cssi/SciSciGPT-SciSciNet huggingface dataset:
Ballistic Transport for Limit-Periodic Jacobi Matrices with Applications to Quantum Many-Body Problems

We study Jacobi matrices that are uniformly approximated by periodic operators. We show that if the rate of approximation is sufficiently rapid, then the associated quantum dynamics are ballistic in a rather strong sense; namely, the (normalized) Heisenberg evolution of the position operator converges strongly to a self-adjoint operator that is injective on the space of absolutely summable sequences. In particular, this means that all transport exponents corresponding to well-localized initial states are equal to one. Our result may be applied to a class of quantum many-body problems. Specifically, we establish a lower bound on the Lieb–Robinson velocity for an isotropic XY spin chain on the integers with limit-periodic couplings.
Retired A Stars: The Effect of Stellar Evolution on the Mass Estimates of Subgiants

Doppler surveys have shown that the occurrence rate of Jupiter-mass planets appears to increase as a function of stellar mass. However, this result depends on the ability to accurately measure the masses of evolved stars. Recently, Lloyd called into question the masses of subgiant stars targeted by Doppler surveys. Lloyd argues that very few observable subgiants have masses greater than 1.5 M_☉, and that most of them have masses in the range 1.0-1.2 M_☉. To investigate this claim, we use Galactic stellar population models to generate an all-sky distribution of stars. We incorporate the effects that make massive subgiants less numerous, such as the initial mass function and differences in stellar evolution timescales. We find that these effects lead to negligibly small systematic errors in stellar mass estimates, in contrast to the ≈50% errors predicted by Lloyd. Additionally, our simulated target sample does in fact include a significant fraction of stars with masses greater than 1.5 M_☉, primarily because the inclusion of an apparent magnitude limit results in a Malmquist-like bias toward more massive stars, in contrast to the volume-limited simulations of Lloyd. The magnitude limit shifts the mean of our simulated distribution toward higher masses and results in a relatively smaller number of evolved stars with masses in the range 1.0-1.2 M_☉. We conclude that, within the context of our present-day understanding of stellar structure and evolution, many of the subgiants observed in Doppler surveys are indeed as massive as main-sequence A stars.
Fast Low-Current Spin-Orbit-Torque Switching of Magnetic Tunnel Junctions through Atomic Modifications of the Free-Layer Interfaces

Developing cache memory cells is of great interest for next-generation integrated circuits, where both high speed and low energy consumption will be essential. This study utilizes the giant spin Hall effect to demonstrate that, by successfully modifying the interfaces in a magnetic tunnel junction to improve its magnetic properties, a significant reduction of switching current can be achieved. The experiments also demonstrate nanosecond-scale pulse switching with high reliability, due to beneficial assistance from fieldlike torque. With clear potential for further optimization, these developments show great promise for high-performance memory technology.
REGULATION OF THE SPECTRAL PEAK IN GAMMA-RAY BURSTS

Observations indicate that the peak of a gamma-ray burst spectrum forms in the opaque region of an ultrarelativistic jet. Recent radiative transfer calculations support this picture and show that the spectral peak is inherited from initially thermal radiation, which is changed by heating into a broad photon distribution with a high-energy tail. We discuss the processes that regulate the observed position of the spectral peak E {sub pk}. The opaque jet has three radial zones: (1) the Planck zone r > 1 where radiation has a Bose-Einstein spectrum, and (3) the Comptonization zone r > R {sub W} where the radiation spectrum develops a high-energy tail. Besides the initial jet temperature, an important factor regulating E {sub pk} is internal dissipation (of bulk motions and magnetic energy) at large distances from the central engine. Dissipation in the Planck zone reduces E {sub pk}, and dissipation in the Wien zone can increase E {sub pk}. In jets with subdominantmore » magnetic fields, the predicted E {sub pk} varies around 1 MeV up to a maximum value of about 10 MeV. If the jet carries an energetically important magnetic field, E {sub pk} can be additionally increased by dissipation of magnetic energy. This increase is suggested by observations, which show E {sub pk} up to about 20 MeV. We also consider magnetically dominated jets; then a simple model of magnetic dissipation gives E {sub pk} Almost-Equal-To 30 {Gamma}{sub W} keV where {Gamma}{sub W} is the jet Lorentz factor at the Wien radius R {sub W}.« less
What types of COVID-19 conspiracies are populated by Twitter bots?

With people moving out of physical public spaces due to containment measures to tackle the novel coronavirus (COVID-19) pandemic, online platforms become even more prominent tools to understand social discussion. Studying social media can be informative to assess how we are collectively coping with this unprecedented global crisis. However, social media platforms are also populated by bots, automated accounts that can amplify certain topics of discussion at the expense of others. In this paper, we study 43.3M English tweets about COVID-19 and provide early evidence of the use of bots to promote political conspiracies in the United States, in stark contrast with humans who focus on public health concerns.
Interference Modeling for Cellular Networks Under Beamforming Transmission

We propose analytical models for the interference power distribution in a cellular system employing MIMO beamforming in rich and limited scattering environments, which capture non line-of-sight signal propagation in the microwave and mm-wave bands, respectively. Two candidate models are considered: the inverse Gaussian and the inverse Weibull, both are two-parameter heavy tail distributions. We further propose a mixture of these two distributions as a model with three parameters. To estimate the parameters of these distributions, three approaches are used: moment matching, individual distribution maximum likelihood estimation (MLE), and mixture distribution MLE with a designed expectation maximization algorithm. We then introduce simple fitted functions for the mixture model parameters as polynomials of the channel path loss exponent and shadowing variance. To measure the goodness of these models, the information-theoretic metric relative entropy is used to capture the distance from the model distribution to a reference one. The interference models are tested against data obtained by simulating a cellular network based on stochastic geometry. The results show that the three-parameter mixture model offers remarkably good fit to simulated interference power. The mixture model is further used to analyze the capacity of a cellular network employing joint transmit and receive beamforming and confirms a good fit with simulation.
Interferometry meets the third and fourth dimensions in galaxies

Radio astronomy began with one array (Jansky's) and one paraboloid of revolution (Reber's) as collecting areas and has now reached the point where a large number of facilities are arrays of paraboloids, each of which would have looked enormous to Reber in 1932. In the process, interferometry has contributed to the counting of radio sources, establishing superluminal velocities in AGN jets, mapping of sources from the bipolar cow shape on up to full grey-scale and colored images, determining spectral energy distributions requiring non-thermal emission processes, and much else. The process has not been free of competition and controversy, at least partly because it is just a little difficult to understand how earth-rotation, aperture-synthesis interferometry works. Some very important results, for instance the mapping of HI in the Milky Way to reveal spiral arms, warping, and flaring, actually came from single moderate-sized paraboloids. The entry of China into the radio astronomy community has given large (40-110 meter) paraboloids a new lease on life.
Renormalization group flows, the a-theorem and conformal bootstrap

Every renormalization group flow in d spacetime dimensions can be equivalently described as spectral deformations of a generalized free CFT in (d − 1) spacetime dimensions. This can be achieved by studying the effective action of the Nambu-Goldstone boson of broken conformal symmetry in anti-de Sitter space and then taking the flat space limit. This approach is particularly useful in even spacetime dimension where the change in the Euler anomaly aUV − aIR can be related to anomalous dimensions of lowest twist multi-trace operators in the dual CFT. As an application, we provide a simple proof of the 4d a-theorem using the dual description. Furthermore, we reinterpret the statement of the a-theorem in 6d as a conformal bootstrap problem in 5d.
The refined transfer, bundle structures, and algebraic K-theory

We give new homotopy theoretic criteria for deciding when a fibration with homotopy finite fibres admits a reduction to a fibre bundle with compact topological manifold fibres. The criteria lead to an unexpected result about homeomorphism groups of manifolds. A tool used in the proof is a surjective splitting of the assembly map for Waldhausen's functor A(X). We also give concrete examples of fibrations having a reduction to a fibre bundle with compact topological manifold fibres but which fail to admit a compact fibre smoothing. The examples are detected by algebraic K-theory invariants. We consider a refinement of the Becker-Gottlieb transfer. We show that a version of the axioms described by Becker and Schultz uniquely determines the refined transfer for the class of fibrations, admitting a reduction to a fibre bundle with compact topological manifold fibres. In the Appendix, we sketch a theory of characteristic classes for fibrations. The classes are primary obstructions to finding a compact fibre smoothing.
Classical Zero-Point Radiation and Relativity: The Problem of Atomic Collapse Revisited

The physicists of the early twentieth century were unaware of two aspects which are vital to understanding some aspects of modern physics within classical theory. The two aspects are: (1) the presence of classical electromagnetic zero-point radiation, and (2) the importance of special relativity. In classes in modern physics today, the problem of atomic collapse is still mentioned in the historical context of the early twentieth century. However, the classical problem of atomic collapse is currently being treated in the presence of classical zero-point radiation where the problem has been transformed. The presence of classical zero-point radiation indeed keeps the electron from falling into the Coulomb potential center. However, the old collapse problem has been replaced by a new problem where the zero-point radiation may give too much energy to the electron so as to cause “self-ionization.” Special relativity may play a role in understanding this modern variation on the atomic collapse problem, just as relativity has proved crucial for a classical understanding of blackbody radiation.
Translating math formula images to LaTeX sequences using deep neural networks with sequence-level training

In this paper, we propose a deep neural network model with an encoder–decoder architecture that translates images of math formulas into their LaTeX markup sequences. The encoder is a convolutional neural network that transforms images into a group of feature maps. To better capture the spatial relationships of math symbols, the feature maps are augmented with 2D positional encoding before being unfolded into a vector. The decoder is a stacked bidirectional long short-term memory model integrated with the soft attention mechanism, which works as a language model to translate the encoder output into a sequence of LaTeX tokens. The neural network is trained in two steps. The first step is token-level training using the maximum likelihood estimation as the objective function. At completion of the token-level training, the sequence-level training objective function is employed to optimize the overall model based on the policy gradient algorithm from reinforcement learning. Our design also overcomes the exposure bias problem by closing the feedback loop in the decoder during sequence-level training, i.e., feeding in the predicted token instead of the ground truth token at every time step. The model is trained and evaluated on the IM2LATEX-100 K dataset and shows state-of-the-art performance on both sequence-based and image-based evaluation metrics.
$W^{s,\frac {n}{s}}$-maps with positive distributional Jacobians

We extend the well-known result that any $f \in W^{1,n}({\Omega }, \mathbb {R}^{n})$ , ${\Omega } \subset \mathbb {R}^{n}$ with strictly positive Jacobian is actually continuous: it is also true for fractional Sobolev spaces $W^{s,\frac {n}{s}}({\Omega })$ for any $s \geq \frac {n}{n+1}$ , where the sign condition on the Jacobian is understood in a distributional sense. Along the way we also obtain extensions to fractional Sobolev spaces $W^{s,\frac {n}{s}}$ of the degree estimates known for W1,n-maps with positive or non-negative Jacobian, such as the sense-preserving property.
Necessity of acceleration-induced nonlocality

The purpose of this paper is to explain clearly why nonlocality must be an essential part of the theory of relativity. In the standard local version of this theory, Lorentz invariance is extended to accelerated observers by assuming that they are pointwise inertial. This locality postulate is exact when dealing with phenomena involving classical point particles and rays of radiation, but breaks down for electromagnetic fields, as field properties in general cannot be measured instantaneously. The problem is corrected in nonlocal relativity by supplementing the locality postulate with a certain average over the past world line of the observer.
Super Heat Kernel and One-Loop Divergence of Super Yang-Mills Theory in Conformal Supergravity

We consider super Yang-Mills Theory in $N=1$ conformal supergravity. Using the background field method and the Feddeev-Popov procedure, the quantized action of the theory is presented. Its one-loop effective action is studied using the heat kernel method. We shall develop a non-iterative scheme, generalizing the non-supersymmetric case, to obtain the super heat kernel coefficients. In particular, the first three coefficients, which govern the one-loop divergence, will be calculated. We shall also demonstrate how to schematically derive the higher order coefficients. The method presented here can be readily applied to various quantum theories. We shall, as an application, derive the full one-loop divergence of SYM in conformal supergravity.
Finite lifespan of solutions of the semilinear wave equation in the Einstein-de Sitter spacetime

We examine the solutions of the semilinear wave equation, and, in particular, of the φq model of quantum field theory in the curved spacetime. More exactly, for 2 < q < 4 we prove that the solution...
Electron and Proton Heating in Transrelativistic Guide Field Reconnection

The plasma in low-luminosity accretion flows, such as the one around the black hole at the center of M87 or Sgr A* at our Galactic Center, is expected to be collisioness and two-temperature, with protons hotter than electrons. Here, particle heating is expected to be controlled by magnetic reconnection in the transrelativistic regime $\sigma_{w}\sim 0.1$-$1$, where the magnetization $\sigma_{w}$ is the ratio of magnetic energy density to plasma enthalpy density. By means of large-scale 2D particle-in-cell simulations, we explore for a fiducial $\sigma_w=0.1$ how the dissipated magnetic energy gets partitioned between electrons and protons, as a function of $\beta_{\rm i}$ (the ratio of proton thermal pressure to magnetic pressure) and of the strength of a guide field $B_{\rm g}$ perpendicular to the reversing field $B_0$. At low $\beta_{\rm i}\;(\lesssim 0.1)$, we find that the fraction of initial magnetic energy per particle converted into electron irreversible heat is nearly independent of $B_{\rm g}/B_0$, whereas protons get heated much less with increasing $B_{\rm g}/B_0$. As a result, for large $B_{\rm g} /B_{0}$, electrons receive the overwhelming majority of irreversible particle heating (${\sim}93\%$ for $B_{\rm g} /B_{0}=6$). This is significantly different than the antiparallel case $B_{\rm g}/B_0=0$, in which electron irreversible heating accounts for only ${\sim}18\%$ of the total particle heating. At $\beta_{\rm i} \sim 2$, when both species start already relativistically hot (for our fiducial $\sigma_w=0.1$), electrons and protons each receive ${\sim}50\%$ of the irreversible particle heating, regardless of the guide field strength. Our results provide important insights into the plasma physics of electron and proton heating in hot accretion flows around supermassive black holes.
New examples of Brunnian theta graphs

The Kinoshita graph is the most famous example of a Brunnian theta graph, a nontrivial spatial theta graph with the property that removing any edge yields an unknot. We produce a new family of diagrams of spatial theta graphs with the property that removing any edge results in the unknot. The family is parameterized by a certain subgroup of the pure braid group on four strands. We prove that infinitely many of these diagrams give rise to non-isotopic Brunnian theta graphs.
On the Origin of Gravitational Lorentz Covariance

We provide evidence that general relativity (GR) is the unique spatially covariant effective field theory of the transverse, traceless graviton degrees of freedom. The Lorentz covariance of GR, having not been assumed in our analysis, is thus plausibly interpreted as an accidental or emergent symmetry of the gravitational sector.
Generic vanishing fails for surfaces in positive characteristic

We show that there exist smooth surfaces violating Generic Vanishing in any characteristic \(p \ge 3\). As a corollary, we recover a result of Hacon and Kovacs, producing counterexamples to Generic Vanishing in dimension 3 and higher.
Gas Accretion Traced in Absorption in Galaxy Spectroscopy

The positive velocity shift of absorption transitions tracing diffuse material observed in a galaxy spectrum is an unambiguous signature of gas flow toward the host system. Spectroscopy probing, e.g., Na I resonance lines in the rest-frame optical or Mg II and Fe II in the near-ultraviolet is in principle sensitive to the infall of cool material at temperatures T ∼ 100–10,000 K anywhere along the line of sight to a galaxy’s stellar component. However, secure detections of this redshifted absorption signature have proved challenging to obtain due to the ubiquity of cool gas outflows giving rise to blueshifted absorption along the same sightlines. In this chapter, we review the bona fide detections of this phenomenon. Analysis of Na I line profiles has revealed numerous instances of redshifted absorption observed toward early-type and/or AGN-host galaxies, while spectroscopy of Mg II and Fe II has provided evidence for ongoing gas accretion onto > 5% of luminous, star-forming galaxies at z ∼ 0. 5–1. We then discuss the potentially ground-breaking benefits of future efforts to improve the spectral resolution of such studies, and to leverage spatially resolved spectroscopy for new constraints on inflowing gas morphology.
The Vertical Structure and Ultraviolet Spectrum of Accretion Disks Heated by Internal Dissipation in Active Galactic Nuclei

We present an improved calculation of the vertical structure and ultraviolet spectrum of a dissipative accretion disk in an active galactic nucleus (AGN). We calculate model spectra in which the viscous stress is proportional to the total pressure, the gas pressure only, and the geometric mean of the radiation and gas pressures. As a result of a more complete treatment of absorptive opacity, we find greater overall spectral curvature than Laor & Netzer did, as well as larger amplitudes in both the Lyman and He II photoionization edges. The local blackbody approximation is not a good description of the near-UV spectrum. With relativistic corrections (appropriate to nonrotating black holes) included, we find that the near-UV spectrum hardens with increasing /m8 ( is the accretion rate in Eddington units, m8 the black hole mass in units of 108 M☉). The near-UV spectrum is consistent with observations if m−18~10−3, but disks this cold would have absorption features at the Lyman edge, which are never seen in real AGNs. The edge amplitude is reduced when /m8 is larger, but then the near-UV slope is too hard to match observations. We conclude that models in which conventional disks orbit nonrotating black holes do not adequately explain UV continuum production in AGNs.
Structure in supersymmetric Yang-Mills theory

We show that requiring sixteen supersymmetries in quantum mechanical gauge theory implies the existence of a web of constrained interactions. Contrary to conventional wisdom, these constraints extend to arbitrary orders in the momentum expansion.
Avalanches and plastic flow in crystal plasticity: an overview

Crystal plasticity is mediated through dislocations, which form knotted configurations in a complex energy landscape. Once they disentangle and move, they may also be impeded by permanent obstacles with finite energy barriers or frustrating long-range interactions. The outcome of such complexity is the emergence of dislocation avalanches as the basic mechanism of plastic flow in solids at the nanoscale. While the deformation behavior of bulk materials appears smooth, a predictive model should clearly be based upon the character of these dislocation avalanches and their associated strain bursts. We provide here a comprehensive overview of experimental observations, theoretical models and computational approaches that have been developed to unravel the multiple aspects of dislocation avalanche physics and the phenomena leading to strain bursts in crystal plasticity.
A ferroelectric semiconductor field-effect transistor

Ferroelectric field-effect transistors employ a ferroelectric material as a gate insulator, the polarization state of which can be detected using the channel conductance of the device. As a result, the devices are potentially of use in non-volatile memory technology, but they suffer from short retention times, which limits their wider application. Here, we report a ferroelectric semiconductor field-effect transistor in which a two-dimensional ferroelectric semiconductor, indium selenide (α-In2Se3), is used as the channel material in the device. α-In2Se3 was chosen due to its appropriate bandgap, room-temperature ferroelectricity, ability to maintain ferroelectricity down to a few atomic layers and its potential for large-area growth. A passivation method based on the atomic layer deposition of aluminium oxide (Al2O3) was developed to protect and enhance the performance of the transistors. With 15-nm-thick hafnium oxide (HfO2) as a scaled gate dielectric, the resulting devices offer high performance with a large memory window, a high on/off ratio of over 108, a maximum on current of 862 μA μm−1 and a low supply voltage. A ferroelectric semiconductor field-effect transistor, which uses the two-dimensional ferroelectric semiconductor α-In2Se3 as a channel material, could offer enhanced capabilities compared with conventional ferroelectric field-effect transistors in non-volatile memory applications.
Polynomiality for Bin Packing with a Constant Number of Item Types

We consider the bin packing problem with d different item sizes si and item multiplicities ai, where all numbers are given in binary encoding. This problem formulation is also known as the one-dimensional cutting stock problem. In this work, we provide an algorithm that, for constant d, solves bin packing in polynomial time. This was an open problem for all d\ge 3. In fact, for constant d our algorithm solves the following problem in polynomial time: Given two d-dimensional polytopes P and Q, find the smallest number of integer points in P whose sum lies in Q. Our approach also applies to high multiplicity scheduling problems in which the number of copies of each job type is given in binary encoding and each type comes with certain parameters such as release dates, processing times, and deadlines. We show that a variety of high multiplicity scheduling problems can be solved in polynomial time if the number of job types is constant.
Controlling Physical Attributes in GAN-Accelerated Simulation of Electromagnetic Calorimeters

High-precision modeling of subatomic particle interactions is critical for many fields within the physical sciences, such as nuclear physics and high energy particle physics. Most simulation pipelines in the sciences are computationally intensive – in a variety of scientific fields, Generative Adversarial Networks have been suggested as a solution to speed up the forward component of simulation, with promising results. An important component of any simulation system for the sciences is the ability to condition on any number of physically meaningful latent characteristics that can effect the forward generation procedure. We introduce an auxiliary task to the training of a Generative Adversarial Network on particle showers in a multi-layer electromagnetic calorimeter, which allows our model to learn an attribute-aware conditioning mechanism.
Constant Threshold Correction to Electrically Charged Dilatonic Black Holes

We investigate the effect of a constant threshold correction to a general non-extreme, static, spherically symmetric, electrically charged black hole solution of the dilatonic Einstein–Maxwell Lagrangian, with an arbitrary coupling β between the electromagnetic tensor and the dilaton field. For a small β, an exact analytical solution is obtained. For an arbitrary β, a close form solution, up to first-order in the constant threshold correction, of the metric and the dilaton are presented. In the extremal limit, the close form solution is reduced to an exact analytical form.
Crush Optimism with Pessimism: Structured Bandits Beyond Asymptotic Optimality

We study stochastic structured bandits for minimizing regret. The fact that the popular optimistic algorithms do not achieve the asymptotic instance-dependent regret optimality (asymptotic optimality for short) has recently alluded researchers. On the other hand, it is known that one can achieve bounded regret (i.e., does not grow indefinitely with $n$) in certain instances. Unfortunately, existing asymptotically optimal algorithms rely on forced sampling that introduces an $\omega(1)$ term w.r.t. the time horizon $n$ in their regret, failing to adapt to the "easiness" of the instance. In this paper, we focus on the finite hypothesis case and ask if one can achieve the asymptotic optimality while enjoying bounded regret whenever possible. We provide a positive answer by introducing a new algorithm called CRush Optimism with Pessimism (CROP) that eliminates optimistic hypotheses by pulling the informative arms indicated by a pessimistic hypothesis. Our finite-time analysis shows that CROP $(i)$ achieves a constant-factor asymptotic optimality and, thanks to the forced-exploration-free design, $(ii)$ adapts to bounded regret, and $(iii)$ its regret bound scales not with $K$ but with an effective number of arms $K_\psi$ that we introduce. We also discuss a problem class where CROP can be exponentially better than existing algorithms in \textit{nonasymptotic} regimes. This problem class also reveals a surprising fact that even a clairvoyant oracle who plays according to the asymptotically optimal arm pull scheme may suffer a linear worst-case regret.
Speed–direction description of turbulent flows

In this note, we introduce speed and direction variables to describe the motion of incompressible viscous fluid. Fluid velocity u is decomposed into u = ur, with u = |u| and r = u/|u|. We consider a directional split of the Navier–Stokes equations into a coupled system of equations for u and for r. The equation for u is particularly simple but solely maintains the energy balance of the system. Under the assumption of a weak correlation between fluctuations in speed and direction in a developed turbulent flow, we further illustrate the application of u–r variables to describe mean statistics of a shear turbulence. The standard (full) Reynolds stress tensor does not appear in a resulting equation for the mean flow profile.
Lehmer points and visible points on affine varieties over finite fields

Let V be an absolutely irreducible affine variety over . A Lehmer point on V is a point whose coordinates satisfy some prescribed congruence conditions, and a visible point is one whose coordinates are relatively prime. Asymptotic results for the number of Lehmer points and visible points on V are obtained, and the distribution of visible points into different congruence classes is investigated.
Star Cluster Ages in the Gaia Era

We use the framework developed as part of the MESA Isochrones and Stellar Tracks (MIST) project to assess the utility of several types of observables in jointly measuring the age and 1D stellar model parameters in star clusters. We begin with a pedagogical overview summarizing the effects of stellar model parameters, such as the helium abundance, mass-loss efficiency, and the mixing length parameter, on observational diagnostics including the color-magnitude diagram, mass-radius relation, and surface abundances, amongst others. We find that these parameters and the stellar age influence observables in qualitatively distinctive, degeneracy-breaking ways. To assess the current state of affairs, we use the recent Gaia Data Release 2 (DR2) along with data from the literature to investigate three well-studied old open clusters---NGC6819, M67, NGC6791---as case studies. Although there is no obvious tension between the existing observations and the MIST models for NGC6819, there are interesting discrepancies in the cases of M67 and NGC6791. At this time, parallax zero point uncertainties in Gaia DR2 remain one of the limiting factors in the analysis of these clusters. With a combination of exquisite photometry, parallax distances, and cluster memberships from Gaia at the end of its mission, we anticipate precise and accurate ages for these and other star clusters in the Galaxy.
On the rotational energy distributions of reactive, non-polar species in the interstellar medium

A basic model for the formation of non-equilibrium rotational energy distributions is described for reactive, homo-polar diatomic molecules and ions in the interstellar medium. Kinetic models were constructed to calculate the rotational populations of $\mathrm{C}_{2}^{+}$ under the conditions it would experience in the diffuse interstellar medium. As the non-polar ion reacts with molecular hydrogen, but not atomic hydrogen, the thermalization of a hot nascent rotational population will be arrested by chemical reaction when the H2 density begins to be significant. Populations that deviate strongly from the local thermodynamic equilibrium are predicted for $\mathrm{C}_{2}^{+}$ in environments where it may be detectable. Consequences of this are discussed and a new optical spectrum is calculated.
TOPOLOGICAL MEASURE AND GRAPH-DIFFERENTIAL GEOMETRY ON THE QUOTIENT SPACE OF CONNECTIONS

Integral calculus on the space of gauge equivalent connections is developed. By carring out a non-linear generalization of the theory of cylindrical measures on topological vector spaces, a faithfull, diffeomorphism invariant measure is introduced on a suitable completion of . The strip (i.e. momentum) operators are densely-defined in the resulting Hilbert space and interact with the measure correctly
Optimal physical preprocessing for example-based super-resolution

Fourier ptychographic microscopy is a technique that achieves a high space-bandwidth product, i.e. high resolution and high field-of-view. In Fourier ptychographic microscopy, variable illumination patterns are used to collect multiple low-resolution images. These low-resolution images are then computationally combined to create an image with resolution exceeding that of any single image from the microscope. Due to the necessity of acquiring multiple low-resolution images, Fourier ptychographic microscopy has poor temporal resolution. Our aim is to improve temporal resolution in Fourier ptychographic microscopy, achieving single-shot imaging without sacrificing space-bandwidth product. We use example-based super-resolution to achieve this goal by trading off generality of the imaging approach. In example-based super-resolution, the function relating low-resolution images to their high-resolution counterparts is learned from a given dataset. We take the additional step of modifying the imaging hardware in order to collect more informative low-resolution images to enable better high-resolution image reconstruction. We show that this "physical preprocessing" allows for improved image reconstruction with deep learning in Fourier ptychographic microscopy. In this work, we use deep learning to jointly optimize a single illumination pattern and the parameters of a post-processing reconstruction algorithm for a given sample type. We show that our joint optimization yields improved image reconstruction as compared with sole optimization of the post-processing reconstruction algorithm, establishing the importance of physical preprocessing in example-based super-resolution.
Homology of analogues of Heisenberg Lie algebras

We calculate the homology of three families of 2-step nilpotent Lie (super)algebras associated with the symplectic, orthogonal, and general linear groups. The symplectic case was considered by Getzler and the main motivation for this work was to complete the calculations started by him. In all three cases, these algebras can be realized as the nilpotent radical of a parabolic subalgebra of a simple Lie algebra, and our first approach relies on a theorem of Kostant, but is otherwise elementary and involves combinatorics of Weyl groups and partitions which may be of independent interest. Our second approach is an application of (un)stable representation theory of the classical groups in the sense of recent joint work of the author with Snowden, which is shorter and more conceptual.
Level-rank duality of the U(N) WZW model, Chern-Simons theory, and 2d qYM theory

We study the WZW, Chern-Simons, and 2d qYM theories with gauge group U(N). The U(N) WZW model is only well-defined for odd level K, and this model is shown to exhibit level-rank duality in a much simpler form than that for SU(N). The U(N) Chern-Simons theory on Seifert manifolds exhibits a similar duality, distinct from the level-rank duality of SU(N) Chern-Simons theory on S3. When q = e2πi/(N+K), the observables of the 2d U(N) qYM theory can be expressed as a sum over a finite subset of U(N) representations. When N and K are odd, the qYM theory exhibits N ↔ K duality, provided q = e2πi/(N+K) and θ = 0 mod 2π/(N + K).
Invariants of objects and their images under surjective maps

We examine the relationships between the differential invariants of objects and of their images under a surjective maps. We analyze both the case when the underlying transformation group is projectable and hence induces an action on the image, and the case when only a proper subgroup of the entire group acts projectably. In the former case, we establish a constructible isomorphism between the algebra of differential invariants of the images and the algebra of fiber-wise constant (gauge) differential invariants of the objects. In the latter case, we describe residual effects of the full transformation group on the image invariants. Our motivation comes from the problem of reconstruction of an object from multiple-view images, with central and parallel projections of curves from three-dimensional space to the two-dimensional plane serving as our main examples.
A New Detection of Extragalactic Anomalous Microwave Emission in a Compact, Optically Faint Region of NGC 4725

We discuss the nature of a discrete, compact radio source (NGC 4725 B) located ≈1.9 kpc from the nucleus in the nearby star-forming galaxy NGC 4725, which we believe to be a new detection of extragalactic anomalous microwave emission (AME). Based on detections at 3, 15, 22, 33, and 44 GHz, NGC 4725 B is a microjansky radio source peaking at ≈33 GHz. While the source is not identified in optical (BVRI) photometry, we detect counterparts in the midinfrared Spitzer/IRAC bands (3.6, 4.5, 5.8, 8.0 μm) that appear to be associated with dust emission in the central region of NGC 4725. Consequently, we conclude that NGC 4725 B is a new detection of AME and is very similar to a recent detection of AME in an outer-disk star-forming region in NGC 6946. We find that models of electric dipole emission from rapidly rotating ultra-small grains are able to reproduce the radio spectrum for reasonable interstellar medium conditions. Given the lack of an optical counterpart and the shape of the radio spectrum, NGC 4725 B appears consistent with a nascent star-forming region in which young (≾ 3 Myr) massive stars are still highly enshrouded by their natal cocoons of gas and dust with insufficient supernovae occurring to produce a measurable amount of synchrotron emission.
The semiclassical coherent state propagator in the Weyl representation

It is shown that the semiclassical coherent state propagator takes its simplest form when the quantum mechanical Hamiltonian is replaced by its Weyl symbol in defining the classical action, in that there is then no need for a Solari-Kochetov correction. It is also shown that such a correction exists if a symbol other than the Weyl symbol is chosen and that its form is different depending on the symbol chosen. The various forms of the propagator based on different symbols are shown to be equivalent provided the correspondingly correct Solari-Kochetov correction is included. All these results are shown for both particle and spin coherent state propagators. The global anomaly in the fluctuation determinant is further elucidated by a study of the connection between the discrete fluctuation determinant and the discrete Jacobi equation.
Entanglement of a class of non-Gaussian states in disordered harmonic oscillator systems

For disordered harmonic oscillator systems over the d-dimensional lattice, we consider the problem of finding the bipartite entanglement of the uniform ensemble of the energy eigenstates associated with a particular number of modes. Such an ensemble defines a class of mixed, non-Gaussian entangled states that are labeled, by the energy of the system, in an increasing order. We develop a novel approach to find the exact logarithmic negativity of this class of states. We also prove entanglement bounds and demonstrate that the low energy states follow an area law.
Quantum decay in renormalizable field theories: quasiparticle formation, Zeno and anti-Zeno effects

Abstract In a renormalizable theory the survival probability of an unstable quantum state features divergences as a consequence of the rapid growth of the density of states with energy. Introducing a high energy cutoff Λ , the transient dynamics during a time scale ≃ 1 ∕ Λ describes the renormalization of the bare into a “quasiparticle” state which decays on longer time scales. During this early transient the decay law features Zeno behavior e − ( t ∕ t Z ) 2 with the Zeno time-scale t Z ∝ 1 ∕ Λ 3 ∕ 2 . We introduce a dynamical renormalization framework that allows to separate consistently the dynamics of formation of the quasiparticle state and its decay on longer time scales by introducing a renormalization time scale along with alternative “schemes”. The survival probability obeys a renormalization group equation with respect to this scale. We find a transient suppression of the decay law for large Lorentz factor as a consequence of the narrowing of the phase space for decay different from the usual time dilation. In the presence of higher mass thresholds, the energy uncertainty associated with transient dynamics leads to an anti Zeno enhancement with a transient acceleration of the decay into heavier particles. There remains memory of the transient effects in the survival probability even at long time. We discuss possible consequences of these effects in cosmology.
A note on G-intersecting families

Consider a graph G and a k-uniform hypergraph H on common vertex set [n]. We say that H is G-intersecting if for every pair of edges in X,Y ∈ H there are vertices x ∈ X and y ∈ Y such that x = y or x and y are joined by an edge in G. This notion was introduced by Bohman, Frieze, Ruszinko and Thoma who proved a natural generalization of the Erdos-Ko-Rado Theorem for G-intersecting k-uniform hypergraphs for G sparse and k = O(n1/4). In this note, we extend this result to k = O(√n).
Resolving Gamma-Ray Burst 000301C with a Gravitational Microlens

The afterglow of the gamma-ray burst (GRB) 000301C exhibited achromatic, short-timescale variability that is difficult to reconcile with the standard relativistic shock model. We interpret the observed light curves as a microlensing event superposed on power-law flux decays typical of afterglows. In general, a relativistic GRB shock appears on the sky as a thin ring expanding at a superluminal speed. Initially the ring is small relative to its angular separation from the lens, and so its flux is magnified by a constant factor. As the ring grows and sweeps across the lens, its magnification reaches a maximum. Subsequently, the flux gradually recovers its unlensed value. This behavior involves only three free parameters in its simplest formulation and was predicted theoretically by A. Loeb & R. Perna. Fitting the available R-band photometric data of GRB 000301C to a simple model of the microlensing event and a broken power law for the afterglow, we find reasonable values for all the parameters and a reduced ?2/degrees of freedom parameter of 1.48 compared with 2.99 for the broken power-law fit alone. The peak magnification of ~2 occurred 3.8 days after the burst. The entire optical to IR data imply a width of the GRB ring of order 10% of its radius, similar to theoretical expectations. The angular resolution provided by microlensing is better than a microarcsecond. We infer a mass of approximately 0.5 M? for a lens located halfway to the source at zs = 2.04. A galaxy 2'' from GRB 000301C might be the host of the stellar lens, but current data provides only an upper limit on its surface brightness at the GRB position.
Leveraging Environmental Correlations: The Thermodynamics of Requisite Variety

Key to biological success, the requisite variety that confronts an adaptive organism is the set of detectable, accessible, and controllable states in its environment. We analyze its role in the thermodynamic functioning of information ratchets—a form of autonomous Maxwellian Demon capable of exploiting fluctuations in an external information reservoir to harvest useful work from a thermal bath. This establishes a quantitative paradigm for understanding how adaptive agents leverage structured thermal environments for their own thermodynamic benefit. General ratchets behave as memoryful communication channels, interacting with their environment sequentially and storing results to an output. The bulk of thermal ratchets analyzed to date, however, assume memoryless environments that generate input signals without temporal correlations. Employing computational mechanics and a new information-processing Second Law of Thermodynamics (IPSL) we remove these restrictions, analyzing general finite-state ratchets interacting with structured environments that generate correlated input signals. On the one hand, we demonstrate that a ratchet need not have memory to exploit an uncorrelated environment. On the other, and more appropriate to biological adaptation, we show that a ratchet must have memory to most effectively leverage structure and correlation in its environment. The lesson is that to optimally harvest work a ratchet’s memory must reflect the input generator’s memory. Finally, we investigate achieving the IPSL bounds on the amount of work a ratchet can extract from its environment, discovering that finite-state, optimal ratchets are unable to reach these bounds. In contrast, we show that infinite-state ratchets can go well beyond these bounds by utilizing their own infinite “negentropy”. We conclude with an outline of the collective thermodynamics of information-ratchet swarms.
The Ryu–Takayanagi Formula from Quantum Error Correction

I argue that a version of the quantum-corrected Ryu–Takayanagi formula holds in any quantum error-correcting code. I present this result as a series of theorems of increasing generality, with the final statement expressed in the language of operator-algebra quantum error correction. In AdS/CFT this gives a “purely boundary” interpretation of the formula. I also extend a recent theorem, which established entanglement-wedge reconstruction in AdS/CFT, when interpreted as a subsystem code, to the more general, and I argue more physical, case of subalgebra codes. For completeness, I include a self-contained presentation of the theory of von Neumann algebras on finite-dimensional Hilbert spaces, as well as the algebraic definition of entropy. The results confirm a close relationship between bulk gauge transformations, edge-modes/soft-hair on black holes, and the Ryu–Takayanagi formula. They also suggest a new perspective on the homology constraint, which basically is to get rid of it in a way that preserves the validity of the formula, but which removes any tension with the linearity of quantum mechanics. Moreover, they suggest a boundary interpretation of the “bit threads” recently introduced by Freedman and Headrick.
Mono-Higgs detection of dark matter at the LHC

Motivated by the recent discovery of the Higgs boson, we investigate the possibility that a missing energy plus Higgs final state is the dominant signal channel for dark matter at the LHC. We consider examples of higher-dimension operators where a Higgs and dark matter pair are produced through an off-shell Z or γ, finding potential sensitivity at the LHC to cutoff scales of around a few hundred GeV. We generalize this production mechanism to a simplified model by introducing a Z′ as well as a second Higgs doublet, where the pseudoscalar couples to dark matter. Resonant production of the Z′ which decays to a Higgs plus invisible particles gives rise to a potential mono-Higgs signal. This may be observable at the 14 TeV LHC at low tan β and when the Z′ mass is roughly in the range 600 GeV to 1.3 TeV.
Multi-modal Experts Network for Autonomous Driving

End-to-end learning from sensory data has shown promising results in autonomous driving. While employing many sensors enhances world perception and should lead to more robust and reliable behavior of autonomous vehicles, it is challenging to train and deploy such network and at least two problems are encountered in the considered setting. The first one is the increase of computational complexity with the number of sensing devices. The other is the phenomena of network overfitting to the simplest and most informative input. We address both challenges with a novel, carefully tailored multi-modal experts network architecture and propose a multi-stage training procedure. The network contains a gating mechanism, which selects the most relevant input at each inference time step using a mixed discrete-continuous policy. We demonstrate the plausibility of the proposed approach on our 1/6 scale truck equipped with three cameras and one LiDAR.