title:
Kitaev-Heisenberg model in a magnetic field: order-by-disorder and
  commensurate-incommensurate transitions

abstract:
  We present a theoretical study of field-induced magnetic phases in the
honeycomb Kitaev-Heisenberg model, which is believed to describe the essential
physics of Mott insulators with strong spin-orbit coupling such as $A_2$IrO$_3$
and $\alpha$-RuCl$_3$. We obtain a finite temperature phase diagram based on
extensive Monte Carlo simulations and analytical calculations. We show that,
while Zeeman coupling favors a symmetric non-coplanar magnetic order, thermal
fluctuations enhances the stability of a collinear zigzag phase that breaks the
rotational symmetry of the lattice. Our large-scale simulations also uncover
intriguing commensurate-incommensurate transitions and multiple-$\mathbf Q$
incommensurate phases at high field. Experimental implications are also
discussed.


title: A numerical relativity scheme for cosmological simulations

abstract:
  Cosmological simulations involving the fully covariant gravitational dynamics
may prove relevant in understanding relativistic/non-linear features and,
therefore, in taking better advantage of the upcoming large scale structure
survey data. We propose a new 3+1 integration scheme for General Relativity in
the case where the matter sector contains a minimally-coupled perfect fluid
field. The original feature is that we completely eliminate the fluid
components through the constraint equations, thus remaining with a set of
unconstrained evolution equations for the rest of the fields. This procedure
does not constrain the lapse function and shift vector, so it holds in
arbitrary gauge and also works for arbitrary equation of state. An important
advantage of this scheme is that it allows one to define and pass an adaptation
of the robustness test to the cosmological context, at least in the case of
pressureless perfect fluid matter, which is the relevant one for late-time
cosmology.


title:
Is there solid-on-solid contact in a sphere-wall collision in a viscous
  fluid?

abstract:
  We study experimentally the collision between a sphere falling through a
viscous fluid, and a solid plate below. It is known that there is a
well-defined threshold Stokes number above which the sphere rebounds from such
a collision. Our experiment tests for direct contact between the colliding
bodies, and contrary to prior theoretical predictions, shows that
solid-on-solid contact occurs even for Stokes numbers just above the threshold
for rebounding. The dissipation is fluid-dominated, though details of the
contact mechanics depend on the surface and bulk properties of the solids. Our
experiments and a model calculation indicate that mechanical contact between
the two colliding objects is generic and will occur for any realistic surface
roughness.


title: Bonferroni-based gatekeeping procedure with retesting option

abstract:
  In complex clinical trials, multiple research objectives are often grouped
into sets of objectives based on their inherent hierarchical relationships.
Consequently, the hypotheses formulated to address these objectives are grouped
into ordered families of hypotheses and thus to be tested in a pre-defined
sequence. In this paper, we introduce a novel Bonferroni based multiple testing
procedure for testing hierarchically ordered families of hypotheses. The
proposed procedure allows the families to be sequentially tested more than once
with updated local critical values. It is proved to control the global
familywise error rate strongly under arbitrary dependence. Implementation of
the procedure is illustrated using two examples. Finally, the procedure is
extended to testing multiple families of hypotheses with a complex two-layer
hierarchical structure.


title: SOL width and intermittent fluctuations in KSTAR

abstract:
  Radial profiles of the ion saturation current and its fluctuation statistics
are presented from probe measurements in L-mode, neutral beam heated plasmas at
the outboard mid-plane region of KSTAR. The familiar two-layer structure, seen
elsewhere in tokamak L-mode discharges, with a steep near-SOL profile and a
broad far-SOL profile, is observed. The profile scale length in the far-SOL
increases drastically with line-averaged density, thereby enhancing plasma
interactions with the main chamber walls. Time series from the far-SOL region
are characterised by large-amplitude bursts attributed to the radial motion of
blob-like plasma filaments. Analysis of a data time series of several seconds
duration under stationary plasma conditions reveals the statistical properties
of these fluctuations, including the rate of level crossings and the average
duration of periods spent above a given threshold level. This is shown to be in
excellent agreement with predictions of a stochastic model, giving novel
predictions of plasma-wall interactions due to transient transport events.


title: Measurement of Anticipative Power of a Retina by Predictive Information

abstract:
  The predictive properties of a retina are studied by measuring the mutual
information (MI) between its stimulation and the corresponding firing rates
while it is being probed by a train of short pulses with stochastic intervals.
Features of the measured MI at various time shifts between the stimulation and
the response are used to characterize the predictive properties of the retina.
By varying the statistical properties of the pulse train, our experiments show
that a retina has the ability to predict future events of the stimulation if
the information rate of the stimulation is low enough. Also, this predictive
property of the retina occurs at a time scale similar to the well established
anticipative phenomenon of omitted stimulus response in a retina. Furthermore,
a retina can make use of its predictive ability to distinguish between time
series created by an Ornstein--Uhlenbeck and a hidden Markovian process.


title: On cycle decompositions in Coxeter groups

abstract:
  The aim of this note is to show that the cycle decomposition of elements of
the symmetric group admits a quite natural formulation in the framework of dual
Coxeter theory, yielding a generalization of it to the family of so-called
parabolic quasi-Coxeter elements of Coxeter groups (in the symmetric group
every element is a parabolic quasi-Coxeter element). We show that such an
element admits an analogue of the cycle decomposition. Elements which are not
in this family still admit a generalized cycle decomposition, but it is not
unique in general.


title:
An open quantum system approach to complementarity in neutral kaon
  interferometry

abstract:
  In bipartite quantum systems, entanglement correlations between the parties
exerts direct influence in the phenomenon of wave-particle duality. This effect
has been quantitatively analyzed in the context of two qubits by M. Jakob and
J. Bergou [Optics Communications 283(5) (2010) 827]. Employing a description of
the $K$-meson propagation in free space where its weak decay states are
included as a second party, we study here this effect in the kaon-antikaon
oscillations. We show that a new quantitative "triality" relation holds,
similar to the one considered by Jakob and Bergou. In our case, it relates the
distinguishability between the decay products states corresponding to the
distinct kaon propagation modes $K_S $, $K_L $, the amount of wave-like path
interference between these states, and the amount of entanglement given by the
reduced von Neumann entropy. The inequality can account for the complementarity
between strangeness oscillations and lifetime information previously considered
in the literature, therefore allowing one to see how it is affected by
entanglement correlations. As we will discuss, it allows one to visualize
clearly through the $K^{0}$$\overline{K}\,^{0}$ oscillations the fundamental
role of entanglement in quantum complementarity.


title: What do we learn from computer simulations of Bell experiments?

abstract:
  Contrary to counterfactual definiteness quantum theory teaches us that
measuring instruments are not passively reading predetermined values of
physical observables. Counterfactual definiteness allows proving Bell
inequalities. If the contextual character of quantum measurements is correctly
taken into account the proofs of these inequalities may not be done. In recent
computer simulations of idealized Bell experiment predetermined successive
outcomes of measurements for each setting and predetermined time delays of
their registrations are calculated. Time windows and time delays are used to
select various samples. Correlations, estimated using these selected samples
are consistent with the predictions of quantum theory and the time window
dependence is similar to the dependence observed in some real experiments. It
is an important example how correlations can be explained without evoking
quantum non-locality. However by using a suitable post-selection one may prove
anything. Since before the post-selection generated samples may not violate
Bell inequalities as significantly as finite samples generated using quantum
predictions thus one may not conclude that counterfactual definiteness is not
able to distinguish classical from quantum physics. Moreover we show that for
each choice of a time window there exists a contextual hidden variable
probabilistic model consistent with the post-selection procedure used by the
authors what explains why they are able to reproduce quantum predictions.


title:
Description of nuclear systems with a self-consistent
  configuration-mixing approach. II: Application to structure and reactions in
  even-even sd-shell nuclei

abstract:
  The variational multiparticle-multihole configuration mixing approach (MPMH)
to nuclei has been proposed about a decade ago. While the first applications
followed rapidly, the implementation of the full formalism of this method has
only been recently completed and applied in [C. Robin, N. Pillet, D. Pe\~na
Arteaga and J.-F. Berger, Phys. Rev. C 93, 024302 (2016)] to $^{12}$C as a
test-case. The main objective of the present paper is to carry on the study
that was initiated in that reference, in order to put the MPMH method to more
stringent tests. To that aim we perform a systematic study of even-even
sd-shell nuclei. The wave function of these nuclei is taken as a configuration
mixing built on orbitals of the sd-shell, and both the mixing coefficients of
the nuclear state and the single-particle wave functions are determined
consistently from the same variational principle. The calculations are done
using the D1S Gogny force. Various ground-state properties are analyzed. In
particular, the correlation content and composition of the wave function as
well as the single-particle orbitals and energies are examined. Binding
energies and charge radii are also calculated and compared to experiment. The
description of the first excited state is also examined and the corresponding
transition densities are used as input for the calculation of inelastic
electron and proton scattering. Special attention is paid to the effect of the
optimization of the single-particle states consistently with the correlations
of the system. Globally, the results are satisfying and encouraging. In
particular, charge radii and excitation energies are nicely reproduced.
However, the chosen valence-space truncation scheme precludes achieving maximum
collectivity in the studied nuclei. Further refinement of the method and a
better-suited interaction are necessary to remedy this situation.


title:
W-waveform Standing Surface Acoustic Waves with Two Equilibrium
  Positions under Linear Phase Modulation for Patterning Microparticles into
  Alternate Grid Patterns

abstract:
  This paper presents W-waveform Standing Surface Acoustic Waves (W-SSAW), and
as its application, patterning of two groups of microparticles with different
sizes alternately without fixing firstly patterned particles. W-SSAW is
constructed by two standing surface acoustic waves of frequencies $f$ and $2f$.
Combined with linear phase modulation to translate Gor'kov potential at a
constant speed, W-SSAW can selectively trap particles. The trapped particles
follow the moving Gor'kov potential maintaining force equilibrium between
Stokes' drag and the radiation force by W-SSAW. There exist two asymmetric
equilibrium positions every period, and by the asymmetry, each group of
particles is trapped at different equilibrium positions to form an alternate
pattern. This technique is extended to two-dimensional alternate patterning by
maintaining phase difference $90^\circ$ between X- and Y-directional W-SSAWs.
The patterning method utilizing W-SSAW is advantageous over SSAW-based
patterning in that it does not require temporal separation to fix firstly
patterned particles.


title: Lorentzian manifolds with transitive conformal group

abstract:
  We study pseudo-Riemanniasn manifolds $(M,g)$ with transitive group of
conformal transformation which is essential, i.e. does not preserves any metric
conformal to $g$. All such manifolds of Lorentz signature with non exact
isotropy representation of the stability subalgebra are described. A
construction of essential conformally homogeneous manifolds with exact isotropy
represenatation is given. Using spinor formalism, we prove that it provides all
4-dimensional non conformally flat Lorentzian 4-dimensional manifolds with
transitive essentially conformal group.


title: Method to study student engagement uniformity in a classroom

abstract:
  We present a method to study engagement level uniformity in a class of
students. We validate our method by comparing two semesters taught using
different methods in a physics and mathematics course. The first semester used
conventional methods while the second semester used graphic spreadsheets-based
laboratories and homework before the introduction of formal methods. We found
that engagement of the students that were below the median at the beginning of
the semester improved by an order of magnitude (by our metric) while the
engagement level of students initially above the median did not change.


title:
Geometric measures of quantum correlations with Bures and Hellinger
  distances

abstract:
  This article contains a survey of the geometric approach to quantum
correlations. We focus mainly on the geometric measures of quantum correlations
based on the Bures and quantum Hellinger distances.


title:
Experimental Demonstration of Degenerate Band Edge in Metallic
  Periodically-Loaded Circular Waveguide

abstract:
  We experimentally demonstrate for the first time the degenerate band edge
(DBE) condition, namely the degeneracy of four Bloch modes, in loaded circular
metallic waveguides. The four modes forming the DBE represent a degeneracy of
fourth order occurring in a periodic structure where four Bloch modes, two
propagating and two evanescent, coalesce. It leads to a very flat
wavenumber-frequency dispersion relation, and the finite length structure's
quality factor scales as $N^5$ where $N$ is the number of unit cells. The
proposed waveguide in which DBE is observed here is designed by periodically
loading a circular waveguide with misaligned elliptical metallic rings,
supported by a low-index dielectric. We validate the existence of the DBE in
such structure using measurements and we report good agreement between
full-wave simulation and the measured response of the waveguide near the DBE
frequency; taking into account metallic losses. We correlate our finding to
theoretical and simulation results utilizing various techniques including
dispersion synthesis, as well as observing how quality factor and group delay
scale as the structure length increases. Moreover, the reported geometry is
only an example of metallic waveguide with DBE: DBE and its characteristics can
also be designed in many other kinds of waveguides and various applications can
be contemplated as high microwave generation in amplifiers and oscillators
based on an electron beam interaction or solid state devices, pulse compressors
and microwave sensors.


title: Importance Sampling with Unequal Support

abstract:
  Importance sampling is often used in machine learning when training and
testing data come from different distributions. In this paper we propose a new
variant of importance sampling that can reduce the variance of importance
sampling-based estimates by orders of magnitude when the supports of the
training and testing distributions differ. After motivating and presenting our
new importance sampling estimator, we provide a detailed theoretical analysis
that characterizes both its bias and variance relative to the ordinary
importance sampling estimator (in various settings, which include cases where
ordinary importance sampling is biased, while our new estimator is not, and
vice versa). We conclude with an example of how our new importance sampling
estimator can be used to improve estimates of how well a new treatment policy
for diabetes will work for an individual, using only data from when the
individual used a previous treatment policy.


title: Protective Molecular Passivation of Black Phosphorous

abstract:
  Black phosphorous (BP) is one of the most interesting layered materials,
bearing promising potential for emerging electronic and optoelectronic device
technologies. The crystalline structure of BP displays in-plane anisotropy in
addition to the out-of-plane anisotropy characteristic to layered materials.
Therefore, BP supports anisotropic optical and transport responses that can
enable unique device architectures. Its thickness-dependent direct bandgap
varies in the range of around 0.3-2.0 eV (from single-layer to bulk,
respectively), making BP suitable to optoelectronics in a broad spectral range.
With high room-temperature mobility, exceeding 1,000 cm2V-1s-1 in thin films,
BP is also a very promising material for electronics. However, BP is sensitive
to oxygen and humidity due to its three-fold coordinated atoms. The surface
electron lone pairs are reactive and can lead to structural degradation upon
exposure to air, leading to significant device performance degradation in
ambient condition. Here, we report a viable solution to overcome degradation in
few-layer BP by passivating the surface with self-assembled monolayers of
octadecyltrichlorosilane (OTS) that provide long-term stability in ambient
conditions. Importantly, we show that this treatment does not cause any
undesired carrier doping of the bulk channel material, thanks to the emergent
hierarchical interface structure. Our approach is compatible with conventional
electronic materials processing technologies thus providing an immediate route
toward practical applications in BP devices.


title:
On Service-Chaining Strategies using Virtual Network Functions in
  Operator Networks

abstract:
  Network functions (e.g., firewalls, load balancers, etc.) have been
traditionally provided through proprietary hardware appliances. Often, hardware
appliances need to be hardwired back to back to form a service chain providing
chained network functions. Hardware appliances cannot be provisioned on demand
since they are statically embedded in the network topology, making creation,
insertion, modification, upgrade, and removal of service chains complex, and
also slowing down service innovation. Hence, network operators are starting to
deploy Virtual Network Functions (VNFs), which are virtualized over commodity
hardware. VNFs can be deployed in Data Centers (DCs) or in Network Function
Virtualization (NFV) capable network elements (nodes) such as routers and
switches. NFV capable nodes and DCs together form a Network enabled Cloud (NeC)
that helps to facilitate the dynamic service chaining required to support
evolving network traffic and its service demands. In this study, we focus on
the VNF service chain placement and traffic routing problem, and build a model
for placing a VNF service chain while minimizing network resource consumption.
Our results indicate that a NeC having a DC and NFV capable nodes can
significantly reduce network-resource consumption.


title: Injective choosability of subcubic planar graphs with girth 6

abstract:
  An injective coloring of a graph $G$ is an assignment of colors to the
vertices of $G$ so that any two vertices with a common neighbor have distinct
colors. A graph $G$ is injectively $k$-choosable if for any list assignment
$L$, where $|L(v)| \geq k$ for all $v \in V(G)$, $G$ has an injective
$L$-coloring. Injective colorings have applications in the theory of
error-correcting codes and are closely related to other notions of
colorability. In this paper, we show that subcubic planar graphs with girth at
least 6 are injectively 5-choosable. This strengthens a result of Lu\v{z}ar,
\v{S}krekovski, and Tancer that subcubic planar graphs with girth at least 7
are injectively 5-colorable. Our result also improves several other results in
particular cases.


title:
Doping driven metal-insulator transitions and charge orderings in the
  extended Hubbard model

abstract:
  We perform a thorough study of an extended Hubbard model featuring local and
nearest-neighbor Coulomb repulsion. Using dynamical mean-field theory we
investigated the zero temperature phase-diagram of this model as a function of
the chemical doping. The interplay between local and non-local interaction
drives a variety of phase-transitions connecting two distinct charge-ordered
insulators, i.e., half-filled and quarter-filled, a charge-ordered metal and a
Mott insulating phase. We characterize these transitions and the relative
stability of the solutions and we show that the two interactions conspire to
stabilize the quarter-filled charge ordered phase.

categories: cond-mat.str-el cond-mat.mtrl-sci cond-mat.quant-gas cond-mat.stat-mech physics.comp-ph


title: Uncertainty in phylogenetic tree estimates

abstract:
  Estimating phylogenetic trees is an important problem in evolutionary
biology, environmental policy and medicine. Although trees are estimated, their
uncertainties are discarded by mathematicians working in tree space. Here we
explicitly model the multivariate uncertainty of tree estimates. We consider
both the cases where uncertainty information arises extrinsically (through
covariate information) and intrinsically (through the tree estimates
themselves). The importance of accounting for tree uncertainty in tree space is
demonstrated in two case studies. In the first instance, differences between
gene trees are small relative to their uncertainties, while in the second, the
differences are relatively large. Our main goal is visualization of tree
uncertainty, and we demonstrate advantages of our method with respect to
reproducibility, speed and preservation of topological differences compared to
visualization based on multidimensional scaling. The proposal highlights that
phylogenetic trees are estimated in an extremely high-dimensional space,
resulting in uncertainty information that cannot be discarded. Most
importantly, it is a method that allows biologists to diagnose whether
differences between gene trees are biologically meaningful, or due to
uncertainty in estimation.


title: The strong coupling from hadronic $\tau$ decays: a critical appraisal

abstract:
  Several different analysis methods have been developed to determine the
strong coupling via finite-energy sum-rule analyses of hadronic $\tau$ decay
data. While most methods agree on the existence of the well-known ambiguity in
the choice of a resummation scheme due to the slow convergence of QCD
perturbation theory at the $\tau$ mass, there is an ongoing controversy over
how to deal properly with non-perturbative effects. These are small, but not
negligible, and include quark-hadron "duality violations" (i.e., resonance
effects) which are not described by the operator product expansion (OPE). In
one approach, an attempt is made to suppress duality violations enough that
they might become negligible. The number of OPE parameters to be fit, however,
then exceeds the number of available sum rules, necessitating an uncontrolled
OPE truncation, in which a number of higher-dimension OPE contributions in
general present in QCD are set to zero by hand. In the second approach,
truncation of the OPE is avoided by construction, and duality violations are
taken into account explicitly, using a physically motivated model. In this
article, we provide a critical appraisal of a recent analysis employing the
first approach and demonstrate that it fails to properly account for
non-perturbative effects, making the resulting determination of the strong
coupling unreliable. The second approach, in contrast, passes all
self-consistency tests, and provides a competitive determination of the strong
coupling from $\tau$ decays.


title: Dirac equation: the stationary and dynamical scattering problems

abstract:
  We prove that for the radial Dirac equation with Coulomb-type potential the
generalized dynamical scattering operator coincides with the corresponding
generalized stationary scattering operator. This fact is a quantum mechanical
analogue of ergodic results in the classical mechanics.

categories: math-ph math.CA math.DS math.MP math.SP quant-ph


title:
String-motivated one-loop amplitudes in gauge theories with half-maximal
  supersymmetry

abstract:
  We compute one-loop amplitudes in six-dimensional Yang-Mills theory with
half-maximal supersymmetry from first principles: imposing gauge invariance and
locality on an ansatz made from string-theory inspired kinematic building
blocks yields unique expressions for the 3- and 4-point amplitudes. We check
that the results are reproduced in the field-theory limit $\alpha' \rightarrow
0$ of string amplitudes in K3 orbifolds, using simplifications made in a
companion string-theory paper 1603.05262.


title: Estimation of teleported and gained parameters in a non-inertial frame

abstract:
  We estimate the teleported and the gained parameters by means of Fisher
information in a non-inertial frame. The sender and the receiver share an
accelerated maximum or partial entangled state. The estimation degree of these
parameters depends on Unruh acceleration, the used single mode
approximation(within/ beyond), the structure of the initial teleported state,
and the entanglement of the initial communication channel. The maximization and
minimization estimation degree of the teleported parameters depend on the
initial encoded information. The estimation degree of the parameters can be
maximized if the partners teleport classical information.


title:
Multistability in Piecewise Linear Systems by Means of the Eigenspectra
  Variation and the Round Function

abstract:
  A multistable system generated by a Piecewise Linear (PWL) system based on
the jerky equation is presented. The systems behaviour is characterised by
means of the Nearest Integer or round(x) function to control the switching
events and to locate the corresponding equilibria among each of the commutation
surfaces. These surfaces are generated by means of the switching function
dividing the space in regions equally distributed along one axis. The
trajectory of this type of system is governed by the eigenspectra of the
coefficient matrix which can be adjusted by means of a bifurcation parameter.
The behaviour of the system can change from multi-scroll attractors into a
mono-stable state to the coexistence of several single-scroll attractors into a
multi-stable state. Numerical results of the dynamics and bifurcation analyses
of their parameters are displayed to depict the multi-stable states.


title: On the Shape of Things: From holography to elastica

abstract:
  We explore the question of which shape a manifold is compelled to take when
immersed in another one, provided it must be the extremum of some functional.
We consider a family of functionals which depend quadratically on the extrinsic
curvatures and on projections of the ambient curvatures. These functionals
capture a number of physical setups ranging from holography to the study of
membranes and elastica. We present a detailed derivation of the equations of
motion, known as the shape equations, placing particular emphasis on the issue
of gauge freedom in the choice of normal frame. We apply these equations to the
particular case of holographic entanglement entropy for higher curvature three
dimensional gravity and find new classes of entangling curves. In particular,
we discuss the case of New Massive Gravity where we show that non-geodesic
entangling curves have always a smaller on-shell value of the entropy
functional. Then we apply this formalism to the computation of the entanglement
entropy for dual logarithmic CFTs. Nevertheless, the correct value for the
entanglement entropy is provided by geodesics. Then, we discuss the importance
of these equations in the context of classical elastica and comment on terms
that break gauge invariance.


title: Quantum Channel Construction with Circuit Quantum Electrodynamics

abstract:
  Quantum channels can describe all transformations allowed by quantum
mechanics. We provide an explicit universal protocol to construct all possible
quantum channels, using a single qubit ancilla with quantum non-demolition
readout and adaptive control. Our construction is efficient in both physical
resources and circuit depth, and can be demonstrated using superconducting
circuits and various other physical platforms. There are many applications of
quantum channel construction, including system stabilization and quantum error
correction, Markovian and exotic channel simulation, implementation of
generalized quantum measurements and more general quantum instruments.
Efficient construction of arbitrary quantum channels opens up exciting new
possibilities for quantum control, quantum sensing and information processing
tasks.


title: Electric dipole moments of charged leptons with sterile fermions

abstract:
  We address the impact of sterile fermions on charged lepton electric dipole
moments. We show that in order to have a non-vanishing contribution to electric
dipole moments, the minimal extension necessitates the addition of at least two
sterile fermion states. Sterile neutrinos can give significant contributions to
the charged lepton electric dipole moments if the masses of the non-degenerate
sterile states are both above the electroweak scale. In addition, the Majorana
nature of neutrinos is also important. Furthermore, we apply the computations
of the electric dipole moments for the most minimal realisation of the Inverse
Seesaw mechanism, in which the Standard Model is extended by two right-handed
neutrinos and two sterile fermion states. We show that the two pairs of (heavy)
pseudo-Dirac mass eigenstates can give significant contributions to the
electron electric dipole moment, lying close to future experimental
sensitivity. We further discuss the possibility of beyond the minimal Inverse
Seesaw models and of having a successful leptogenesis in this framework.


title: Combinatorics of canonical bases revisited: Type A

abstract:
  We initiate a new approach to the study of the combinatorics of several
parametrizations of canonical bases. In this work we deal with Lie algebras of
type $A$. Using geometric objects called Rhombic tilings we derive a "crossing
formula" to compute the actions of the crystal operators on Lusztig data for an
arbitrary reduced word of the longest Weyl group element. We provide the
following three applications of this result. Using the tropical Chamber Ansatz
of Berenstein-Fomin-Zelevinsky we prove an enhanced version of the
Anderson-Mirkovi\'c conjecture for the crystal structure on MV polytopes. We
establish a duality between Kashiwara's string and Lusztig's parametrization,
revealing that each of them is controlled by the crystal structure of the
other. We identify the potential functions of the unipotent radical of $SL_n$
defined by Berenstein-Kazhdan and Gross-Hacking-Keel-Kontsevich, respectively,
with a function arising from the crystal structure on Lusztig data.


title:
Syntactic Enhancement to VSIMM for Roadmap Based Anomalous Trajectory
  Detection: A Natural Language Processing Approach

abstract:
  The aim of syntactic tracking is to classify spatio-temporal patterns of a
target's motion using natural language processing models. In this paper, we
generalize earlier work by considering a constrained stochastic context free
grammar (CSCFG) for modeling patterns confined to a roadmap. The constrained
grammar facilitates modeling specific directions and road names in a roadmap.
We present a novel particle filtering algorithm that exploits the CSCFG model
for estimating the target's patterns. This meta-level algorithm operates in
conjunction with a base-level tracking algorithm. Extensive numerical results
using simulated ground moving target indicator (GMTI) radar measurements show
substantial improvement in target tracking accuracy.


title: Enhanced UV light detection using a p-terphenyl wavelength shifter

abstract:
  UV-glass photomultiplier tubes (PMTs) have poor photon detection efficiency
for wavelengths below $300\,\text{nm}$ due to the opaqueness of the window
material. Costly quartz PMTs could be used to enhance the efficiency below
$300\,\text{nm}$. A less expensive solution that dramatically improves this
efficiency is the application of a thin film of a p-terphenyl (PT) wavelength
shifter on UV-glass PMTs. This improvement was quantified for Photonis XP4500B
PMTs for wavelengths between $200\,\text{nm}$ and $400\,\text{nm}$. The gain
factor ranges up to 5.4 $\pm$ 0.5 at a wavelength of $215\,\text{nm}$, with a
material load of $110\pm10\,\mu\text{g}/\text{cm}^2$ ($894\,\text{nm}$). The
wavelength shifter was found to be fully transparent for wavelengths greater
than $300\,\text{nm}$. The resulting gain in detection efficiency, when used in
a typical Cherenkov counter, was estimated to be of the order of 40\%.
Consistent coating quality was assured by a rapid gain testing procedure using
narrow-band UV LEDs. Based on these results, 200 Photonis XP4500B PMTs were
treated with PT for the upgraded low-threshold Cherenkov counter (LTCC) to be
used in the CEBAF Large Acceptance Spectrometer upgraded detector (CLAS12) at
the Thomas Jefferson National Accelerator Facility.


title:
Non-renormalizable Operators for Solar Mass Generation in Split SuSy
  with Bilinear R-parity Violation

abstract:
  The Minimal Supersymmetric Extension of the Standard Model (MSSM) is able to
explain the current data from neutrino physics. Unfortunately Split
Supersymmetry as low energy approximation of this theory fails to generate a
solar square mass difference, including after the addition of bilinear R-Parity
Violation. In this work, it is shown how one can derive an effective low energy
theory from the MSSM in the spirit of Split Supersymmetry, which has the
potential of explaining the neutrino phenomenology. This is achieved by going
beyond leading order in the process of integrating out heavy scalars from the
original theory, which results in non-renormalizable operators in the effective
low energy theory. It is found that in particular a $d=8$ operator is crucial
for the generation of the neutrino mass differences.


title:
Evaluating Urbanization from Satellite and Aerial Images by means of a
  statistical approach to the texture analysis

abstract:
  Statistical methods are usually applied in the processing of digital images
for the analysis of the textures displayed by them. Aiming to evaluate the
urbanization of a given location from satellite or aerial images, here we
consider a simple processing to distinguish in them the 'urban' from the
'rural' texture. The method is based on the mean values and the standard
deviations of the colour tones of image pixels. The processing of the input
images allows to obtain some maps from which a quantitative evaluation of the
textures can be obtained.


title: Moving the CFT into the bulk with $T\bar T$

abstract:
  Recent work by Zamolodchikov and others has uncovered a solvable irrelevant
deformation of general 2D CFTs, defined by turning on the dimension 4 operator
$T \bar T$, the product of the left- and right-moving stress tensor. We propose
that in the holographic dual, this deformation represents a geometric cutoff
that removes the asymptotic region of AdS and places the QFT on a Dirichlet
wall at finite radial distance $r = r_c$ in the bulk. As a quantitative check
of the proposed duality, we compute the signal propagation speed, energy
spectrum, and thermodynamic relations on both sides. In all cases, we obtain a
precise match. We derive an exact RG flow equation for the metric dependence of
the effective action of the $T \bar T$ deformed theory, and find that it
coincides with the Hamilton-Jacobi equation that governs the radial evolution
of the classical gravity action in AdS.


title:
Extreme diffusion limited electropolishing of niobium radiofrequency
  cavities

abstract:
  A deeply modulated, regular, continuous, oscillating current waveform is
reliably and repeatably achieved during electropolishing of niobium single-cell
elliptical radiofrequency cavities. Details of the technique and cavity test
results are reported here. The method is applicable for cavity frequencies in
the range 500 MHz to 3.9 GHz and can be extended to multicell structures.


title: Universal Quantum Algorithm

abstract:
  Quantum amplitude amplification and quantum phase estimation are two
fundamental quantum algorithms. All known quantum algorithms are derived from
these two algorithms. Even the adiabatic quantum algorithms can also be
efficiently simulated using quantum phase estimation. We present a universal
quantum algorithm which explains these two algorithms as special cases. An
interesting result is that we do not need quantum fourier transform to do
quantum phase estimation.


title:
Statistical Query Lower Bounds for Robust Estimation of High-dimensional
  Gaussians and Gaussian Mixtures

abstract:
  We describe a general technique that yields the first {\em Statistical Query
lower bounds} for a range of fundamental high-dimensional learning problems
involving Gaussian distributions. Our main results are for the problems of (1)
learning Gaussian mixture models (GMMs), and (2) robust (agnostic) learning of
a single unknown Gaussian distribution. For each of these problems, we show a
{\em super-polynomial gap} between the (information-theoretic) sample
complexity and the computational complexity of {\em any} Statistical Query
algorithm for the problem. Our SQ lower bound for Problem (1) is qualitatively
matched by known learning algorithms for GMMs. Our lower bound for Problem (2)
implies that the accuracy of the robust learning algorithm
in~\cite{DiakonikolasKKLMS16} is essentially best possible among all
polynomial-time SQ algorithms.
  Our SQ lower bounds are attained via a unified moment-matching technique that
is useful in other contexts and may be of broader interest. Our technique
yields nearly-tight lower bounds for a number of related unsupervised
estimation problems. Specifically, for the problems of (3) robust covariance
estimation in spectral norm, and (4) robust sparse mean estimation, we
establish a quadratic {\em statistical--computational tradeoff} for SQ
algorithms, matching known upper bounds. Finally, our technique can be used to
obtain tight sample complexity lower bounds for high-dimensional {\em testing}
problems. Specifically, for the classical problem of robustly {\em testing} an
unknown mean (known covariance) Gaussian, our technique implies an
information-theoretic sample lower bound that scales {\em linearly} in the
dimension. Our sample lower bound matches the sample complexity of the
corresponding robust {\em learning} problem and separates the sample complexity
of robust testing from standard (non-robust) testing.

categories: cs.LG cs.CC cs.DS cs.IT math.IT math.ST stat.TH


title:
Efficient and Qualified Mesh Generation for Gaussian Molecular Surface
  Using Piecewise Trilinear Polynomial Approximation

abstract:
  Recent developments for mathematical modeling and numerical simulation of
biomolecular systems raise new demands for qualified, stable, and efficient
surface meshing, especially in implicit-solvent modeling. In our former work,
we have developed an algorithm for manifold triangular meshing for large
Gaussian molecular surfaces, TMSmesh. In this paper, we present new algorithms
to greatly improve the meshing efficiency and qualities, and implement into a
new program version, TMSmesh 2.0. In TMSmesh 2.0, in the first step, a new
adaptive partition and estimation algorithm is proposed to locate the cubes in
which the surface are approximated by piecewise trilinear surface with
controllable precision. Then, the piecewise trilinear surface is divided into
single valued pieces by tracing along the fold curves, which ensures that the
generated surface meshes are manifolds. Numerical test results show that
TMSmesh 2.0 is capable of handling arbitrary sizes of molecules and achieves
ten to hundreds of times speedup over the previous algorithm. The result
surface meshes are manifolds and can be directly used in boundary element
method (BEM) and finite element method (FEM) simulation. The binary version of
TMSmesh 2.0 is downloadable at the web page
http://lsec.cc.ac.cn/~lubz/Meshing.html.


title:
Near infrared light amplification in Gold diffused Silicon-on-Insulator
  waveguides

abstract:
  We report near infrared optical amplification in gold diffused
silicon-on-insulator waveguides by visible optical pumping. More then 30dB/cm
gain was measured for a light carrier at a wavelength of 1.55 microns


title: Cosmic Transit and Anisotropic Models in f(R,T) Gravity

abstract:
  Accelerating cosmological models are constructed in a modified gravity theory
dubbed as $f(R,T)$ gravity at the backdrop of an anisotropic Bianchi type-III
universe. $f(R,T)$ is a function of the Ricci scalar $R$ and the trace $T$ of
the energy-momentum tensor and it replaces the Ricci scalar in the
Einstein-Hilbert action of General Relativity. The models are constructed for
two different ways of modification of the Einstein-Hilbert action. Exact
solutions of the field equations are obtained by a novel method of integration.
We have explored the behaviour of the cosmic transit from an decelerated phase
of expansion to an accelerated phase to get the dynamical features of the
universe. Within the formalism of the present work, it is found that, the
modification of the Einstein-Hilbert action does not affect the scale factor.
However the dynamics of the effective dark energy equation of state is
significantly affected.


title: Song From PI: A Musically Plausible Network for Pop Music Generation

abstract:
  We present a novel framework for generating pop music. Our model is a
hierarchical Recurrent Neural Network, where the layers and the structure of
the hierarchy encode our prior knowledge about how pop music is composed. In
particular, the bottom layers generate the melody, while the higher levels
produce the drums and chords. We conduct several human studies that show strong
preference of our generated music over that produced by the recent method by
Google. We additionally show two applications of our framework: neural dancing
and karaoke, as well as neural story singing.


title: Spiked Instantons from Intersecting D-branes

abstract:
  The moduli space of spiked instantons that arises in the context of the
BPS/CFT correspondence is realised as the moduli space of classical vacua, i.e.
low-energy open string field configurations, of a certain stack of intersecting
D1-branes and D5-branes in Type IIB string theory. The presence of a constant
B-field induces an interesting dynamics involving the tachyon condensation.


title:
Ring-down gravitational waves and lensing observables: How far can a
  wormhole mimic those of a black hole?

abstract:
  It has been argued that the recently detected ring-down gravity waveforms
could be indicative only of the presence of light rings in a horizonless
object, such as a surgical Schwarzschild wormhole, with the frequencies
differing drastically from those of the horizon quasinormal mode frequencies
$\omega _{\text{QNM}}$ at late times. While the possibility of such a
horizonless alternative is novel by itself, we show by the example of
Ellis-Bronnikov wormhole that the differences in $\omega _{\text{QNM}}$ in the
eikonal limit (large $l$) need not be drastic. This result will be reached by
exploiting the connection between $\omega _{\text{QNM}}$ and the Bozza strong
field lensing parameters. We shall also show that the lensing observables of
the Ellis-Bronnikov wormhole can also be very close to those of a black hole
(say, SgrA$^{\ast }$ hosted by our galaxy) of the same mass. This situation
indicates that the ring-down frequencies and lensing observables of the
Ellis-Bronnikov wormhole can remarkably mimic those of a black hole. The
constraint on wormhole parameter $\gamma $ imposed by experimental accuracy is
briefly discussed. We also provide independent arguments supporting the
stability of the Ellis-Bronnikov wormhole proven recently.


title: A note on the order of the antipode of a pointed Hopf algebra

abstract:
  Let $k$ be a field and let $H$ denote a pointed Hopf $k$-algebra with
antipode $S$. We are interested in determining the order of $S$. Building on
the work done by Taft and Wilson $[7]$, we define an invariant for $H$, denoted
$m_{H}$, and prove that the value of this invariant is connected to the order
of $S$. In the case where $\operatorname{char}k=0$, it is shown that if $S$ has
finite order then it is either the identity or has order $2m_{H}$. If in
addition $H$ is assumed to be coradically graded, it is shown that the order of
$S$ is finite if and only if $m_{H}$ is finite. We also consider the case where
$\operatorname{char}k=p>0$, generalising the results of $[7]$ to the
infinite-dimensional setting.


title:
The adiabatic/entropy decomposition in $P(\phi^I,X^{IJ})$ theories with
  multiple sound speeds

abstract:
  We consider $P(\phi^I,X^{IJ})$ theories of multi-field inflation and ask the
question of how to define the adiabatic and entropy perturbations, widely used
in calculating the curvature and isocurvature power spectra, in this general
context. It is found that when the field perturbations propagate with different
speeds, these adiabatic and entropy modes are not generally the fundamental
(most natural to canonically quantise) degrees of freedom that propagate with a
single speed. The alternative fields which do propagate with a single speed are
found to be a rotation in field space of the adiabatic and entropy
perturbations. We show how this affects the form of the horizon-crossing power
spectrum, when there is not a single "adiabatic sound speed" sourcing the
curvature perturbation. Special cases of our results are discussed, including
$P(X)$ theories where the adiabatic and entropy perturbations are fundamental.
We finally look at physical motivations for considering multi-speed models of
inflation, particularly showing that disformal couplings can naturally lead to
the kind of kinetic interactions which cause fields to have different sound
speeds.


title:
Reconfigurable Dual Mode IEEE 802.15.4 Digital Baseband Receiver for
  Diverse IoT Applications

abstract:
  IEEE 802.15.4 takes a center stage in IoT as Low- Rate Wireless Personal Area
Networks(LR-WPANs). The standard specifies Offset Quadrature Phase Shift Keying
Physical Layer (O-QPSK PHY) with half-sine pulse shaping which can be either
analyzed under the class of M-ary PSK signals (QPSK signal with offset) or as
Minimum Shift Keying (MSK) signal. M-ary PSK demodulation is requires perfect
carrier and has minimal error. MSK signals which falls under Continuous Phase
Frequency Shift Keying can be demodulated non-coherently but error performance
is not as good. In our paper, this dual nature of IEEE 802.15.4 PHY is
exploited to propose a dual mode receiver comprising of QPSK demodulator chain
and MSK demodulator chain as a single system on chip. The mode can be
configured manually depending on the type of application or based on the
feedback from a Signal to Noise (SNR) indicator employed in the proposed
receiver. M-ary PSK chain is selected for lower SNRs and MSK for higher SNRs.
Each of these properties are analyzed in detail for both demodulator chains and
we go on to prove that MSK detection can be used for low power, low complex and
low latency while QPSK detection is employed for minimal error.


title: A Study of confinement for $Q\bar{Q}$ potentials on D3, M2 & M5 branes

abstract:
  We study analytically and numerically the interaction potentials between a
pair of quark an anti-quark on D3, M2 and M5 branes. These potentials are
obtained using Maldacena's method involving Wilson loops and present confining
and non-confining behaviours in different situations that we explore in this
work. In particular, at the near horizon geometry the potentials are
non-confining in agreement with conformal field theory expectations. On the
other side, far from horizon, the dual field theories are no longer conformal
and the potentials present confinement. This is in agreement with the behaviour
of strings in flat space where the string mimics the expected flux tube of QCD.
A study of the transition between the confining/non-confining regimes in the
three different scenarios (D3, M2, M5) is also performed.


title:
More on the conformal mapping of quasi-local masses: The Hawking-Hayward
  case

abstract:
  The conformal transformation of the Hawking-Hayward quasi-local mass is
reexamined. It has been found recently that the conformal transformation of the
latter exhibits the 'wrong' conformal factor compared to the way usual masses
transform under conformal transformations of spacetime. We show, in analogy
with what was found recently for the Misner-Sharp mass, that unlike the purely
geometric definition of the Hawking-Hayward mass, the latter exhibits the
'right' conformal factor whenever expressed in terms of its material content
via the field equations. The case of conformally invariant scalar-tensor
theories of gravity is also examined. The equivalence between the Misner-Sharp
mass and the Hawking-Hayward mass for spherically symmetric spacetimes
manifests itself by giving identical peculiar behaviors under conformal
transformations.


title:
Quadrature formulas with variable nodes and Jackson-Nikolskii
  inequalities for rational functions

abstract:
  We obtain new parametric quadrature formulas with variable nodes for
integrals of complex rational functions over circles, segments of the real axis
and the real axis itself. Basing on these formulas we derive
$(q,p)$-inequalities of Jackson-Nikolskii type for various classes of rational
functions, complex polynomials and their logarithmic derivatives (simple
partial fractions). It is shown that our $(\infty,2)$- and
$(\infty,4)$-inequalities are sharp in a number of main theorems. Our
inequalities extend and refine several results obtained earlier by other
authors.


title:
Comparative Analysis of Phenomenological Approximations of the Light
  Curves of Eclipsing Binary Stars with Additional Parameters

abstract:
  A comparative analysis of the special shapes (patterns, profiles) of the
eclipses applied for the phenomenological modeling of the light curves of
eclipsing binary stars is conducted. Families of functions are considered,
generalizing local approximations (Andronov, 2010, 2012) and the functions
theoretically unlimited in a width, based on a Gaussian (Mikulasek, 2015). For
an analysis, the light curve of the star V0882 Car = 2MASS J11080308 - 6145589
of the classic Algol - subtype (\beta Persei) is used. By analyzing dozens of
modified functions with additional parameters, it was chosen the 14 best ones
according to the criterion of the least sum of squares of deviations. The best
are the functions with an additional parameter, describing profiles, which are
limited in phase.


title:
The $SW(3/2,2)$ superconformal algebra via a Quantum Hamiltonian
  Reduction of $osp(3|2)$

abstract:
  We prove that the family of non-linear $W$-algebras $SW(3/2,2)$ which are
extensions of the $N=1$ superconformal algebra by a primary supercurrent of
conformal weight $2$ can be realized as a quantum Hamiltonian reduction of the
Lie superalgebra $osp(3|2)$. In consequence we obtain an explicit free field
realization of the algebra in terms of the screening operators. At central
charge $c=12$ the $SW(3/2,2)$ superconformal algebra corresponds to the
superconformal algebra associated to sigma models based on eight-dimensional
manifolds with special holonomy $Spin(7)$, i.e., the Shatashvili-Vafa $Spin(7)$
superconformal algebra.


title:
Prevalence of algorithm-based qualitative (ABQ) method osteoporotic
  vertebral fracture in elderly Chinese men and women with reference to
  semi-quantitative (SQ) method: Mr. Os and Ms Os. (Hong Kong) studies

abstract:
  Introduction: This study evaluated algorithm-based qualitative (ABQ) method
for vertebral fracture (VF) evaluation with reference to semi-quantitative (SQ)
method and bone mineral density (BMD) measurement. Methods: Mr. OS (Hong Kong)
and Ms. OS (Hong Kong) represent the first large-scale cohort studies on bone
health in elderly Chinese men and women. The current study compared Genant's SQ
method and ABQ method in these two cohorts. Based on quantitative measurement,
the severity of ABQ method detected fractures was additionally classified into
grade-1, grad-2, and grade-3 according to SQ's deformity criteria. The
radiographs of 1,954 elderly Chinese men (mean: 72.3 years) and 1,953 elderly
Chinese women (mean: 72.5 years) were evaluated. Results: according to ABQ,
grade-1,-2,-3 VFs accounted for 1.89%, 1.74%, 2.25% in men, and 3.33%, 3.07%,
and 5.53% in women. In men and women, 15.7% (35/223) and 34.5% (48/139) of
vertebrae with SQ grade-1 deformity were ABQ(+, with fracture) respectively. In
men and women, 89.7% (35/39) and 66.7% (48/72) of vertebrae with ABQ grade-1
fracture had SQ grade-1 deformity. For grade-1 change, SQ (-, negative without
fracture) & ABQ (+, positive with vertebral cortex line fracture) subjects tend
to have a lower BMD than the SQ(+)& ABQ(-) subjects. In subjects with SQ
grade-2 deformity, those were also ABQ(+) tended to have a lower BMD than those
were ABQ(-). In all grades, SQ(-)&ABQ(-) subjects tended to have highest BMD,
while SQ(+)&ABQ(+)subjects tended to have lowest BMD. Conclusion: ABQ method
may be more sensitive to VF associated mild lower BMD than SQ method.


title: A Spectacular Bow Shock in the 11 keV Galaxy Cluster Around 3C 438

abstract:
  We present results of deep 153 ks Chandra observations of the hot, 11 keV,
galaxy cluster associated with the radio galaxy 3C 438. By mapping the
morphology of the hot gas and analyzing its surface brightness and temperature
distributions, we demonstrate the presence of a merger bow shock. We identify
the presence of two jumps in surface brightness and in density located at
$\sim$400 kpc and $\sim$800 kpc from the cluster's core. At the position of the
inner jump, we detect a factor of $2.3\pm 0.2$ density jump, while at the
location of the outer jump, we detect a density drop of a factor of $3.5 \pm
0.7$. Combining this with the temperature distribution within the cluster, we
establish that the pressure of the hot gas is continuous at the 400 kpc jump,
while there is a factor of $6.2 \pm 2.8$ pressure discontinuity at 800 kpc
jump. From the magnitude of the outer pressure discontinuity, using the
Rankine-Hugoniot jump conditions, we determine that the sub-cluster is moving
at $M = 2.3\pm 0.5$, or approximately $2600\pm 565$ km/s through the
surrounding intracluster medium, creating the conditions for a bow shock. Based
on these findings, we conclude that the pressure discontinuity is likely the
result of an ongoing major merger between two massive clusters. Since few
observations of bow shocks in clusters have been made, this detection can
contribute to the study of the dynamics of cluster mergers, which offers
insight on how the most massive clusters may have formed.


title: Mesons from (non) Abelian T-dual backgrounds

abstract:
  In this work we study mesonic excitations in a Quantum Field Theory dual to
the non Abelian T-dual of $AdS_5\times S^5$, using a D6 brane probe on the
Sfetsos-Thompson background. Before and after the duality, we observe
interesting differences between the spectra and interpret them. The spectrum of
masses and the interactions among mesonic excitations teach valuable lessons
about the character of non-Abelian T-duality and its implications for
Holography. The case of Abelian T-duality is also studied.


title: de Sitter Harmonies: Cosmological Spacetimes as Resonances

abstract:
  The aim of this work is to provided the details of a calculation summarized
in the recent paper by Maltz and Susskind which conjectured a potentially
rigorous framework where the status of de Sitter space is the same as that of a
resonance in a scattering process. The conjecture being that transition
amplitudes between certain states with asymptotically supersymmetric flat vacua
contain resonant poles characteristic metastable intermediate states. A
calculation employing constrained instantons is presented that illustrates this
idea.


title: Self-interacting Dark Matter Without Direct Detection Constraints

abstract:
  We explore the self-interacting dark matter scenario in a simple dark sector
model where the dark matter interacts through a dark photon. Splitting a Dirac
fermion dark matter into two levels using a small Majorana mass can evade
strong direct detection constraints on the kinetic mixing between the dark and
normal photons, thus allowing the dark sector to be more visible at high
intensity and/or high energy experiments. It is pointed out that such a mass
splitting has a strong impact on the dark matter self-interaction strength. We
derive the new parameter space of a pseudo-Dirac self-interacting dark matter.
Interestingly, with increasing mass splitting, a weak scale dark matter mass
window survives that could be probed by the LHC and future colliders.


title: Radiation and the classical double copy for color charges

abstract:
  We construct perturbative classical solutions of the Yang-Mills equations
coupled to dynamical point particles carrying color charge. By applying a set
of color to kinematics replacement rules first introduced by Bern, Carrasco and
Johansson (BCJ), these are shown to generate solutions of d-dimensional dilaton
gravity, which we also explicitly construct. Agreement between the gravity
result and the gauge theory double copy implies a correspondence between
non-Abelian particles and gravitating sources with dilaton charge. When the
color sources are highly relativistic, dilaton exchange decouples, and the
solutions we obtain match those of pure gravity. We comment on possible
implications of our findings to the calculation of gravitational waveforms in
astrophysical black hole collisions, directly from computationally simpler
gluon radiation in Yang-Mills theory.


title:
Something borrowed, something blue: The nature of blue metal-poor stars
  inferred from their colours and chemical abundances

abstract:
  Blue metal-poor stars (BMPs) are main sequence stars that appear bluer and
more luminous than normal turnoff stars. They were originally singled out by
using B-V and U-B colour cuts. Early studies found that a larger fraction of
field BMP stars were binaries compared to normal halo stars. Thus, BMP stars
are ideal field blue straggler candidates for investigating internal stellar
evolution processes and binary interaction. In particular, the presence or
depletion in lithium in their spectra is a powerful indicator as to their
origin. They are either old, halo blue stragglers experiencing internal mixing
processes or mass transfer (Li-depletion), or intermediate-age, single stars of
possibly extragalactic origin (2.2dex halo plateau Li). However, we note that
internal mixing processes can lead to an increased level of Li. Hence, this
study combines photometry and spectroscopy to unveil the origin of various BMP
stars. We first show how to separate binaries from young blue stars using
photometry, metallicity, and lithium. Using a sample of 80 BMP stars (T>6300K),
we find that 97% of the BMP binaries have V-Ks_0 < 1.08$\pm0.03$, while BMP
stars that are not binaries lie above this cut in 2/3 of the cases. This cut
can help classify stars which lack radial velocities from follow-up
observations. We trace the origin of two BMP stars from the photometric sample
by conducting a full chemical analysis using new high-resolution and high SN
spectra. Based on their radial velocities, Li, alpha, and s- and r-process
abundances we show that BPS CS22874-042 is a single star
(A(Li)$=2.38\pm0.10$dex) while with A(Li)$=2.23\pm0.07$dex CD-48 2445 is a
binary, contrary to earlier findings. Our analysis emphasises that field blue
stragglers can be segregated from single metal-poor stars, using V-Ks colours
with a fraction of single stars polluting the binary sample, but not vice
versa.(Abridged)


title: Proxima's orbit around Alpha Centauri

abstract:
  Proxima and Alpha Centauri AB have almost identical distances and proper
motions with respect to the Sun. Although the probability of such similar
parameters is in principle very low, the question as to whether they actually
form a single gravitationally bound triple system has been open since the
discovery of Proxima one century ago. Owing to HARPS high precision absolute
radial velocity measurements and the recent revision of the parameters of the
Alpha Cen pair, we show that Proxima and Alpha Cen are gravitationally bound
with a high degree of confidence. The orbital period of Proxima is
approximately 550 000 years. With an excentricity of 0.50 (+0.08 -0.09),
Proxima comes within 4.3 (+1.1 -0.9) kau of Alpha Cen at periastron. Its
orbital phase is currently close to apastron (13.0 +0.3 -0.1 kau). This orbital
motion may have influenced the formation or evolution of the recently
discovered planet orbiting Proxima as well as circumbinary planet formation
around Alpha Cen.


title: Geminga's puzzling pulsar wind nebula

abstract:
  We report on six new Chandra observations of the Geminga pulsar wind nebula
(PWN). The PWN consists of three distinct elongated structures - two $\approx
0.2 d_{250}$ pc long lateral tails and a segmented axial tail of $\approx 0.05
d_{250}$ pc length, where $d_{250}=d/(250 {\rm pc})$. The photon indices of the
power law spectra of the lateral tails, $\Gamma \approx 1$, are significantly
harder than those of the pulsar ($\Gamma \approx 1.5$) and the axial tail
($\Gamma \approx 1.6$). There is no significant diffuse X-ray emission between
the lateral tails -- the ratio of the X-ray surface brightness between the
south tail and this sky area is at least 12. The lateral tails apparently
connect directly to the pulsar and show indication of moving footpoints. The
axial tail comprises time-variable emission blobs. However, there is no
evidence for constant or decelerated outward motion of these blobs. Different
physical models are consistent with the observed morphology and spectra of the
Geminga PWN. In one scenario, the lateral tails could represent an azimuthally
asymmetric shell whose hard emission is caused by the Fermi acceleration
mechanism of colliding winds. In another scenario, the lateral tails could be
luminous, bent polar outflows, while the blobs in the axial tail could
represent a crushed torus. In a resemblance to planetary magnetotails, the
blobs of the axial tail might also represent short-lived plasmoids which are
formed by magnetic field reconnection in the relativistic plasma of the pulsar
wind tail.


title:
Comparing semi-analytic particle tagging and hydrodynamical simulations
  of the Milky Way's stellar halo

abstract:
  Particle tagging is an efficient, but approximate, technique for using
cosmological N-body simulations to model the phase-space evolution of the
stellar populations predicted, for example, by a semi-analytic model of galaxy
formation. We test the technique developed by Cooper et al. (which we call
STINGS here) by comparing particle tags with stars in a smooth particle
hydrodynamic (SPH) simulation. We focus on the spherically averaged density
profile of stars accreted from satellite galaxies in a Milky Way (MW)-like
system. The stellar profile in the SPH simulation can be recovered accurately
by tagging dark matter (DM) particles in the same simulation according to a
prescription based on the rank order of particle binding energy. Applying the
same prescription to an N-body version of this simulation produces a density
profile differing from that of the SPH simulation by <10 per cent on average
between 1 and 200 kpc. This confirms that particle tagging can provide a
faithful and robust approximation to a self-consistent hydrodynamical
simulation in this regime (in contradiction to previous claims in the
literature). We find only one systematic effect, likely due to the
collisionless approximation, namely that massive satellites in the SPH
simulation are disrupted somewhat earlier than their collisionless
counterparts. In most cases this makes remarkably little difference to the
spherically averaged distribution of their stellar debris. We conclude that,
for galaxy formation models that do not predict strong baryonic effects on the
present-day DM distribution of MW-like galaxies or their satellites,
differences in stellar halo predictions associated with the treatment of star
formation and feedback are much more important than those associated with the
dynamical limitations of collisionless particle tagging.


title:
On the Quantisation of Complex Higher Derivative Theories and Avoiding
  the Ostrogradsky Ghost

abstract:
  Generic higher derivative theories are believed to be fundamentally
unphysical because they contain Ostrogradsky ghosts. We show that within
complex classical mechanics it is possible to construct higher derivative
theories that circumvent the Ostrogradsky theorem and have a real energy
spectrum that is bounded from below. The complex theory can be canonically
quantised. The resulting quantum theory does not suffer from the kinetic
instability and maintains the usual probabilistic interpretation without
violating the correspondence principle. As a proof of concept, we construct a
class of stable interacting complex higher derivative theories. This consistent
and canonical framework allows us to analyse previous attempts to avoid the
ghosts that use non-canonical quantisation schemes, such as the Lee-Wick
theories, Dirac-Pauli quantisation or PT-symmetric quantum mechanics. The key
to understand the would-be ghosts in any kinetically stable higher derivative
theory is to accept the complex system behind it.


title: Morpho-kinematics of z~1 galaxies probe the hierarchical scenario

abstract:
  We have studied a representative sample of intermediate-mass galaxies at z~1,
observed by the kinematic survey KMOS3D. We have re-estimated the kinematical
parameters from the published kinematic maps and analysed photometric data from
HST to measure optical disk inclinations and PAs. We find that only half of the
z~1 galaxies show kinematic properties consistent with rotating disks, using
the same classification scheme than that adopted by the KMOS3D team. Because
merger orbital motions can also brought rotation, we have also analysed galaxy
morphologies from the available HST imagery. Combining these results to those
from kinematics, it leads to a full morpho-kinematic classification. To test
the robustness of the latter for disentangling isolated disks from mergers, we
confronted the results with an analysis of pairs from the open-grism redshift
survey 3D-HST. All galaxies found in pairs are affected by either kinematic
and/or morphological perturbations. Conversely, all galaxies classified as
virialized spirals are found to be isolated. A significant fraction (one
fourth) of rotating disks classified from kinematics by the KMOS3D team are
found in pairs, which further supports the need for a morpho-kinematic
classification. It results that only one third of z~1 galaxies are isolated and
virialized spirals, while 58% of them are likely involved in a merger sequence,
from first approach to disk rebuilding. The later fraction is in good agreement
with the results of semi-empirical {\Lambda}CDM models, supporting a
merger-dominated hierarchical scenario as being the main driver of galaxy
formation at least during the last 8 billion years.


title: Bolting Multicenter Solutions

abstract:
  We introduce a solvable system of equations that describes non-extremal
multicenter solutions to six-dimensional ungauged supergravity coupled to
tensor multiplets. The system involves a set of functions on a
three-dimensional base metric. We obtain a family of non-extremal axisymmetric
solutions that generalize the known multicenter extremal solutions, using a
particular base metric that introduces a bolt. We analyze the conditions for
regularity, and in doing so we show that this family does not include solutions
that contain an extremal black hole and a smooth bolt. We determine the
constraints that are necessary to obtain smooth horizonless solutions involving
a bolt and an arbitrary number of Gibbons-Hawking centers.


title: The Chandra Deep Field-South Survey: 7 Ms Source Catalogs

abstract:
  We present X-ray source catalogs for the $\approx7$ Ms exposure of the
Chandra Deep Field-South (CDF-S), which covers a total area of 484.2
arcmin$^2$. Utilizing WAVDETECT for initial source detection and ACIS Extract
for photometric extraction and significance assessment, we create a main source
catalog containing 1008 sources that are detected in up to three X-ray bands:
0.5-7.0 keV, 0.5-2.0 keV, and 2-7 keV. A supplementary source catalog is also
provided including 47 lower-significance sources that have bright ($K_s\le23$)
near-infrared counterparts. We identify multiwavelength counterparts for 992
(98.4%) of the main-catalog sources, and we collect redshifts for 986 of these
sources, including 653 spectroscopic redshifts and 333 photometric redshifts.
Based on the X-ray and multiwavelength properties, we identify 711 active
galactic nuclei (AGNs) from the main-catalog sources. Compared to the previous
$\approx4$ Ms CDF-S catalogs, 291 of the main-catalog sources are new
detections. We have achieved unprecedented X-ray sensitivity with average flux
limits over the central $\approx1$ arcmin$^2$ region of
$\approx1.9\times10^{-17}$, $6.4\times10^{-18}$, and $2.7\times10^{-17}$ erg
cm$^{-2}$ s$^{-1}$ in the three X-ray bands, respectively. We provide
cumulative number-count measurements observing, for the first time, that normal
galaxies start to dominate the X-ray source population at the faintest 0.5-2.0
keV flux levels. The highest X-ray source density reaches $\approx50\,500$
deg$^{-2}$, and $47\%\pm4\%$ of these sources are AGNs ($\approx23\,900$
deg$^{-2}$).


title:
How to employ $\bar{B}^0_d \to J/\psi(\pi\eta,\bar{K}K)$ decays to
  extract information on $\pi\eta$ scattering

abstract:
  We demonstrate that dispersion theory allows one to deduce crucial
information on $\pi\eta$ scattering from the final-state interactions of the
light mesons visible in the spectral distributions of the decays $\bar{B}^0_d
\to J/\psi(\pi^0\eta,K^+K^-,K^0\bar{K}^0)$. Thus high-quality measurements of
these differential observables are highly desired. The corresponding rates are
predicted to be of the same order of magnitude as those for $\bar{B}^0_d \to
J/\psi\pi^+\pi^-$ measured recently at LHCb, letting the corresponding
measurement appear feasible.


title:
Realistic estimation for the detectability of dark matter sub-halos with
  Fermi-LAT

abstract:
  Numerical simulations of structure formation have recorded a remarkable
progress in the recent years, in particular due to the inclusion of baryonic
physics evolving with the dark matter component. We generate Monte Carlo
realizations of the dark matter sub-halo population based on the results of the
recent hydrodynamical simulation suite of Milky Way-sized galaxies. We then
simulate the gamma-ray sky for both the setup of the 3FGL and 2FHL Fermi Large
Area Telescope (LAT) catalogs, including the contribution from the annihilation
of dark matter in the sub-halos. We find that the flux sensitivity threshold
strongly depends on the particle dark matter mass, and more mildly also on its
annihilation channel and the observation latitude. The results differ for the
3FGL and 2FHL catalogs, given their different energy thresholds. We also
predict that the number of dark matter sub-halos among the unassociated sources
is very small. A null number of detectable sub-halos in the Fermi-LAT 3FGL
catalog would imply upper limits on the dark matter annihilation cross section
into $b\bar{b}$ of $2 \cdot 10^{-26}$ ($5 \cdot 10^{-25}$) cm$^3$/s with
$M_{\rm DM}$= 50 (1000) GeV. We find less than one extended sub-halo in the
Fermi-LAT 3FGL catalog. As a matter of fact, the differences in the spatial and
mass distribution of sub-halos between hydrodynamic and dark matter-only runs
do not have significant impact on the gamma-ray dark matter phenomenology.


title:
Topological Electromagnetic Responses of Bosonic Quantum Hall,
  Topological Insulator, and Chiral Semi-Metal phases in All Dimensions

abstract:
  We calculate the topological part of the electromagnetic response of Bosonic
Integer Quantum Hall (BIQH) phases in odd (spacetime) dimensions, and Bosonic
Topological Insulator (BTI) and Bosonic chiral semi-metal (BCSM) phases in even
dimensions. To do this we use the Nonlinear Sigma Model (NLSM) description of
bosonic symmetry-protected topological (SPT) phases, and the method of gauged
Wess-Zumino (WZ) actions. We find the surprising result that for BIQH states in
dimension $2m-1$ ($m=1,2,\dots$), the bulk response to an electromagnetic field
$A_{\mu}$ is characterized by a Chern-Simons term for $A_{\mu}$ with a level
quantized in integer multiples of $m!$ (factorial). We also show that BTI
states (which have an extra $\mathbb{Z}_2$ symmetry) can exhibit a
$\mathbb{Z}_2$ breaking Quantum Hall effect on their boundaries, with this
boundary Quantum Hall effect described by a Chern-Simons term at level
$\frac{m!}{2}$. We show that the factor of $m!$ can be understood by requiring
gauge invariance of the exponential of the Chern-Simons term on a general
Euclidean manifold, and we also use this argument to characterize the
electromagnetic and gravitational responses of fermionic SPT phases with $U(1)$
symmetry in all odd dimensions. We then use our gauged boundary actions for the
BIQH and BTI states to (i) construct a bosonic analogue of a chiral semi-metal
(BCSM) in even dimensions, (ii) show that the boundary of the BTI state
exhibits a bosonic analogue of the parity anomaly of Dirac fermions in odd
dimensions, and (iii) study anomaly inflow at domain walls on the boundary of
BTI states. In a series of Appendices we derive important formulas and
additional results. In particular, in Appendix A we use the connection between
equivariant cohomology and gauged WZ actions to give a mathematical
interpretation of the actions for the BIQH and BTI boundaries constructed in
this paper.


title: Do We Really Understand the Cosmos?

abstract:
  Our knowledge about the universe has increased tremendously in the last three
decades or so --- thanks to the progress in observations --- but our
understanding has improved very little. There are several fundamental questions
about our universe for which we have no answers within the current,
operationally very successful, approach to cosmology. Worse still, we do not
even know how to address some of these issues within the conventional approach
to cosmology. This fact suggests that we are missing some important theoretical
ingredients in the overall description of the cosmos. I will argue that these
issues --- some of which are not fully appreciated or emphasized in the
literature --- demand a paradigm shift: We should not think of the universe as
described by a specific solution to the gravitational field equations; instead,
it should be treated as a special physical system governed by a different
mathematical description, rooted in the quantum description of spacetime. I
will outline how this can possibly be done.


title:
Estimating gravitational radiation from super-emitting compact binary
  systems

abstract:
  Binary black hole mergers are among the most violent events in the Universe,
leading to extreme warping of spacetime and copious emission of gravitational
radiation. Even though black holes are the most compact objects they are not
necessarily the most efficient emitters of gravitational radiation in binary
systems. The final black hole resulting from a binary black hole merger retains
a significant fraction of the pre-merger orbital energy and angular momentum. A
non-vacuum system can in principle shed more of this energy than a black hole
merger of equivalent mass. We study these super-emitters through a toy model
that accounts for the possibility that the merger creates a compact object that
retains a long-lived time-varying quadrupole moment. This toy model can capture
the merger of neutron stars, but it can also be used to consider more exotic
compact binaries. We hope that this toy model can serve as a guide to more
rigorous numerical investigations into these systems.


title: LHCb anomalies from a natural perspective

abstract:
  Tension between the Standard Model (SM) and data concerning $b \rightarrow s$
processes has become apparent. Most notoriously, concerning the $R_K$ ratio,
which probes lepton non-universality in $b$ decays, and measurements involving
the decays $B \rightarrow K^* \mu^+ \mu^-$ and $B_s \rightarrow \phi \mu^+
\mu^-$. Careful analysis of a wide range of $b \rightarrow s$ data shows that
certain kinds of new physics can significantly ameliorate agreement with
experiment. Here, we show that these $b \rightarrow s$ anomalies can be
naturally accommodated in the context of Natural Scherk-Schwarz Theories of the
Weak Scale -- a class of models designed to address the hierarchy problem. No
extra states need to be introduced in order to accommodate these anomalies, and
the assumptions required regarding flavor violating couplings are very mild.
Moreover, the structure of the theory makes sharp predictions regarding $B$
meson decays into final states including $\tau^+ \tau^-$ pairs, which will
provide a future test of these models.


title:
X-rays across the galaxy population I: tracing the main sequence of star
  formation

abstract:
  We use deep Chandra imaging to measure the distribution of X-ray luminosities
(L_X) for samples of star-forming galaxies as a function of stellar mass and
redshift, using a Bayesian method to push below the nominal X-ray detection
limits. Our luminosity distributions all show narrow peaks at L_X < 10^{42}
erg/s that we associate with star formation, as opposed to AGN that are traced
by a broad tail to higher L_X. Tracking the luminosity of these peaks as a
function of stellar mass reveals an "X-ray main sequence" with a constant slope
~0.63 +/- 0.03 over 8.5 < log M*/Msun < 11.5 and 0.1 < z < 4, with a
normalization that increases with redshift as (1+z)^{3.79+/-0.12}. We also
compare the peak X-ray luminosities with UV-to-IR tracers of star formation
rates (SFRs) to calibrate the scaling between L_X and SFR. We find that L_X
\propto SFR^{0.83} x (1+z)^{1.3}, where the redshift evolution and
non-linearity likely reflect changes in high-mass X-ray binary populations of
star-forming galaxies. Using galaxies with a broader range of SFR, we also
constrain a stellar-mass-dependent contribution to L_X, likely related to
low-mass X-ray binaries. Using this calibration, we convert our X-ray main
sequence to SFRs and measure a star-forming main sequence with a constant slope
~0.76+/-0.06 and a normalization that evolves with redshift as
(1+z)^{2.95+/-0.33}. Based on the X-ray emission, there is no evidence for a
break in the main sequence at high stellar masses, although we cannot rule out
a turnover given the uncertainties in the scaling of L_X to SFR.


title:
The H$\alpha$ emission of nearby M dwarfs and its relation to stellar
  rotation

abstract:
  The high-energy emission from low-mass stars is mediated by the magnetic
dynamo. Although the mechanisms by which fully convective stars generate
large-scale magnetic fields are not well understood, it is clear that, as for
solar-type stars, stellar rotation plays a pivotal role. We present 270 new
optical spectra of low-mass stars in the Solar Neighborhood. Combining our
observations with those from the literature, our sample comprises 2202
measurements or non-detections of H$\alpha$ emission in nearby M dwarfs. This
includes 466 with photometric rotation periods. Stars with masses between 0.1
and 0.6 solar masses are well-represented in our sample, with fast and slow
rotators of all masses. We observe a threshold in the mass-period plane that
separates active and inactive M dwarfs. The threshold coincides with the
fast-period edge of the slowly rotating population, at approximately the
rotation period at which an era of rapid rotational evolution appears to cease.
The well- defined active/inactive boundary indicates that H$\alpha$ activity is
a useful diagnostic for stellar rotation period, e.g. for target selection for
exoplanet surveys, and we present a mass-period relation for inactive M dwarfs.
We also find a significant, moderate correlation between
$L_{\mathrm{H}\alpha}/L_{\mathrm{bol}}$ and variability amplitude: more active
stars display higher levels of photometric variability. Consistent with
previous work, our data show that rapid rotators maintain a saturated value of
$L_{\mathrm{H}\alpha}/L_{\mathrm{bol}}$. Our data also show a clear power-law
decay in $L_{\mathrm{H}\alpha}/L_{\mathrm{bol}}$ with Rossby number for slow
rotators, with an index of $-1.7 \pm 0.1$.


title:
The Diversity of Diffuse Ly$\alpha$ Nebulae around Star-Forming Galaxies
  at High Redshift

abstract:
  We report the detection of diffuse Ly$\alpha$ emission, or Ly$\alpha$ halos
(LAHs), around star-forming galaxies at $z\approx3.78$ and $2.66$ in the NOAO
Deep Wide-Field Survey Bo\"otes field. Our samples consist of a total of
$\sim$1400 galaxies, within two separate regions containing spectroscopically
confirmed galaxy overdensities. They provide a unique opportunity to
investigate how the LAH characteristics vary with host galaxy large-scale
environment and physical properties. We stack Ly$\alpha$ images of different
samples defined by these properties and measure their median LAH sizes by
decomposing the stacked Ly$\alpha$ radial profile into a compact galaxy-like
and an extended halo-like component. We find that the exponential scale-length
of LAHs depends on UV continuum and Ly$\alpha$ luminosities, but not on
Ly$\alpha$ equivalent widths or galaxy overdensity parameters. The full
samples, which are dominated by low UV-continuum luminosity Ly$\alpha$ emitters
($M_{\rm UV} \gtrsim -21$), exhibit LAH sizes of 5$\,-\,6\,$kpc. However, the
most UV- or Ly$\alpha$-luminous galaxies have more extended halos with
scale-lengths of 7$\,-\,9\,$kpc. The stacked Ly$\alpha$ radial profiles decline
more steeply than recent theoretical predictions that include the contributions
from gravitational cooling of infalling gas and from low-level star formation
in satellites. On the other hand, the LAH extent matches what one would expect
for photons produced in the galaxy and then resonantly scattered by gas in an
outflowing envelope. The observed trends of LAH sizes with host galaxy
properties suggest that the physical conditions of the circumgalactic medium
(covering fraction, HI column density, and outflow velocity) change with halo
mass and/or star-formation rates.


title: Witnessing eigenstates for quantum simulation of Hamiltonian spectra

abstract:
  The efficient calculation of Hamiltonian spectra, a problem often intractable
on classical machines, can find application in many fields, from physics to
chemistry. Here, we introduce the concept of an "eigenstate witness" and
through it provide a new quantum approach which combines variational methods
and phase estimation to approximate eigenvalues for both ground and excited
states. This protocol is experimentally verified on a programmable silicon
quantum photonic chip, a mass-manufacturable platform, which embeds entangled
state generation, arbitrary controlled-unitary operations, and projective
measurements. Both ground and excited states are experimentally found with
fidelities >99%, and their eigenvalues are estimated with 32-bits of precision.
We also investigate and discuss the scalability of the approach and study its
performance through numerical simulations of more complex Hamiltonians. This
result shows promising progress towards quantum chemistry on quantum computers.


title:
A large H$\alpha$ survey of star formation in relaxed and merging galaxy
  cluster environments at $z\sim0.15-0.3$

abstract:
  We present the first results from the largest H$\alpha$ survey of star
formation and AGN activity in galaxy clusters. Using 9 different narrow band
filters, we select $>3000$ H$\alpha$ emitters within $19$ clusters and their
larger scale environment over a total volume of $1.3\times10^5$ Mpc$^3$. The
sample includes both relaxed and merging clusters, covering the $0.15-0.31$
redshift range and spanning from $5\times10^{14}$ $M_{\odot}$ to
$30\times10^{14}$ $M_{\odot}$. We find that the H$\alpha$ luminosity function
(LF) for merging clusters has a higher characteristic density $\phi^*$ compared
to relaxed clusters. $\phi^*$ drops from cluster core to cluster outskirts for
both merging and relaxed clusters, with the merging cluster values $\sim0.3$
dex higher at each projected radius. The characteristic luminosity $L^*$ drops
over the $0.5-2.0$ Mpc distance from the cluster centre for merging clusters
and increases for relaxed objects. Among disturbed objects, clusters hosting
large-scale shock waves (traced by radio relics) are overdense in H$\alpha$
emitters compared to those with turbulence in their intra-cluster medium
(traced by radio haloes). We speculate that the increase in star formation
activity in disturbed, young, massive galaxy clusters can be triggered by
interactions between gas-rich galaxies, shocks and/or the intra-cluster medium,
as well as accretion of filaments and galaxy groups. Our results indicate that
disturbed clusters represent vastly different environments for galaxy evolution
compared to relaxed clusters or average field environments.


title: Quantitative nullhomotopy and rational homotopy type

abstract:
  In \cite{GrOrang}, Gromov asks the following question: given a nullhomotopic
map $f:S^m \to S^n$ of Lipschitz constant $L$, how does the Lipschitz constant
of an optimal nullhomotopy of $f$ depend on $L$, $m$, and $n$? We establish
that for fixed $m$ and $n$, the answer is at worst quadratic in $L$. More
precisely, we construct a nullhomotopy whose \emph{thickness} (Lipschitz
constant in the space variable) is $C(m,n)(L+1)$ and whose \emph{width}
(Lipschitz constant in the time variable) is $C(m,n)(L+1)^2$.
  More generally, we prove a similar result for maps $f:X \to Y$ for any
compact Riemannian manifold $X$ and $Y$ a compact simply connected Riemannian
manifold in a class which includes complex projective spaces, Grassmannians,
and all other simply connected homogeneous spaces. Moreover, for all simply
connected $Y$, asymptotic restrictions on the size of nullhomotopies are
determined by rational homotopy type.


title: Uniqueness of solitary waves in the high-energy limit of FPU-type chains

abstract:
  Recent asymptotic results by the authors provided detailed information on the
shape of solitary high-energy travelling waves in FPU atomic chains. In this
note we use and extend the methods to understand the linearisation of the
travelling wave equation. We show that there are not any other zero eigenvalues
than those created by the translation symmetry and this implies a local
uniqueness result. The key argument in our asymptotic analysis is to replace
the linear advance-delay-differential equation for the eigenfunctions by an
approximate ODE.


title:
Tunable and high purity room-temperature single photon emission from
  atomic defects in hexagonal boron nitride

abstract:
  Two-dimensional van der Waals materials have emerged as promising platforms
for solid-state quantum information processing devices with unusual potential
for heterogeneous assembly. Recently, bright and photostable single photon
emitters were reported from atomic defects in layered hexagonal boron nitride
(hBN), but controlling inhomogeneous spectral distribution and reducing
multi-photon emission presented open challenges. Here, we demonstrate that
strain control allows spectral tunability of hBN single photon emitters over 6
meV, and material processing sharply improves the single-photon purity. We
report high single photon count rates exceeding 10^7 counts/sec at saturation,
which is the highest single photon detection rate for room-temperature single
photon emitters, to our knowledge. Furthermore, these emitters are stable to
material transfer to other substrates. High-purity and photostable single
photon emission at room temperature, together with spectral tunability and
transferability, opens the door to scalable integration of high-quality quantum
emitters in photonic quantum technologies.


title: Kepler Planet Masses and Eccentricities from TTV Analysis

abstract:
  We conduct a uniform analysis of the transit timing variations (TTVs) of 145
planets from 55 Kepler multiplanet systems to infer planet masses and
eccentricities. Eighty of these planets do not have previously reported mass
and eccentricity measurements. We employ two complementary methods to fit TTVs:
Markov chain Monte Carlo simulations based on N-body integration and an
analytic fitting approach. Mass measurements of 49 planets, including 12
without previously reported masses, meet our criterion for classification as
robust. Using mass and radius measurements, we infer the masses of planets'
gaseous envelopes for both our TTV sample as well as transiting planets with
radial velocity observations. Insight from analytic TTV formulae allows us to
partially circumvent degeneracies inherent to inferring eccentricities from TTV
observations. We find that planet eccentricities are generally small, typically
a few percent, but in many instances are non-zero.


title:
Compositional phase stability of strongly correlated electron materials
  within DFT+$U$

abstract:
  Predicting the compositional phase stability of strongly correlated electron
materials is an outstanding challenge in condensed matter physics. In this
work, we employ the DFT+U formalism to address the effects of local
correlations due to transition metal d electrons on compositional phase
stability in the prototype phase stable and separating materials LixCoO2 and
olivine LixFePO4, respectively. We exploit a new spectral decomposition of the
DFT+U total energy, revealing the distinct roles of the filling and ordering of
the d orbital correlated subspace. The on-site interaction U drives both of
these very different materials systems towards phase separation, stemming from
enhanced ordering of the d orbital occupancies in the x=0 and x=1 species,
whereas changes in the overall filling of the d shell contribute negligibly. We
show that DFT+U formation energies are qualitatively consistent with
experiments for phase stable LixCoO2, phase separating LixFePO4, and phase
stable LixCoPO4. However, we find that charge ordering plays a critical role in
the energetics at intermediate x, strongly dampening the tendency for the
Hubbard U to drive phase separation. Most relevantly, the phase stability of
Li1/2CoO2 within DFT+U is qualitatively incorrect without allowing charge
ordering, which is problematic given that neither charge ordering nor the band
gap that it induces are observed in experiment. We demonstrate that charge
ordering arises from the correlated subspace interaction energy as opposed to
the double counting. Additionally, we predict the Li order-disorder transition
temperature for Li1/2CoO2, demonstrating that the unphysical charge ordering
within DFT+U renders the method problematic, often producing unrealistically
large results. Our findings motivate the need for other advanced techniques,
such as DFT+DMFT, for total energies in strongly correlated materials.


title: Dynamic Analysis of Chevron Structures in Liquid Crystal Cells

abstract:
  If a surface stabilized ferroelectric liquid crystal cell is cooled from the
smectic-A to the smectic-C phase, its layers thin causing V-shaped (chevron
like) defects to form. These create an energy barrier that can prevent
switching between equilibrium patterns. We examine a gradient flow for a
mesoscopic Chen-Lubensky energy $\mathcal{F}(\psi,\mathbf{n})$ that allows the
order parameter to vanish, so that the energy barrier does not diverge if the
layer thickness becomes small. The liquid crystal can evolve during switching
in such a way that the layers are allowed to melt and heal near the chevron tip
in the process.


title:
Evolutionary optimization of a charge transfer ionic potential model for
  Ta/Ta-oxide hetero-interfaces

abstract:
  Tantalum, tantalum oxide and their hetero-interfaces are of tremendous
technological interest in several applications spanning electronics, thermal
management, catalysis and biochemistry. For example, local oxygen stoichiometry
variation in TaOx memristors comprising of metallic (Ta) and insulating oxide
(Ta2O5) have been shown to result in fast switching on the sub-nanosecond
timescale over a billion cycles, relevant to neuromorphic computation. Despite
its broad importance, an atomistic scale understanding of oxygen stoichiometry
variation across Ta/TaOx hetero-interfaces, such as during early stages of
oxidation and oxide growth, is not well understood. This is mainly due to the
lack of a variable charge interatomic potential model for tantalum oxides that
can accurately describe the ionic interactions in the metallic (Ta) and oxide
(TaOx) environment as well as at their interfaces. To address this challenge,
we introduce a charge transfer ionic potential (CTIP) model for Ta/Ta-oxide
system by training against lattice parameters, cohesive energies, equations of
state, and elastic properties of various experimentally observed Ta2O5
polymorphs. The best set of CTIP parameters are determined by employing a
single-objective global optimization scheme driven by genetic algorithms
followed by local Simplex optimization. Our newly developed CTIP potential
accurately predicts structure, thermodynamics, energetic ordering of
polymorphs, as well as elastic and surface properties of both Ta and Ta2O5, in
excellent agreement with DFT calculations and experiments. We employ our newly
parameterized CTIP potential to investigate the early stages of oxidation of Ta
at different temperatures and atomic/molecular nature of the oxidizing species.


title:
Visible Light Triggered Drug Release from TiO2 Nanotube Arrays: A Novel
  Controllable Antibacterial Platform

abstract:
  In this work, we use a double-layered stack of TiO2 nanotubes (TiNTs) to
construct a visible-light triggered drug delivery system. Key for visible-light
drug release is a hydrophobic cap on the nanotubes containing Au nanoparticles
(AuNPs). The AuNPs allow for a photocatalytic scission of the hydrophobic chain
under visible light. To demonstrate the principle, we loaded antibiotic
(ampicillin sodium (AMP)) in the lower part of the TiO2 nanotube stack,
triggered visible light induced release, and carried out antibacterial studies.
The release from the platform becomes most controllable if the drug is
silane-grafted in hydrophilic bottom layer for drug storage. Thus visible-light
photocatalysis can also determine the release kinetics of the active drug from
the nanotube wall.


title: Evolved stars at high angular resolution: present and future

abstract:
  The late evolutionary stages of stellar evolution are a key ingredient for
our understanding in many fields of astrophysics, including stellar evolution
and the enrichment of the interstellar medium (ISM) via stellar yields. Already
the first interferometric campaigns identified evolved stars as the primary
targets because of their extended and partially optically thin atmospheres, and
the brightness in the infrared. Interferometric studies spanning different
wavelength ranges, from visual to mid-infrared, have greatly increased our
knowledge of the complex atmospheres of these objects where different dynamic
processes are at play. In less than two decades this technique went from
measuring simple diameters to produce the first images of stellar surfaces. By
scanning the extended atmospheres we constrained theoretical models, learnt
about molecular stratification, dust formation, and stellar winds, and there is
still a lot to be done. In this contribution I will review the recent results
that optical/infrared interferometry has made on our current understanding of
cool evolved stars. The presentation will focus on asymptotic giant branch
stars, and red supergiants. I will discuss the challenges of image
reconstruction, and highlight how this field of research will benefit from the
synergy of the current interferometric instrument(s) with the second generation
VLTI facilities GRAVITY and MATISSE. Finally I will conclude with a short
introspection on applications of a visible interferometer and of the the Planet
Formation Imager (PFI) to the field of evolved stars.