematical
foundations of this theory, together with computational methods adapted from
Reiter, De Kleer (1987) and Inoue (1992). Finally, recently proposed techniques
for computing degrees of support are presented.


title: Partially Specified Belief Functions

abstract:
  This paper presents a procedure to determine a complete belief function from
the known values of belief for some of the subsets of the frame of discerment.
The method is based on the principle of minimum commitment and a new principle
called the focusing principle. This additional principle is based on the idea
that belief is specified for the most relevant sets: the focal elements. The
resulting procedure is compared with existing methods of building complete
belief functions: the minimum specificity principle and the least commitment
principle.


title: Jeffrey's rule of conditioning generalized to belief functions

abstract:
  Jeffrey's rule of conditioning has been proposed in order to revise a
probability measure by another probability function. We generalize it within
the framework of the models based on belief functions. We show that several
forms of Jeffrey's conditionings can be defined that correspond to the
geometrical rule of conditioning and to Dempster's rule of conditioning,
respectively.


title: Inference with Possibilistic Evidence

abstract:
  In this paper, the concept of possibilistic evidence which is a possibility
distribution as well as a body of evidence is proposed over an infinite
universe of discourse. The inference with possibilistic evidence is
investigated based on a unified inference framework maintaining both the
compatibility of concepts and the consistency of the probability logic.


title: Constructing Lower Probabilities

abstract:
  An elaboration of Dempster's method of constructing belief functions suggests
a broadly applicable strategy for constructing lower probabilities under a
variety of evidentiary constraints.


title: Belief Revision in Probability Theory

abstract:
  In a probability-based reasoning system, Bayes' theorem and its variations
are often used to revise the system's beliefs. However, if the explicit
conditions and the implicit conditions of probability assignments `me properly
distinguished, it follows that Bayes' theorem is not a generally applicable
revision rule. Upon properly distinguishing belief revision from belief
updating, we see that Jeffrey's rule and its variations are not revision rules,
either. Without these distinctions, the limitation of the Bayesian approach is
often ignored or underestimated. Revision, in its general form, cannot be done
in the Bayesian approach, because a probability distribution function alone
does not contain the information needed by the operation.


title: The Assumptions Behind Dempster's Rule

abstract:
  This paper examines the concept of a combination rule for belief functions.
It is shown that two fairly simple and apparently reasonable assumptions
determine Dempster's rule, giving a new justification for it.


title: A Belief-Function Based Decision Support System

abstract:
  In this paper, we present a decision support system based on belief functions
and the pignistic transformation. The system is an integration of an evidential
system for belief function propagation and a valuation-based system for
Bayesian decision analysis. The two subsystems are connected through the
pignistic transformation. The system takes as inputs the user's "gut feelings"
about a situation and suggests what, if any, are to be tested and in what
order, and it does so with a user friendly interface.


title: Energy Landscape of the Finite-Size Mean-field 3-Spin Spherical Model

abstract:
  We study the 3-spin spherical model with mean-field interactions and Gaussian
random couplings. For moderate system sizes of up to 20 spins, we obtain all
stationary points of the energy landscape by means of the numerical polynomial
homotopy continuation method. On the basis of these stationary points, we
analyze the complexity and other quantities related to the glass transition of
the model and compare these finite-system quantities to their exact
counterparts in the thermodynamic limit.


title: Double-Disk Dark Matter

abstract:
  Based on observational constraints on large scale structure and halo
structure, dark matter is generally taken to be cold and essentially
collisionless. On the other hand, given the large number of particles and
forces in the visible world, a more complex dark sector could be a reasonable
or even likely possibility. This hypothesis leads to testable consequences,
perhaps portending the discovery of a rich hidden world neighboring our own. We
consider a scenario that readily satisfies current bounds that we call
Partially Interacting Dark Matter (PIDM). This scenario contains
self-interacting dark matter, but it is not the dominant component. Even if
PIDM contains only a fraction of the net dark matter density, comparable to the
baryonic fraction, the subdominant component's interactions can lead to
interesting and potentially observable consequences. Our primary focus will be
the special case of Double-Disk Dark Matter (DDDM), in which self-interactions
allow the dark matter to lose enough energy to lead to dynamics similar to
those in the baryonic sector. We explore a simple model in which DDDM can cool
efficiently and form a disk within galaxies, and we evaluate some of the
possible observational signatures. The most prominent signal of such a scenario
could be an enhanced indirect detection signature with a distinctive spatial
distribution. Even though subdominant, the enhanced density at the center of
the galaxy and possibly throughout the plane of the galaxy can lead to large
boost factors, and could even explain a signature as large as the 130 GeV Fermi
line. Such scenarios also predict additional dark radiation degrees of freedom
that could soon be detectable and would influence the interpretation of future
data, such as that from Planck and from the Gaia satellite. We consider this to
be the first step toward exploring a rich array of new possibilities for dark
matter dynamics.

categories: astro-ph.CO astro-ph.GA astro-ph.HE hep-ph


title:
On RG Flow of tau_{RR} for Supersymmetric Field Theories in
  Three-Dimensions

abstract:
  The coefficient tau_{RR} of the two-point function of the superconformal
U(1)_R currents of N=2 SCFTs in three-dimensions is recently shown to be
obtained by differentiating the partition function on a squashed three-sphere
with respect to the squashing parameter. With this method, we compute the
tau_{RR} for N=2 Wess-Zumino models and SQCD numerically for small number of
flavors and analytically in the large number limit. We study the behavior of
tau_{RR} under an RG flow by adding superpotentials to the theories. While the
tau_{RR} decreases for the gauge theories, we find an N=2 Wess-Zumino model
whose tau_{RR} increases along the RG flow. Since tau_{RR} is proportional to
the coefficient C_T of the two-point correlation function of the stress-energy
tensors for N=2 superconformal field theories, this rules out the possibility
of C_T being a measure of the degrees of freedom which monotonically decreases
along RG flows in three-dimensions.


title: Inflation, Cosmic Perturbations and Non-Gaussianities

abstract:
  We review the theory of inflationary perturbations. Perturbations at both
linear and nonlinear orders are reviewed. We also review a variety of inflation
models, emphasizing their signatures on cosmic perturbations.


title:
Anomalous Supercurrent from Majorana States in Topological Insulator
  Josephson Junctions

abstract:
  We propose a Josephson junction setup based on a topological insulator (TI)
thin film to detect Majorana states, which exploits the unique helical and
extended nature of the TI surface state. When the magnetic flux through the
junction is close to an integer number of flux quanta, Majorana states, present
on both surfaces of the film, give rise to a narrow peak-dip structure in the
current- phase relation by hybridizing at the edge of the junction. Moreover,
the maximal Majorana-state contribution to Josephson current takes a (nearly)
universal value, approximately equal to the supercurrent capacity of a single
quantum-channel. These features provide a characteristic signature of Majorana
states based entirely on supercurrent.


title: The a theorem for Gauge-Yukawa theories beyond Banks-Zaks

abstract:
  We investigate the a theorem for nonsupersymmetric gauge-Yukawa theories
beyond the leading order in perturbation theory. The exploration is first
performed in a model-independent manner and then applied to a specific relevant
example. Here, a rich fixed point structure appears including the presence of a
merging phenomenon between non-trivial fixed points for which the a theorem has
not been tested so far.


title: Modified Higgs Sectors and NLO Associated Production

abstract:
  Many beyond the Standard Model (BSM) scenarios involve Higgs couplings to
additional electroweak fields. It is well established that these new fields may
modify Higgs gamma-gamma and gamma-Z decays at one-loop. However, one
unexplored aspect of such scenarios is that by electroweak symmetry one should
also expect modifications to the Higgs Z-Z coupling at one-loop and, more
generally, modifications to Higgs production and decay channels beyond
tree-level. In this paper we investigate the full BSM modified electroweak
corrections to associated Higgs production at both the LHC and a future lepton
collider in two simple SM extensions. From both inclusive and differential NLO
associated production cross sections we find BSM-NLO corrections can be as
large as O(>10%) when compared to the SM expectation, consistent with other
precision electroweak measurements, even in scenarios where modifications to
the Higgs diphoton rate are not significant. At the LHC such corrections are
comparable to the involved QCD uncertainties. At a lepton collider the Higgs
associated production cross section can be measured to high accuracy (O(1%)
independent of uncertainties in total width and other couplings), and such a
deviation could be easily observed even if the new states remain beyond
kinematic reach. This should be compared to the expected accuracy for a
model-independent determination of the Higgs diphoton coupling at a lepton
collider, which is O(15%). This work demonstrates that precision measurements
of the Higgs associated production cross section constitute a powerful probe of
modified Higgs sectors and will be valuable for indirectly exploring BSM
scenarios.


title: Massive Nambu-Goldstone Bosons

abstract:
  Nicolis and Piazza have recently pointed out the existence of
Nambu-Goldstone-like excitations in relativistic systems at finite density,
whose gap is exactly determined by the chemical potential and the symmetry
algebra. We show that the phenomenon is much more general than anticipated and
demonstrate the presence of such modes in a number of systems from
(anti)ferromagnets in magnetic field to superfluid phases of quantum
chromodynamics. Furthermore, we prove a counting rule for these massive
Nambu-Goldstone bosons and construct a low-energy effective Lagrangian that
captures their dynamics.

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


title:
I-Love-Q Relations in Neutron Stars and their Applications to
  Astrophysics, Gravitational Waves and Fundamental Physics

abstract:
  The exterior gravitational field of a slowly-rotating neutron star can be
characterized by its multipole moments, the first few being the neutron star
mass, moment of inertia, and quadrupole moment to quadratic order in spin. In
principle, all of these quantities depend on the neutron star's internal
structure, and thus, on unknown nuclear physics at supra-nuclear energy
densities. We here find relations between the moment of inertia, the Love
numbers and the quadrupole moment (I-Love-Q relations) that do not depend
sensitively on the neutron star's internal structure. Three important
consequences derive from these I-Love-Q relations. On an observational
astrophysics front, the measurement of a single member of the I-Love-Q trio
would automatically provide information about the other two, even when the
latter may not be observationally accessible. On a gravitational wave front,
the I-Love-Q relations break the degeneracy between the quadrupole moment and
the neutron-star spins in binary inspiral waveforms, allowing second-generation
ground-based detectors to determine the (dimensionless) averaged spin to
$\mathcal{O}(10)%$, given a sufficiently large signal-to-noise ratio detection.
On a fundamental physics front, the I-Love-Q relations allow for tests of
General Relativity in the neutron-star strong-field that are both theory- and
internal structure-independent. As an example, by combining gravitational-wave
and electromagnetic observations, one may constrain dynamical Chern-Simons
gravity in the future by more than 6 orders of magnitude more stringently than
Solar System and table-top constraints.


title:
The Herschel and JCMT Gould Belt Surveys: Constraining Dust Properties
  in the Perseus B1 Clump with PACS, SPIRE, and SCUBA-2

abstract:
  We present Herschel observations from the Herschel Gould Belt Survey and
SCUBA-2 science verification observations from the JCMT Gould Belt Survey of
the B1 clump in the Perseus molecular cloud. We determined the dust emissivity
index using four different techniques to combine the Herschel PACS+SPIRE data
at 160 - 500 microns with the SCUBA-2 data at 450 microns and 850 microns. Of
our four techniques, we found the most robust method was to filter-out the
large-scale emission in the Herschel bands to match the spatial scales
recovered by the SCUBA-2 reduction pipeline. Using this method, we find beta ~
2 towards the filament region and moderately dense material and lower beta
values (beta > 1.6) towards the dense protostellar cores, possibly due to dust
grain growth. We find that beta and temperature are more robust with the
inclusion of the SCUBA-2 data, improving estimates from Herschel data alone by
factors of ~ 2 for beta and by ~ 40% for temperature. Furthermore, we find core
mass differences of < 30% compared to Herschel-only estimates with an adopted
beta = 2, highlighting the necessity of long wavelength submillimeter data for
deriving accurate masses of prestellar and protostellar cores.


title:
Analysis of Far-UV Data of Central Stars of Planetary Nebulae:
  Occurrence and Variability of Stellar Winds

abstract:
  The occurrence of stellar wind in central stars planetary nebulae (CSPNe) can
be revealed by the presence of P Cygni profiles of high-excitation lines
overimposed on the stellar continuum. We have examined the entire FUSE archive
and merged all useful observations of CSPNe to produce the highest quality
spectra that can be used to assess the occurrence of stellar winds.
Furthermore, the individual spectra of each CSPN have been searched for
variability in the P Cygni profile. P Cygni profiles of high-excitation lines
have been found in 44 CSPNe, with a clear correlation between the line
ionization potential and the star effective temperature. We introduce a
prescription to derive the terminal wind velocity (v_inf) from saturated and
unsaturated P Cygni profiles and provide new values of v_inf for these stars.
Another 23 CSPNe do not show P Cygni profiles or their FUSE data are not
conclusive to determine the occurrence of P Cygni profiles. Variability in the
P Cygni profile of high-excitation far-UV lines is found for the first time in
six CSPNe, namely Hen 2-131, NGC 40, NGC 1535, NGC 2392, Sp 3, and SwSt 1,
increasing up to 13 the number of CSPNe with variable P Cygni profiles in the
UV, including those previously reported using IUE or FUSE observations.
Variability is seen preferentially in the unsaturated P V and Si IV lines, but
also in saturated C III and O VI lines. The CSPNe with variable P Cygni
profiles have similar stellar properties (relatively low log(g) and T_eff) that
suggests they are less evolved CSPNe. Some of the CSPNe with variable P Cygni
profiles show O VI lines, while their T_eff is insufficient to produce this
ion. We suggest that such ion is produced by Auger ionization from X-rays
associated to shocks in their stellar winds as is the case in massive OB stars
of high ionization potential ions which cannot be abundantly produced by
photoionizations.


title:
PS1-10bzj: A Fast, Hydrogen-Poor Superluminous Supernova in a Metal Poor
  Host Galaxy

abstract:
  We present observations and analysis of PS1-10bzj, a superluminous supernova
(SLSN) discovered in the Pan-STARRS Medium Deep Survey at a redshift z = 0.650.
Spectroscopically, PS1-10bzj is similar to the hydrogen-poor SLSNe 2005ap and
SCP 06F6, though with a steeper rise and lower peak luminosity (M_bol = -21.4
mag) than previous events. We construct a bolometric light curve, and show that
while PS1-10bzj's energetics were less extreme than previous events, its
luminosity still cannot be explained by radioactive nickel decay alone. We
explore both a magnetar spin-down and circumstellar interaction scenario and
find that either can fit the data. PS1-10bzj is located in the Extended Chandra
Deep Field South and the host galaxy is imaged in a number of surveys,
including with the Hubble Space Telescope. The host is a compact dwarf galaxy
(M_B ~ -18 mag, diameter < 800 pc), with a low stellar mass (M_* ~ 2.4 * 10^7
M_sun), young stellar population (\tau_* ~ 5 Myr), and a star formation rate of
~ 2-3 M_sun/yr. The specific star formation rate is the highest seen in a SLSN
host so far (~ 100 Gyr^{-1}). We detect the [O III]\lambda 4363 line, and find
a low metallicity: 12+(O/H) = 7.8 +/- 0.2 (~ 0.1 Z_sun). Together, this
indicates that at least some of the progenitors of SLSNe come from young,
low-metallicity populations.


title: Superstring Amplitudes as a Mellin Transform of Supergravity

abstract:
  At the tree level, the maximally helicity violating amplitudes of N gauge
bosons in open superstring theory and of N gravitons in supergravity are known
to have simple representations in terms of tree graphs. For superstrings, the
graphs encode integral representations of certain generalized Gaussian
hypergeometric functions of kinematic invariants while for supergravity, they
represent specific kinematic expressions constructed from spinor-helicity
variables. We establish a superstring/supergravity correspondence for this
class of amplitudes, by constructing a mapping between the positions of gauge
boson vertices at the disk boundary and the helicity spinors associated to
gravitons. After replacing vertex positions by a larger set of N(N-3)/2
coordinates, the superstring amplitudes become (multiple) Mellin transforms of
supergravity amplitudes, from the projective space into the dual Mellin space
of N(N-3)/2 kinematic invariants. Similarly, inverse Mellin transforms
transmute open superstrings into supergravity. We elaborate on the properties
of multiple Mellin and inverse Mellin transforms in the framework of
superstring/supergravity correspondence.


title:
Challenges to our understanding of radio relics: X-ray observations of
  the Toothbrush cluster

abstract:
  The cluster 1RXS J0603.3+4214 is a merging galaxy cluster that hosts three
radio relics and a giant radio halo. The northern relic, the Toothbrush, is
1.9-Mpc long and has an unusual linear morphology. According to simple
diffusive shock acceleration theory, its radio spectral index indicates a Mach
number of 3.3-4.6. Here, we present results from a deep XMM-Newton observation
of the cluster. We observe two distinct cluster cores that have survived the
merger. The presence of three shocks at or near the locations of the radio
relics is confirmed by density and temperature discontinuities. However, the
observation poses several puzzles that challenge our understanding of radio
relics: (i) at the Toothbrush, the shock Mach number is not larger than 2, in
apparent conflict with the shock strength predicted from the radio spectrum;
(ii) at the Toothbrush, the shock front is, in part, spatially offset from the
radio emission; (iii) at the eastern relic, we detect a temperature jump
corresponding to a Mach number of approximately 2.5, but there is no associated
surface brightness discontinuity. We discuss possible explanations for these
findings.


title:
Measuring the slopes of mass profiles for dwarf spheroidals in triaxial
  CDM potentials

abstract:
  We generate stellar distribution functions (DFs) in triaxial haloes in order
to examine the reliability of slopes $\Gamma\equiv \Delta {\rm log} M / \Delta
{\rm log} r$ inferred by applying mass estimators of the form $M\propto
R_e\sigma^2$ (i.e. assuming spherical symmetry, where $R_e$ and $\sigma$ are
luminous effective radius and global velocity dispersion, respectively) to two
stellar sub-populations independently tracing the same gravitational potential.
The DFs take the form $f(E)$, are dynamically stable, and are generated within
triaxial potentials corresponding directly to subhaloes formed in cosmological
dark-matter-only simulations of Milky Way and galaxy cluster haloes.
Additionally, we consider the effect of different tracer number density
profiles (cuspy and cored) on the inferred slopes of mass profiles. For the
isotropic DFs considered here, we find that halo triaxiality tends to introduce
an anti-correlation between $R_e$ and $\sigma$ when estimated for a variety of
viewing angles. The net effect is a negligible contribution to the systematic
error associated with the slope of the mass profile, which continues to be
dominated by a bias toward greater overestimation of masses for
more-concentrated tracer populations. We demonstrate that simple mass estimates
for two distinct tracer populations can give reliable (and cosmologically
meaningful) lower limits for $\Gamma$, irrespective of the degree of
triaxiality or shape of the tracer number density profile.


title:
The Structure of the Gravitational Action and its relation with Horizon
  Thermodynamics and Emergent Gravity Paradigm

abstract:
  If gravity is an emergent phenomenon, as suggested by several recent results,
then the structure of the action principle for gravity should encode this fact.
With this motivation we study several features of the Einstein-Hilbert action
and establish direct connections with horizon thermodynamics. We begin by
introducing the concept of holographically conjugate variables (HCVs) in terms
of which the surface term in the action has a specific relationship with the
bulk term. In addition to g_{ab} and its conjugate momentum \sqrt{-g} M^{cab},
this procedure allows us to (re)discover and motivate strongly the use of
f^{ab}=\sqrt{-g}g^{ab} and its conjugate momentum N^c_{ab}. The gravitational
action can then be interpreted as a momentum space action for these variables.
We also show that many expressions in classical gravity simplify considerably
in this approach. For example, the field equations can be written in a form
analogous to Hamilton's equations for a suitable Hamiltonian if we use these
variables. More importantly, the variation of the surface term, evaluated on
any null surface which acts a local Rindler horizon can be given a direct
thermodynamic interpretation. The term involving the variation of the dynamical
variable leads to T\delta S while the term involving the variation of the
conjugate momentum leads to S\delta T. We have found this correspondence only
for the choice of variables (g_{ab}, \sqrt{-g} M^{cab}) or (f^{ab}, N^c_{ab}).
We use this result to provide a direct thermodynamical interpretation of the
boundary condition in the action principle, when it is formulated in a
spacetime region bounded by the null surfaces. We analyse these features from
several different perspectives and provide a detailed description, which offers
insights about the nature of classical gravity and emergent paradigm.


title: New Insights: the Accretion Process and Variable Wind from TW Hya

abstract:
  For the first time in a classical T Tauri star, we are able to trace an
accretion event signaled by an hour-long enhancement of X-rays from the
accretion shock and revealed through substantial sequential changes in optical
emission line profiles. Downflowing turbulent material appears in H-alpha and
H-beta emission. He D3 (5876 Angstrom) broadens, coupled with an increase in
flux. Two hours after the X-ray accretion event, the optical veiling increases
due to continuum emission from the hot splashdown region. The response of the
stellar coronal emission to the heated photosphere follows about 2.4 hours
later, giving direct evidence that the stellar corona is heated in part by
accretion. Then, the stellar wind becomes re-established. A model that
incorporates the dynamics of this sequential series of events includes: an
accretion shock, a cooling downflow in a supersonically turbulent region,
followed by photospheric and later, coronal heating. This model naturally
explains the presence of broad optical and ultraviolet lines, and affects the
mass accretion rates currently determined from emission line profiles. These
results, coupled with the large heated coronal region revealed from X-ray
diagnostics, suggest that current models are not adequate to explain the
accretion process in young stars.


title: On the theory of composition in physics

abstract:
  We develop a theory for describing composite objects in physics. These can be
static objects, such as tables, or things that happen in spacetime (such as a
region of spacetime with fields on it regarded as being composed of smaller
such regions joined together). We propose certain fundamental axioms which, it
seems, should be satisfied in any theory of composition. A key axiom is the
order independence axiom which says we can describe the composition of a
composite object in any order. Then we provide a notation for describing
composite objects that naturally leads to these axioms being satisfied. In any
given physical context we are interested in the value of certain properties for
the objects (such as whether the object is possible, what probability it has,
how wide it is, and so on). We associate a generalized state with an object.
This can be used to calculate the value of those properties we are interested
in for for this object. We then propose a certain principle, the composition
principle, which says that we can determine the generalized state of a
composite object from the generalized states for the components by means of a
calculation having the same structure as the description of the generalized
state. The composition principle provides a link between description and
prediction.


title: Reconstructing quantum theory

abstract:
  We discuss how to reconstruct quantum theory from operational postulates. In
particular, the following postulates are consistent only with for classical
probability theory and quantum theory. Logical Sharpness: There is a one-to-one
map between pure states and maximal effects such that we get unit probability.
This maximal effect does not give probability equal to one for any other pure
state. Information Locality: A maximal measurement is effected on a composite
system if we perform maximal measurements on each of the components.
Tomographic Locality: The state of a composite system can be determined from
the statistics collected by making measurements on the components.
Permutability: There exists a reversible transformation on any system effecting
any given permutation of any given maximal set of distinguishable states for
that system. Sturdiness: Filters are non-flattening. To single out quantum
theory we need only add any requirement that is inconsistent with classical
probability theory and consistent with quantum theory.


title: Majorana zero modes in dislocations of Sr$_2$RuO$_4$

abstract:
  We study the topologically protected Majorana zero modes induced by lattice
dislocations in chiral topological superconductors. Dislocations provide a new
way to realize Majorana zero modes at zero magnetic field. In particular, we
study several different types of dislocations in the candidate material ${\rm
Sr_2RuO_4}.$ We also discuss the properties of linked dislocation lines and
linked dislocation and flux lines. Various experimental consequences are
predicted which provide a new approach to determine whether nature of the
superconducting phase of ${\rm Sr_2RuO_4}.$


title: Simulating extreme-mass-ratio systems in full general relativity

abstract:
  We introduce a new method for numerically evolving the full Einstein field
equations in situations where the spacetime is dominated by a known background
solution. The technique leverages the knowledge of the background solution to
subtract off its contribution to the truncation error, thereby more efficiently
achieving a desired level of accuracy. We demonstrate the method by applying it
to the radial infall of a solar-type star into supermassive black holes with
mass ratios $\geq 10^6$. The self-gravity of the star is thus consistently
modeled within the context of general relativity, and the star's interaction
with the black hole computed with moderate computational cost, despite the over
five orders of magnitude difference in gravitational potential (as defined by
the ratio of mass to radius). We compute the tidal deformation of the star
during infall, and the gravitational wave emission, finding the latter is close
to the prediction of the point-particle limit.


title:
More Realistic Hamiltonians for the Fractional Quantum Hall Regime in
  GaAs and Graphene

abstract:
  We construct an effective Hamiltonian for electrons in the fractional quantum
Hall regime for GaAs and graphene that takes into account Landau level mixing
(for both GaAs and graphene) and subband mixing (for GaAs, due to the nonzero
width of the quantum well). This mixing has the important qualitative effect of
breaking particle-hole symmetry as well as renormalizing the strength of the
interparticle interactions. Both effects could have important consequences for
the prospect that the fractional quantum Hall effect at $\nu=5/2$ is described
by states that support non-Abelian excitations such as the Moore-Read Pfaffian
or anti-Pfaffian states. For GaAs, Landau level and subband mixing break
particle-hole symmetry in all Landau levels and subband mixing, due to finite
thickness, causes additional short-distance softening of the Coulomb
interaction, further renormalizing the Hamiltonian; additionally, the Landau
level and subband energy spacings are comparable so it is crucial to consider
both effects simultaneously. We find that in graphene, Landau level mixing only
breaks particle-hole symmetry outside of the lowest Landau level ($N\neq0$).
Landau level mixing is likely to be especially important in graphene since the
Landau level mixing parameter is independent of the external magnetic field and
is of order one. Our realistic Hamiltonians will serve as starting points for
future numerical studies.


title: Helical nuclear spin order in two-subband quantum wires

abstract:
  In quantum wires, the hyperfine coupling between conduction electrons and
nuclear spins can lead to a (partial) ordering of both of them at low
temperatures. By an interaction-enhanced mechanism, the nuclear spin order,
caused by RKKY exchange, acts back onto the electrons and gaps out part of
their spectrum. In wires with two subbands characterized by distinct Fermi
momenta kF1 and kF2, the nuclear spins form a superposition of two helices with
pitches {\pi}/kF1 and {\pi}/kF2, thus exhibiting a beating pattern. This order
results in a reduction of the electronic conductance in two steps upon lowering
the temperature.


title: Hurwitz numbers, ribbon graphs, and tropicalization

abstract:
  Double Hurwitz numbers have at least four equivalent definitions. Most
naturally, they count covers of the Riemann sphere by genus g curves with
certain specified ramification data. This is classically equivalent to counting
certain collections of permutations. More recently, double Hurwitz numbers have
been expressed as a count of certain ribbon graphs, or as a weighted count of
certain labeled graphs.
  This note is an expository account of the equivalences between these
definitions, with a few novelties. In particular, we give a simple
combinatorial algorithm to pass directly between the permutation and ribbon
graph definitions. The two graph theoretic points of view have been used to
give proofs that double Hurwitz numbers are piecewise polynomial. We use our
algorithm to compare these two proofs.


title:
Can one observe quantum-gravitational effects in the cosmic microwave
  background?

abstract:
  In order to find the correct theory of quantum gravity, one has to look for
observational effects in any candidate theory. Here, we focus on canonical
quantum gravity and calculate the quantum-gravitational contributions to the
anisotropy spectrum of the cosmic microwave background that arise from a
semiclassical approximation to the Wheeler-DeWitt equation. While the resulting
modification of the power spectrum at large scales is too weak to be
observable, we find an upper bound on the energy scale of inflation.


title: On computing higher-order Alexander modules of knots

abstract:
  Cochran defined the nth-order integral Alexander module of a knot in the
three sphere as the first homology group of the knot's (n+1)th-iterated abelian
cover. The case n=0 gives the classical Alexander module (and polynomial).
After a localization, one can get a finitely presented module over a principal
ideal domain, from which one can extract a higher-order Alexander polynomial.
We present an algorithm to compute the first-order Alexander module for any
knot. As applications, we show that these higher-order Alexander polynomials
provide a better bound on the knot genus than does the classical Alexander
polynomial, and that they detect mutation. Included in this algorithm is a
solution to the word problem in finitely presented Z[Z]-modules.


title:
Finite temperature stability and dimensional crossover of exotic
  superfluidity in lattices

abstract:
  We investigate exotic paired states of spin-imbalanced Fermi gases in
anisotropic lattices, tuning the dimension between one and three. We calculate
the finite temperature phase diagram of the system using real-space dynamical
mean-field theory in combination with the quantum Monte Carlo method. We find
that regardless of the intermediate dimensions examined, the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state survives to reach about one third
of the BCS critical temperature of the spin-density balanced case. We show how
the gapless nature of the state found is reflected in the local spectral
function. While the FFLO state is found at a wide range of polarizations at low
temperatures across the dimensional crossover, with increasing temperature we
find out strongly dimensionality-dependent melting characteristics of shell
structures related to harmonic confinement. Moreover, we show that intermediate
dimension can help to stabilize an extremely uniform finite temperature FFLO
state despite the presence of harmonic confinement.


title: a New Conformal Window Bound from the a theorem

abstract:
  We propose a novel constraint on the gauge dynamics of strongly interacting
gauge theories stemming from the a theorem. The inequality we suggest is used
to provide a lower bound on the conformal window of four dimensional gauge
theories.


title:
Frequency Precision of Two-Dimensional Lattices of Coupled Oscillators
  with Spiral Patterns

abstract:
  Two-dimensional lattices of N synchronized oscillators with reactive coupling
are considered as high-precision frequency sources in the case where a spiral
pattern is formed. The improvement of the frequency precision is shown to be
independent of N for large N, unlike the case of purely dissipative coupling
where the improvement is proportional to N, but instead depends on just those
oscillators in the core of the spiral that acts as the source region of the
waves. Our conclusions are based on numerical simulations of up to N=29929
oscillators, and analytic results for a continuum approximation to the lattice
in an infinite system. We derive an expression for the dependence of the
frequency precision on the reactive component of the coupling constant,
depending on a single parameter given by fitting the frequency of the spiral
waves to the numerical simulations.


title: Excluding Source Models with Multiple Astrophysical Observations

abstract:
  We describe a general method to observationally exclude a theoretical model
for gravitational wave (GW) emission from a transient astrophysical source
(event) by using a null detection from a network of GW detectors. In the case
of multiple astrophysical events with no GW detection, statements about
individual events can be combined to increase the exclusion confidence. We
frame and demonstrate the method using a population of hypothetical core
collapse supernovae.


title: A Sample of OB Stars That Formed in the Field

abstract:
  We present a sample of 14 OB stars in the Small Magellanic Cloud that meet
strong criteria for having formed under extremely sparse star-forming
conditions in the field. These stars are a minimum of 28 pc in projection from
other OB stars, and they are centered within symmetric, round HII regions. They
show no evidence of bow shocks, implying that the targets are not transverse
runaway stars. Their radial velocities relative to local HI also indicate that
they are not line-of-sight runaway stars. A friends-of-friends analysis shows
that 9 of the objects present a few low-mass companion stars, with typical mass
ratios for the two highest-mass stars of around 0.1. This further substantiates
that these OB stars formed in place, and that they can and do form in extremely
sparse conditions. This poses strong constraints on theories of star formation
and challenges proposed relations between cluster mass and maximum stellar
mass.


title: The Minimal Automorphism-Free Tree

abstract:
  A finite tree $T$ with $|V(T)| \geq 2$ is called {\it automorphism-free} if
there is no non-trivial automorphism of $T$. Let $\mathcal{AFT}$ be the poset
with the element set of all finite automorphism-free trees (up to graph
isomorphism) ordered by $T_1 \preceq T_2$ if $T_1$ can be obtained from $T_2$
by successively deleting one leaf at a time in such a way that each
intermediate tree is also automorphism-free. In this paper, we prove that
$\mathcal{AFT}$ has a unique minimal element. This result gives an affirmative
answer to the question asked by Rupinski.


title:
The VIRUS-P Exploration of Nearby Galaxies (VENGA): Survey Design, Data
  Processing, and Spectral Analysis Methods

abstract:
  We present the survey design, data reduction, and spectral fitting pipeline
for the VIRUS-P Exploration of Nearby Galaxies (VENGA). VENGA is an integral
field spectroscopic survey, which maps the disks of 30 nearby spiral galaxies.
Targets span a wide range in Hubble type, star formation activity, morphology,
and inclination. The VENGA data-cubes have 5.6'' FWHM spatial resolution, ~5A
FWHM spectral resolution, sample the 3600A-6800A range, and cover large areas
typically sampling galaxies out to ~0.7 R_25. These data-cubes can be used to
produce 2D maps of the star formation rate, dust extinction, electron density,
stellar population parameters, the kinematics and chemical abundances of both
stars and ionized gas, and other physical quantities derived from the fitting
of the stellar spectrum and the measurement of nebular emission lines. To
exemplify our methods and the quality of the data, we present the VENGA
data-cube on the face-on Sc galaxy NGC 628 (a.k.a. M 74). The VENGA
observations of NGC 628 are described, as well as the construction of the
data-cube, our spectral fitting method, and the fitting of the stellar and
ionized gas velocity fields. We also propose a new method to measure the
inclination of nearly face-on systems based on the matching of the stellar and
gas rotation curves using asymmetric drift corrections. VENGA will measure
relevant physical parameters across different environments within these
galaxies, allowing a series of studies on star formation, structure assembly,
stellar populations, chemical evolution, galactic feedback, nuclear activity,
and the properties of the interstellar medium in massive disk galaxies.


title: Hot Electromagnetic Outflows I: Acceleration and Spectra

abstract:
  The theory of cold, relativistic, magnetohydrodynamic outflows is generalized
by the inclusion of an intense radiation source. In some contexts, such the
breakout of a gamma-ray burst jet from a star, the outflow is heated to a high
temperature at a large optical depth. Eventually it becomes transparent and is
pushed to a higher Lorentz factor by a combination of the Lorentz force and
radiation pressure. We obtain its profile, both inside and outside the fast
magnetosonic critical point, when the poloidal magnetic field is radial and
monopolar. Most of the energy flux is carried by the radiation field and the
toroidal magnetic field that is wound up close to the rapidly rotating engine.
Although the entrained matter carries little energy, it couples the radiation
field to the magnetic field. Then the fast critical point is pushed inward from
infinity and, above a critical radiation intensity, the outflow is accelerated
mainly by radiation pressure. We identify a distinct observational signature of
this hybrid outflow: a hardening of the radiation spectrum above the peak of
the seed photon distribution, driven by bulk Compton scattering. The
non-thermal spectrum -- obtained by a Monte Carlo method -- is most extended
when the Lorentz force dominates the acceleration, and the seed photon beam is
wider than the Lorentz cone of the MHD fluid. This effect is a generic feature
of hot, magnetized outflows interacting with slower relativistic material. It
may explain why some GRB spectra appear to peak at photon energies above the
original Amati et al. scaling. A companion paper addresses the case of jet
breakout, where diverging magnetic flux surfaces yield strong MHD acceleration
over a wider range of Lorentz factor.


title: Hot Electromagnetic Outflows II: Jet Breakout

abstract:
  We consider the interaction between radiation, matter and a magnetic field in
a compact, relativistic jet. The entrained matter accelerates outward as the
jet breaks out of a star or other confining medium. In some circumstances, such
as gamma-ray bursts (GRBs), the magnetization of the jet is greatly reduced by
an advected radiation field while the jet is optically thick to scattering.
Where magnetic flux surfaces diverge rapidly, a strong outward Lorentz force
develops and radiation and matter begin to decouple. The increase in
magnetization is coupled to a rapid growth in Lorentz factor. We take two
approaches to this problem. The first examines the flow outside the fast
magnetosonic critical surface, and calculates the flow speed and the angular
distribution of the radiation field over a range of scattering depths. The
second considers the flow structure on both sides of the critical surface in
the optically thin regime, using a relaxation method. In both approaches, we
find how the terminal Lorentz factor, and radial profile of the outflow, depend
on the radiation intensity and optical depth at breakout. The effect of bulk
Compton scattering on the radiation spectrum is calculated by a Monte Carlo
method, while neglecting the effects of internal dissipation. The peak of the
scattered spectrum sits near the seed peak if radiation pressure dominates the
acceleration, but is pushed to a higher frequency if the Lorentz force
dominates, and especially if the seed photon cone is broadened by interaction
with a slower component of the outflow.


title:
Summability of formal solutions of linear partial differential equations
  with divergent initial data

abstract:
  We study the Cauchy problem for a general homogeneous linear partial
differential equation in two complex variables with constant coefficients and
with divergent initial data. We state necessary and sufficient conditions for
the summability of formal power series solutions in terms of properties of
divergent Cauchy data. We consider both the summability in one variable t (with
coefficients belonging to some Banach space of Gevrey series with respect to
the second variable z) and the summability in two variables (t,z). The results
are presented in the general framework of moment-PDEs.


title:
Resonant high energy graviton to photon conversion at post recombination
  epoch

abstract:
  Resonant conversion of high energy gravitons into photons in large scale
cosmological magnetic fields at the post recombination epoch is considered. It
is shown that the probability of the resonance photon production is much higher
than the non-resonant one. As a result an observable isotropic background of
cosmic gamma rays might be created. As shown in our previous paper, an early
population of primordial black holes (PBHs) prior to big bang nucleosynthesis
(BBN) could be an efficient source of high frequency gravitational waves. For
the primordial black hole mass about $10^8$ g the produced photons would be the
dominant component of the soft to hard Cosmic X-ray Background (CXB) and for
lower masses the spectrum is shifted down to the ultraviolet and optic.


title:
Mixed-State Effect on the Low-Energy Spin Dynamics in Optimally-doped
  Iron Pnictide Superconductors

abstract:
  Based on a phenomenological model with $s_{\pm}$ or s-wave pairing symmetry,
the mixed-state effect on the low-energy spin dynamics in optimally-doped iron
pnictide superconductors is studied by solving Bogoliubov-de Gennes equations.
Our results of the spin susceptibility at $\mathbf{q}=\mathbf{Q}$ in the
normal, superconducting and mixed states agree qualitatively with recent
neutron scattering experiments. We also propose that the field-induced
intensity change shows different behaviors between the $s_{\pm}$ and s-wave
symmetries in both momentum and real space, thus it can be used to distinguish
these two pairing symmetries.


title: Subleading Corrections To Thrust Using Effective Field Theory

abstract:
  We calculate the subleading corrections to the thrust rate using
Soft-Collinear Effective Theory to factorize the rate and match onto jet and
soft operators that describe the degrees of freedom of the relevant scales. We
work in the perturbative regime where all the scales are well above
\Lambda_QCD. The thrust rate involves an incomplete sum over final states that
is enforced by a measurement operator. Subleading corrections require matching
onto not only the higher dimensional dijet operators, but also matching onto
subleading measurement operators in the effective theory. We explicitly show
how to factorize the O(\alpha_s \tau) thrust rate into a hard function
multiplied by the convolution of the vacuum expectation value of jet and soft
operators. Our approach can be generalized to other jet shapes and rates.


title: On Resilient Graph Spanners

abstract:
  We introduce and investigate a new notion of resilience in graph spanners.
Let $S$ be a spanner of a graph $G$. Roughly speaking, we say that a spanner
$S$ is resilient if all its point-to-point distances are resilient to edge
failures. Namely, whenever any edge in $G$ fails, then as a consequence of this
failure all distances do not degrade in $S$ substantially more than in $G$
(i.e., the relative distance increases in $S$ are very close to those in the
underlying graph $G$). In this paper we show that sparse resilient spanners
exist, and that they can be computed efficiently.


title: On growth of random groups of intermediate growth

abstract:
  We study the growth of typical groups from the family of $p$-groups of
intermediate growth constructed by the second author. We find that, in the
sense of category, a generic group exhibits oscillating growth with no
universal upper bound. At the same time, from a measure-theoretic point of view
(i.e., almost surely relative to an appropriately chosen probability measure),
the growth function is bounded by $e^{n^\alpha}$ for some $\alpha<1$.


title:
Queuing Theoretic Analysis of Power-performance Tradeoff in
  Power-efficient Computing

abstract:
  In this paper we study the power-performance relationship of power-efficient
computing from a queuing theoretic perspective. We investigate the interplay of
several system operations including processing speed, system on/off decisions,
and server farm size. We identify that there are oftentimes "sweet spots" in
power-efficient operations: there exist optimal combinations of processing
speed and system settings that maximize power efficiency. For the single server
case, a widely deployed threshold mechanism is studied. We show that there
exist optimal processing speed and threshold value pairs that minimize the
power consumption. This holds for the threshold mechanism with job batching.
For the multi-server case, it is shown that there exist best processing speed
and server farm size combinations.


title:
Numerical simulation of ejected molten metal-nanoparticles liquefied by
  laser irradiation: Interplay of geometry and dewetting

abstract:
  Metallic nanoparticles, liquefied by fast laser irradiation, go through a
rapid change of shape attempting to minimize their surface energy. The
resulting nanodrops may be ejected from the substrate when the mechanisms
leading to dewetting are sufficiently strong, as in the experiments involving
gold nanoparticles [Habenicht et al., Science 309, 2043 (2005)]. We use a
direct continuum-level approach to accurately model the process of liquid
nanodrop formation and the subsequent ejection from the substrate. Our
computations show a significant role of inertial effects and an elaborate
interplay of initial geometry and wetting properties: e.g., we can control the
direction of ejection by prescribing appropriate initial shape and/or wetting
properties. The basic insight regarding ejection itself can be reached by
considering a simple effective model based on an energy balance. We validate
our computations by comparing directly with the experiments specified above
involving the length scales measured in hundreds of nanometers, and with
molecular dynamics simulations on much shorter scales measured in tens of
atomic diameters, as in [M. Fuentes-Cabrera et al., Phys. Rev. E 83, 041603
(2011)]. The quantitative agreement, in addition to illustrating how to
controlling particle ejection, shows utility of continuum-based simulation in
describing dynamics on nanoscale quantitatively, even in a complex setting as
considered here.


title: Annihilation rate of $2^{-+}$ charmonium and bottomonium

abstract:
  The $1^1D_2 (c\bar c)$ state is the ground state of spin-singlet D-wave
charmonia. Although it has not been found yet, the experimental data accumulate
rapidly. This charmonium attracts more and more attention, especially when the
BaBar Collaboration finds that the X(3872) particle has negative parity. In
this paper we calculate the double-gamma and double-gluon annihilation
processes of $^1D_2$ charmonia and bottomonia by using the instantaneous
Bethe-Salpeter method. We find the relativistic corrections make the decay
widths of $1^1D_2 (c\bar c)$ 2$\sim$5 times smaller than the non-relativistic
results. If this state is below the $D^0{D^{0}}^\ast$ threshold, we can use the
sum of annihilation widths and EM transition widths to estimate the total decay
width. Our result for $1{^1D_2} (c\bar c)$ with $m=3820$ GeV is $\Gamma= 432$
keV. The dominant decay channel $1^1D_2 (c\bar c)\to h_c \gamma$, whose
branching ratio is about 90%, can be used to discover this state.


title: The HAWC observatory as a GRB detector

abstract:
  The High Altitude Water Cherenkov Observatory (HAWC) is an air shower array
currently under construction in Mexico at an altitude of 4100 m. HAWC will
consist of 300 large water tanks covering an area of about 22000 square meters
and instrumented with 4 photomultipliers each. The experimental design allows
for highly efficient detection of photon-induced air showers in the TeV and
sub-TeV range and gamma-hadron separation. We show that HAWC has a reasonable
chance to observe the high-energy power law components of GRBs that extend to
50 GeV. In particular, HAWC will be capable of observing events similar to GRB
090510 and GRB 090902B. The observations (or non-observations) of GRBs by HAWC
will provide information on the high-energy spectra of GRBs. An engineering
array consisting of 6 water tanks was operated at the HAWC site since September
2011, collecting 3 months of data. An upper limit on high energy emission from
GRB 111016B is derived from these data.


title:
SN 2009js at the crossroads between normal and subluminous Type IIP
  supernovae: optical and mid-infrared evolution

abstract:
  We present a study of SN 2009js in NGC 918. Multi-band Kanata optical
photometry covering the first ~120 days show the source to be a Type IIP SN.
Reddening is dominated by that due to our Galaxy. One-year-post-explosion
photometry with the NTT, and a Subaru optical spectrum 16 days post-discovery,
both imply a good match with the well-studied subluminous SN 2005cs. The
plateau phase luminosity of SN 2009js and its plateau duration are more similar
to the intermediate luminosity IIP SN 2008in. Thus, SN 2009js shares
characteristics with both subluminous and intermediate luminosity SNe. Its
radioactive tail luminosity lies between SN 2005cs and SN 2008in, whereas its
quasi-bolometric luminosity decline from peak to plateau (quantified by a
newly-defined parameter Delta[logL] measuring adiabatic cooling following shock
breakout) is much smaller than both the others. We estimate the ejected mass of
56Ni to be low (~0.007 Msun). The SN explosion energy appears to have been
small, similar to SN 2005cs. SN 2009js is the first subluminous SN IIP to be
studied in the mid-infrared. It was serendipitously caught by Spitzer at very
early times. In addition, it was detected by WISE 105 days later with a
significant 4.6 micron flux excess above the photosphere. The infrared excess
luminosity relative to the photosphere is clearly smaller than that of SN
2004dj extensively studied in the mid-infrared. The excess may be tentatively
assigned to heated dust with mass ~3e-5 Msun, or to CO fundamental emission as
a precursor to dust formation.


title:
Topological Defects, Surface Geometry and Cohesive Energy of Twisted
  Filament Bundles

abstract:
  Cohesive assemblies of filaments are a common structural motif found in
diverse contexts, ranging from biological materials such as fibrous proteins,
to artificial materials such as carbon nanotube ropes and micropatterned
filament arrays. In this paper, we analyze the complex dependence of cohesive
energy on twist, a key structural parameter of both self-assembled and
fabricated filament bundles. Based on the analysis of simulated ground states
of cohesive bundles, we show that the non-linear influence of twist derives
from two distinct geometric features of twisted bundles: (i) the geometrical
frustration of inter-filament packing in the bundle cross-section; and (ii) the
evolution of the surface geometry of bundles with twist, which dictates the
cohesive cost of non-contacting filaments at the surface. Packing frustration
in the bundle core gives rise to the appearance of a universal sequence of
topological defects, excess 5-fold disclinations, with increasing twist, while
the evolution of filament contact at the surface of the bundle generically
favors twisted geometries for sufficiently long filaments. Our analysis of both
continuum and discrete models of filament bundles shows that, even in the
absence of external torque or intrinsic chirality, cohesive energy universally
favors twisted ground states above a critical (length/radius) aspect ratio and
below a critical filament stiffness threshold.


title:
Global stability and local bifurcations in a two-fluid model for tokamak
  plasma

abstract:
  We study a two-fluid description of high and low temperature components of
the electron velocity distribution of an idealized tokamak plasma. We refine
previous results on the laminar steady-state solution. On the one hand, we
prove global stability outside a parameter set of possible linear instability.
On the other hand, for a large set of parameters, we prove the primary
instabilities for varying temperature difference stem from the lowest spatial
harmonics. We moreover show that any codimension-one bifurcation is a
supercritical Andronov-Hopf bifurcation, which yields stable periodic solutions
in the form of traveling waves. In the degenerate case, where the instability
region in the temperature difference is a point, we prove that the bifurcating
periodic orbits form an arc of stable periodic solutions. We provide numerical
simulations to illustrate and corroborate our analysis. These also suggest that
the stable periodic orbit, which bifurcated from the steady-state, undergoes
additional bifurcations.


title: Big Heegner point Kolyvagin system for a family of modular forms

abstract:
  The principal goal of this paper is to develop Kolyvagin's descent to apply
with the big Heegner point Euler system constructed by Howard for the big
Galois representation $\mathbb{T}$ attached to a Hida family $\mathbb{F}$ of
elliptic modular forms. In order to achieve this, we interpolate and control
the Tamagawa factors attached to each member of the family $\mathbb{F}$ at bad
primes, which should be of independent interest. Using this, we then work out
the Kolyvagin descent on the big Heegner point Euler system so as to obtain a
big Kolyvagin system that interpolates the collection of Kolyvagin systems
obtained by Fouquet for each member of the family individually. This
construction has standard applications to Iwasawa theory, which we record at
the end.


title: Divergence of the Thermal Conductivity in Uniaxially Strained Graphene

abstract:
  We investigate the effect of strain and isotopic disorder on thermal
transport in suspended graphene by equilibrium molecular dynamics simulations.
We show that the thermal conductivity of unstrained graphene, calculated from
the fluctuations of the heat current at equilibrium is finite and converges
with size at finite temperature. In contrast, the thermal conductivity of
strained graphene diverges logarithmically with the size of the models, when
strain exceeds a relatively large threshold value of 2%. An analysis of phonon
populations and lifetimes explains the divergence of the thermal conductivity
as a consequence of changes in the occupation of low-frequency out-of-plane
phonons and an increase in their lifetimes due to strain.


title:
Localized Many-Particle Majorana Modes with Vanishing Time-Reversal
  Symmetry Breaking in Double Quantum Dots

abstract:
  We introduce the concept of spinful many-particle Majorana modes with local
odd operator products, thereby preserving their local statistics. We consider a
superconductor-double-quantum-dot system where these modes can arise with
negligible Zeeman splitting when Coulomb interactions are present. We find a
reverse Mott-insulator transition, where the even- and odd-parity bands become
degenerate. Above this transition, Majorana operators move the system between
the odd-parity ground state, associated with elastic cotunneling, and the
even-parity ground state, associated with crossed Andreev reflection. These
Majorana modes are described in terms of one, three, and five operator
products. Parity conservation results in a 4% periodic supercurrent in the even
state and no supercurrent in the odd state.


title:
Reduced-rank Adaptive Constrained Constant Modulus Beamforming
  Algorithms based on Joint Iterative Optimization of Filters

abstract:
  This paper proposes a reduced-rank scheme for adaptive beamforming based on
the constrained joint iterative optimization of filters. We employ this scheme
to devise two novel reduced-rank adaptive algorithms according to the constant
modulus (CM) criterion with different constraints. The first devised algorithm
is formulated as a constrained joint iterative optimization of a projection
matrix and a reduced-rank filter with respect to the CM criterion subject to a
constraint on the array response. The constrained constant modulus (CCM)
expressions for the projection matrix and the reduced-rank weight vector are
derived, and a low-complexity adaptive algorithm is presented to jointly
estimate them for implementation. The second proposed algorithm is extended
from the first one and implemented according to the CM criterion subject to a
constraint on the array response and an orthogonal constraint on the projection
matrix. The Gram-Schmidt (GS) technique is employed to achieve this orthogonal
constraint and improve the performance. Simulation results are given to show
superior performance of the proposed algorithms in comparison with existing
methods.


title: Structural and vibrational properties of phenanthrene under pressure

abstract:
  The structural and vibrational properties of phenanthrene are measured at
high pressures up to 30.2 GPa by Raman spectroscopy and synchrotron x-ray
diffraction techniques. Two phase transitions are observed in raman spectra
under pressures of 2.3 GPa and 5.4 GPa with significant changes of
intermolecular and intramolecular vibrational modes, and all the raman peaks
disappeared in the luminesce background above 10.2 GPa. Upon further
compression above 20.0 GPa, three broad bands are observed respectively around
1600, 2993 and 3181 cm$^{-1}$ in Raman spectra, strongly indicating that
phenanthrene has transformed into amorphous hydrogenated carbon. Based on x-ray
diffraction, the structures of corresponding phases observed in Raman spectra
are identified with space group of $P_{\rm}2_{1}$ for phase I at 0-2.2 GPa,
$P_{\rm}$2/\emph{m} for phase II at 2.2-5.6 GPa and
$P_{\rm}$2/\emph{m}+\emph{Pmmm} for phase III at 5.6-11.4 GPa, and the
structure above 11.4 GPa is identified with space group of \emph{Pmmm}.
Although phenanthrene has amorphized above 20.0 GPa, the amorphous hydrogenated
carbon clusters still remain the crystalline characteristic based on x-ray
diffraction patterns. Our results suggest that the long-range periodicity and
the local disorder state coexist in phenanthrene at high pressures.


title:
Magnetography of Solar Flaring Loops with Microwave Imaging
  Spectropolarimetry

abstract:
  We have developed a general framework for modeling gyrosynchrotron and
free-free emission from solar flaring loops and used it to test the premise
that 2D maps of source parameters, particularly magnetic field, can be deduced
from spatially resolved microwave spectropolarimetry data. In this paper we
show quantitative results for a flaring loop with a realistic magnetic
geometry, derived from a magnetic field extrapolation, and containing an
electron distribution with typical thermal and nonthermal parameters, after
folding through the instrumental profile of a realistic interferometric array.
We compare the parameters generated from forward fitting a homogeneous source
model to each line of sight through the folded image data cube with both the
original parameters used in the model and with parameters generated from
forward fitting a homogeneous source model to the original (unfolded) image
data cube. We find excellent agreement in general, but with systematic effects
that can be understood as due to finite resolution in the folded images and the
variation of parameters along the line of sight, which are ignored in the
homogeneous source model. We discuss the use of such 2D parameter maps within a
larger framework of 3D modeling, and the prospects for applying these methods
to data from a new generation of multifrequency radio arrays now or soon to be
available.


title:
Observational constraints from SNe Ia and Gamma-Ray Bursts on a clumpy
  universe

abstract:
  The luminosity distance describing the effect of local inhomogeneities in the
propagation of light proposed by Zeldovich-Kantowski-Dyer-Roeder (ZKDR) is
tested with two probes for two distinct ranges of redshifts: supernovae Ia (SNe
Ia) in 0.015 < z < 1.414 and gamma-ray bursts (GRBs) in 1.547 < z < 3.57. Our
analysis is performed by a Markov Chain Monte Carlo (MCMC) code that allows us
to constrain the matter density parameter \Omega_m as well as the smoothness
parameter $\alpha$ that measures the inhomogeneous-homogeneous rate of the
cosmic fluid in a flat \LambdaCDM model. The obtained best fits are
(\Omega_m=0.285^{+0.019}_{-0.018}, \alpha= 0.856^{+0.106}_{-0.176}) from SNe Ia
and (\Omega_m=0.259^{+0.028}_{-0.028}, \alpha=0.587^{+0.201}_{-0.202}) from
GRBs, while from the joint analysis the best fits are
(\Omega_m=0.284^{+0.021}_{-0.020}, \alpha= 0.685^{+0.164}_{-0.171}) with a
\chi^2_{\rm red}=0.975. The value of the smoothness parameter $\alpha$
indicates a clumped universe however it does not have an impact on the amount
of dark energy (cosmological constant) needed to fit observations. This result
may be an indication that the Dyer-Roeder approximation does not describe in a
precise form the effects of clumpiness in the expansion of the universe.


title: A unified approach to Fierz identities

abstract:
  We summarize a unified and computationally efficient treatment of Fierz
identities for form-valued pinor bilinears in various dimensions and
signatures, using concepts and techniques borrowed from a certain approach to
spinors known as geometric algebra. Our formulation displays the real, complex
and quaternionic structures in a conceptually clear manner, which is moreover
amenable to implementation in various symbolic computation systems.


title:
Lyman continuum leaking galaxies - Search strategies and local
  candidates

abstract:
  Star-forming dwarf galaxies leaking Lyman-continuum (LyC) radiation may have
played an important role in the reionization of the Universe. Local galaxies
exhibiting LyC leakage could shed light on the escape mechanisms, but so far
only two such cases have been identified. Here we want to investigate whether
the lack of local LyC emitters can be caused in part by biased selection
criteria (e.g. strong H-alpha emission), and we present a novel method of
selecting targets with high escape fractions. By applying these criteria, we
assemble a sample of observation targets to study their basic properties.
  We introduce a new strategy where potential LyC leakers are selected by their
blue colours and weak (instead of strong) emission lines. We take a closer look
at 8 LyC leaking candidates at z ~ 0.03, selected from the Sloan Digital Sky
Survey (SDSS), which we observe with ESO/NTT in broadband B and H-alpha. We
find that 7 of the 8 galaxies are involved in interaction with neighbours or
show signs of mergers. In 7 cases the young stellar population is clearly
displaced from the main body of the galaxies. Half of our targets show
absorption spectra with post-starburst signatures. The scale lengths in H-alpha
are typically 30% smaller than those of the stellar continua, indicating ram
pressure stripping. We tentatively identify a few conditions favourable for
leakage: 1) the combined effects of ram pressure stripping with supernova winds
from young stars formed in the front, 2) merger events that increase the star
formation rate and displace stars from gas, 3) starbursts in the centres of
post-starburst galaxies, and 4) a low dust content.


title:
On a real analogue of Bezout inequality and the number of connected
  components of sign conditions

abstract:
  Let $\mathrm{R}$ be a real closed field and $Q_1, \ldots, Q_{\ell} \in
\mathrm{R}[X_1, \ldots,X_k]$ such that for each $i, 1 \leq i \leq \ell$,
$\mathrm{deg} (Q_i) \leq d_i$. For $1 \leq i \leq \ell$, denote by
$\mathcal{Q}_i = \{Q_1, \ldots, Q_i \}$, $V_i$ the real variety defined by
$\mathcal{Q}_i$, and $k_i$ an upper bound on the real dimension of $V_i$ (by
convention $V_0 = \mathrm{R}^k$ and $k_0 = k$). Suppose also that \[ 2 \leq d_1
\leq d_2 \leq \frac{1}{k + 1} d_3 \leq \frac{1}{(k + 1)^2} d_4 \leq \cdots \leq
\frac{1}{(k + 1)^{\ell - 3}} d_{\ell - 1} \leq \frac{1}{(k + 1)^{\ell - 2}}
d_{\ell}, \] and that $\ell \leq k$. We prove that the number of
semi-algebraically connected components of $V_{\ell}$ is bounded by \[ O (k)^{2
k} \left(\prod_{1 \leq j < \ell} d_j^{k_{j - 1} - k_j} \right)
d_{\ell}^{k_{\ell - 1}}. \] This bound can be seen as a weak extension of the
classical Bezout inequality (which holds only over algebraically closed fields
and is false over real closed fields) to varieties defined over real closed
fields. Additionally, if $\mathcal{P} \subset \mathrm{R}[X_1, \ldots, X_k]$ is
a finite family of polynomials with $\mathrm{deg} (P) \leq d$ for all $P \in
\mathcal{P}$, $\mathrm{card}( \mathcal{P}) = s$, and $d_{\ell} \leq \frac{1}{k
+ 1} d$, we prove that the number of semi-algebraically connected components of
the realizations of all realizable sign conditions of the family $\mathcal{P}$
restricted to $V_{\ell}$ is bounded by \[ O (k)^{2 k} (s d)^{k_{\ell}}
\left(\prod_{1 \leq j \leq \ell} d_j^{k_{j - 1} - k_j} \right). \]


title: Spaces of quasi-exponentials and representations of the Yangian Y(gl_N)

abstract:
  We consider a tensor product $V(b)= \otimes_{i=1}^n\C^N(b_i)$ of the Yangian
$Y(gl_N)$ evaluation vector representations. We consider the action of the
commutative Bethe subalgebra $B^q \subset Y(gl_N)$ on a $gl_N$-weight subspace
$V(b)_\lambda \subset V(b)$ of weight $\lambda$. Here the Bethe algebra depends
on the parameters $q=(q_1,...,q_N)$. We identify the $B^q$-module
$V(b)_\lambda$ with the regular representation of the algebra of functions on a
fiber of a suitable discrete Wronski map. If $q=(1,...,1)$, we study the action
of $B^{q=1}$ on a space $V(b)^{sing}_\lambda$ of singular vectors of a certain
weight. Again, we identify the $B^{q=1}$-module $V(b)^{sing}_\lambda$ with the
regular representation of the algebra of functions on a fiber of another
suitable discrete Wronski map.
  These results we announced earlier in relation with a description of the
quantum equivariant cohomology of the cotangent bundle of a partial flag
variety and a description of commutative subalgebras of the group algebra of a
symmetric group.


title: Algorithmic construction of Hurwitz maps

abstract:
  We describe an algorithm that, given a k-tuple of permutations representing
the monodromy of a rational map, constructs an arbitrarily precise
floating-point complex approximation of that map.
  We then explain how it has been used to study a problem in dynamical systems
raised by Cui.


title:
Spin and Orbital Splitting in Ferromagnetic Contacted Single Wall Carbon
  Nanotube Devices

abstract:
  We observed the coulomb blockade phenomena in ferromagnetic contacting single
wall semiconducting carbon nanotube devices. No obvious Coulomb peaks shift was
observed with existing only the Zeeman splitting at 4K. Combining with other
effects, the ferromagnetic leads prevent the orbital spin states splitting with
magnetic field up to 2 Tesla at 4K. With increasing magnetic field further,
both positive or negative coulomb peaks shift slopes are observed associating
with clockwise and anticlockwise orbital state splitting. The strongly
suppressed/enhanced of the conductance has been observed associating with the
magnetic field induced orbital states splitting/converging.


title: Empirical evidence for a double step climate change in twentieth century

abstract:
  In this study we used the sea surface temperature (SST), El-Nino southern
oscillation (ENSO) and Pacific decadal oscillation (PDO) time-series for the
time period 1900-2012 in order to investigate plausible manifestation of sharp
increases in temperature.
  It was found that the widely observed warming in the past century did not
occur smoothly but sharply. This fact is more pronounced at the latitude zone
30S - 60N during the years 1925/1926 and 1987/1988. We hypothesise that there
were two major climate regime shifts in 1925/1926 and 1987/1988 years. During
these shifts the mean value of temperature rises, over which natural
variability associated with ENSO, PDO and other factors occurs. During each
sharp increase mean SST in tropics/north middle latitudes increased by about
0.28/0.36 {\deg}C. Most of other temperature anomalies are explained by ENSO
and PDO. The existence of these shifts tends to be masked by natural
variability.
  This hypothesis has allowed us to develop very simple linear regression
models which explain the main features of temperature anomalies from 30oS to
60oN observed in the past century. Additionally, two remarkable outcomes
revealed from this analysis. The first one is that linear regression
coefficients can be calculated by employing a limited length of the temperature
time-series (e.g., from 1910 till 1940) and reproduce quite well the whole
time-series from 1900 up to now. The second one is that a good quality of
reproduction is achieved by using only two factors (ENSO/PDO and sharp changes
for tropics/northern middle altitudes).


title:
Complete monotonicity of a difference between the exponential and
  trigamma functions

abstract:
  In the paper, by directly verifying an inequality which gives a lower bound
for the first order modified Bessel function of the first kind, the authors
supply a new proof for the complete monotonicity of a difference between the
exponential function $e^{1/t}$ and the trigamma function $\psi'(t)$ on
$(0,\infty)$.


title:
Black Hole Spin via Continuum Fitting and the Role of Spin in Powering
  Transient Jets

abstract:
  The spins of ten stellar black holes have been measured using the
continuum-fitting method. These black holes are located in two distinct classes
of X-ray binary systems, one that is persistently X-ray bright and another that
is transient. Both the persistent and transient black holes remain for long
periods in a state where their spectra are dominated by a thermal accretion
disk component. The spin of a black hole of known mass and distance can be
measured by fitting this thermal continuum spectrum to the thin-disk model of
Novikov and Thorne; the key fit parameter is the radius of the inner edge of
the black hole's accretion disk. Strong observational and theoretical evidence
links the inner-disk radius to the radius of the innermost stable circular
orbit, which is trivially related to the dimensionless spin parameter a_* of
the black hole (|a_*| < 1). The ten spins that have so far been measured by
this continuum-fitting method range widely from a_* \approx 0 to a_* > 0.95.
The robustness of the method is demonstrated by the dozens or hundreds of
independent and consistent measurements of spin that have been obtained for
several black holes, and through careful consideration of many sources of
systematic error. Among the results discussed is a dichotomy between the
transient and persistent black holes; the latter have higher spins and larger
masses. Also discussed is recently discovered evidence in the transient sources
for a correlation between the power of ballistic jets and black hole spin.


title: Conciseness of coprime commutators in finite groups

abstract:
  Let $G$ be a finite group. We show that the order of the subgroup generated
by coprime $\gamma_k$-commutators (respectively $\delta_k$-commutators) is
bounded in terms of the size of the set of coprime $\gamma_k$-commutators
(respectively $\delta_k$-commutators). This is in parallel with the classical
theorem due to Turner-Smith that the words $\gamma_k$ and $\delta_k$ are
concise.


title: Computing Similarity between a Pair of Trajectories

abstract:
  With recent advances in sensing and tracking technology, trajectory data is
becoming increasingly pervasive and analysis of trajectory data is becoming
exceedingly important. A fundamental problem in analyzing trajectory data is
that of identifying common patterns between pairs or among groups of
trajectories. In this paper, we consider the problem of identifying similar
portions between a pair of trajectories, each observed as a sequence of points
sampled from it.
  We present new measures of trajectory similarity --- both local and global
--- between a pair of trajectories to distinguish between similar and
dissimilar portions. Our model is robust under noise and outliers, it does not
make any assumptions on the sampling rates on either trajectory, and it works
even if they are partially observed. Additionally, the model also yields a
scalar similarity score which can be used to rank multiple pairs of
trajectories according to similarity, e.g. in clustering applications. We also
present efficient algorithms for computing the similarity under our measures;
the worst-case running time is quadratic in the number of sample points.
  Finally, we present an extensive experimental study evaluating the
effectiveness of our approach on real datasets, comparing with it with earlier
approaches, and illustrating many issues that arise in trajectory data. Our
experiments show that our approach is highly accurate in distinguishing similar
and dissimilar portions as compared to earlier methods even with sparse
sampling.


title:
Emergent Exclusion Statistics of Fibonacci Anyons in 2D Topological
  Phases

abstract:
  We demonstrate how the generalized Pauli exclusion principle emerges for
quasiparticle excitations in 2d topological phases. As an example, we examine
the Levin-Wen model with the Fibonacci data (specified in the text), and
construct the number operator for fluxons living on plaquettes. By numerically
counting the many-body states with fluxon number fixed, the matrix of exclusion
statistics parameters is identified and is shown to depend on the spatial
topology (sphere or torus) of the system. Our work reveals the structure of the
(many-body) Hilbert space and some general features of thermodynamics for
quasiparticle excitations in topological matter.


title: Quantum critical metals in $d=3+1$

abstract:
  We study the problem of disorder-free metals near a continuous Ising nematic
quantum critical point in $d=3+1$ dimensions. We begin with perturbation theory
in the `Yukawa' coupling between the electrons and undamped bosons (nematic
order parameter fluctuations) and show that the perturbation expansion breaks
down below energy scales where the bosons get substantially Landau damped.
Above this scale however, we find a regime in which low-energy fermions obtain
an imaginary self-energy that varies linearly with frequency, realizing the
`marginal Fermi liquid' phenomenology\cite{Varma}. We discuss a large N theory
in which the marginal Fermi liquid behavior is enhanced while the role of
Landau damping is suppressed, and show that quasiparticles obtain a decay rate
parametrically larger than their energy.


title: Translation of an article by Paul Drude in 1904

abstract:
  English translation of P. Drude, Annalen der Physik 13, 512 (1904), an
article by Paul Drude about Tesla transformers and wireless telegraphy.
Includes a discussion of the derivation of an equivalent circuit and the
prediction of nonreciprocal mutual inductance for Tesla transformers in the
article, which is supplementary material for B. McGuyer, PLoS ONE 9, e115397
(2014).


title: Minimum requirements for feedback enhanced force sensing

abstract:
  The problem of estimating an unknown force driving a linear oscillator is
revisited. When using linear measurement, feedback is often cited as a
mechanism to enhance bandwidth or sensitivity. We show that as long as the
oscillator dynamics are known, there exists a real-time estimation strategy
that reproduces the same measurement record as any arbitrary feedback protocol.
Consequently some form of nonlinearity is required to gain any advantage beyond
estimation alone. This result holds true in both quantum and classical systems,
with non-stationary forces and feedback, and in the general case of
non-Gaussian and correlated noise. Recently, feedback enhanced incoherent force
sensing has been demonstrated [Nat. Nano. \textbf{7}, 509 (2012)], with the
enhancement attributed to a feedback induced modification of the mechanical
susceptibility. As a proof-of-principle we experimentally reproduce this result
through straightforward filtering.