title: Stacked Periodograms as a Probe of Exoplanetary Populations

abstract:
  Ongoing, extreme-precision Doppler radial velocity surveys seek planets with
masses less than several M$_\oplus$; population-level studies to determine the
distribution of planetary masses, however, remain difficult due to the required
observational time investment, as well as challenges associated with robustly
detecting the lowest mass planets. We outline a novel approach that leverages
extensive, existing RV datasets to constrain masses of exoplanet populations:
stacking periodograms of RV timeseries across many targets. We show that an
exoplanet population may be statistically identifiable in the stacked
periodogram, even when individual planets do not pass the threshold of
detection. We discuss analytical, statistical properties of the stacked
periodogram, perform simulations to demonstrate the efficacy of the method, and
investigate the influence of semi-structured window functions and stellar
activity. Analysis of the Lick-Carnegie Exoplanet Survey data set reveals a
marginally significant ($1.6\sigma$) signal consistent with a population of
exoplanets occupying $3-7$ day periods with typical $K$ between $1.6-5.1$ m
s$^{-1}$. More detailed investigation of signals associated with stellar
activity and yearly systematics may be necessary to confirm this result or
detect other underlying Keplerian contributions.


title: The mass profile of NGC 3377 from a Bayesian approach

abstract:
  The mass profile for the moderately bright elliptical NGC 3377 is studied
through an spherical Jeans analysis, combined with a Bayesian approach. The
prior distributions are generated from dark matter simulations and
observational constraints. The observational data set consist of Gemini/GMOS
long-slit observations aligned with the major and minor axes of the galaxy, and
are supplemented with data from the literature for the diffuse stellar
component, globular clusters and planetary nebulae. Although the galaxy is
assumed to alternatively reside in central and satellite haloes, the comparison
with literature results prefer the latter option. Several options of constant
anisotropy are considered, as well as both NFW and Einasto mass profiles. The
analysis points to an intermediate mass halo, presenting a virial mass around
$(3.6\pm0.6)\times 10^{11}\,{\rm M_{\odot}}$.


title:
Retraction based Direct Search Methods for Derivative Free Riemannian
  Optimization

abstract:
  Direct search methods represent a robust and reliable class of algorithms for
solving black-box optimization problems.
  In this paper, we explore the application of those strategies to Riemannian
optimization, wherein minimization is to be performed with respect to variables
restricted to lie on a manifold. More specifically, we consider classic and
line search extrapolated variants of direct search, and, by making use of
retractions, we devise tailored strategies for the minimization of both smooth
and nonsmooth functions.
  As such we analyze, for the first time in the literature, a class of
retraction based algorithms for minimizing nonsmooth objectives on a Riemannian
manifold without having access to (sub)derivatives. Along with convergence
guarantees we provide a set of numerical performance illustrations on a
standard set of problems.


title:
Adsorption, self-assembly and self-metalation of tetra-cyanophenyl
  porphyrins on semiconducting CoO(100) films

abstract:
  The adsorption properties of free base
5,10,15,20-tetrakis(p-cyanophenyl)porphyrin (2H-TCNPP) on thin films of rock
salt (rs) CoO(100) on Au(111) was studied in ultra-high vacuum by a combination
of low-temperature scanning tunneling microscopy and spectroscopy (STM/STS) and
density functional theory (DFT). Films of rs-CoO(100) on Au(111) are prepared
with excellent quality in a suitable thickness range. Particularly, we found
that films of only 1 nm thickness show a semiconducting energy gap of
$E_\mathrm{g}=(2.5\pm 0.2)\,\textrm{eV}$. Upon deposition at 300 K, 2H-TCNPP
adsorbs flat-lying and self-assembles in a long-range ordered superstructure
that is stable at 80 K. The adsorption geometry of the molecules on the surface
and within the self-assembly is analyzed by DFT. We find that the
self-assemblies are stabilized by hydrogen bridge bonding via the functional
cyano groups. Our STS data shows molecular states within the fundamental gap of
the CoO. By comparison with the calculated DOS we determine the energetic
positions of the frontier orbitals and find that the first three LUMO states
2H-TCNPP are located within the band gap, whereas the HOMO is shifted 1 eV
below the CoO conduction band edge. Upon annealing to 420 K the molecules
change their appearance in STM images and a new prominent electronic state
located at the center of the molecule is formed. We interpret this changed
configuration as Co-TCNPP created by self-metalation on the oxide surface.


title:
A Parkes "Murriyang" Search for Pulsars and Transients in the Large
  Magellanic Cloud

abstract:
  We report on the latest results of a Parkes multibeam survey for pulsars and
dispersed radio bursts in the Large Magellanic Cloud (LMC). We conducted both
periodicity and single-pulse searches at a much larger range of trial
dispersion measures (DMs) than previously searched. We detected 229 single
pulses with signal-to-noise ratio ($\rm{S/N}) > 7$ that were classified by the
deep learning network FETCH as being real (with $> 90$% likelihood), of which 9
were from the known giant-pulse-emitting pulsar PSR B0540$-$69. Two possibly
repeating sources were detected with DMs suggesting that they lie within the
LMC, but these require confirmation. Only 3 of the 220 unknown pulses had S/N
greater than 8, and the DM distribution for these detected pulses follows an
exponential falloff with increasing DM and does not show any excess of signals
at DM values expected for the LMC. These features suggest that the detected
pulses are not likely to be real, although they are visually compelling. We
also report the discovery of a new pulsar (PSR J0556$-$67) in our periodicity
search. This pulsar has a spin period of 791 ms, a DM of 71 cm$^{-3}$ pc, an
estimated 1400 MHz flux density of $\sim 0.12$ mJy, and shows no evidence of
binary motion. Future observations may be able to confirm whether any of the
weak but promising candidates in our single pulse and periodicity searches,
including our two possible repeaters, are real or not.


title:
RMF-Owl: A Collision-Tolerant Flying Robot for Autonomous Subterranean
  Exploration

abstract:
  This work presents the design, hardware realization, autonomous exploration
and object detection capabilities of RMF-Owl, a new collision-tolerant aerial
robot tailored for resilient autonomous subterranean exploration. The system is
custom built for underground exploration with focus on collision tolerance,
resilient autonomy with robust localization and mapping, alongside
high-performance exploration path planning in confined, obstacle-filled and
topologically complex underground environments. Moreover, RMF-Owl offers the
ability to search, detect and locate objects of interest which can be
particularly useful in search and rescue missions. A series of results from
field experiments are presented in order to demonstrate the system's ability to
autonomously explore challenging unknown underground environments.


title: Quantum regression in dephasing phenomena

abstract:
  We investigate the validity of quantum regression for a family of quantum
Hamiltonians on a multipartite system leading to phase-damping reduced
dynamics. After finding necessary and sufficient conditions for the
CP-divisibility of the corresponding channel, we evaluate a hierarchy of
equations equivalent to the validity of quantum regression under arbitrary
interventions; in particular, we find necessary conditions for a nontrivial
dephasing to be compatible with quantum regression. In this framework, we study
a class of dephasing-type generalized spin-boson (GSB) models, investigating
the existence of qubit-environment coupling functions that ensure the exact
validity of quantum regression.


title:
Survey of Orion Disks with ALMA (SODA) I: Cloud-level demographics of
  873 protoplanetary disks

abstract:
  (Abridged) Surveys of protoplanetary disks in nearby star-forming regions
(SFRs) have provided important information on their demographics, but due to
their sample sizes, they cannot be used to study how disk properties vary with
the environment. We conduct a survey of the unresolved millimeter continuum
emission of 873 protoplanetary disks identified by Spitzer in the L1641 and
L1647 regions of the Orion A cloud. This is the largest such survey yet,
allowing us to identify even weak trends in the median disk mass as a function
of position in the cloud and cluster membership. The sample detection rates and
median masses are also compared to those of nearby (<300 pc) SFRs. The sample
was observed with ALMA at 225 GHz, with a median rms of 0.08 mJy/beam (1.5
M$_{\oplus}$). The data were reduced and imaged using an innovative parallel
data processing approach. We detect 58% (502/873) of the observed disks. This
includes 20 disks with dust masses >100 M$_{\oplus}$, and two objects
associated with extended dust emission. We infer a median disk dust mass in the
full sample of $2.2^{+0.2}_{-0.2}$ M$_{\oplus}$. In L1641 and L1647 median dust
masses are $2.1^{+0.2}_{-0.2}$ M$_{\oplus}$ and $2.6^{+0.4}_{-0.5}$
M$_{\oplus}$, respectively. The disk mass distribution of the full sample is
similar to that of nearby low-mass SFRs at similar ages of 1-3 Myr. We find
only weak trends in disk (dust) masses with galactic longitude and between the
YSO clusters identified in the sample, with median masses varying by $\lesssim$
50%. Age differences may explain these median disk mass variations. Apart from
this, disk masses are essentially constant at scales of ~100 pc. This also
suggests that the majority of disks, even in different SFRs, are formed with
similar initial masses and evolve at similar rates, assuming no external
irradiation, with disk mass loss rates of $\sim 10^{-8}$ M$_{\odot}$/yr.


title: Transfer matrices for AdS3/CFT2

abstract:
  We work out the algebraic Bethe ansatz for the worldsheet theory of the
$AdS_3\times S^3\times T^4$ superstring, and use it to derive the transfer
matrices for fundamental particles and bound states of the string and mirror
model. We also show how the Bethe equations and transfer matrices are modified
in the presence of an Abelian twist. These will be an important ingredient in
the exploration of the mirror thermodynamic Bethe ansatz equations recently
proposed by Frolov and Sfondrini, and their generalisation to twisted and
deformed models.


title:
Fundamental invariants of tensors, Latin hypercubes, and rectangular
  Kronecker coefficients

abstract:
  We study polynomial SL-invariants of tensors, mainly focusing on fundamental
invariants which are of smallest degrees. In particular, we prove that certain
3-dimensional analogue of the Alon--Tarsi conjecture on Latin cubes considered
previously by B\"urgisser and Ikenmeyer, implies positivity of (generalized)
Kronecker coefficients at rectangular partitions and as a result provides
values for degree sequences of fundamental invariants.


title:
Universal approximation of credit portfolio losses using Restricted
  Boltzmann Machines

abstract:
  We introduce a new portfolio credit risk model based on Restricted Boltzmann
Machines (RBMs), which are stochastic neural networks capable of universal
approximation of loss distributions. We test the model on an empirical dataset
of default probabilities of 30 investment-grade US companies and we show that
it outperforms commonly used parametric factor copula models -- such as the
Gaussian or the t factor copula models -- across several credit risk management
tasks. In particular, the model leads to better out-of-sample fits for the
empirical loss distribution and more accurate risk measure estimations. We
introduce an importance sampling procedure which allows risk measures to be
estimated at high confidence levels in a computationally efficient way and
which is a substantial improvement over the Monte Carlo techniques currently
available for copula models. Furthermore, the statistical factors extracted by
the model admit an interpretation in terms of the underlying portfolio sector
structure and provide practitioners with quantitative tools for the management
of concentration risk. Finally, we show how to use the model for stress testing
by estimating stressed risk measures (e.g. stressed VaR) for our empirical
portfolio under various macroeconomic stress test scenarios, such as those
specified by the FRB's Dodd-Frank Act stress test.


title: In This Apportionment Lottery, the House Always Wins

abstract:
  Apportionment is the problem of distributing $h$ indivisible seats across
states in proportion to the states' populations. In the context of the US House
of Representatives, this problem has a rich history and is a prime example of
interactions between mathematical analysis and political practice. Grimmett
suggested to apportion seats in a randomized way such that each state receives
exactly their proportional share $q_i$ of seats in expectation (ex ante
proportionality) and receives either $\lfloor q_i \rfloor$ or $\lceil q_i
\rceil$ many seats ex post (quota). However, there is a vast space of
randomized apportionment methods satisfying these two axioms, and so we
additionally consider prominent axioms from the apportionment literature. Our
main result is a randomized method satisfying quota, ex ante proportionality
and house monotonicity - a property that prevents paradoxes when the number of
seats changes and which we require to hold ex post. This result is based on a
generalization of dependent rounding on bipartite graphs, which we call
cumulative rounding and which might be of independent interest, as we
demonstrate via applications beyond apportionment.


title: The relative heat content for submanifolds in sub-Riemannian geometry

abstract:
  We study the small-time asymptotics of the relative heat content for
submanifolds in sub-Riemannian geometry. First, we prove the existence of a
smooth tubular neighborhood for submanifolds of any codimension, assuming they
do not have characteristic points. Next, we propose a definition of relative
heat content for submanifolds of codimension $k\geq 1$ and we build an
approximation of this quantity, via smooth tubular neighborhoods. Finally, we
show that this approximation fails to recover the asymptotic expansion of the
relative heat content of the submanifold, by studying an explicit example.


title: Nested spheroidal figures of equilibrium II. Generalization to L layers

abstract:
  We present a vectorial formalism to determine the approximate solutions to
the problem of a composite body made of $L$ homogeneous, rigidly rotating
layers bounded by spheroidal surfaces. The method is based on the 1st-order
expansion of the gravitational potential over confocal parameters, thereby
generalizing the method described in Paper I for $L=2$. For a given relative
geometry of the ellipses and a given set of mass-density jumps at the
interfaces, the sequence of rotation rates and interface pressures is obtained
analytically by recursion. A wide range of equilibria result when layers rotate
in an asynchronous manner, although configurations with a negative oblateness
gradient are more favorable. In contrast, states of global rotation (all layers
move at the same rate), found by solving a linear system of $L-1$ equations,
are much more constrained. In this case, we mathematically demonstrate that
confocal and coelliptical configurations are not permitted. Approximate formula
for small ellipticities are derived. These results reinforce and prolongate
known results and classical theorems restricted to small elliptiticities.
Comparisons with the numerical solutions computed from the
Self-Consistent-Field method are successful.


title: Occupation similarity through bipartite graphs

abstract:
  Similarity between occupations is a crucial piece of information when making
career decisions. However, the notion of a single and unified occupation
similarity measure is more of a limitation than an asset. The goal of the study
is to assess multiple explainable occupation similarity measures that can
provide different insights into inter-occupation relations. Several such
measures are derived using the framework of bipartite graphs. Their viability
is assessed on more than 450,000 job transitions occurring in Slovenia in the
period between 2012 and 2021. The results support the hypothesis that several
similarity measures are plausible and that they present different feasible
career paths. The complete implementation and part of the datasets are
available at https://repo.ijs.si/pboskoski/bipartite_job_similarity_code.


title:
Radio spectra of narrow-line Seyfert 1 galaxies observed with ATCA and
  VLASS

abstract:
  We present radio spectral analyses for a sample of 29 radio-quiet (RQ) and
three radio-loud (RL) narrow-line Seyfert 1 galaxies (NLS1s) detected with the
Australia Telescope Compact Array at both 5.5 GHz and 9.0 GHz. The sample is
characterized by L_bol/L_Edd > 0.15. The radio slopes in 25 of the 29 RQ NLS1s
are steep (alpha_5.5-9.0 < -0.5), as found in earlier studies of RQ high
L_bol/L_Edd AGN. This steep radio emission may be related to AGN-driven
outflows, which are likely more prevalent in high L_bol/L_Edd AGN. In two of
the three RL NLS1s, the radio slopes are flat or inverted (alpha_5.5-9.0 >
-0.5), indicating a compact optically-thick source, likely a relativistic jet.
Archival data at 3.0 GHz, 1.4 GHz, and 0.843 GHz are also compiled, yielding a
sample of 17 NLS1s detected in three bands or more. In nine objects, the radio
spectra flatten at lower frequencies, with median slopes of alpha_5.5-9.0 =
-1.21 +/- 0.17, flattening to alpha_3.0-5.5 = -0.97 +/- 0.27, and to
alpha_1.4-3.0 = -0.63 +/- 0.16. A parabolic fit suggests a median spectral
turnover of ~ 1 GHz, which implies synchrotron self-absorption in a source with
a size of only a fraction of 1 pc, possibly a compact wind or a weak jet. Two
objects show significant spectral steepening to alpha < -2 above 3 GHz or 5
GHz, which may suggest relic emission from past ejection of radio emitting
plasma, of the order of a few years to a few decades ago. Finally, two objects
present a single spectral slope consistent with star-forming activity.


title:
Outing Power Outages: Real-time and Predictive Socio-demographic
  Analytics for New York City

abstract:
  Electrical outages continue to occur despite technological innovations and
improvements to electric power distribution infrastructure. In this paper, we
describe a tool that was designed to acquire and collect data on electric power
outages in New York City since July 2020. The electrical outages are then
displayed on a front-end application, which is publicly available. We use the
collected outage data to analyze these outages and their socio-economic impacts
on electricity vulnerable population groups. We determined that there was a
slightly negative linear relationship between income and number of outages.
Finally, a Markov Influence Graph was created to better understand the spatial
and temporal relationships between outages.


title: Information-driven transitions in projections of underdamped dynamics

abstract:
  Low-dimensional representations of underdamped systems often provide
insightful grasps and analytical tractability. Here, we build such
representations via information projections, obtaining an optimal model that
captures the most information on observed spatial trajectories. We show that,
in paradigmatic systems, the minimization of the information loss drives the
appearance of a discontinuous transition in the optimal model parameters. Our
results raise serious warnings for general inference approaches and unravel
fundamental properties of effective dynamical representations, impacting
several fields, from biophysics to dimensionality reduction.


title: Development of a real-time tritium-in-water monitor

abstract:
  In this paper, we report the development and performance of a detector module
envisaging a tritium-in-water real-time activity monitor. The monitor is based
on modular detection units whose number can be chosen according to the required
sensitivity. The full system must achieve a Minimum Detectable Activity (MDA)
of 100\,Bq/L of tritium-in-water activity which is the limit established by the
E.U. Council Directive 2013/51/Euratom for water intended for human
consumption. The first detector module was characterized, commissioned and
installed immediately after the discharge channel of the Arrocampo dam (Almaraz
nuclear power plant, Spain) on the Tagus river. Due to the high sensitivity of
the single detection modules, the system requires radioactive background
mitigation techniques through the use of active and passive shielding. We have
extrapolated a MDA of 3.6\,kBq/L for a single module being this value limited
by the cosmic background. The obtained value for a single module is already
compatible with a real-time pre-alert system for a nuclear power plant
regarding tritium-in water environmental surveillance. Further optimization of
the single-module sensitivity will imply the reduction of the number of modules
and the cost of the detector system.


title: Generalised bayesian sample copula of order $m$

abstract:
  In this work we propose a semiparametric bivariate copula whose density is
defined by a picewise constant function on disjoint squares. We obtain the
maximum likelihood estimators which reduce to the sample copula under specific
conditions. We carry out a full Bayesian analysis of the model and propose a
spatial dependent prior distribution for the model parameters. This prior
allows the parameters to borrow strength across neighbouring regions to produce
smooth posterior estimates. We implement a simulation study and illustrate the
performance of our model with a real dataset.


title:
Surface-tension-driven evolution of a viscoplastic liquid coating the
  interior of a cylindrical tube

abstract:
  One mechanism for airway closure in the lung is the surface-tension-driven
instability of the mucus layer which lines the airway wall. We study the
instability of an axisymmetric layer of viscoplastic Bingham liquid coating the
interior of a rigid tube, which is a simple model for an airway that takes into
account the yield stress of mucus. An evolution equation for the thickness of
the liquid layer is derived using long-wave theory, from which we also derive a
simpler thin-film evolution equation. In the thin-film case, we show that two
branches of marginally-yielded static solutions of the evolution equation can
be used to both predict the size of initial perturbation required to trigger
instability and quantify how increasing the capillary Bingham number (a
parameter measuring yield stress relative to surface tension) reduces the final
deformation of the layer. Using numerical solutions of the long-wave evolution
equation, we quantify how the critical layer thickness required to form a
liquid plug in the tube increases as the capillary Bingham number is increased.
We discuss the significance of these findings for modelling airway closure in
obstructive conditions such as cystic fibrosis where the mucus layer is often
thicker and has a higher yield stress.


title: Cold atoms in low dimensions -- a laboratory for quantum dynamics

abstract:
  Cold atomic gases have become a paradigmatic system for exploring fundamental
physics, while at the same time allowing to explore applications in quantum
technologies. The accelerating developments in the field have led to a highly
advanced set of engineering techniques that, among others, can tune
interactions, shape the external geometry, select among a large set of atomic
species with different properties, as well as control the number of atoms. In
particular, it is possible to operate in lower dimensions and drive atomic
systems in the strongly correlated regime. In this review, we discuss recent
advances in few-body cold atom systems confined in low dimensions from a
theoretical viewpoint. We mainly focus on bosonic systems in one dimension and
provide an introduction to the well-known static properties before we discuss
the state-of-the-art quantum dynamical processes stimulated by the presence of
correlations. Besides describing the fundamental physical phenomena arising in
these systems, we also provide an overview of the tools and methods that are
commonly used, thus delivering a balanced and comprehensive overview of the
field. We conclude by giving an outlook on possible future directions that are
interesting to explore in these correlated systems.

categories: cond-mat.quant-gas cond-mat.other physics.atom-ph quant-ph


title:
Kolmogorov equations on the space of probability measures associated to
  the nonlinear filtering equation: the viscosity approach

abstract:
  We study the backward Kolmogorov equation on the space of probability
measures associated to the Kushner-Stratonovich equation of nonlinear
filtering. We prove existence and uniqueness in the viscosity sense and, in
particular, we provide a comparison theorem. In the context of stochastic
filtering it is natural to consider measure-valued processes that satisfy
stochastic differential equations. The associated backward Kolmogorov equations
have been studied mainly assuming that these processes admit a density.
  Our approach is different and we work directly with measures. The equation we
study is then a second-order partial differential equation of parabolic type on
the space of probability measures. In the literature only few results are
available on viscosity solutions for this kind of problems and in particular
the uniqueness is a very challenging issue. Here we provide a uniqueness result
via comparison theorem, which is obtained combining a variational principle (in
the sense of Borwein-Preiss) and a smooth way to approximate a solution.


title: Magnetic properties of equiatomic CrMnFeCoNi

abstract:
  Magnetic, specific heat, and structural properties of the equiatomic Cantor
alloy system are reported for temperatures between 5 kelvin and 300 kelvin, and
up to fields of 70 kilo-oersted. Magnetization measurements performed on
as-cast, annealed, and cold-worked samples reveal a strong processing history
dependence and that high-temperature annealing after cold-working does not
restore the alloy to a pristine state. Measurements on known precipitates show
that the two transitions, detected at 43 kelvin and 85 kelvin, are intrinsic to
the Cantor alloy and not the result of an impurity phase. Experimental and ab
initio density functional theory (DFT) computational results suggest that these
transitions are a weak ferrimagnetic transition and a spin-glass-like
transition, respectively, and magnetic and specific heat measurements provide
evidence of significant Stoner enhancement and electron-electron interactions
within the material.


title:
A weak tail-bound probabilistic condition for function estimation in
  stochastic derivative-free optimization

abstract:
  In this paper, we use tail bounds to define a tailored probabilistic
condition for function estimation that eases the theoretical analysis of
stochastic derivative-free optimization methods. In particular, we focus on the
unconstrained minimization of a potentially non-smooth function, whose values
can only be estimated via stochastic observations, and give a simplified
convergence proof for both a direct search and a basic trust-region scheme.


title:
Constrained Visual-Inertial Localization With Application And Benchmark
  in Laparoscopic Surgery

abstract:
  We propose a novel method to tackle the visual-inertial localization problem
for constrained camera movements. We use residuals from the different
modalities to jointly optimize a global cost function. The residuals emerge
from IMU measurements, stereoscopic feature points, and constraints on possible
solutions in SE(3). In settings where dynamic disturbances are frequent, the
residuals reduce the complexity of the problem and make localization feasible.
We verify the advantages of our method in a suitable medical use case and
produce a dataset capturing a minimally invasive surgery in the abdomen. Our
novel clinical dataset MITI is comparable to state-of-the-art evaluation
datasets, contains calibration and synchronization and is available at
https://mediatum.ub.tum.de/1621941.


title: Topological Universality of the Art Gallery Problem

abstract:
  We prove that any compact semi-algebraic set is homeomorphic to the solution
space of some art gallery problem. Previous works have established similar
universality theorems, but holding only up to homotopy equivalence, rather than
homeomorphism, and prior to this work, the existence of art galleries even for
simple spaces such as the M\"obius strip or the three-holed torus were unknown.
Our construction relies on an elegant and versatile gadget to copy guard
positions with minimal overhead, and is thus simpler than previous
constructions, consisting of a single rectangular room with convex slits cut
out from the edges. We additionally show that both the orientable and
non-orientable surfaces of genus $n$ require galleries with only $O(n)$
vertices.


title: Kinetic Field Theory for Cosmic Structure Formation

abstract:
  We apply kinetic field theory to non-linear cosmic structure formation.
Kinetic field theory decomposes the cosmic density field into particles and
follows their trajectories through phase space. We assume that initial particle
momenta are drawn from a Gaussian random field. We place particular emphasis on
the late-time, asymptotic behaviour on small spatial scales of low-order
statistical measures for the distribution of particles in configuration and
velocity space. Our main result is that the power spectra for density and
velocity fluctuations in ensembles of particles freely streaming along
Zel'dovich trajectories asymptotically fall off with wave number $k$ like
$k^{-3}$ for $k\to\infty$, irrespective of the cosmological model and the type
of dark matter assumed, with the exponent set only by the number of spatial
dimensions. This conclusion remains valid for density-fluctuation power spectra
if particle interactions are taken into account in a mean-field approximation.
We also show that the bispectrum of freely-streaming particles falls off
asymptotically like $k^{-11/2}$ under the same general conditions.


title: An interpolating particle method for the Vlasov-Poisson equation

abstract:
  In this paper we present a novel particle method for the Vlasov--Poisson
equation. Unlike in conventional particle methods, the particles are not
interpreted as point charges, but as point values of the distribution function.
In between the particles, the distribution function is reconstructed using
mesh-free interpolation. Our numerical experiments confirm that this approach
results in significantly increased accuracy and noise reduction. At the same
time, many benefits of the conventional schemes are preserved.


title: Reward-Free Policy Space Compression for Reinforcement Learning

abstract:
  In reinforcement learning, we encode the potential behaviors of an agent
interacting with an environment into an infinite set of policies, the policy
space, typically represented by a family of parametric functions. Dealing with
such a policy space is a hefty challenge, which often causes sample and
computation inefficiencies. However, we argue that a limited number of policies
are actually relevant when we also account for the structure of the environment
and of the policy parameterization, as many of them would induce very similar
interactions, i.e., state-action distributions. In this paper, we seek for a
reward-free compression of the policy space into a finite set of representative
policies, such that, given any policy $\pi$, the minimum R\'enyi divergence
between the state-action distributions of the representative policies and the
state-action distribution of $\pi$ is bounded. We show that this compression of
the policy space can be formulated as a set cover problem, and it is inherently
NP-hard. Nonetheless, we propose a game-theoretic reformulation for which a
locally optimal solution can be efficiently found by iteratively stretching the
compressed space to cover an adversarial policy. Finally, we provide an
empirical evaluation to illustrate the compression procedure in simple domains,
and its ripple effects in reinforcement learning.


title:
The R136 star cluster dissected with Hubble Space Telescope/STIS. III.
  The most massive stars and their clumped winds

abstract:
  Context: The star cluster R136 inside the LMC hosts a rich population of
massive stars, including the most massive stars known. The strong stellar winds
of these very luminous stars impact their evolution and the surrounding
environment. We currently lack detailed knowledge of the wind structure that is
needed to quantify this impact. Aims: To observationally constrain the stellar
and wind properties of the massive stars in R136, in particular the parameters
related to wind clumping. Methods: We simultaneously analyse optical and UV
spectroscopy of 53 O-type and 3 WNh-stars using the FASTWIND model atmosphere
code and a genetic algorithm. The models account for optically thick clumps and
effects related to porosity and velocity-porosity, as well as a non-void
interclump medium. Results: We obtain stellar parameters, surface abundances,
mass-loss rates, terminal velocities and clumping characteristics and compare
these to theoretical predictions and evolutionary models. The clumping
properties include the density of the interclump medium and the
velocity-porosity of the wind. For the first time, these characteristics are
systematically measured for a wide range of effective temperatures and
luminosities. Conclusions: We confirm a cluster age of 1.0-2.5 Myr and derive
an initial stellar mass of $\geq 250 {\rm M}_\odot$ for the most massive star
in our sample, R136a1. The winds of our sample stars are highly clumped, with
an average clumping factor of $f_{\rm cl}=29\pm15$. We find tentative trends in
the wind-structure parameters as a function of mass-loss rate, suggesting that
the winds of stars with higher mass-loss rates are less clumped. We compare
several theoretical predictions to the observed mass-loss rates and terminal
velocities and find that none satisfactorily reproduces both quantities. The
prescription of Krti\v{c}ka & Kub\'at (2018) matches best the observed
mass-loss rates.


title:
Constraints on the mass and self-coupling of Ultra-Light Scalar Field
  Dark Matter using observational limits on galactic central mass

abstract:
  It is well known that Ultra-Light Dark Matter (ULDM), usually scalar fields
of mass $m \sim 10^{-22}~{\rm eV}$, can solve some of the outstanding problems
of the Cold Dark Matter (CDM) paradigm. Such a scalar field could have
non-negligible self-coupling $\lambda$. In this work, using the known
observational upper limit on the amount of centrally concentrated dark matter
in a galaxy, we arrive at the observational constraints in the $\lambda - m$
(self coupling $-$ mass) parameter space. It is found that the observational
limit on the mass $m$ of the ULDM depends upon the sign and strength of the
self-interactions. We demonstrate that, for $m \sim 10^{-22}~{\rm eV}$,
self-coupling values of ${\cal O}(10^{-96})$ (corresponding to a scattering
length of $a_s \sim 10^{-82}~{\rm m}$) can be probed using limits on the dark
matter mass within 10 pc of the centre of M87 galaxy. Our analysis suggests
that if Ultra Light Axions (ULAs) form all of dark matter, its mass has to be
less than $\sim 6 \times 10^{-23}$ eV.


title:
A Survey on Scalable LoRaWAN for Massive IoT: Recent Advances,
  Potentials, and Challenges

abstract:
  Long Range (LoRa) is the most widely used technology for enabling Low Power
Wide Area Networks (LPWANs) on unlicensed frequency bands. Despite its modest
Data Rates (DRs), it provides extensive coverage for low-power devices, making
it an ideal communication system for many Internet of Things (IoT)
applications. In general, LoRa radio is considered as the physical layer,
whereas Long Range Wide Area Networks (LoRaWAN) is the MAC layer of the LoRa
stack that adopts star topology to enable communication between multiple End
Devices (EDs) and the network Gateway (GW). The Chirp Spread Spectrum (CSS)
modulation deals with LoRa signals interference and ensures long-range
communication. At the same time, the Adaptive Data Rate (ADR) mechanism allows
EDs to dynamically alter some LoRa features such as the Spreading Factor (SF),
Code Rate (CR), and carrier frequency to address the time variance of
communication conditions in dense networks. Despite the high LoRa connectivity
demand, LoRa signals interference and concurrent transmission collisions are
major limitations. Therefore, to enhance LoRaWAN capacity, the LoRa alliance
released many LoRaWAN versions, and the research community provided numerous
solutions to develop scalable LoRaWAN technology. Hence, we thoroughly examined
LoRaWAN scalability challenges and the state-of-the-art solutions in both the
PHY and MAC layers. Most of these solutions rely on SF, logical, and frequency
channel assignment, while others propose new network topologies or implement
signal processing schemes to cancel the interference and allow LoRaWAN to
connect more EDs efficiently. A summary of the existing solutions in the
literature is provided at the end of the paper by describing the advantages and
drawbacks of each solution and suggesting possible enhancements as future
research directions.


title: Higher regularity for singular K\"ahler-Einstein metrics

abstract:
  We study singular K\"ahler-Einstein metrics that are obtained as
non-collapsed limits of polarized K\"ahler-Einstein manifolds. Our main result
is that if the metric tangent cone at a point is locally isomorphic to the germ
of the singularity, then the metric converges to the metric on its tangent cone
at a polynomial rate on the level of K\"ahler potentials. When the tangent cone
at the point has a smooth cross section, then the result implies polynomial
convergence of the metric in the usual sense, generalizing a result due to
Hein-Sun. We show that a similar result holds even in certain cases where the
tangent cone is not locally isomorphic to the germ of the singularity. Finally
we prove a rigidity result for complete $\partial\bar\partial$-exact Calabi-Yau
metrics with maximal volume growth. This generalizes a result of Conlon-Hein,
which applies to the case of asymptotically conical manifolds.


title: Artificial Viscosity -- Then and Now

abstract:
  In this paper, we recount the history of artificial viscosity, beginning with
its origin in previously unpublished and unavailable documents, continuing on
to current research and ending with recent work describing its physical basis
that suggests new directions for improvement. We focus on the underlying ideas
that recognize the finiteness of scale and of measurement.

categories: physics.comp-ph astro-ph.HE astro-ph.IM math-ph math.MP


title:
Dynamical scaling as a signature of multiple phase competition in
  Yb$_2$Ti$_2$O$_7$

abstract:
  $\rm Yb_2Ti_2O_7$ is a celebrated example of a pyrochlore magnet with
highly-frustrated, anisotropic exchange interactions. To date, attention has
largely focused on its unusual, static properties, many of which can be
understood as coming from the competition between different types of magnetic
order. Here we use inelastic neutron scattering with exceptionally high energy
resolution to explore the dynamical properties of $\rm Yb_2Ti_2O_7$. We find
that spin correlations exhibit dynamical scaling, analogous to behavior found
near to a quantum critical point. We show that the observed scaling collapse
can be explained within a phenomenological theory of multiple--phase
competition, and confirm that a scaling collapse is also seen in
semi--classical simulations of a microscopic model of $\rm Yb_2Ti_2O_7$. These
results suggest a general picture for dynamics in systems with competing ground
states.


title: StickyLand: Breaking the Linear Presentation of Computational Notebooks

abstract:
  How can we better organize code in computational notebooks? Notebooks have
become a popular tool among data scientists, as they seamlessly weave text and
code together, supporting users to rapidly iterate and document code
experiments. However, it is often challenging to organize code in notebooks,
partially because there is a mismatch between the linear presentation of code
and the non-linear process of exploratory data analysis. We present StickyLand,
a notebook extension for empowering users to freely organize their code in
non-linear ways. With sticky cells that are always shown on the screen, users
can quickly access their notes, instantly observe experiment results, and
easily build interactive dashboards that support complex visual analytics. Case
studies highlight how our tool can enhance notebook users's productivity and
identify opportunities for future notebook designs. StickyLand is available at
https://github.com/xiaohk/stickyland.


title:
Semi-Blind Joint Channel and Symbol Estimation in IRS-Assisted
  Multi-User MIMO Networks

abstract:
  Intelligent reflecting surface (IRS) is a promising technology for beyond 5th
Generation of the wireless communications. In fully passive IRS-assisted
systems, channel estimation is challenging and should be carried out only at
the base station or at the terminals since the elements of the IRS are
incapable of processing signals. In this letter, we formulate a tensor-based
semi-blind receiver that solves the joint channel and symbol estimation problem
in an IRS-assisted multi-user multiple-input multiple-output system. The
proposed approach relies on a generalized PARATUCK tensor model of the signals
reflected by the IRS, based on a two-stage closed-form semi-blind receiver
using Khatri-Rao and Kronecker factorizations. Simulation results demonstrate
the superior performance of the proposed semi-blind receiver, in terms of the
normalized mean squared error and symbol error rate, as well as a lower
computational complexity, compared to recently proposed parallel factor
analysis-based receivers.


title:
A gradient-free subspace-adjusting ensemble sampler for
  infinite-dimensional Bayesian inverse problems

abstract:
  Sampling of sharp posteriors in high dimensions is a challenging problem,
especially when gradients of the likelihood are unavailable. In low to moderate
dimensions, affine-invariant methods, a class of ensemble-based gradient-free
methods, have found success in sampling concentrated posteriors. However, the
number of ensemble members must exceed the dimension of the unknown state in
order for the correct distribution to be targeted. Conversely, the
preconditioned Crank-Nicolson (pCN) algorithm succeeds at sampling in high
dimensions, but samples become highly correlated when the posterior differs
significantly from the prior. In this article we combine the above methods in
two different ways as an attempt to find a compromise. The first method
involves inflating the proposal covariance in pCN with that of the current
ensemble, whilst the second performs approximately affine-invariant steps on a
continually adapting low-dimensional subspace, while using pCN on its
orthogonal complement.


title: Counterfactual Phenotyping with Censored Time-to-Events

abstract:
  Estimation of treatment efficacy of real-world clinical interventions
involves working with continuous outcomes such as time-to-death,
re-hospitalization, or a composite event that may be subject to censoring.
Causal reasoning in such scenarios requires decoupling the effects of
confounding physiological characteristics that affect baseline survival rates
from the effects of the interventions being assessed. In this paper, we present
a latent variable approach to model heterogeneous treatment effects by
proposing that an individual can belong to one of latent clusters with distinct
response characteristics. We show that this latent structure can mediate the
base survival rates and helps determine the effects of an intervention. We
demonstrate the ability of our approach to discover actionable phenotypes of
individuals based on their treatment response on multiple large randomized
clinical trials originally conducted to assess appropriate treatments to reduce
cardiovascular risk.


title:
Total insecurity of communication via strong converse for quantum
  privacy amplification

abstract:
  Quantum privacy amplification is a central task in quantum cryptography.
Given shared randomness, which is initially correlated with a quantum system
held by an eavesdropper, the goal is to extract uniform randomness which is
decoupled from the latter. The optimal rate for this task is known to satisfy
the strong converse property and we provide a lower bound on the corresponding
strong converse exponent. In the strong converse region, the distance of the
final state of the protocol from the desired decoupled state converges
exponentially fast to its maximal value, in the asymptotic limit. We show that
this necessarily leads to totally insecure communication by establishing that
the eavesdropper can infer any sent messages with certainty, when given very
limited extra information. In fact, we prove that in the strong converse
region, the eavesdropper has an exponential advantage in inferring the sent
message correctly, compared to the achievability region. Additionally we
establish the following technical result, which is central to our proofs, and
is of independent interest: the smoothing parameter for the smoothed
max-relative entropy satisfies the strong converse property.


title:
Efficient and Differentiable Conformal Prediction with General Function
  Classes

abstract:
  Quantifying the data uncertainty in learning tasks is often done by learning
a prediction interval or prediction set of the label given the input. Two
commonly desired properties for learned prediction sets are \emph{valid
coverage} and \emph{good efficiency} (such as low length or low cardinality).
Conformal prediction is a powerful technique for learning prediction sets with
valid coverage, yet by default its conformalization step only learns a single
parameter, and does not optimize the efficiency over more expressive function
classes.
  In this paper, we propose a generalization of conformal prediction to
multiple learnable parameters, by considering the constrained empirical risk
minimization (ERM) problem of finding the most efficient prediction set subject
to valid empirical coverage. This meta-algorithm generalizes existing conformal
prediction algorithms, and we show that it achieves approximate valid
population coverage and near-optimal efficiency within class, whenever the
function class in the conformalization step is low-capacity in a certain sense.
Next, this ERM problem is challenging to optimize as it involves a
non-differentiable coverage constraint. We develop a gradient-based algorithm
for it by approximating the original constrained ERM using differentiable
surrogate losses and Lagrangians. Experiments show that our algorithm is able
to learn valid prediction sets and improve the efficiency significantly over
existing approaches in several applications such as prediction intervals with
improved length, minimum-volume prediction sets for multi-output regression,
and label prediction sets for image classification.

categories: cs.LG cs.AI math.ST stat.ME stat.ML stat.TH


title: ReorientBot: Learning Object Reorientation for Specific-Posed Placement

abstract:
  Robots need the capability of placing objects in arbitrary, specific poses to
rearrange the world and achieve various valuable tasks. Object reorientation
plays a crucial role in this as objects may not initially be oriented such that
the robot can grasp and then immediately place them in a specific goal pose. In
this work, we present a vision-based manipulation system, ReorientBot, which
consists of 1) visual scene understanding with pose estimation and volumetric
reconstruction using an onboard RGB-D camera; 2) learned waypoint selection for
successful and efficient motion generation for reorientation; 3) traditional
motion planning to generate a collision-free trajectory from the selected
waypoints. We evaluate our method using the YCB objects in both simulation and
the real world, achieving 93% overall success, 81% improvement in success rate,
and 22% improvement in execution time compared to a heuristic approach. We
demonstrate extended multi-object rearrangement showing the general capability
of the system.


title: The Surface Group Conjectures for groups with two generators

abstract:
  The Surface Group Conjectures are statements about recognising surface groups
among one-relator groups, using either the structure of their finite-index
subgroups, or all subgroups. We resolve these conjectures in the two generator
case. More generally, we prove that every two-generator one-relator group with
every infinite-index subgroup free is itself either free or a surface group.


title: GroupViT: Semantic Segmentation Emerges from Text Supervision

abstract:
  Grouping and recognition are important components of visual scene
understanding, e.g., for object detection and semantic segmentation. With
end-to-end deep learning systems, grouping of image regions usually happens
implicitly via top-down supervision from pixel-level recognition labels.
Instead, in this paper, we propose to bring back the grouping mechanism into
deep networks, which allows semantic segments to emerge automatically with only
text supervision. We propose a hierarchical Grouping Vision Transformer
(GroupViT), which goes beyond the regular grid structure representation and
learns to group image regions into progressively larger arbitrary-shaped
segments. We train GroupViT jointly with a text encoder on a large-scale
image-text dataset via contrastive losses. With only text supervision and
without any pixel-level annotations, GroupViT learns to group together semantic
regions and successfully transfers to the task of semantic segmentation in a
zero-shot manner, i.e., without any further fine-tuning. It achieves a
zero-shot accuracy of 51.2% mIoU on the PASCAL VOC 2012 and 22.3% mIoU on
PASCAL Context datasets, and performs competitively to state-of-the-art
transfer-learning methods requiring greater levels of supervision. Project page
is available at https://jerryxu.net/GroupViT.


title:
The Dichotomous Affiliate Stable Matching Problem: Approval-Based
  Matching with Applicant-Employer Relations

abstract:
  While the stable marriage problem and its variants model a vast range of
matching markets, they fail to capture complex agent relationships, such as the
affiliation of applicants and employers in an interview marketplace. To model
this problem, the existing literature on matching with externalities permits
agents to provide complete and total rankings over matchings based off of both
their own and their affiliates' matches. This complete ordering restriction is
unrealistic, and further the model may have an empty core. To address this, we
introduce the Dichotomous Affiliate Stable Matching (DASM) Problem, where
agents' preferences indicate dichotomous acceptance or rejection of another
agent in the marketplace, both for themselves and their affiliates.
  We also assume the agent's preferences over entire matchings are determined
by a general weighted valuation function of their (and their affiliates')
matches. Our results are threefold: (1) we use a human study to show that
real-world matching rankings follow our assumed valuation function; (2) we
prove that there always exists a stable solution by providing an efficient,
easily-implementable algorithm that finds such a solution; and (3) we
experimentally validate the efficiency of our algorithm versus a
linear-programming-based approach.


title: Radio Signals from Axion Star-Neutron Star Binaries

abstract:
  Axion stars could form binaries with neutron stars. Given the extremely
strong external magnetic field exhibited by individual neutron stars, there can
be a substantial conversion of axions to photons in these binaries. The photon
emission is doubly modulated due to the neutron star spinning and the axion
star orbiting, yielding a unique discovery signal. Similar features are also
generated in binaries between a neutron star and an axion-clouded black hole.
Encouragingly, such binaries are found to be within the reach of ongoing and
upcoming experiments (e.g., the Five hundred meter Aperture Spherical Telescope
and the future Square Kilometer Array) for certain parameter regions. They thus
provide a promising astronomical laboratory for detecting axions and axion dark
matter.


title: Message passing all the way up

abstract:
  The message passing framework is the foundation of the immense success
enjoyed by graph neural networks (GNNs) in recent years. In spite of its
elegance, there exist many problems it provably cannot solve over given input
graphs. This has led to a surge of research on going "beyond message passing",
building GNNs which do not suffer from those limitations -- a term which has
become ubiquitous in regular discourse. However, have those methods truly moved
beyond message passing? In this position paper, I argue about the dangers of
using this term -- especially when teaching graph representation learning to
newcomers. I show that any function of interest we want to compute over graphs
can, in all likelihood, be expressed using pairwise message passing -- just
over a potentially modified graph, and argue how most practical implementations
subtly do this kind of trick anyway. Hoping to initiate a productive
discussion, I propose replacing "beyond message passing" with a more tame term,
"augmented message passing".


title:
Hybrid Learning for Orchestrating Deep Learning Inference in Multi-user
  Edge-cloud Networks

abstract:
  Deep-learning-based intelligent services have become prevalent in
cyber-physical applications including smart cities and health-care.
Collaborative end-edge-cloud computing for deep learning provides a range of
performance and efficiency that can address application requirements through
computation offloading. The decision to offload computation is a
communication-computation co-optimization problem that varies with both system
parameters (e.g., network condition) and workload characteristics (e.g.,
inputs). Identifying optimal orchestration considering the cross-layer
opportunities and requirements in the face of varying system dynamics is a
challenging multi-dimensional problem. While Reinforcement Learning (RL)
approaches have been proposed earlier, they suffer from a large number of
trial-and-errors during the learning process resulting in excessive time and
resource consumption. We present a Hybrid Learning orchestration framework that
reduces the number of interactions with the system environment by combining
model-based and model-free reinforcement learning. Our Deep Learning inference
orchestration strategy employs reinforcement learning to find the optimal
orchestration policy. Furthermore, we deploy Hybrid Learning (HL) to accelerate
the RL learning process and reduce the number of direct samplings. We
demonstrate efficacy of our HL strategy through experimental comparison with
state-of-the-art RL-based inference orchestration, demonstrating that our HL
strategy accelerates the learning process by up to 166.6x.


title:
Roto-Translation Equivariant Super-Resolution of Two-Dimensional Flows
  Using Convolutional Neural Networks

abstract:
  Convolutional neural networks (CNNs) often apparently process vectors as
quantities that have no direction such as colors in images. This study
investigates the effect of considering vectors as geometric objects in terms of
super-resolution of velocity on two-dimensional fluids. Vector is distinguished
from scalar by the transformation law associated with a change in basis, which
can be incorporated as the prior knowledge using the equivariant deep learning.
The existing CNNs are converted into equivariant ones by rendering each layer
equivariant with respect to rotation and translation. The training data in the
low- and high-resolution are generated with the downsampling or spectral
nudging. With the date inheriting the rotational symmetry, the equivariant CNNs
exhibit comparable accuracy with the non-equivariant ones. Owing to the smaller
number of parameters in the equivariant CNNs, these models are trainable with a
smaller size of the data. In this case, the transformation law of vector should
be incorporated as the prior knowledge, where vector is treated as a quantity
having direction. Two examples are presented to demonstrate the possibility of
symmetry of the data being broken. In the first case, the downsampling method
renders the correspondence between low- and high-resolution patterns dependent
on the orientation. In the second case, the input data are insufficient to
recognize the rotation of coordinates. In both cases, the accuracy of the CNNs
deteriorates if the equivariance is forcefully imposed, and the conventional
CNNs should be used, where vector is not processed as a quantity having
direction.


title: Triangular lattice quantum dimer model with variable dimer density

abstract:
  We present large-scale quantum Monte Carlo simulation results on an extension
of the triangular lattice quantum dimer model with terms in the Hamiltonian
annihilating and creating single dimers. We find distinct odd and even
$\mathbb{Z}_2$ spin liquids, along with several phases with no topological
order: a staggered crystal, a nematic phase, and a trivial symmetric phase with
no obvious broken symmetry. We also present dynamic spectra of the phases, and
note implications for experiments on Rydberg atoms trapped in arrays of optical
tweezers.

categories: cond-mat.str-el cond-mat.stat-mech physics.atom-ph quant-ph


title:
TDCOSMO. IX. Systematic comparison between lens modelling software
  programs: time delay prediction for WGD 2038$-$4008

abstract:
  The importance of alternative methods to measure the Hubble constant such as
time-delay cosmography is highlighted by the recent Hubble tension. It is
paramount to thoroughly investigate and rule out systematic biases in all
measurement methods before we can accept new physics as the source of this
tension. In this study, we perform a check for systematic biases in the lens
modelling procedure of time-delay cosmography by comparing independent and
blind time-delay predictions of the system WGD 2038$-$4008 from two teams using
two different software programs: Glee and lenstronomy. The predicted time
delays from both teams incorporate the stellar kinematics of the deflector and
the external convergence from line-of-sight structures. The unblinded
time-delay predictions from the two teams agree within $1.2\sigma$ implying
that once the time delay is measured the inferred Hubble constant will also be
mutually consistent. However, there is a $\sim$4$\sigma$ discrepancy between
the power-law model slope and external shear, which is a significant
discrepancy at the level of lens models before incorporating the stellar
kinematics and the external convergence. We identify the difference in the
reconstructed point spread function (PSF) to be the source of this discrepancy.
If the same reconstructed PSF is used by both teams, then we achieve excellent
agreement within $\sim$0.6$\sigma$, indicating that potential systematics
stemming from source reconstruction algorithms and investigator choices are
well under control. We recommend future studies to supersample the PSF as
needed and marginalize over multiple algorithms/realizations for the PSF
reconstruction to mitigate the systematic associated with the PSF. A future
study will measure the time delays of the system WGD 2038$-$4008 and infer the
Hubble constant based on our mass models.


title: The Boring Monopole

abstract:
  We study false vacuum decays catalysed by magnetic monopoles which act as
tunnelling sites with exponentially enhanced decay rates. The field profiles
describing the decay do not have the typically assumed $O(3)/O(4)$ symmetry,
thus requiring an extension of the usual decay rate calculation. To numerically
determine the saddle point solutions which describe the tunnelling process we
use a new algorithm based on the mountain pass theorem. This method can be
applied more widely to phase transitions with reduced symmetry, such as decays
away from the zero and infinite temperature limits. Our results show that
monopole-catalysed tunnelling can dominate over the homogeneous false vacuum
decay for a wide range of parameters, significantly modify the gravitational
wave signal or trigger phase transitions which would otherwise never complete.
A single boring monopole in our Hubble patch may determine the lifetime of the
Standard Model vacuum.


title: Nonlinear optical responses in nodal line semimetals

abstract:
  Shift current and second harmonic generation (SHG) are nonlinear optical
responses that are often used for photovoltaic effect and the detection of
subtle symmetry breaking patterns in materials. It has been recently shown that
topological semimetals such as Weyl semimetals with broken inversion symmetry
can generate large nonlinear optical responses. In this paper, we investigate
both shift current and SHG in a class of topological nodal line semimetal
(NLSM) systems with broken inversion symmetry, which may arise intrinsically or
via an applied electric field. It is shown that certain classes of NLSM systems
offer more singular shift current and SHG in comparison to the well-known Weyl
semimetal systems.


title: A duality connecting neural network and cosmological dynamics

abstract:
  We demonstrate that the dynamics of neural networks trained with gradient
descent and the dynamics of scalar fields in a flat, vacuum energy dominated
Universe are structurally profoundly related. This duality provides the
framework for synergies between these systems, to understand and explain neural
network dynamics and new ways of simulating and describing early Universe
models. Working in the continuous-time limit of neural networks, we
analytically match the dynamics of the mean background and the dynamics of
small perturbations around the mean field, highlighting potential differences
in separate limits. We perform empirical tests of this analytic description and
quantitatively show the dependence of the effective field theory parameters on
hyperparameters of the neural network. As a result of this duality, the
cosmological constant is matched inversely to the learning rate in the gradient
descent update.


title:
Extremely Buried Nucleus of IRAS 17208$-$0014 Observed at Sub-Millimeter
  and Near-Infrared Wavelengths

abstract:
  The ultraluminous infrared galaxy IRAS 17208$-$0014 is a late-stage merger
that hosts a buried active galactic nucleus (AGN). To investigate its nuclear
structure, we performed high spatial resolution
($\sim0.\!\!^{\prime\prime}04\sim32\,\mathrm{pc}$) Atacama Large
Millimeter/submillimeter Array (ALMA) observations in Band 9
($\sim$450\,\micron\ or $\sim$660\,GHz), along with near-infrared AKARI
spectroscopy in 2.5--5.0\,\micron. The Band 9 dust continuum peaks at the AGN
location, and toward this position CO($J$=6--5) and CS($J$=14--13) are detected
in absorption. Comparison with non-local thermal equilibrium calculations
indicates that, within the central beam ($r\sim20\,\mathrm{pc}$), there exists
a concentrated component that is dense ($10^7\,\mathrm{cm}^{-2}$) and warm
($>$200\,K) and has a large column density
($N_\mathrm{H_2}>10^{23}\,\mathrm{cm}^{-2}$). The AKARI spectrum shows deep and
broad CO ro-vibrational absorption at 4.67\,\micron. Its band profile is well
reproduced with a similarly dense and large column but hotter ($\sim$1000\,K)
gas. The region observed through absorption in the near-infrared is highly
likely in the nuclear direction, as in the sub-millimeter, but with a narrower
beam including a region closer to the nucleus. The central component is
considered to possess a hot structure where vibrationally excited HCN emission
originates. The most plausible heating source for the gas is X-rays from the
AGN. The AKARI spectrum does not show other AGN signs in 2.5--4\,\micron, but
this absence may be usual for AGNs buried in a hot mid-infrared core. Besides,
based on our ALMA observations, we relate various nuclear structures of IRAS
17208$-$0014 that have been proposed in the literature.


title: Kaon electromagnetic form factors in dispersion theory

abstract:
  The electromagnetic form factors of charged and neutral kaons are strongly
constrained by their low-energy singularities, in the isovector part from
two-pion intermediate states and in the isoscalar contribution in terms of
$\omega$ and $\phi$ residues. The former can be predicted using the respective
$\pi\pi\to\bar K K$ partial-wave amplitude and the pion electromagnetic form
factor, while the latter parameters need to be determined from electromagnetic
reactions involving kaons. We present a global analysis of time- and spacelike
data that implements all of these constraints. The results enable manifold
applications: kaon charge radii, elastic contributions to the kaon
electromagnetic self energies and corrections to Dashen's theorem, kaon boxes
in hadronic light-by-light (HLbL) scattering, and the $\phi$ region in hadronic
vacuum polarization (HVP). Our main results are: $\langle
r^2\rangle_\text{c}=0.359(3)\,\text{fm}^2$, $\langle
r^2\rangle_\text{n}=-0.060(4)\,\text{fm}^2$ for the charged and neutral radii,
$\epsilon=0.63(40)$ for the elastic contribution to the violation of Dashen's
theorem, $a_\mu^{K\text{-box}}=-0.48(1)\times 10^{-11}$ for the charged kaon
box in HLbL scattering, and $a_\mu^\text{HVP}[K^+K^-, \leq
1.05\,\text{GeV}]=184.5(2.0)\times 10^{-11}$, $a_\mu^\text{HVP}[K_SK_L, \leq
1.05\,\text{GeV}]=118.3(1.5)\times 10^{-11}$ for the HVP integrals around the
$\phi$ resonance. The global fit to $\bar K K$ gives $\bar
M_\phi=1019.479(5)\,\text{MeV}$, $\bar \Gamma_\phi=4.207(8)\,\text{MeV}$ for
the $\phi$ resonance parameters including vacuum-polarization effects.


title:
The XMM Cluster Survey analysis of the SDSS DR8 redMaPPer Catalogue:
  Implications for scatter, selection bias, and isotropy in cluster scaling
  relations

abstract:
  In this paper we present the X-ray analysis of SDSS DR8 redMaPPer (SDSSRM)
clusters using data products from the $XMM$ Cluster Survey (XCS). In total,
1189 SDSSRM clusters fall within the $XMM$-Newton footprint. This has yielded
456 confirmed detections accompanied by X-ray luminosity ($L_{X}$)
measurements. Of the detected clusters, 382 have an associated X-ray
temperature measurement ($T_{X}$). This represents one of the largest samples
of coherently derived cluster $T_{X}$ values to date. Our analysis of the X-ray
observable to richness ($\lambda$) scaling relations has demonstrated that
scatter in the $T_{X}-\lambda$ relation is roughly a third of that in the
$L_{X}-\lambda$ relation, and that the $L_{X}-\lambda$ scatter is intrinsic,
i.e. will not be significantly reduced with larger sample sizes. Our analysis
of the scaling relation between $L_{X}$ and $T_{X}$ has shown that the fits are
sensitive to the selection method of the sample, i.e. whether the sample is
made up of clusters detected "serendipitously" compared to those deliberately
targeted by $XMM$. These differences are also seen in the $L_{X}-\lambda$
relation and, to a lesser extent, in the $T_{X}-\lambda$ relation. Exclusion of
the emission from the cluster core does not make a significant impact to the
findings. A combination of selection biases is a likely, but as yet unproven,
reason for these differences. Finally, we have also used our data to probe
recent claims of anisotropy in the $L_{X}-T_{X}$ relation across the sky. We
find no evidence of anistropy, but stress that this may be masked in our
analysis by the incomplete declination coverage of the SDSS DR8 sample.


title: Spacetime curvature from ultra rapid measurements of quantum fields

abstract:
  We write the curvature of spacetime in terms of the excitation probability of
particle detectors ultra-rapidly coupled to a quantum field. More precisely, we
provide an expansion for the excitation probability of a smeared UDW detector
delta-coupled to a real scalar quantum field in a curved background. Using a
short distance expansion for the Wightman function, we express the excitation
probability of a detector as the transition probability in Minkowski spacetime
plus correction terms written as a function of the curvature tensors and the
detector size. Comparing the excitation probability in curved spacetimes with
its flat analog, we are able to express the components of the Ricci and Riemann
curvature tensors as a function of physically measurable excitation
probabilities of different shaped detectors.


title: Dense polar active fluids in a disordered environment

abstract:
  We examine the influence of quenched disorder on the flocking transition of
dense polar active matter. We consider incompressible systems of active
particles with aligning interactions under the effect of either quenched random
forces or random dilution. The system displays a continuous disorder-order
(flocking) transition, and the associated scaling behavior is described by a
new universality class which is controlled by a quenched Navier-Stokes fixed
point. We determine the critical exponents through a perturbative
renormalization group analysis. We show that the two forms of quenched
disorder, random force and random mass (dilution), belong to the same
universality class, in contrast with the situation at equilibrium.


title:
A Maximum Likelihood Calibration of the Tip of the Red Giant Branch
  Luminosity from High Latitude Field Giants using Gaia Early Data Release 3
  Parallaxes

abstract:
  The calibration of the tip of the red giant branch (TRGB) in the I-band has a
direct role in determinations of the Hubble constant, a subject of recent
interest. We present a maximum likelihood (ML) method designed to obtain an
independent calibration of the brightness of TRGB using Gaia parallaxes from
the Early Data Release 3 (EDR3) of Milky Way field Giants at high Galactic
latitude. We adopt simple parameterizations for the Milky Way stellar
luminosity function and density law and and optimize the likelihood of the
observed sample as a function of those parameters. Using parameters to
partially constrain the luminosity function from other galaxies similar to the
Milky Way for which high quality TRGB data are available, we find values of the
TRGB magnitude of $ M_I^{TRGB} $ = $-3.978$ $\pm$ $0.031$ (stat) $\pm$ $0.045$
(sys) mag, where the systematic uncertainty covers the range of shape
parameters found in our reference galaxies. While current data are insufficient
to simultaneously characterize the shape of the Milky Way luminosity function
we estimate that the photometry from Gaia Data Release 3 (mid-2022) will allow
better constraints on the shape, and lower statistical uncertainties on the tip
by a factor of 3. With expected releases of improved parallax measurements from
Gaia, the method of calibrating the TRGB luminosity from field Giants is
expected to reach $\sim$ 0.01 mag uncertainty, which is an important step
toward a precise TRGB-based determination of the Hubble constant.


title: Charged Moments in $W_3$ Higher Spin Holography

abstract:
  We consider the charged moments in $SL(3,\mathbb{R})$ higher spin holography,
as well as in the dual two-dimensional conformal field theory with $W_3$
symmetry. For the vacuum state and a single entangling interval, we show that
the $W_3$ algebra of the conformal field theory induces an entanglement $W_3$
algebra acting on the quantum state in the entangling interval. The algebra
contains a spin 3 modular charge which commutes with the modular Hamiltonian.
The reduced density matrix is characterized by the modular energy and modular
charge, hence our definition of the charged moments is also with respect to
these conserved quantities. We evaluate the logarithm of the charged moments
perturbatively in the spin 3 modular chemical potential, by computing the
corresponding connected correlation functions of the modular charge operator up
to quartic order in the chemical potential. This method provides access to the
charged moments without using charged twist fields. Our result matches known
results for the charged moment obtained from the charged topological black hole
picture in $SL(3,\mathbb{R})$ higher spin gravity. Since our charged moments
are not Gaussian in the chemical potential any longer, we conclude that the
dual $W_3$ conformal field theories must feature breakdown of equipartition of
entanglement to leading order in the large $c$ expansion.

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


title: A Highly Variable Magnetized Environment in a Fast Radio Burst Source

abstract:
  Fast radio bursts are brief, intense flashes of radio waves that arise from
unknown sources in galaxies across the universe. Observations of the
polarization properties in repeating fast radio bursts have shown they can
reside in highly magnetized environments, such as in the immediate vicinity of
a recent supernova or massive black hole. We have observed the actively
repeating FRB 20190520B over a span of fourteen months and found that its
Faraday rotation measure is both large in magnitude and rapidly varying,
including two sign changes which indicate time-dependent orientation changes of
the magnetic field along our line of sight. The FRB also depolarizes rapidly at
lower frequencies. These phenomena can be explained in terms of multi-path
propagation through a highly turbulent, dense magnetized screen within a range
of 8 AU to 100 pc away from the FRB source, distinctly narrowing the possible
physical configurations that could give rise to the emission seen in FRB
20190520B.


title:
Reduced density matrix and entanglement in interacting quantum field
  theory with Hamiltonian truncation

abstract:
  Entanglement is the fundamental difference between classical and quantum
systems and has become one of the guiding principles in the exploration of
high- and low-energy physics. The calculation of entanglement entropies in
interacting quantum field theories, however, remains challenging. Here, we
present the first method for the explicit computation of reduced density
matrices of interacting quantum field theories using truncated Hamiltonian
methods. The method is based on constructing an isomorphism between the Hilbert
space of the full system and the tensor product of Hilbert spaces of
sub-intervals. This naturally enables the computation of the von Neumann and
arbitrary R\'enyi entanglement entropies as well as mutual information,
logarithmic negativity and other measures of entanglement. Our method is
applicable to equilibrium states and non-equilibrium evolution in real time. It
is model independent and can be applied to any Hamiltonian truncation method
that uses a free basis expansion. We benchmark the method on the free
Klein-Gordon theory finding excellent agreement with the analytic results. We
further demonstrate its potential on the interacting sine-Gordon model,
studying the scaling of von Neumann entropy in ground states and real time
dynamics following quenches of the model.


title: Twist-three cross-sections in deeply virtual Compton scattering

abstract:
  We study the deeply virtual Compton scattering process with both twist-two
and twist-three Compton form factors and present our cross-sections formulas
with all polarization configurations. While the twist-three contributions are
generally assumed to be negligible in the literature due to the kinematical
suppression, we compare them with the twist-two ones at typical JLab 6 GeV and
12 GeV kinematics as well as EIC kinematics and show their kinematical
suppression explicitly, justifying the leading-twist approximation made in the
literature. In addition, we also estimate the twist-three Compton form factors
using Wandzura-Wilczek relations and inputs of twist-two generalized parton
distributions based on a reggeized spectator model. With those estimated
Compton form factors, we analyze the kinematical behavior of twist-two and
twist-three cross-sections in a wide range of kinematics, and discuss the
optimal regions for separating the leading-twist effects from the higher-twist
ones.


title:
Certain exact many-body results for Hubbard model ground states testable
  in small quantum dot arrays

abstract:
  We present two interesting phenomena related to flatband ferromagnetism in
the Hubbard model. The first is a mathematical theorem stating certain
conditions under which a flatband ferromagnetic must necessarily be degenerate
with a nonferromagnetic state. This theorem is generally applicable and
geometry-independent, but holds only for a small number of holes in an
otherwise filled band. The second phenomenon is a peculiar example where the
intuition fails that particles prefer to doubly occupy low-energy states before
filling higher-energy states. Both of these examples require only a small
number of lattice sites, and may be observable in quantum dot arrays currently
available as laboratory spin qubit arrays.


title: Do Radio Active Galactic Nuclei Reflect X-ray Binary Spectral States?

abstract:
  Over recent years there has been mounting evidence that accreting
supermassive black holes in active galactic nuclei (AGN) and stellar mass black
holes have similar observational signatures: thermal emission from the
accretion disk, X-ray corona, and relativisitic jets. Further, there have been
investigations into whether or not AGN have spectral states similar to that of
X-ray binaries (XRBs) and what parallels can be drawn between the two using a
hardness-intensity diagram (HID). To address whether AGN jets might be related
to accretion states as in XRBs, we explore whether populations of radio-AGN
classified according to their radio jet morphology (Fanaroff-Riley classes I
and II; FR I and II), excitation class (HERG and LERG), and radio jet linear
extent (compact to giant) occupy different and distinct regions of the AGN
hardness-intensity diagram (total luminosity vs. hardness). We do this by cross
correlating 15 catalogs of radio galaxies with the desired characteristics from
the literature withXMM_Newton and Swift X-ray and ultraviolet (UV) source
catalogs. We calculate the luminosity and hardness from the X-ray and UV
photometry, place the sources on the AGN hardness-intensity diagram, and search
for separation of populations and analogies with the XRB spectral state HID. We
find that (a) FR Is and IIs, (b) HERGs and LERGs, (c) FR I-LERGs and FR
II-HERGs occupy distinct areas of the HID at a statistically significant level
(p-value < 0.05) and no clear evidence for population distinction between the
different radio jet linear extents. The separation between FR I-LERG and FR
II-HERG populations is the strongest in this work.Our results indicate that
radio-loud AGN occupy distinct areas of the HID depending on the morphology and
excitation class, showing strong similarities to XRBs.


title:
Nonlinear optical processes in centrosymmetric systems by
  strong-coupling-induced symmetry breaking

abstract:
  Nonlinear optical processes associated with even-order nonlinear
susceptibilities are critical for both classical and quantum technologies.
Inversion symmetry, however, prevents nonlinear optical responses mediated by
even-order susceptibilities in several material systems pertinent for
applications in nanophotonics. Here, we demonstrate induced nonlinear optical
processes, namely second- and fourth-harmonic generation that are naturally
forbidden in an inversion symmetric system, by strongly coupling to a photon
mode of a high-Q optical cavity. As an illustrative system with an inversion
symmetry, we consider a semiconductor quantum ring of GaAs that features a
single effective electron. For the coupled system, we control the inversion
symmetry breaking by changing the light-matter coupling strength which at the
same time allows to tune the nonlinear conversion efficiency. We find that the
harmonic generation yield can be significantly increased by increasing the
light-matter coupling strength in an experimentally feasible way. In the
few-photon limit where the incident pump field is a coherent state with just a
few photons, we find that the harmonic conversion efficiency is increased for
strong coupling as opposed to using intense pump fields. This new approach is
applicable to a wide variety of centrosymmetric systems as the symmetry
breaking rest on the properties of the photonic environment used to achieve
strong light-matter interaction. Our work constitutes a step forward in the
direction of realizing physically forbidden nonlinear optical processes in
centrosymmetric materials widely adopted for applications in integrated
photonics.


title:
The ALMA REBELS Survey: the dust content of $z \sim 7$ Lyman Break
  Galaxies

abstract:
  We include a fully coupled treatment of metal and dust enrichment into the
Delphi semi-analytic model of galaxy formation to explain the dust content of
13 Lyman Break Galaxies (LBGs) detected by the Atacama Large millimetre Array
(ALMA) REBELS Large Program at $z\simeq 7$. We find that the galaxy dust mass,
$M_d$, is regulated by the combination of SNII dust production, astration,
shock destruction, and ejection in outflows; grain growth (with a standard
timescale $\tau_0= 30$ Myr) plays a negligible role. The model predicts a
dust-to-stellar mass ratio of $\sim 0.07-0.1\%$ and a UV-to-total star
formation rate relation such that $log (\psi_{\rm UV}) = -0.05 ~[log
(\psi)]^{2} + 0.86 ~log(\psi) -0.05$ (implying that 55-80\% of the star
formation is obscured) for REBELS galaxies with stellar mass $M_* = 10^{9-10}
M_\odot$. This relation reconciles the intrinsic UV luminosity of LBGs with
their observed luminosity function at $z=7$. However, 2 out of the 13 systems
show dust-to-stellar mass ratios ($\sim 0.94-1.1\%$) that are up to $18\times$
larger than expected from the fiducial relation. Due to the physical coupling
between dust and metal enrichment, even decreasing $\tau_0$ to very low values
(0.3 Myr) only increases the dust-to-stellar mass ratio by a factor $ \sim 2$.
Given that grain growth is not a viable explanation for such high observed
ratios of the dust-to-stellar mass, we propose alternative solutions.


title: 3D RMHD simulations of jet-wind interactions in High Mass X-ray Binaries

abstract:
  The interaction of jets in High-Mass X-ray Binaries (HMXBs) with the strong
winds driven by the hot companion star in the vicinity of the compact object is
fundamental to understand the jet dynamics, non-thermal emission and long-term
stability. However, the role of the jet magnetic field in this process is
unclear. We study the dynamical role of weak and moderate-to-strong toroidal
magnetic fields during the first hundreds of seconds of jet propagation,
focusing on the magnetized flow dynamics and the mechanisms of energy
conversion. We have developed the code L\'ostrego v1.0, a new 3D RMHD code to
simulate astrophysical plasmas in Cartesian coordinates. Using this tool, we
performed the first 3D RMHD numerical simulations of relativistic magnetized
jets propagating through the clumpy stellar wind in a HMXB. The overall
morphology and dynamics of weakly magnetized jet models is similar to previous
hydrodynamical simulations, where the jet head generates a strong shock in the
ambient medium and the initial over-pressure with respect to the stellar wind
drives one or more recollimation shocks. In the time scales of our simulations,
these jets are ballistic and seem to be more stable against internal
instabilities than jets with the same power in the absence of fields. However,
moderate-to-strong toroidal magnetic fields favour the development of
current-driven instabilities and the disruption of the jet within the binary. A
detailed analysis of the energy distribution in the relativistic outflow and
the ambient medium reveals that both magnetic and internal energies can
contribute to the effective acceleration of the jet. We certify that the jet
feedback into the ambient medium is highly dependent on the jet energy
distribution at injection, where hotter, more dilute and/or more magnetized
jets are more efficient, as anticipated by feedback studies in the case of jets
in active galaxies.


title:
toise: a framework to describe the performance of high-energy neutrino
  detectors

abstract:
  Neutrinos offer a unique window to the distant, high-energy universe. Several
next-generation instruments are being designed and proposed to characterize the
flux of TeV--EeV neutrinos. The projected physics reach of the detectors is
often quantified with simulation studies. However, a complete Monte Carlo
estimate of detector performance is costly from a computational perspective,
restricting the number of detector configurations considered when designing the
instruments. In this paper, we present a new Python-based software framework,
toise, which forecasts the performance of a high-energy neutrino detector using
parameterizations of the detector performance, such as the effective areas,
angular and energy resolutions, etc. The framework can be used to forecast
performance of a variety of physics analyses, including sensitivities to
diffuse fluxes of neutrinos and sensitivity to both transient and steady state
point sources. This parameterized approach reduces the need for extensive
simulation studies in order to estimate detector performance, and allows the
user to study the influence of single performance metrics, like the angular
resolution, in isolation. The framework is designed to allow for multiple
detector components, each with different responses and exposure times, and
supports paramterization of both optical- and radio-Cherenkov (Askaryan)
neutrino telescopes. In the paper, we describe the mathematical concepts behind
toise and provide detailed instructive examples to introduce the reader to use
of the framework.


title: Absorption-based Circumgalactic Medium Line Emission Estimates

abstract:
  Motivated by the integral field units on large aperture telescopes and
proposals for ultraviolet-sensitive space telescopes to probe circumgalactic
medium (CGM) emission, we survey the most promising CGM emission lines and how
such observations can inform our understanding of the CGM and its relation to
galaxy formation. We tie our emission estimates to HST/COS absorption
measurements of ions around z= 0.2 Milky Way mass halos and motivated models
for the density and temperature of gas, and we provide formulas that simplify
extending our estimates to other samples and physical scenarios. We find that
OIII 5007 A and NII 6583 A, which at fixed ionic column density are primarily
sensitive to the thermal pressure of the gas they inhabit, may be detectable
with KCWI and especially IFUs on 30 m telescopes out to half a virial radius.
We comment on the implications of existing OIII and NII stacking measurements
by Zhang and coworkers (2018). OV 630 A and OVI 1032,1038 A are perhaps the
most promising ultraviolet lines, with motivated models predicting intensities
>100 $\gamma$ cm$^{-2}$ s$^{-1}$ sr$^{-1}$ in the inner 100 kpc of Milky
Way-like systems. A detection would confirm the collisionally ionized picture
and constrain the density profile of the CGM. Other ultraviolet metal lines
constrain the amount of gas that is actively cooling and mixing. We find that
CIII 978 A and CIV 1548 A may be detectable if an appreciable fraction of the
observed OVI column is associated with mixing or cooling gas. Hydrogen n>2
Lyman-series lines are too weak to be detectable, and H$\alpha$ emission within
100 kpc of Milky Way-like galaxies is within the reach of current integral
field units even for the minimum signal from ionizing background fluorescence.


title: Wilson loops in the Hamiltonian formalism

abstract:
  In a gauge theory, the gauge invariant Hilbert space is unchanged by the
coupling to arbitrary local operators. In the presence of Wilson loops, though,
the physical Hilbert space must be enlarged by adding test electric charges
along the loop. I discuss how at nonzero temperature Polyakov loops are
naturally related to the propagator of a test charge. 't Hooft loops represent
the propagation of a test magnetic charge, and so do not alter the physical
Hilbert space.


title: On Gauge Consistency In Gauge-Fixed Yang-Mills Theory

abstract:
  We investigate BRST invariance in Landau gauge Yang-Mills theory with
functional methods. To that end, we solve the coupled systems of functional
renormalisation group for the momentumdependent ghost and gluon propagator,
ghost-gluon, and three- and four-gluon vertex dressings. The equations for
both, transverse and longitudinal correlation functions are solved
self-consistently: all correlation functions are fed back into the loops.
Additionally, we also use the Slavnov-Taylor identities for computing the
longitudinal correlation functions on the basis of the above results. Then, the
gauge consistency of the solutions is checked by comparing the respective
longitudinal correlation functions. We find good agreement of these results,
hinting at the gauge consistency of our setup.


title: Learning with Free Object Segments for Long-Tailed Instance Segmentation

abstract:
  One fundamental challenge in building an instance segmentation model for a
large number of classes in complex scenes is the lack of training examples,
especially for rare objects. In this paper, we explore the possibility to
increase the training examples without laborious data collection and
annotation. We find that an abundance of instance segments can potentially be
obtained freely from object-centric images, according to two insights: (i) an
object-centric image usually contains one salient object in a simple
background; (ii) objects from the same class often share similar appearances or
similar contrasts to the background. Motivated by these insights, we propose a
simple and scalable framework FreeSeg for extracting and leveraging these
"free" object foreground segments to facilitate model training in long-tailed
instance segmentation. Concretely, we investigate the similarity among
object-centric images of the same class to propose candidate segments of
foreground instances, followed by a novel ranking of segment quality. The
resulting high-quality object segments can then be used to augment the existing
long-tailed datasets, e.g., by copying and pasting the segments onto the
original training images. Extensive experiments show that FreeSeg yields
substantial improvements on top of strong baselines and achieves
state-of-the-art accuracy for segmenting rare object categories.


title:
How viscous bubbles collapse: topological and symmetry-breaking
  instabilities in curvature-driven hydrodynamics

abstract:
  The duality between the mechanical equilibrium of elastic bodies and
non-inertial flow in viscous liquids has been a guiding principle in decades of
research. However, this duality is broken whenever the Gaussian curvature of
viscous films evolves rapidly in time. In such a case the film evolves through
a non-inertial yet geometrically nonlinear surface dynamics, which has remained
largely unexplored. We reveal the driver of such dynamics as the flow of
currents of Gaussian curvature of the evolving surface, rather than the
existence of an energetically favored target metric, as in the elastic
analogue. Focusing on the prototypical example of a bubble collapsing after
rapid depressurization, we show that the spherically-shaped viscous film
evolves via a topological instability, whose elastic analogue is forbidden by
the existence of an energy barrier. The topological transition brings about
compression within the film, triggering another, symmetry breaking instability
and radial wrinkles that grow in amplitude and invade the flattening film.
Building on an analogy between surface currents of Gaussian curvature and
polarization in electrostatic conductors, we obtain quantitative predictions
for the evolution of the flattening film. We propose that this classical
dynamics has ramifications in the emerging field of viscous hydrodynamics of
strongly correlated electrons in two-dimensional materials.


title:
A photometric and astrometric study of the open clusters NGC 1664 and
  NGC 6939

abstract:
  This study calculated astrophysical parameters, as well as kinematic and
galactic orbital parameters, of the open clusters NGC 1664 and NGC 6939. The
work is based on CCD UBV and Gaia photometric and astrometric data from ground
and space-based observations. Considering Gaia Early Data Release 3 (EDR3)
astrometric data, we determined membership probabilities of stars located in
both of the clusters. We used two-color diagrams to determine $E(B-V)$ color
excesses for NGC 1664 and NGC 6939 as $0.190 \pm 0.018$ and $0.380 \pm 0.025$
mag, respectively. Photometric metallicities for the two clusters were
estimated as [Fe/H] = $-0.10 \pm 0.02$ dex for NGC 1664 and as [Fe/H] = $-0.06
\pm 0.01$ dex for NGC 6939. Using the reddening and metallicity calculated in
the study, we obtained distance moduli and ages of the clusters by fitting
PARSEC isochrones to the color-magnitude diagrams based on the most likely
member stars. Isochrone fitting distances are $1289 \pm 47$ pc and $1716 \pm
87$ pc, which coincide with ages of $675 \pm 50$ Myr and $1.5 \pm 0.2$ Gyr for
NGC 1664 and NGC 6939, respectively. We also derived the distances to the
clusters using Gaia trigonometric parallaxes and compared these estimates with
the literature. We concluded that the results are in good agreement with those
given by the current study. Present day mass function slopes were calculated as
$\Gamma=-1.22\pm0.33$ and $\Gamma=-1.18\pm0.21$ for NGC 1664 and NGC 6939,
respectively, which are compatible with the Salpeter (1955) slope. Analyses
showed that both of clusters are dynamically relaxed. The kinematic and dynamic
orbital parameters of the clusters were calculated, indicating that the
birthplaces of the clusters are outside the solar circle.


title: Goldilocks Modes and the Three Scattering Bases

abstract:
  We consider massless scattering from the point of view of the position,
momentum, and celestial bases. In these three languages different properties of
physical processes become manifest or obscured. Within the soft sector, they
highlight distinct aspects of the infrared triangle: quantum field theory soft
theorems arise in the limit of vanishing energy $\omega$, memory effects are
described via shifts of fields at the boundary along the null time coordinate
$u$, and celestial symmetry algebras are realized via currents that appear at
special values of the conformal dimension $\Delta$. We focus on the subleading
soft theorems at $\Delta=1-s$ for gauge theory $(s=1)$ and gravity $(s=2)$ and
explore how to translate the infrared triangle to the celestial basis. We
resolve an existing tension between proposed overleading gauge transformations
as examined in the position basis and the `Goldstone-like' modes where we
expect celestial symmetry generators to appear. In the process we elucidate
various order-of-limits issues implicit in the celestial formalism. We then
generalize our construction to the tower of $w_{1+\infty}$ generators in
celestial CFT, which probe further subleading-in-$\omega$ soft behavior and are
related to subleading-in-$r$ vacuum transitions that measure higher multipole
moments of scatterers. In the end we see that the celestial basis is `just
right' for identifying the symmetry structure.


title: Strong photon interactions from weakly interacting particles

abstract:
  The hybridization of light and matter excitations in the form of polaritons
has enabled major advances in understanding and controlling optical
nonlinearities. Entering the quantum regime of strong interactions between
individual photons has however remained challenging since the strength of
achievable polariton interactions is typically limited by the available
interactions in the material. Here, we investigate collisions between
dark-state polaritons in three-level systems and discover a resonant process
that yields effective interactions, which are much larger than the underlying
interaction between their matter constituents. We systematically investigate
the underlying mechanism and demonstrate a substantial enhancement of polariton
interactions by several orders of magnitude. This suggests a promising approach
to quantum nonlinear optics in a range of physical settings, from atomic gases
to excitons in semiconductors and two-dimensional bilayer materials.


title: Technology to scale up diversity in astronomy education

abstract:
  The San Antonio Teacher Training Astronomy Academy (SATTAA) completed its
fourth annual iteration in June 2021 . While the program began as a
face-to-face professional development opportunity for future and current school
teachers, it transitioned to a fully online opportunity in 2020. In our efforts
to offer an astronomy education program that is inclusive and particularly
attentive to highly diverse populations, the transition to online programming
became a core aspect of scaling up the program. The 2021 iteration featured an
international facilitation team, and, for the first time, supported teachers
from across the State of Texas. In this paper, we share data on how the
facilitation team transitioned from a local to an international group, and on
how the participant pool expanded from local to state-wide.