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  • We critically assess limits on the maximum energy of protons accelerated within superbubbles around massive stellar clusters, considering a number of different scenarios. In particular, we derive under which circumstances acceleration of protons above peta-electronvolt (PeV) energies can be expected. While the external forward shock of the superbubble may account for acceleration of particles up to 100 TeV, internal primary shocks such as supernova remnants expanding in the low density medium or the collective wind termination shock which forms around a young compact cluster provide more favourable channels to accelerate protons up to 1 PeV, and possibly beyond. Under reasonable conditions, clustered supernovae launching powerful shocks into the magnetised wind of a young and compact massive star cluster are found to be the most promising systems to accelerate protons above 10 PeV. On the other hand, stochastic re-acceleration in the strongly turbulent plasma is found to be much less effective than claimed in previous works, with a maximum proton energy of at most a few hundred TeV.
    Supernova remnantTurbulenceMassive starsCosmic raySuperbubbleForward shockStarTerminal shockBohm diffusionDiffusion coefficient...
  • We present the results of a cluster search in the gamma-ray sky images of the Large Magellanic Cloud (LMC) region by means of the Minimum Spanning Tree (MST) and DBSCAN algorithms, at energies higher than 6 and 10 GeV, using 12 years of Fermi-LAT data. Several significant clusters were found, the majority of which associated with previously known gamma-ray sources. We confirm our previous detection of the Supernova Remnants N 49B and N 63A and found new significant clusters associated with the SNRs N 49, N 186D and N 44. These sources are among the brightest X-ray remnants in the LMC and corresponds to core-collapse supernovae interacting with dense HII regions, indicating that an hadronic origin of high energy photons is the most likely process.
    Large Magellanic CloudMinimum spanning treeDBSCANSupernova remnantCosmic rayX-ray luminosityCore collapseAngular separationLuminosityCore-collapse supernova...
  • In this paper, we investigate the stabilization of a one-dimensional Lorenz piezoelectric (Stretching system) with partial viscous dampings. First, by using Lorenz gauge conditions, we reformulate our system to achieve the existence and uniqueness of the solution. Next, by using General criteria of Arendt-Batty, we prove the strong stability in different cases. Finally, we prove that it is sufficient to control the stretching of the center-line of the beam in x-direction to achieve the exponential stability. Numerical results are also presented to validate our theoretical result.
    Exponential stabilityLorenz gauge condition
  • Supernova remnants have long been considered as a promising candidate for sources of Galactic cosmic rays. However, modelling cosmic-ray transport around these sources is complicated by the fact that the overdensity of cosmic rays close to their acceleration site can lead to self-confinement, that is the generation of turbulence upon which these particles scatter. Such a highly non-linear problem can be addressed by numerically solving the coupled differential equations describing the evolution in space and time of the escaping particles and of the turbulent plasma waves. In this work, we focus essentially on the propagation of cosmic rays from supernova remnants in the warm ionized and warm neutral phases of the interstellar medium and propose an extended framework to take into account also the effect of energy loss relevant for cosmic rays of energy below 10 GeV. Interestingly, the diffusion coefficient of low-energy cosmic rays could be suppressed by up to 2 orders of magnitude for several tens of kiloyears after the escape from the shock. The cosmic-ray spectrum outside the supernova remnant flattens below 1 GeV at a sufficiently late time reminiscient of the spectral behaviour observed by Voyager. We also find the grammage accumulated around the source to be non-negligible, with important implications for precision fitting of the cosmic-ray spectra.
    Diffusion coefficientTurbulenceCosmic rayConfinementSupernova remnantTwo-stream instabilityDamping ratePhase space densityMagnetohydrodynamic turbulenceIntensity...
  • Supernova remnants (SNRs), star formation regions (SFRs), and pulsar wind nebulae (PWNe) are prime candidates for Galactic PeVatrons. The nonthermal high-energy (HE, $\varepsilon>100 \textrm{ MeV}$) and very high-energy (VHE, $\varepsilon>100 \textrm{ GeV}$) $\gamma$-ray emission from these sources should be a promising manifestation of acceleration processes. We investigate the possibility to explain the HE and VHE $\gamma$-ray emission from the sky region of the magnetar SGR 1900+14 as a signature of cosmic rays accelerated in above mentioned sources. To this end, we simulate the $\gamma$-ray emission from the extended Fermi-LAT HE source 4FGL J1908.6+0915e, the extended VHE H.E.S.S. source candidate HOTS J1907+091, and the point-like HAWC TeV source 3HWC J1907+085, which are spatially coincident with the SNR G42.8+0.6, the magnetar SGR 1900+14 and the star forming region W49A. The simulations are performed within the hadronic and leptonic models. We show that the observed $\gamma$-ray emission from the region of the magnetar SGR 1900+14 can, in principle, include contributions of different intensities from all three types of (potentially confused) sources. The considered in detail cases of a magnetar-connected but still undetected SNR and a PWN are the most promising ones, but with a serious requirement on the energy reserve of radiated CR particles - of order of $10^{51}d_{\textrm{10kpc}}^{2}$ erg for sources at a distance of $d\sim 10$ kpc. Such energy reserve can be provided by the magnetar-related Hypernova and/or magnetar wind nebula remnant created by the newborn millisecond magnetar with the large supply of rotational energy $E_{\textrm{rot}}\sim 10^{52}\textrm{ erg}$.
    MagnetarSGR 1900+14Supernova remnantPulsar wind nebulaEjectaHypernovaInfrared limitTest statisticPulsarStar...
  • The Parker Solar Probe mission provides a unique opportunity to characterize several features of the solar wind at different heliocentric distances. Recent findings have shown the existence of a different scale-invariant nature when moving away from the Sun. Here we provide, for the first time, how to reconcile these observational results on the nature of the radial evolution of the magnetic and velocity field fluctuations across the inertial range with two scenarios drawn from the magnetohydrodynamic theory. In details, we evidence (i) a magnetically-dominated scenario up to 0.4 AU and (ii) a fluid-like at larger distances. The observed breakdown is the result of the radial evolution of magnetic field fluctuations and plasma thermal expansion affecting the distribution of between magnetic and kinetic fluctuations. The two scenarios can be reconciled with those of Iroshnikov-Kraichnan and Kolmogorov pictures of turbulence in terms of an evolving nature of the coupling between fields. Our findings have important implications for turbulence studies and modeling approaches.
    SunTurbulenceSolar windMagnetohydrodynamicsScale invarianceEarthThermal ExpansionHelicityHeliosphereFinal state...
  • We analyse synthetic $^{12}$CO, $^{13}$CO, and [CII] emission maps of simulated molecular clouds of the SILCC-Zoom project, which include an on-the-fly evolution of H$_2$, CO, and C$^+$. We use simulations of hydrodynamical and magnetohydrodynamical clouds, both with and without stellar feedback. We introduce a novel post-processing of the C$^+$ abundance using CLOUDY, to account for further ionization states of carbon due to stellar radiation. We report the first self-consistent synthetic emission maps of [CII] in feedback bubbles, largely devoid of emission inside them, as recently found in observations. The C$^+$ mass is only poorly affected by stellar feedback but the [CII] luminosity increases by $50 - 85$ per cent compared to runs without feedback. Furthermore, we investigate the capability of the CO/[CII] line ratio as a tracer of the amount of H$_2$ in the clouds and their evolutionary stage. We obtain, for both $^{12}$CO and $^{13}$CO, no clear trend of the luminosity ratio, $L_\mathrm{CO}/L_\mathrm{[CII]}$. It can therefore \textit{not} be used as a reliable measure of the H$_2$ mass fraction. We note a monotonic relation between $L_\mathrm{CO}/L_\mathrm{[CII]}$ and the H$_2$ fraction when considering the ratio for individual pixels of our synthetic maps, but with large scatter. Moreover, we show that assuming chemical equilibrium results in an overestimation of H$_2$ and CO masses of up to 110 and 30 per cent, respectively, and in an underestimation of H and C$^+$ masses of 65 and 7 per cent, respectively. In consequence, $L_\mathrm{CO}$ would be overestimated by up to 50 per cent, and $L_\mathrm{C[II]}$ be underestimated by up to 35 per cent. Hence, the assumption of chemical equilibrium in molecular cloud simulations introduces intrinsic errors of a factor of up to $\sim2$ in chemical abundances, luminosities and luminosity ratios.
    LuminosityStellar feedbackMolecular cloudStarIntensityChemical equilibriumLine of sightLine emissionInterstellar mediumChemical abundance...
  • We perform a detailed study of the stellar populations in a sample of massive Fornax dwarf galaxies using a set of newly defined line indices. Using data from the Integral field spectroscopic data, we study abundance ratios of eight dEs with stellar mass ranging from 10$^8$ to 10$^{9.5}$ M$_\odot$ in the Fornax cluster. We present the definitions of a new set of high-resolution Lick-style indices to be used for stellar population studies of unresolved small stellar systems. We identify 23 absorption features and continuum regions, mainly dominated by 12 elements (Na, Ca, Sc, Ti, V, Cr, Mn, Fe, Ni, Y, Ba and Nd) in the wavelength range 4700 - 5400 \r{A} and characterise them as a function of age, metallicity and alpha element abundance ratios. We analyse eight dEs and interpret the line strengths, measured in our new high resolution system of indices, with the aid of stellar population models with high enough spectral resolution. We obtain abundance ratio proxies for a number of elements that have never been studied before for dwarf ellipticals outside the Local Group. These proxies represent relative deviations from predicted index-strengths of base stellar population models built-up following the abundance pattern of The Galaxy. The abundance proxy trend results are compared to abundance ratios from resolved stars in the Local Group, and indices from integrated light of larger early-type galaxies. We find that all our dwarfs show a pattern of abundance ratios consistent with the disk of the Milky Way, indicative of slow formation in comparison to their high mass counterparts.
    Abundance ratioMetallicityGalaxyStellar populationsMilky WayHigh-resolutionStarNatriumPEGASEFornax Cluster...
  • We propose the scenario to interpret the overall observational features of the SS433--W50 system. The most unique features of SS433 are the presence of the precessing, mildly relativistic jets and the obscuration of the central engine, which are considered to be due to a supercritical accretion on to the central compact object. The jets are likely to be ejected from the innermost region of the accretion flow. The concept of the accretion ring (Inoue 2021, PASJ, 73,795) is applied to the outer boundary of the accretion flow and the ring is supposed to have a precession. The accretion ring is expected to extend a two-layer outflow of a thin excretion disk and a thick excretion flow, as well as the accretion flow. The thin excretion disk is discussed to eventually form the optically thick excretion belt along the Roche lobe around the compact object, contributing to the obscuration of the central engine. The thick excretion flow is likely to turn to the supersonic wind (disk wind) with the terminal velocity of $\sim 10^{8}$ cm s$^{-1}$ and to collide with the SNR matter at the distance of $\sim 10^{18}$ cm. The interactions of the jets with the disk wind are considered to cause the features of the jets observed at the distances of 10$^{14} \sim 10^{15}$ cm and $\sim 10^{17}$ cm. Finally, it is discussed that the jets are braked by the SNR matter at the distance of $\sim$10 pc and the momentum carried by the jet is transferred to the SNR matter shoved by the jet. The SNR matter pushed to the inside of the precession cone is expected to gather along the cone axis and to form the elongated structures in the east and west directions from the main W50 structure.
    AccretionCompact starW50Accretion flowHard X-rayAccretion diskSoft X-rayStarRoche LobeLight curve...
  • Vanilla Federated learning (FL) relies on the centralized global aggregation mechanism and assumes that all clients are honest. This makes it a challenge for FL to alleviate the single point of failure and dishonest clients. These impending challenges in the design philosophy of FL call for blockchain-based federated learning (BFL) due to the benefits of coupling FL and blockchain (e.g., democracy, incentive, and immutability). However, one problem in vanilla BFL is that its capabilities do not follow adopters' needs in a dynamic fashion. Besides, vanilla BFL relies on unverifiable clients' self-reported contributions like data size because checking clients' raw data is not allowed in FL for privacy concerns. We design and evaluate a novel BFL framework, and resolve the identified challenges in vanilla BFL with greater flexibility and incentive mechanism called FAIR-BFL. In contrast to existing works, FAIR-BFL offers unprecedented flexibility via the modular design, allowing adopters to adjust its capabilities following business demands in a dynamic fashion. Our design accounts for BFL's ability to quantify each client's contribution to the global learning process. Such quantification provides a rational metric for distributing the rewards among federated clients and helps discover malicious participants that may poison the global model.
    BlockchainPrivacyFederated learningSecurityRandom sequential adsorptionEncryptionCluster of nodesStochastic gradient descentAnomaly detectionIntelligence...
  • In this chapter we present basic concepts of neutrino physics. We start with a brief introduction to the standard model electroweak sector, followed by calculations of some relevant neutrino interaction cross sections. We obtain the oscillation formalism from the Dirac equation, alongside with a self-contained derivation of matter effects from the standard model electroweak lagrangian. Some key features of neutrino oscillation phenomenology are discussed as well. We then review the most precise oscillation measurements and finalize with some broad discussion of the current open questions in neutrino physics.
    NeutrinoStandard ModelNeutrino massAntineutrinoWeak interactionNeutrino oscillationsHamiltonianSolar neutrinoDeep inelastic scatteringMixing angle...
  • Symbolic regression, i.e. predicting a function from the observation of its values, is well-known to be a challenging task. In this paper, we train Transformers to infer the function or recurrence relation underlying sequences of integers or floats, a typical task in human IQ tests which has hardly been tackled in the machine learning literature. We evaluate our integer model on a subset of OEIS sequences, and show that it outperforms built-in Mathematica functions for recurrence prediction. We also demonstrate that our float model is able to yield informative approximations of out-of-vocabulary functions and constants, e.g. $\operatorname{bessel0}(x)\approx \frac{\sin(x)+\cos(x)}{\sqrt{\pi x}}$ and $1.644934\approx \pi^2/6$. An interactive demonstration of our models is provided at https://symbolicregression.metademolab.com.
    RegressionTransformerWolfram MathematicaAttentionMachine learningArchitectureNeural networkPermutationEntropyGround truth...
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    We present cosmological parameter results from the final full-mission Planck measurements of the CMB anisotropies. We find good consistency with the standard spatially-flat 6-parameter $\Lambda$CDM cosmology having a power-law spectrum of adiabatic scalar perturbations (denoted "base $\Lambda$CDM" in this paper), from polarization, temperature, and lensing, separately and in combination. A combined analysis gives dark matter density $\Omega_c h^2 = 0.120\pm 0.001$, baryon density $\Omega_b h^2 = 0.0224\pm 0.0001$, scalar spectral index $n_s = 0.965\pm 0.004$, and optical depth $\tau = 0.054\pm 0.007$ (in this abstract we quote $68\,\%$ confidence regions on measured parameters and $95\,\%$ on upper limits). The angular acoustic scale is measured to $0.03\,\%$ precision, with $100\theta_*=1.0411\pm 0.0003$. These results are only weakly dependent on the cosmological model and remain stable, with somewhat increased errors, in many commonly considered extensions. Assuming the base-$\Lambda$CDM cosmology, the inferred late-Universe parameters are: Hubble constant $H_0 = (67.4\pm 0.5)$km/s/Mpc; matter density parameter $\Omega_m = 0.315\pm 0.007$; and matter fluctuation amplitude $\sigma_8 = 0.811\pm 0.006$. We find no compelling evidence for extensions to the base-$\Lambda$CDM model. Combining with BAO we constrain the effective extra relativistic degrees of freedom to be $N_{\rm eff} = 2.99\pm 0.17$, and the neutrino mass is tightly constrained to $\sum m_\nu< 0.12$eV. The CMB spectra continue to prefer higher lensing amplitudes than predicted in base -$\Lambda$CDM at over $2\,\sigma$, which pulls some parameters that affect the lensing amplitude away from the base-$\Lambda$CDM model; however, this is not supported by the lensing reconstruction or (in models that also change the background geometry) BAO data. (Abridged)
    Baryon acoustic oscillationsCosmologyCosmological parametersCMB lensingCalibrationReionizationNeutrino massRecombinationDark energyCMB power spectra...
  • Context. Level population inversion of hydrogen atoms in ionized gas may lead to stimulated emission of hydrogen recombination lines, and the level populations can in turn be affected by powerful stimulated emissions. Aims. In this work the interaction of the radiation fields and the level population inversion of hydrogen atoms is studied. The effect of the stimulated emissions on the line profiles is also investigated. Methods. Our previous nl-model for calculating level populations of hydrogen atoms and hydrogen recombination lines is improved. The effects of line and continuum radiation fields on the level populations are considered in the improved model. By using this method the properties of simulated hydrogen recombination lines and level populations are used in analyses. Results. The simulations show that hydrogen radio recombination lines are often emitted from the energy level with an inverted population. The widths of Hn$\alpha$ lines can be significantly narrowed by strong stimulated emissions to be even less than 10 km s$^{-1}$. The amplification of hydrogen recombination lines is more affected by the line optical depth than by the total optical depth. The influence of stimulated emission on the estimates of electron temperature and density of ionized gas is evaluated. We find that comparing multiple line-to-continuum ratios is a reliable method for estimating the electron temperature, while the effectiveness of the estimation of electron density is determined by the relative significance of stimulated emission.
    Local thermal equilibriumEmission measureIntensityElectron temperatureRecombinationCompact H II regionH II regionMaserHydrogen atomContinuum emission...
  • We demonstrate the ability of convolutional neural networks (CNNs) to mitigate systematics in the virial scaling relation and produce dynamical mass estimates of galaxy clusters with remarkably low bias and scatter. We present two models, CNN$_\mathrm{1D}$ and CNN$_\mathrm{2D}$, which leverage this deep learning tool to infer cluster masses from distributions of member galaxy dynamics. Our first model, CNN$_\text{1D}$, infers cluster mass directly from the distribution of member galaxy line-of-sight velocities. Our second model, CNN$_\text{2D}$, extends the input space of CNN$_\text{1D}$ to learn on the joint distribution of galaxy line-of-sight velocities and projected radial distances. We train each model as a regression over cluster mass using a labeled catalog of realistic mock cluster observations generated from the MultiDark simulation and UniverseMachine catalog. We then evaluate the performance of each model on an independent set of mock observations selected from the same simulated catalog. The CNN models produce cluster mass predictions with lognormal residuals of scatter as low as $0.132$ dex, greater than a factor of 2 improvement over the classical $M$-$\sigma$ power-law estimator. Furthermore, the CNN model reduces prediction scatter relative to similar machine learning approaches by up to $17\%$ while executing in drastically shorter training and evaluation times (by a factor of 30) and producing considerably more robust mass predictions (improving prediction stability under variations in galaxy sampling rate by $30\%$).
    Convolution Neural NetworkGalaxyVirial cluster massMachine learningLine of sightStatistical estimatorCluster of galaxiesLine of sight velocityDeep Neural NetworksArchitecture...
  • Recent work has suggested that an additional $\lesssim 6.9 \rm{\, eV}$ per baryon of heating in the intergalactic medium is needed to reconcile hydrodynamical simulations with Lyman-$\alpha$ forest absorption line widths at redshift $z\simeq 0.1$. Resonant conversion of dark photon dark matter into low frequency photons is a viable source of such heating. We perform the first hydrodynamical simulations including dark photon heating and show that dark photons with mass $m_{A'}\sim 8\times 10^{-14}\rm\,eV\,c^{-2}$ and kinetic mixing $\epsilon \sim 5\times 10^{-15}$ can alleviate the heating excess. A prediction of this model is a non-standard thermal history for underdense gas at $z \gtrsim 3$.
    Hydrodynamical simulationsDark Photon Dark MatterLyman-alpha forestHidden photonKinetic mixingAbsorption lineIntergalactic mediumRedshiftBaryonsPhoton...
  • Thermal forces drive several nonequilibrium phenomena able to set a fluid in motion without pressure gradients. Although the most celebrated effect is thermophoresis, also known as Ludwig-Soret effect, probably the simplest example where thermal forces are at play is thermo-osmosis: The motion of a {\it confined} fluid exclusively due to the presence of a temperature gradient. We present a concise but complete derivation of the microscopic theory of thermo-osmosis based on linear response theory. This approach is applied to a simple fluid confined in a slab geometry, mimicking the flow through a pore in a membrane separating two fluid reservoirs at different temperatures. We consider both the case of an open channel, where the fluid can flow freely, and that of a closed channel, where mass transport is inhibited and a pressure drop sets in at the boundaries. Quantitative results require the evaluation of generalized transport coefficients, but a preliminary check on a specific prediction of the theory has been successfully performed via nonequilibrium molecular dynamics simulations.
    LiquidsEnthalpyLinear response theoryOsmosisMembraneTwo-point correlation functionHamiltonianContinuity equationPhase space densityNumerical simulation...
  • We study the dynamics of a one-dimensional run and tumble particle subjected to confining potentials of the type $V(x) = \alpha \, |x|^p$, with $p>0$. The noise that drives the particle dynamics is telegraphic and alternates between $\pm 1$ values. We show that the stationary probability density $P(x)$ has a rich behavior in the $(p, \alpha)$-plane. For $p>1$, the distribution has a finite support in $[x_-,x_+]$ and there is a critical line $\alpha_c(p)$ that separates an active-like phase for $\alpha > \alpha_c(p)$ where $P(x)$ diverges at $x_\pm$, from a passive-like phase for $\alpha < \alpha_c(p)$ where $P(x)$ vanishes at $x_\pm$. For $p<1$, the stationary density $P(x)$ collapses to a delta function at the origin, $P(x) = \delta(x)$. In the marginal case $p=1$, we show that, for $\alpha < \alpha_c$, the stationary density $P(x)$ is a symmetric exponential, while for $\alpha > \alpha_c$, it again is a delta function $P(x) = \delta(x)$. For the special cases $p=2$ and $p=1$, we obtain exactly the full time-dependent distribution $P(x,t)$, that allows us to study how the system relaxes to its stationary state. In addition, in these two cases, we also study analytically the full distribution of the first-passage time to the origin. Numerical simulations are in complete agreement with our analytical predictions.
    Steady stateLangevin equationStationary distributionRelaxationSurvival probabilityPassage timeLaplace transformPhase diagramCritical lineFokker-Planck equation...
  • A particle that is immersed in a uniform temperature bath performs Brownian diffusion, as discussed by Einstein. But Sinai has realized that in a "random environment" the diffusion is suppressed. Follow-up works have pointed out that in the presence of bias $f$ there are delocalization and sliding transitions, with threshold value $f_c$ that depends on the disorder strength. We discuss in a critical way the emergence of Sinai physics for both passive and active Brownian particles. Tight-binding and Fokker-Planck versions of the model are addressed on equal footing. We assume that the transition rates between sites are enhanced either due to a driving mechanism or due to self-propulsion mechanism that are induced by an irradiation source. Consequently, counter intuitively, the dynamics becomes sub-diffusive and the relaxation modes become over-damped. For a finite system, spontaneous delocalization may arise, due to residual bias that is induced by the irradiation.
    DisorderDiffusion coefficientRelaxationLattice (order)Steady stateJanus particlesFinite sizeCoarse grainingPlanck missionIntensity...
  • Recent attempts towards a theory of active matter utilize concepts and methods from hydrodynamics, kinetic theory, and non-equilibrium statistical physics. However, such approaches typically do not seem to recognize the critical feature of some kinds of active matter (particularly the biological ones), namely, the role of purpose, and the naturally attendant concept of the pursuit of maximum utility, which we believe is the crucial difference between active and passive matter. Here we introduce a novel game-theoretic framework, statistical teleodynamics, that accounts for this feature explicitly and show how it can be integrated with conventional statistical mechanics to develop a unified theory of arbitrage equilibrium in active and passive matter. We propose a spectrum of self-actualizing capabilities, going from none to completely strategic decision-making, and envision the various examples of active matter systems occupying someplace in this spectrum. We show how statistical teleodynamics reduces to familiar results in statistical mechanics in the limit of zero self-actualization. At the other extreme, in an economic setting, it provides novel insights about the emergence of income distributions and their fairness in an ideal free-market society. As examples of agents in between these limits, we show how our theory predicts the behavior of active Brownian particles, the emergence of ant craters, and phase equilibria in social segregation dynamics. We suggest that our theory offers a novel systems theoretic perspective of emergent phenomena that could serve as the starting point for a more comprehensive theory of design, control, and optimization through self-organization.
    Statistical mechanicsPotential gameGame theoryMarketEntropyStatistical physicsNash equilibriumSelf-organizationKinetic theoryOptimization...
  • The Gibbs distribution universally characterizes states of thermal equilibrium. In order to extend the Gibbs distribution to non-equilibrium steady states, one must relate the self-information $\mathcal{I}(x) = -\log(P_\text{ss}(x))$ of microstate $x$ to measurable physical quantities. This is a central problem in non-equilibrium statistical physics. By considering open systems described by stochastic dynamics which become deterministic in the macroscopic limit, we show that changes $\Delta \mathcal{I} = \mathcal{I}(x_t) - \mathcal{I}(x_0)$ in steady state self-information along deterministic trajectories can be bounded by the macroscopic entropy production $\Sigma$. This bound takes the form of an emergent second law $\Sigma + k_b \Delta \mathcal{I}\geq 0$, which contains the usual second law $\Sigma \geq 0$ as a corollary, and is saturated in the linear regime close to equilibrium. We thus obtain a tighter version of the second law of thermodynamics that provides a link between the deterministic relaxation of a system and the non-equilibrium fluctuations at steady state. In addition to its fundamental value, our result leads to novel methods for computing non-equilibrium distributions, providing a deterministic alternative to Gillespie simulations or spectral methods.
    Steady stateEntropy productionEntropyNon-equilibrium steady statesComplementary metal-oxide-semiconductorCoarse grainingStatistical physicsMaster equationVorticityDissipation...
  • In the Metaverse, the physical space and the virtual space co-exist, and interact simultaneously. While the physical space is virtually enhanced with information, the virtual space is continuously refreshed with real-time, real-world information. To allow users to process and manipulate information seamlessly between the real and digital spaces, novel technologies must be developed. These include smart interfaces, new augmented realities, efficient storage and data management and dissemination techniques. In this paper, we first discuss some promising co-space applications. These applications offer experiences and opportunities that neither of the spaces can realize on its own. We then argue that the database community has much to offer to this field. Finally, we present several challenges that we, as a community, can contribute towards managing the Metaverse.
    Machine learningPrivacyOptimizationArchitectureData fusionSecuritySocial networkRFIDDecision makingVideo analysis...
  • One of the most important questions in blazar physics is the origin of broadband emission and fast-flux variation. In this work, we studied the broadband temporal and spectral properties of a TeV blazar 1ES 1727+502 and explore the one-zone synchrotron-self Compton (SSC) model to fit the broadband spectral energy distribution (SED). We collected the long-term (2014-2021) multiband data which includes both the low and high flux states of the source. The entire light curve is divided into three segments of different flux states and the best-fit parameters obtained by broadband SED modeling corresponding to three flux states were then compared. The TeV blazar 1ES 1727+502 has been observed to show the brightest flaring episode in X-ray followed by optical-UV and gamma-ray. The fractional variability estimated during various segments behaves differently in multiple wavebands, suggesting a complex nature of emission in this source. This source has shown a range of variability time from days scale to month scale during this long period of observations between 2014-2021. A "harder-when-brighter" trend is not prominent in X-ray but seen in optical-UV and an opposite trend is observed in gamma-ray. The complex nature of correlation among various bands is observed. The SED modeling suggests that the one-zone SSC emission model can reproduce the broadband spectrum in the energy range from optical-UV to very high energy gamma-ray.
    Spectral energy distributionBlazarLight curveSynchrotron Self-Compton radiationTeV blazarBL LacertaeX-ray spectrumSynchrotronCharged particleFERMI telescope...
  • Stationary non-equilibrium states describe steady flows through macroscopic systems. Although they represent the simplest generalization of equilibrium states, they exhibit a variety of new phenomena. Within a statistical mechanics approach, these states have been the subject of several theoretical investigations, both analytic and numerical. The macroscopic fluctuation theory, based on a formula for the probability of joint space-time fluctuations of thermodynamic variables and currents, provides a unified macroscopic treatment of such states for driven diffusive systems. We give a detailed review of this theory including its main predictions and most relevant applications.
    Fluid dynamicsTime-reversal symmetryPhase transitionsHamiltonianDissipationHamilton-Jacobi equationRenormalizationEntropyTransport coefficientContinuity equation...
  • We analyse the long-lasting effects of initial conditions on fluctuations in one-dimensional diffusive systems. We consider both the fluctuations of current for non-interacting diffusive particles starting from a step-like initial density profile, and the mean-square displacement of tracers in homogeneous systems with single-file diffusion. For these two cases, we show analytically (via the propagator and Macroscopic Fluctuation Theory, respectively) that the long-term memory of initial conditions is mediated by a single static quantity: a generalized compressibility that quantifies the density fluctuations of the initial state. We thereby identify a universality class of hyperuniform initial states whose dynamical variances coincide with the `quenched' cases studied previously; we also describe a continuous family of other classes among which equilibrated (or `annealed') initial conditions are but one family member. We verify our predictions through extensive Monte Carlo simulations.
    CompressibilityDiffusion coefficientWhite noisePropagatorOrientationUniversality classStatisticsQuenchingBrownian motionMonte Carlo method...
  • We uncover an unforeseen asymmetry in relaxation -- for a pair of thermodynamically equidistant temperature quenches, one from a lower and the other from a higher temperature, the relaxation at the ambient temperature is faster in case of the former. We demonstrate this finding on hand of two exactly solvable many-body systems relevant in the context of single-molecule and tracer-particle dynamics. We prove that near stable minima and for all quadratic energy landscapes it is a general phenomenon that also exists in a class of non-Markovian observables probed in single-molecule and particle-tracking experiments. The asymmetry is a general feature of reversible overdamped diffusive systems with smooth single-well potentials and occurs in multi-well landscapes when quenches disturb predominantly intra-well equilibria. Our findings may be relevant for the optimization of stochastic heat engines.
    RelaxationQuenchingEntropyGreen's functionOrnstein-Uhlenbeck processMpemba effectDegree of freedomKullback-Leibler divergenceOptimizationSingle-molecule experiment...
  • In the paper we apply asymptotic technique based on the method of stationary phase and obtain the approximate analytical description of thermal motions caused by a source on an isotopic defect of an arbitrary mass in a 1D harmonic crystal. It is well known that localized oscillation is possible in this system in the case of a light defect. We consider the unsteady heat propagation and obtain formulae, which provide continualization (everywhere excepting a neighbourhood of a defect) and asymptotic uncoupling of the thermal motion into the sum of the slow and fast components. The slow motion is related with ballistic heat transport, whereas the fast motion is energy oscillation related with transformation of the kinetic energy into the potential one and in the opposite direction. To obtain the propagating component of the fast and slow motions we estimate the exact solution in the integral form on a moving point of observation. We demonstrate that the propagating parts of the slow and the fast motions are ``anti-localized'' near the defect. The physical meaning of the anti-localization is a tendency for the unsteady propagating wave-field to avoid a neghbourhood of a defect. The effect of anti-localization increases with the absolute value of the difference between the mass of the isotope and the mass for other particles, and, therefore, more energy concentrates just behind the leading wave-fronts of the propagating component. The obtained solution is valid in a wide range of a spatial co-ordinate (i.e., a particle number), everywhere excepting a neighbourhood of the leading wavefront.
    Fundamental solutionIsotopyParticle velocityLattice (order)Exact solutionIsotopeGreen's functionCritical pointGrapheneSteady state...
  • Fluctuations in active matter systems frequently cause qualitatively distinguished behavior as rare events such as slit passing and escape from near-wall trapping. As a first step to analyzing these rare events, we investigate the most probable path of a single active Brownian particle using the Onsager-Machlup integral and its variational principle. We show that the most probable path obeys the extremum conditions by demonstrating an analogy with the pendulum equation. As a demonstration, we numerically solve the extremum conditions for the case of front translation and obtain multiple independent paths. We conclude that the nontrivial U-shaped path is the most probable after comparing the probability of each obtained path. We also discuss further applications of our methods in evaluating the rare events in the active matter.
    Passage timeVariational principleFinal stateEntropy productionOrientationLangevin equationPhase spaceMicroswimmerDiscretizationMobility...
  • A cosmological model with a time-varying mass of electrons seems a promising solution for the so-called Hubble tension. We examine the big bang nucleosynthesis (BBN) constraints on the time-varying electron mass model, because a larger electron mass gives rise to the smaller neutron decay rate which could affect the light element abundance. Additionally, different inferred cosmological parameters, primarily baryon asymmetry, to keep the cosmic background power spectrum unchanged could affect the abundance of light element. We find that the predicted helium fraction becomes larger and the deuterium abundance becomes smaller as the electron mass at the BBN time becomes larger. Thus, we conclude that an acceptable electron mass at the BBN time would be only approximately 1% greater than the current electron mass.
    Electron massBig bang nucleosynthesisHubble constant tensionLight element abundancesDecay rateCosmic microwave backgroundNeutron decaySound horizonDeuterium AbundanceCosmological parameters...
  • We present a numerical method to simulate non-equilibrium Floquet steady states of one-dimensional periodically-driven (Floquet) many-body systems coupled to a dissipative bath, called open-system Floquet DMRG (OFDMRG). This method is based on a matrix product operator ansatz for the Floquet density matrix in frequency-space, and enables access to large systems beyond the reach of exact master-equation or quantum trajectory simulations, while retaining information about the periodic micro-motion in Floquet steady states. An excited-state extension of this technique also allows computation of the dynamical approach to the steady state on asymptotically long timescales. We benchmark the OFDMRG approach with a driven-dissipative Ising model, and apply it to study the possibility of dissipatively stabilizing pre-thermal discrete time-crystalline order by coupling to a cold bath.
    HamiltonianSteady stateDensity matrixMaster equationCoolingDensity matrix renormalization groupMatrix product statesIsing modelDissipationGibbs state...
  • Landauer's bound is the minimum thermodynamic cost for erasing one bit of information. As this bound is achievable only for quasistatic processes, finite-time operation incurs additional energetic costs. We find a tight finite-time Landauer's bound by establishing a general form of the classical speed limit. This tight bound well captures the divergent behavior associated with the additional cost of a highly irreversible process, which scales differently from a nearly irreversible process. We also find an optimal dynamics which saturates the equality of the bound. We demonstrate the validity of this bound via discrete one-bit and coarse-grained bit systems. Our work implies that more heat dissipation than expected occurs during high-speed irreversible computation.
    Coarse grainingDissipationCoolingErasureUncertainty principleEntropyLangevin equationFinal stateArchitectureSteady state...
  • We discuss the secondary cosmic microwave background (CMB) anisotropy due to kinetic Sunyaev-Zel'dovich (kSZ) effect from ionized bubbles around individual quasars prior to the reionization of the Universe. The bubbles create local ionization modulations which move with the large scale structure linear bulk flow and acts as source kSZ. We improve upon previous calculations of this effect, using a halo model based description of quasar abundance, and find that the kSZ distortion power spectrum, $C_\ell$, from the bubbles to be sub-dominant to kSZ from patchy reionization driven by galaxies. However, the shape of the two $C_\ell$'s are very different with the quasar bubble $C_\ell$ having a peak at $\ell \approx 500-700$ whereas the $C_\ell$ due to patchy reionization flattening out at $\ell > 1000$ thus making it plausible to separate the two using $C_\ell$ template-fitting in a future survey like CMB-HD. We also show that the amplitude of the quasar bubble induced power spectrum has a strong dependence on the epoch of reionization, and can be negligible for early reionization models. Next, we look at the imprint of a single quasar bubble on the CMB and show that it can be detected in a high-resolution, ambitious effort like CMB-HD. The amplitude and the oscillatory features of a single bubble power spectrum can be used to constrain the apparent asymmetric shape of the relativistically expanding ionized bubble, and depends on intrinsic quasar physics parameters such as the quasar photon emission rate and the quasar lifetime and cosmological probes like high redshift large scale linear velocity and the neutral hydrogen fraction. A detection of a high redshift quasar bubble in the CMB would carry complimentary information to its detection in HI or Lyman-$\alpha$ and a joint analysis can be used to break parameter degeneracies.
    QuasarReionizationIonizationHalo modelNeutral hydrogen gasLuminosityIndividual quasarsAnisotropyGalaxyIonization fronts...
  • We combine the isothermal Jeans model and the model of adiabatic halo contraction into a simple semi-analytic procedure for computing the density profile of self-interacting dark-matter (SIDM) haloes with the gravitational influence from the inhabitant galaxies. We show that the model agrees well with cosmological SIDM simulations over the entire core-forming stage and up to the onset of gravothermal core-collapse. Using this model, we show that the halo response to baryons is more diverse in SIDM than in CDM and depends sensitively on galaxy size, a desirable link in the context of the structural diversity of bright dwarf galaxies. The fast speed of the method facilitates analyses that would be challenging for numerical simulations -- notably, 1) we quantify the SIDM halo response as functions of the baryonic properties, on a fine mesh grid spanned by the baryon-to-total-mass ratio, $M_{\rm b}/M_{\rm vir}$, and galaxy compactness, $r_{1/2}/R_{\rm vir}$; 2) we show with high statistical precision that for typical Milky-Way-like systems, the SIDM profiles are similar to their CDM counterparts; and 3) we delineate the regime of gravothermal core-collapse in the $M_{\rm b}/M_{\rm vir}$-$r_{1/2}/R_{\rm vir}$ space, for a given cross section and a given halo concentration. Finally, we compare the isothermal Jeans model with the more sophisticated gravothermal fluid model, and show that the former yields faster core formation and agrees better with cosmological simulations. We attribute the difference to whether the target CDM halo is used as a boundary condition or as the initial condition for the gravothermal evolution, and thus comment on possible future improvements of the fluid model. We have made our programs for the model publicly available at https://github.com/JiangFangzhou/SIDM.
    Self-interacting dark matterCore collapseGalaxyNavarro-Frenk-White profileDark matterMilky WayVelocity dispersionDwarf galaxyHalo concentrationsAdiabatic contraction of dark matter...
  • Using Multi-Unit Spectroscopic Explorer (MUSE) spectroscopy, we analyse the stellar kinematics of 18 brightest group early-type (BGEs) galaxies, selected from the Complete Local-Volume Groups Sample (CLoGS). We analyse the kinematic maps for distinct features, and measure specific stellar angular momentum within one effective radius ($\lambda_{e}$). We classify the BGEs as fast (10/18) or slow (8/18) rotators, suggesting at least two different evolution paths. We quantify the anti-correlation between higher-order kinematic moment $h_{3}$ and V/$\sigma$ (using the $\xi_{3}$ parameter), and the kinematic misalignment angle between the photometric and kinematic position angles (using the $\Psi$ parameter), and note clear differences between these parameter distributions of the fast and slow rotating BGEs. We find that all 10 of our fast rotators are aligned between the morphological and kinematical axis, consistent with an oblate galaxy shape, whereas the slow rotators are spread over all three classes: oblate (1/8), triaxial (4/8), and prolate (3/8). We place the results into context using known radio properties, X-ray properties, and observations of molecular gas. We find consistent merger histories inferred from observations for the fast-rotating BGEs, indicating that they experienced gas-rich mergers or interactions, and these are very likely the origin of the cold gas. Observational evidence for the slow rotators are consistent with gas-poor mergers. For the slow rotators with cold gas, all evidence point to cold gas cooling from the intragroup medium.
    GalaxyKinematicsStellar kinematicsMulti Unit Spectroscopic ExplorerIntra Group MediumCoolingStar formationEuropean Southern ObservatoryMilky WayPosition angle...
  • Collisionless, magnetized turbulence offers a promising framework for the generation of non-thermal high-energy particles in various astrophysical sites. Yet, the detailed mechanism that governs particle acceleration has remained subject to debate. By means of 2D and 3D PIC, as well as 3D (incompressible) magnetohydrodynamic (MHD) simulations, we test here a recent model of non-resonant particle acceleration in strongly magnetized turbulence~\cite{2021PhRvD.104f3020L}, which ascribes the energization of particles to their continuous interaction with the random velocity flow of the turbulence, in the spirit of the original Fermi model. To do so, we compare, for a large number of particles that were tracked in the simulations, the predicted and the observed histories of particles momenta. The predicted history is that derived from the model, after extracting from the simulations, at each point along the particle trajectory, the three force terms that control acceleration: the acceleration of the field line velocity projected along the field line direction, its shear projected along the same direction, and its transverse compressive part. Overall, we find a clear correlation between the model predictions and the numerical experiments, indicating that this non-resonant model can successfully account for the bulk of particle energization through Fermi-type processes in strongly magnetized turbulence. We also observe that the parallel shear contribution tends to dominate the physics of energization in the PIC simulations, while in the MHD incompressible simulation, both the parallel shear and the transverse compressive term provide about equal contributions.
    TurbulenceHydrodynamical simulationsGyroradiusShearedMean fieldNumerical simulationLorentz factorMagnetic mirrorMagnetizationDiffusion coefficient...
  • Distances to the $k$-nearest-neighbor ($k$NN) data points from volume-filling query points are a sensitive probe of spatial clustering. Here we present the first application of $k$NN summary statistics to observational clustering measurement, using the 1000 richest redMaPPer clusters ($0.1\leqslant z\leqslant 0.3$) from the SDSS DR8 catalog. A clustering signal is defined as a difference in the cumulative distribution functions (CDFs) of $k$NN distances from fixed query points to the observed clusters versus a set of unclustered random points. We find that the $k=1,2$-NN CDFs of redMaPPer deviate significantly from the randoms' across scales of 35 to 155 Mpc, which is a robust signature of clustering. In addition to $k$NN, we also measure the two-point correlation function for the same set of redMaPPer clusters versus random points, which shows a noisier and less significant clustering signal within the same radial scales. Quantitatively, the $\chi^2$ distribution for both the $k$NN-CDFs and the two-point correlation function measured on the randoms peak at $\chi^2\sim 50$ (null hypothesis), whereas the $k$NN-CDFs ($\chi^2\sim 300$, $p = 1.54\times 10^{-36}$) pick up a much more significant clustering signal than the two-point function ($\chi^2\sim 100$, $p = 1.16\times 10^{-6}$) when measured on redMaPPer. Finally, the measured 3NN and 4NN CDFs deviate from the predicted $k=3, 4$-NN CDFs assuming an ideal Gaussian field, indicating a non-Gaussian clustering signal for redMaPPer clusters, although its origin might not be cosmological due to observational systematics. Therefore, $k$NN serves as a more sensitive probe of clustering complementary to the two point correlation function, providing a novel approach for constraining cosmology and galaxy-halo connection.
    Cumulative distribution functionsTwo-point correlation functionStatisticsSloan Digital Sky SurveyNearest-neighbor siteCosmologyMassive clusterCosmic voidIntrinsic scatterCluster sampling...
  • New astronomical tasks are often related to earlier tasks for which labels have already been collected. We adapt the contrastive framework BYOL to leverage those labels as a pretraining task while also enforcing augmentation invariance. For large-scale pretraining, we introduce GZ-Evo v0.1, a set of 96.5M volunteer responses for 552k galaxy images plus a further 1.34M comparable unlabelled galaxies. Most of the 206 GZ-Evo answers are unknown for any given galaxy, and so our pretraining task uses a Dirichlet loss that naturally handles unknown answers. GZ-Evo pretraining, with or without hybrid learning, improves on direct training even with plentiful downstream labels (+4% accuracy with 44k labels). Our hybrid pretraining/contrastive method further improves downstream accuracy vs. pretraining or contrastive learning, especially in the low-label transfer regime (+6% accuracy with 750 labels).
    GalaxyContrastive learningGalaxy ZooMilky WayGalaxy classification systemsClassifierDark Energy Camera Legacy SurveyTelescopesHyperparameterDirichlet distribution...
  • We combine cosmic chronometer and growth of structure data to derive the redshift evolution of the dark energy equation of state $w$, using a novel agnostic approach. The background and perturbation equations lead to two expressions for $w$, one purely background-based and the other relying also on the growth rate of large-scale structure. We compare the features and performance of the growth-based $w$ to the background $w$, using Gaussian Processes for the reconstructions. We find that current data is not precise enough for robust reconstruction of the two forms of $w$. By using mock data expected from next-generation surveys, we show that the reconstructions will be robust enough and that the growth-based $w$ will out-perform the background $w$. Furthermore, any disagreement between the two forms of $w$ will provide a new test for deviations from the standard model of cosmology.
    Dark energyStandard ModelEquation of state of dark energyTwo-formGaussian processBaryon acoustic oscillationsLarge scale structureRedshift-space distortionLambda-CDM modelModified gravity...
  • The origins of the elements and isotopes of cosmic material is a critical aspect of understanding the evolution of the universe. Nucleosynthesis typically requires physical conditions of high temperatures and densities. These are found in the Big Bang, in the interiors of stars, and in explosions with their compressional shocks and high neutrino and neutron fluxes. Many different tools are available to disentangle the composition of cosmic matter, in material of extraterrestrial origins such as cosmic rays, meteorites, stardust grains, lunar and terrestrial sediments, and through astronomical observations across the electromagnetic spectrum. Understanding cosmic abundances and their evolution requires combining such measurements with approaches of astrophysical, nuclear theories and laboratory experiments, and exploiting additional cosmic messengers, such as neutrinos and gravitational waves. Recent years have seen significant progress in almost all these fields; they are presented in this review. Models are required to explore nuclear fusion of heavier elements. These have been confirmed by observations of nucleosynthesis products in the ejecta of stars and supernovae, as captured by stardust grains and by characteristic lines in spectra seen from these objects, and also by ejecta material captured by Earth over millions of years in sediments. All these help to piece together how cosmic materials are transported in interstellar space and re-cycled into and between generations of stars. Our description of cosmic compositional evolution needs observational support, as it rests on several assumptions that appear challenged. This overview presents the flow of cosmic matter and the various sites of nucleosynthesis, as understood from combining many techniques and observations, towards the current knowledge of how the universe is enriched with elements.
    NucleosynthesisStarIsotopeSupernovaMassive starsSunSolar systemEjectaMeteoritesNeutrino...
  • We use a large N-body simulation to study the characteristic scales in the density gradient profiles in and around halos with masses ranging from $10^{12}$ to $10^{15} h^{-1}{\rm M_\odot}$. We investigate the profiles separately along the major (T_1) and minor (T_3) axes of the local tidal tensor and how the characteristic scales depend on halo mass, formation time, and environment. We find two kinds of prominent characteristic features in the gradient profiles, a deep `valley' and a prominent `peak'. We use the Gaussian Process Regression to fit the gradient profiles and identify the local extrema to determine the scales associate with these features. Around the valley, we identify three types of distinct local minima, corresponding to caustics of particles orbiting around halos. The appearance and depth of the three caustics depend significantly on the direction defined by the local tidal field, formation time and environment of halos. The first caustic is located at a radius r>0.8R_{200}, corresponding to the splashback feature, and is dominated by particles at their first apocenter after infall. The second and third caustics, around 0.6R_{200} and 0.4R_{200} respectively, can be determined reliably only for old halos. The first caustic is always the most prominent feature along T_3, but may not be the case along T_1 or in azimuthally-averaged profiles, suggesting that caution must be taken when using averaged profiles to investigate the splashback radius. We find that the splashback feature is approximately isotropic when proper separations are made between the first and the other caustics. We also identify a peak feature located at $\sim$ 2.5R_{200} in the density gradient profile. This feature is the most prominent along T_1 and is produced by mass accumulations from the structure outside halos. We also discuss the origins of these features and their observational implications.
    Phase space causticVirial massSplashback radiusAnisotropyApocenterAccretionVirial radiusHalo formation historyPhase spaceMean mass density...
  • Mock member stars for 28 dwarf galaxies are constructed from the cosmological Auriga simulation, which reflect the true dynamical status of realistic tracers. The axis-symmetric Jeans Anisotropic Multi-Gaussian Expansion (JAM) modeling is applied to 6,000 star particles for each, to recover the underlying matter distribution. The stellar or dark matter component individually is poorly recovered, but the total profile is constrained reasonably. The mass within the half-mass radius of tracers is recovered the tightest, and the mass between 200 and 300~pc, $M(200-300\mathrm{pc})$, is constrained ensemble unbiasedly, with a scatter of 0.169~dex. Using a smaller sample of 2,000 particles and only line-of-sight velocities with errors, the scatter in $M(200-300\mathrm{pc})$ is increased by $\sim$40%. Quiescent Sagittarius dSph-like systems and star-forming systems with outflows show distinct features, with $M(200-300\mathrm{pc})$ mostly under-estimated for the former, and more likely over-estimated for the latter. The biases correlate with the dynamical status, which is a result of contractions due to tidal effects in quiescent systems or prominent galactic winds in star-forming systems, driving the systems out of equilibrium. After including Gaia DR3 proper motion errors, we find proper motions are as useful as line-of-sight velocities for nearby systems at $<\sim$60~kpc. The expected proper motion errors of the China Space Station Telescope is useful at $<\sim$20~kpc. Extrapolating the density profiles and the dynamical constraints down to scales below the resolution, we find the mass within 150~pc can be constrained ensemble unbiasedly, with a scatter of $\sim$0.3~dex. In the end, we show that the contraction of member stars in nearby systems is detectable with Gaia DR3 proper motion errors.
    StarProper motionChina Space Station TelescopeLine of sight velocityStar formationDwarf galaxySteady stateGalactic windTidal effectsObservational error...
  • The classical dynamics of collisionless cold dark matter, commonly described by fluid variables or a phase-space distribution, can be captured in a single semiclassical wavefunction. We illustrate how classical multi-streaming creates wave interference in a toy model corresponding to the dynamics of the Zel'dovich approximation and link it to diffraction optics. Wave interference dresses the classical skeleton of cold dark matter with universal features akin to the physical imprints of wavelike (or fuzzy) dark matter. We untangle this wave interference to obtain single-stream wavefunctions corresponding to the classical fluid streams, by writing the wavefunction in an integral form. Our wave decomposition captures the full phase-space information and isolates the multi-stream phenomena related to vorticity and velocity dispersion. We link the wave interference features of our system to the standard forms of diffraction catastrophe integrals, which produce bright caustics in optical fields analogous to the cold dark matter density field. Our two complementary descriptions of dark matter wave-fields present rich universal features that can unlock new ways of modelling and probing wavelike dark matter on the scales of the cosmic web.
    WavefunctionPhase space causticInterferencePhase spaceShell crossingBranch pointDark matterVelocity dispersionCold dark matterZeldovich approximation...
  • The angular momentum of galaxies controls the kinematics of their stars, which in turn drives observable quantities such as the apparent radius, the bulge fraction, and the alignment with other nearby structures. To show how angular momentum of galaxies is determined, we build high (${35}\,\mathrm{pc}$) resolution numerical experiments in which we increase or decrease the angular momentum of the Lagrangian patches in the early universe. We simulate three galaxies over their histories from $z=200$ to $z=2$, each with five different choices for the angular momentum (fifteen simulations in total). Our results show that altering early-universe angular momentum changes the timing and orbital parameters of mergers, which in turn changes the total stellar angular momentum within a galaxy's virial radius in a predictable manner. Of our three galaxies, one has no large satellite at $z=2$; in this case, the specific angular momentum is concentrated in the central galaxy. We modify its stellar angular momentum over $0.7\,\mathrm{dex}$ (from $61$ to $320\,\mathrm{kpc.km.s^{-1}}$) and show that this causes its effective radius to grow by $40\,\%$, its $v/\sigma$ parameter to grow by a factor $\times 2.6$ and its bulge fraction to decrease from $0.72$ to $0.57$. The ability to control angular momentum will allow future studies to probe the causal origin of scaling relations between galaxy mass, angular momentum and morphology, and to better understand the origin of galactic intrinsic alignments.
    GalaxyVirial radiusStarDark matterMilky WayStellar massThe early UniverseMass ratioInitial conditions for cosmological simulationsIntrinsic alignment...
  • The presence of gaseous X-ray halos around massive galaxies is a basic prediction of all past and modern structure formation simulations. The importance of these X-ray halos is further emphasized by the fact that they retain signatures of the physical processes that shape the evolution of galaxies from the highest redshift to the present day. In this review, we overview our current observational and theoretical understanding of hot gaseous X-ray halos around nearby massive galaxies and we also describe the prospects of observing X-ray halos with future instruments.
    GalaxyCircumgalactic mediumMilky WayX-ray haloHot gasMassive galaxiesDark matter haloX-ray luminosityElliptical galaxyDisk galaxy...
  • State-of-the-art computer vision systems are trained to predict a fixed set of predetermined object categories. This restricted form of supervision limits their generality and usability since additional labeled data is needed to specify any other visual concept. Learning directly from raw text about images is a promising alternative which leverages a much broader source of supervision. We demonstrate that the simple pre-training task of predicting which caption goes with which image is an efficient and scalable way to learn SOTA image representations from scratch on a dataset of 400 million (image, text) pairs collected from the internet. After pre-training, natural language is used to reference learned visual concepts (or describe new ones) enabling zero-shot transfer of the model to downstream tasks. We study the performance of this approach by benchmarking on over 30 different existing computer vision datasets, spanning tasks such as OCR, action recognition in videos, geo-localization, and many types of fine-grained object classification. The model transfers non-trivially to most tasks and is often competitive with a fully supervised baseline without the need for any dataset specific training. For instance, we match the accuracy of the original ResNet-50 on ImageNet zero-shot without needing to use any of the 1.28 million training examples it was trained on. We release our code and pre-trained model weights at https://github.com/OpenAI/CLIP.
    Natural languageImage ProcessingTraining setOptical Character RecognitionLogistic regressionEmbeddingArchitectureComputational linguisticsDeep learningAttention...
  • We review recent experimental results indicating the band flattening and Landau level merging at the chemical potential in strongly-correlated two-dimensional (2D) electron systems. In ultra-clean, strongly interacting 2D electron system in SiGe/Si/SiGe quantum wells, the effective electron mass at the Fermi level monotonically increases in the entire range of electron densities, while the energy-averaged mass saturates at low densities. The qualitatively different behavior of the two masses reveals a precursor to the interaction-induced single-particle spectrum flattening at the chemical potential in this electron system, in which case the fermion "condensation" at the Fermi level occurs in a range of momenta, unlike the condensation of bosons. In strong magnetic fields, perpendicular to the 2D electron layer, a similar effect of different fillings of quantum levels at the chemical potential -- the merging of the spin- and valley-split Landau levels at the chemical potential -- is observed in Si inversion layers and bilayer 2D electron system in GaAs. Indication of merging of the quantum levels of composite fermions with different valley indices is also reported in ultra-clean SiGe/Si/SiGe quantum wells.
    Quantum levelLandau levelEffective massFermi levelEllipticityComposite fermionsFilling fractionQuantum wellBandsDisorder...
  • In this paper, we have studied how the text of an ancient literature on how their integrity has been preserved for several centuries. Specifically, The Vedas is an ancient literature, which has its text remained preserved without any corruption for thousands of years. As we studied the system that protects the integrity of the text, pronunciation and semantics of the The Vedas, we discovered a number of similarities it has with the current concept of blockchain technology. It is surprising that the notion of de-centralized trust and mathematical encodings have existed since thousands of years in order to protect this work of literature. We have presented our findings and analysis of the similarities. There are also certain technical mechanisms that The Vedic integrity system uses, which can be used to enhance the current digital blockchain platforms in terms of its security and robustness.
    SecurityNetworksLanguageDimensionsCompilersPotentialFrequency...
  • The Ethereum platform allows developers to implement and deploy applications called Dapps onto the blockchain for public use through the use of smart contracts. To execute code within a smart contract, a paid transaction must be issued towards one of the functions that are exposed in the interface of a contract. However, such a transaction is only processed once one of the miners in the peer-to-peer network selects it, adds it to a block, and appends that block to the blockchain This creates a delay between transaction submission and code execution. It is crucial for Dapp developers to be able to precisely estimate when transactions will be processed, since this allows them to define and provide a certain Quality of Service (QoS) level (e.g., 95% of the transactions processed within 1 minute). However, the impact that different factors have on these times have not yet been studied. Processing time estimation services are used by Dapp developers to achieve predefined QoS. Yet, these services offer minimal insights into what factors impact processing times. Considering the vast amount of data that surrounds the Ethereum blockchain, changes in processing times are hard for Dapp developers to predict, making it difficult to maintain said QoS. In our study, we build random forest models to understand the factors that are associated with transaction processing times. We engineer several features that capture blockchain internal factors, as well as gas pricing behaviors of transaction issuers. By interpreting our models, we conclude that features surrounding gas pricing behaviors are very strongly associated with transaction processing times. Based on our empirical results, we provide Dapp developers with concrete insights that can help them provide and maintain high levels of QoS.
    Random forestEngineeringShapley valueRankTraining setGoogle.comHyperparameterMachine learningBase rateEigenstate Thermalization Hypothesis...
  • 2110.13885  , 
    Halo-mediated mass and energy cascades are key to understand dark matter flow. Both cascades origin from the mass exchange between halo and out-of-halo sub-systems. Kinetic energy can be from the motion of halos and particle motion in halos. Similarly, potential energy can be due to the inter- and intra-halo interactions. Intra-halo virial equilibrium is established much faster than inter-halo. Change of energy of entire system comes from virilization in halos. At statistically steady state, continuous mass exchange is required to sustain growth of total halo mass $M_h\propto a^{1/2}$ and energy $E\propto a^{3/2}$, where $a$ is scale factor. Inverse cascade is identified for kinetic energy that is transferred from the smallest scale to large mass scales. This is sustained by the direct cascade of potential energy from large to small scale. Both energies have a scale- and time-independent flux in propagation range that is proportional to mass flux. Energy cascade is mostly facilitated by mass cascade, which can be quantitatively described by mass accretion of typical halos. Halo radial, angular momentum, and angular velocity are modelled and inverse cascade is identified for the coherent radial and rotational motion in halos. In turbulence, vortex stretching (shape changing) along its axis of spin enables energy cascade from large to small length scales. However, change in halo shape is not the dominant mechanism for energy cascade as the moment of inertial gained from shape changing is less than 2 times. Large halos exhibit preference for prolateness over oblateness and most halos have spin axis perpendicular to major axis. Since mass cascade is local in mass space, halo shape evolves continuously in mass space with halos formed by incrementally inheriting structure from progenitor halos. A unique evolution path of halos is found that gradually approaches sphere with increasing size.
    TurbulenceDark matterVirial massInverse cascadeVortex stretchingAccretionEnstrophySteady stateMass transferVorticity...