Recently bookmarked papers

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  • This paper is the first of several parts introducing a new powerful algebra: the algebra of the pseudo-observables. This is a C*-algebra whose set is formed by formal expressions involving observables. The algebra is constructed by applying the Occam's razor principle, in order to obtain the minimal description of physical reality. Proceeding in such a manner, every aspect of quantum mechanics acquires a clear physical interpretation or a logical explanation, providing, for instance, in a natural way the reason for the structure of complex algebra and the matrix structure of Werner Heisenberg's formulation of quantum mechanics. Last but not least, the very general hypotheses assumed, allow one to state that quantum mechanics is the unique minimal description of physical reality.
    Quantum mechanicsWavefunctionQuantum theoryInterpretations of quantum mechanicsAssociative propertyCopenhagen interpretationCommutative propertyComplex numberMeasurement problemPilot wave...
  • We estimate the gravitational radiation signature of the electron/positron annihilation-driven neutrino burst accompanying the asymmetric collapse of an initially hydrostatic, radiation-dominated supermassive object suffering the Feynman-Chandrasekhar instability. An object with a mass $5\times10^4M_\odot<M<5\times10^5M_\odot$, with primordial metallicity, is an optimal case with respect to the fraction of its rest mass emitted in neutrinos as it collapses to a black hole: lower initial mass objects will be subject to scattering-induced neutrino trapping and consequently lower efficiency in gravitational radiation generation; while higher masses will not get hot enough to radiate significant neutrino energy before producing a black hole. The optimal case collapse will radiate several percent of the star's rest mass in neutrinos and, with an assumed small asymmetry in temperature at peak neutrino production, produces a characteristic linear memory gravitational wave burst signature. The timescale for this signature, depending on redshift, is $\sim1{\rm~s}$ to $10{\rm~s}$, optimal for proposed gravitational wave observatories like DECIGO. Using the response of that detector, and requiring a signal-to-noise ratio SNR $>$ 5, we estimate that collapse of a $\sim 10^5M_\odot$ supermassive star could produce a neutrino burst-generated gravitational radiation signature detectable to redshift $z\lesssim10$. These events could be detected to even higher redshifts with the ultimate DECIGO design sensitivity.
    NeutrinoGravitational waveBlack holeGravitational radiationDeci-hertz Interferometer Gravitational wave ObservatorySupermassive starsStarEntropyInstabilityAnisotropy...
  • We analyze the morphologies of three core collapse supernova remnants (CCSNRs) and the energy of jets in other CCSNRs and in Super Luminous Supernovae (SLSNe) of type Ib/Ic/IIb, and conclude that these properties are well explained by the last jets' episode as expected in the jet feedback explosion mechanism of core collapse supernovae (CCSNe). The presence of two opposite protrusions, termed ears, and our comparison of the CCSNR morphologies with morphologies of planetary nebulae strengthen the claim that jets play a major role in the explosion mechanism of CCSNe. We crudely estimate the energy that was required to inflate the ears in two CCSNRs, and assume that the ears were inflated by jets. We find that the energies of the jets that inflated ears in 11 CCSNRs span a range that is similar to that of jets in some energetic CCSNe (SLSNe), and that this energy, only of the last jets' episode, is much less than the explosion energy. This finding is compatible with the jet feedback explosion mechanism of CCSNe, where only the last jets, that carry a small fraction of the total energy carried by earlier jets, are expected to influence the outer parts of the ejecta. We reiterate our call for a paradigm shift from neutrino-driven to jet-driven explosion models of CCSNe.
    Astrophysical jetCore-collapse supernovaPlanetary nebulaEjectaNeutron starStarNeutrinoInterstellar mediumSupernovaSupernova remnant...
  • Deep learning owes its success to three key factors: scale of data, enhanced models to learn representations from data, and scale of computation. This book chapter presented the importance of the data-driven approach to learn good representations from both big data and small data. In terms of big data, it has been widely accepted in the research community that the more data the better for both representation and classification improvement. The question is then how to learn representations from big data, and how to perform representation learning when data is scarce. We addressed the first question by presenting CNN model enhancements in the aspects of representation, optimization, and generalization. To address the small data challenge, we showed transfer representation learning to be effective. Transfer representation learning transfers the learned representation from a source domain where abundant training data is available to a target domain where training data is scarce. Transfer representation learning gave the OM and melanoma diagnosis modules of our XPRIZE Tricorder device (which finished $2^{nd}$ out of $310$ competing teams) a significant boost in diagnosis accuracy.
    Convolutional neural networkClassificationInductive transferSmall dataBig dataActivation functionNeural networkMultilayer perceptronOptimizationDeep learning...
  • As wide-field surveys yield ever more precise measurements, cosmology has entered a phase of high precision requiring highly accurate and fast theoretical predictions. At the heart of most cosmological model predictions is a numerical solution of the Einstein-Boltzmann equations governing the evolution of linear perturbations in the Universe. We present PyCosmo, a new Python-based framework to solve this set of equations using a special pur- pose solver based on symbolic manipulations, automatic generation of C++ code and sparsity optimisation. The code uses a consistency relation of the field equations to adapt the time step and does not rely on physical approximations for speed-up. After reviewing the system of first-order linear homogeneous differential equations to be solved, we describe the numerical scheme implemented in PyCosmo. We then compare the predictions and performance of the code for the computation of the transfer functions of cosmological perturbations and compare it to existing cosmological Boltzmann codes. We find that we achieve comparable execution times for comparable accuracies. While PyCosmo does not yet have all the features of other codes, our approach is complementary to existing cosmological Boltzmann solvers and can be used as an independent test of their numerical solutions. The symbolic representation of the Einstein-Boltzmann equation system in PyCosmo provides a convenient interface for implementing extended cosmological models. We also discuss how the PyCosmo framework can also be used as a general framework to compute cosmological quantities as well as observables for both interactive and high-performance batch jobs applications. Information about the PyCosmo package and future code releases are available at http://www.cosmology.ethz.ch/research/software-lab.html.
    Boltzmann codeBoltzmann transport equationCosmological modelTransfer functionCosmologyEinstein field equationsNewtonian gaugePythonNeutrinoCosmological perturbations...
  • We present results from general-relativistic (GR) three-dimensional (3D) core-collapse simulations with approximate neutrino transport for three non-rotating progenitors (11.2, 15, and 40 Msun) using different nuclear equations of state (EOSs). We find that the combination of progenitor's higher compactness at bounce and the use of softer EOS leads to stronger activity of the standing accretion shock instability (SASI). We confirm previous predications that the SASI produces characteristic time modulations both in neutrino and gravitational-wave (GW) signals. By performing a correlation analysis of the SASI-modulated neutrino and GW signals, we find that the correlation becomes highest when we take into account the time-delay effect due to the advection of material from the neutrino sphere to the proto-neutron star core surface. Our results suggest that the correlation of the neutrino and GW signals, if detected, would provide a new signature of the vigorous SASI activity in the supernova core, which can be hardly seen if neutrino-convection dominates over the SASI.
    NeutrinoGravitational waveStationary accretion shock instabilityCore-collapse supernovaProto-neutron starTime delayFluid dynamicsNeutrino sphereSupernovaIceCube Neutrino Observatory...
  • In this paper, a model is proposed to solve the gauge hierarchy problem. Beyond the standard model, we introduce an extra scalar field that non-minimally couples to gravity. The fundamental scale is set at weak scale and Planck scale emerges dynamically by a spontaneous symmetry breaking mechanism.
    Scalar fieldElectroweak scalePlanck scaleHierarchy problemCosmological constantStandard ModelNon-minimal couplingHiggs boson massDilatonHiggs boson...
  • We constrain the history of reionization using the data from Planck 2015 Cosmic Microwave Background (CMB) temperature and polarization anisotropy observations. We also use prior constraints on the reionization history at redshifts $\sim7-8$ obtained from Lyman-$\alpha$ emission observations. Using the free electron fractions at different redshifts as free parameters, we construct the complete reionization history using polynomials. Our construction provides an extremely flexible framework to search for the history of reionization as a function of redshifts. We present a conservative and an optimistic constraint on reionization that are categorized by the flexibilities of the models and datasets used to constrain them, and we report that CMB data marginally favors extended reionization histories. In both the cases, we find the mean values of optical depth to be larger ($\approx0.09$ and $0.1$) than what we find in standard steplike reionization histories ($0.079\pm0.017$). At the same time we also find that the maximum free electron fraction allowed by the data for redshifts more than 15 is $\sim0.25$ at 95.4\% confidence limit in the case of optimistic constraint.
    ReionizationHistory of the reionizationPlanck missionCosmic microwave backgroundIonizationAnisotropyNeutral hydrogen gasQuasarLine of sightCosmological parameters...
  • We consider the dynamics in and near galaxy clusters. Gas, dark matter and galaxies are presently falling into the clusters between approximately 1 and 5 virial radii. At very large distances, beyond 10 virial radii, all matter is following the Hubble flow, and inside the virial radius the matter particles have on average zero radial velocity. The cosmological parameters are imprinted on the infall profile of the gas, however, no method exists, which allows a measurement of it. We consider the results of two cosmological simulations (using the numerical codes RAMSES and Gadget) and find that the gas and dark matter radial velocities are very similar. We derive the relevant dynamical equations, in particular the generalized hydrostatic equilibrium equation, including both the expansion of the Universe and the cosmological background. This generalized gas equation is the main new contribution of this paper. We combine these generalized equations with the results of the numerical simulations to estimate the contribution to the measured cluster masses from the radial velocity: inside the virial radius it is negligible, and inside two virial radii the effect is below 40%, in agreement the earlier analyses for DM. We point out how the infall velocity in principle may be observable, by measuring the gas properties to distance of about two virial radii, however, this is practically not possible today.
    Dark matterRadial velocityVirial radiusHydrostatic equilibriumJeans equationMass excessCluster of galaxiesInfall velocityNumerical simulationGalaxy...
  • The realization of multimessenger astrophysics will open new vistas upon the most energetic events in the universe. Messenger particles of all four of nature's fundamental forces, recorded by detectors on the ground and satellites in space, enable coincidence searches for multimessenger phenomena that will allow us to discover, observe, and explore these sources. The Astrophysical Multimessenger Observatory Network (AMON) links multiple high-energy neutrino, cosmic ray, and gamma-ray observatories as well as gravitational wave facilities into a single virtual system, enabling near real-time coincidence searches for multimessenger astrophysical transients and their electromagnetic counterparts, and providing alerts to follow-up observatories. The science case, design elements, partner observatories, and status of the AMON project are presented, followed by recent results from AMON real-time and archival analyses.
    ObservatoriesIceCube Neutrino ObservatoryNeutrinoFERMI telescopeHAWCCosmic rayPierre Auger ObservatoryHigh energy neutrinosLaser Interferometer Gravitational-Wave ObservatoryPython...
  • This article deals with the first detection of gravitational waves by the advanced Laser Interferometer Gravitational Wave Observatory (LIGO) detectors on 14 September 2015, where the signal was generated by two stellar mass black holes with masses 36 $ M_{\odot}$ and 29 $ M_{\odot}$ that merged to form a 62 $ M_{\odot}$ black hole, releasing 3 $M_{\odot}$ energy in gravitational waves, almost 1.3 billion years ago. We begin by providing a brief overview of gravitational waves, their sources and the gravitational wave detectors. We then describe in detail the first detection of gravitational waves from a binary black hole merger. We then comment on the electromagnetic follow up of the detection event with various telescopes. Finally, we conclude with the discussion on the tests of gravity and fundamental physics with the first gravitational wave detection event.
    Gravitational waveBlack holeGeneral relativityLaser Interferometer Gravitational-Wave ObservatoryNeutron starInspiralGravitational radiationNumerical relativityLIGO GW150914 eventBinary black hole system...
  • The Fermat numbers have many notable properties, including order universality, coprimality, and definition by a recurrence relation. We use arbitrary elliptic curves and rational points of infinite order to generate sequences that are analogous to the Fermat numbers. We demonstrate that these sequences have many of the same properties as the Fermat numbers, and we discuss results about the prime factors of sequences generated by specific curves and points.
    Fermat numberElliptic curveHomomorphismMersenne primeLagrange's theoremFourth powerNonnegativeCoprimeFinite ringSage...
  • We use the Aurora radiation-hydrodynamical simulations to study the mean free path (MFP) for hydrogen ionizing photons during the epoch of reionization. We directly measure the MFP by averaging the distance 1 Ry photons travel before reaching an optical depth of unity along random lines-of-sight. During reionization the free paths tend to end in neutral gas with densities near the cosmic mean, while after reionizaton the end points tend to be overdense but highly ionized. Despite the increasing importance of discrete, over-dense systems, the cumulative contribution of systems with $N_{\rm{HI}} \lesssim 10^{16.5}~{\rm cm^{-2}}$ suffices to drive the MFP at $z \approx 6$, while at earlier times higher column densities are more important. After reionization the typical size of HI systems is close to the local Jeans length, but during reionization it is much larger. The mean free path for photons originating close to galaxies, $\rm{MFP_{gal}}$, is much smaller than the cosmic MFP. After reionization this enhancement can remain significant up to starting distances of $\sim 1$ comoving Mpc. During reionization, however, $\rm{MFP_{gal}}$ for distances $\sim 10^2 - 10^3$ comoving kpc typically exceeds the cosmic MFP. These findings have important consequences for models that interpret the intergalactic MFP as the distance escaped ionizing photons can travel from galaxies before being absorbed and may cause them to under-estimate the required escape fraction from galaxies, and/or the required emissivity of ionizing photons after reionization.
    ReionizationIntergalactic mediumGalaxyLine of sightIonizing radiationOpacityEpoch of reionizationMean free pathAuroraVirial mass...
  • We review the literature on what classical physics has to say about the Meissner effect and the London equations. We first discuss the relevance of the Bohr-van Leeuwen theorem for the perfect diamagnetism of superconductors. The conclusion is that the theorem is based on assumptions that are not valid. We also point out results in the literature which prove that the magnetic flux expulsion from a sample cooled to superconductivity can be simply understood as an approach to the magnetostatic energy minimum. These results have been published several times but still many textbooks on magnetism claim that there is no classical diamagnetism, and virtually all books on superconductivity repeat Meissner's 1933 statement that flux expulsion has no classical explanation.
    DiamagnetSuperconductorMeissner effectSuperconductivityBohr-van Leeuwen theoremHamiltonianCharged particleLondon equationCoolingOhm's law...
  • This is a brief introduction to general relativity, designed for both students and teachers of the subject. While there are many excellent expositions of general relativity, few adequately explain the geometrical meaning of the basic equation of the theory: Einstein's equation. Here we give a simple formulation of this equation in terms of the motion of freely falling test particles. We also sketch some of its consequences, and explain how the formulation given here is equivalent to the usual one in terms of tensors. Finally, we include an annotated bibliography of books, articles and websites suitable for the student of relativity.
    Einstein field equationsGeneral relativityCurvaturePlanetCosmologyParallel transportGravitational waveSpecial relativityGeodesicBig Bang...
  • An important source of innovation in nanophotonics is the idea to scale down known radio wave technologies to the optical regime. One thoroughly investigated example of this approach are metallic nanoantennas which employ plasmonic resonances to couple localized emitters to selected far-field modes. While metals can be treated as perfect conductors in the microwave regime, their response becomes Drude-like at optical frequencies. Thus, plasmonic nanoantennas are inherently lossy. Moreover, their resonant nature requires precise control of the antenna geometry. A promising way to circumvent these problems is the use of broadband nanoantennas made from low-loss dielectric materials. Here, we report on highly directional emission from active dielectric leaky-wave nanoantennas made of Hafnium dioxide. Colloidal semiconductor quantum dots deposited in the nanoantenna feed gap serve as a local light source. The emission patterns of active nanoantennas with different sizes are measured by Fourier imaging. We find for all antenna sizes a highly directional emission, underlining the broadband operation of our design.
    IntensityQuantum dotsIndex of refractionFar-fieldOrientationDielectric nanoantennaGlassSemiconductorElectron beam lithographyFourier imaging...
  • The tunneling Hamiltonian describes a particle transfer from one region to the other. While there is no particle storage in the tunneling region itself, it has associated certain amount of energy. We name the corresponding flux energy reactance since, like an electrical reactance, it manifests itself in time-dependent transport only. Noticeably, this quantity is crucial to reproduce the universal charge relaxation resistance for a single-channel quantum capacitor at low temperatures. We show that a conceptually simple experiment is capable of demonstrating the existence of the energy reactance.
    Quantum dotsCapacitorHamiltonianRelaxationGreen's functionDensity of statesHigh temperature limitCharged currentFermi-Dirac statisticsHybridization...
  • The total number and luminosity function of the population of dwarf galaxies of the Milky Way (MW) provide important constraints on the nature of the dark matter and on the astrophysics of galaxy formation at low masses. However, only a partial census of this population exists because of the flux limits and restricted sky coverage of existing Galactic surveys. We combine the sample of satellites recently discovered by the Dark Energy Survey (DES) survey with the satellites found in Sloan Digital Sky Survey (SDSS) Data Release 9 (together these surveys cover nearly half the sky) to estimate the total luminosity function of satellites down to $M_{\rm V}=0$. We apply a new Bayesian inference method in which we assume that the radial distribution of satellites follows that of subhaloes selected according to their peak maximum circular velocity. We find that there should be at least $142^{+53}_{-34}$ ($1\sigma$ CL) satellites brighter than $M_{\rm V}=0$ within $300$ kpc of the Sun. As a result of our use of new data and better simulations, and a more robust statistical method, we infer a much smaller population of satellites than reported in previous studies using earlier SDSS data only; we also address an underestimation of the uncertainties in earlier work by accounting for discreteness effects. We find that the inferred number of faint satellites depends only weakly on the assumed mass of the MW halo and we provide scaling relations to extend our results to different assumed halo masses and outer radii. We predict that half of our estimated total satellite population of the MW should be detected by the Large Synoptic Survey Telescope (LSST).
    Dark matter subhaloMilky WayVirial massMilky Way haloLuminosity functionDwarf galaxyGalaxyBayesian approachDark matterAbsolute magnitude...
  • Techniques in time- and angle-resolved photoemission spectroscopy have facilitated a number of recent advances in the study of quantum materials. We review developments in this field related to the study of incoherent nonequilibrium electron dynamics, the analysis of interactions between electrons and collective excitations, the exploration of dressed-state physics, and the illumination of unoccupied band structure. Future prospects are also discussed.
    Angular resolved photoemission spectroscopyQuantum materialsPump pulseElectronic band structureCharge density waveLasersTime-resolved ARPESElectron-boson couplingProbe pulseSuperconductivity...
  • Gravitational waves from merging neutron stars are expected to be observed in the next 5 years. We explore the potential impact of matter effects on gravitational waves from merging double neutron-star binaries. If neutron star binaries exist with chirp masses less than roughly 1 solar mass and typical neutron-star radii are larger than roughly 14 km, or if neutron-star radii are larger than 15-16 km for the chirp masses of galactic neutron-star binaries, then matter will have a significant impact on the effectiveness of a point-particle-based search at Advanced LIGO design sensitivity (roughly 5% additional loss of signals). In a configuration typical of LIGO's first observing run, extreme matter effects lead to up to 10% potential loss in the most extreme cases.
    Laser Interferometer Gravitational-Wave ObservatoryNeutron starGravitational waveTidal effectsNeutron star radiiHorizonDouble Neutron StarNumerical simulationMatched filterSolar mass...
  • These lecture notes are based on the short course presented in the XVI Brazilian School of Cosmology and Gravitation held at the Brazilian Center for Physical Research (CBPF) in July 2017. The objective of this course was to introduce the students to the notion and analysis of black hole quasinormal modes, starting from the linear perturbation theory, including a brief discussion of numerical methods and astrophysical implications in the gravitational wave signals recently detected by LIGO.
    Black holeQuasinormal modesGravitational waveLaser Interferometer Gravitational-Wave ObservatoryGravastarNeutron starWave equationStarEinstein field equationsEvent horizon...
  • Berg and Ulfberg and Amano and Maruoka have used CNF-DNF-approximators to prove exponential lower bounds for the monotone network complexity of the clique function and of Andreev's function. We show that these approximators can be used to prove the same lower bound for their non-monotone network complexity. This implies P not equal NP.
    GraphConjunctionTopological orderBipartite networkNode of the graphUndirected graphFast Fourier transformNetworksPolynomialTransformations...
  • These lectures are a brief introduction to scattering amplitudes. We begin with a review of basic kinematical concepts like the spinor helicity formalism, followed by a tutorial on bootstrapping tree-level scattering amplitudes. Afterwards, we discuss on-shell recursion relations and soft theorems, emphasizing their broad applicability to gravity, gauge theory, and effective field theories. Lastly, we report on some of the new field theoretic structures which have emerged from the on-shell picture, focusing primarily on color-kinematics duality.
    KinematicsScattering amplitudeS-matrixFeynman diagramsYang-Mills theoryGravitonHelicityLittle groupQuantum field theoryEffective field theory...
  • The Catalogue of Spacetimes is a collection of four-dimensional Lorentzian spacetimes in the context of the General Theory of Relativity (GR). The aim of the catalogue is to give a quick reference for students who need some basic facts of the most well-known spacetimes in GR.
    TetradGeneral relativityGeodesicChristoffel symbolsRicci tensorLine elementKretschmann scalarLocally non-rotating frameFermi-Walker transportExact solution...
  • We discuss the non-conservation of fermion number (or chirality breaking, depending on the fermionic charge assignment) in Abelian gauge theories at finite temperature. We study different mechanisms of fermionic charge disappearance in the high temperature plasma, with the use of both analytical estimates and real-time classical numerical simulations. We investigate the random walk of the Chern-Simons number $N_{\rm CS} \propto \int d^4x F_{\mu\nu}{\tilde F}^{\mu\nu}$, and show that it has a diffusive behaviour in the presence of an external magnetic field $B$. This indicates that the mechanism for fermionic number non-conservation for $B \neq 0$, is due to fluctuations of the gauge fields, similarly as in the case of non-Abelian gauge theories. We determine numerically the rate of chirality non-conservation associated with this diffusion, finding it larger by a factor $\sim 60$ compared to previous theoretical estimates. We also perform numerical simulations for the system which contains a chemical potential $\mu$ representing a fermionic charge density, again both with and without an external magnetic field. When $B=0$, we observe clearly the expected instability of the system for $\mu \neq 0$, as long as the chemical potential exceeds a critical value $\mu > \mu_c(L)$, which depends on the size $L$ of the system. When $B \neq 0$, the fluctuations of bosonic fields lead to the transfer of chemical potential into Chern-Simons number for arbitrary $\mu$.
    Gauge coupling constantChern-Simons numberGauge fieldInstabilityStatistical errorDecay rateCritical valueChern-Simons termAbelian gauge theoryLattice calculations...
  • Axion dark matter models have been thoroughly studied in the recent literature, in particular under the prescription of a free scalar field, but a full treatment of the axion field is still required mainly because nonlinearities in a more realistic potential may play an important role in the cosmological dynamics. In this paper, we show how to solve the cosmological equations of an axion field for both the background and the linear perturbations with the aid of an amended version of the Boltzmann code CLASS, and contrast our results with those of cold dark matter and the free axion case. We conclude that there is a slight delay in the onset of the axion field oscillations when nonlinearities in the axion potential are taken into account, and that the characteristic cut-off in the MPS shifts towards smaller scales (larger wavenumbers). Likewise, we identify a tachyonic instability of the linear modes that results in the presence of a bump in the power spectrum at small scales. Some comments are in turn about the true source of the tachyonic instability, how the parameters of the axion-like potential can be constrained by Lyman-$\alpha$ observations, and the consequences in the stability of self-gravitating equilibrium configurations made of axions.
    AxionCold dark matterInstabilityScalar fieldAxion potentialBumpingDark matterAxion massCosmic linear anisotropy solving systemLight dark matter...
  • We consider theories with fermionic degrees of freedom that have a fixed point of Wilson-Fisher type in non-integer dimension $d = 4-2\epsilon$. Due to the presence of evanescent operators, i.e., operators that vanish in integer dimensions, these theories contain families of infinitely many operators that can mix with each other under renormalization. We clarify the dependence of the corresponding anomalous-dimension matrix on the choice of renormalization scheme beyond leading order in $\epsilon$-expansion. In standard choices of scheme, we find that eigenvalues at the fixed point cannot be extracted from a finite-dimensional block. We illustrate in examples a truncation approach to compute the eigenvalues. These are observable scaling dimensions, and, indeed, we find that the dependence on the choice of scheme cancels. As an application, we obtain the IR scaling dimension of four-fermion operators in QED in $d=4-2\epsilon$ at order $\mathcal{O}(\epsilon^2)$.
    Scaling dimensionAnomalous dimensionDegree of freedomRenormalization schemeQuantum electrodynamicsRenormalizationTheoryDimensionsEigenvalueFermion...
  • Joint electromagnetic and gravitational-wave (GW) observation is a major goal of both the GW astronomy and electromagnetic astronomy communities for the coming decade. One way to accomplish this goal is to direct follow-up of GW candidates. Prompt electromagnetic emission may fade quickly, therefore it is desirable to have GW detection happen as quickly as possible. A leading source of latency in GW detection is the whitening of the data. We examine the performance of a zero-latency whitening filter in a detection pipeline for compact binary coalescence (CBC) GW signals. We find that the filter reproduces signal-to-noise ratio (SNR) sufficiently consistent with the results of the original high-latency and phase-preserving filter for both noise and artificial GW signals (called "injections"). Additionally, we demonstrate that these two whitening filters show excellent agreement in $\chi^2$ value, a discriminator for GW signals.
    Gravitational waveSignal to noise ratioShort gamma-ray burstMatched filterTime SeriesDiscrete Fourier transformLaser Interferometer Gravitational-Wave ObservatoryGaussian distributionTwo-point correlation functionPower spectral density...
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    The Large Synoptic Survey Telescope is designed to provide an unprecedented optical imaging dataset that will support investigations of our Solar System, Galaxy and Universe, across half the sky and over ten years of repeated observation. However, exactly how the LSST observations will be taken (the observing strategy or "cadence") is not yet finalized. In this dynamically-evolving community white paper, we explore how the detailed performance of the anticipated science investigations is expected to depend on small changes to the LSST observing strategy. Using realistic simulations of the LSST schedule and observation properties, we design and compute diagnostic metrics and Figures of Merit that provide quantitative evaluations of different observing strategies, analyzing their impact on a wide range of proposed science projects. This is work in progress: we are using this white paper to communicate to each other the relative merits of the observing strategy choices that could be made, in an effort to maximize the scientific value of the survey. The investigation of some science cases leads to suggestions for new strategies that could be simulated and potentially adopted. Notably, we find motivation for exploring departures from a spatially uniform annual tiling of the sky: focusing instead on different parts of the survey area in different years in a "rolling cadence" is likely to have significant benefits for a number of time domain and moving object astronomy projects. The communal assembly of a suite of quantified and homogeneously coded metrics is the vital first step towards an automated, systematic, science-based assessment of any given cadence simulation, that will enable the scheduling of the LSST to be as well-informed as possible.
    Large Synoptic Survey TelescopeWide Field Infrared Survey TelescopeSupernovaLight curveGalaxySchedulingAirmassPhotometric redshiftTwilightTime delay...
  • We show that the inferred merger rate and chirp masses of binary black holes (BBHs) detected by advanced LIGO (aLIGO) can be used to constrain the rate of double neutron star (DNS) and neutron star - black hole (NSBH) mergers in the universe. We explicitly demonstrate this by considering a set of publicly available population synthesis models of \citet{Dominik:2012kk} and show that if all the BBH mergers, GW150914, LVT151012, GW151226, and GW170104, observed by aLIGO arise from isolated binary evolution, the predicted DNS merger rate may be constrained to be $0.6-295$ Gpc$^{-3}$yr$^{-1}$ and that of NSBH mergers will be constrained to $0.3-88$ Gpc$^{-3}$yr$^{-1}$ which are tightened by a factor of $\sim 2$ and $\sim4$, respectively, as compared to the previous rates. These rate estimates may have implications for short Gamma Ray Burst progenitor models assuming they are powered (solely) by DNS or NSBH mergers. While these results are based on a set of open access population synthesis models which may not necessarily be the representative ones, the proposed method is very general and can be applied to any number of models thereby yielding more realistic constraints on the DNS and NSBH merger rates from the inferred BBH rate and chirp mass. These constraints on DNS and NSBH merger rates will be further tightened by future detections of BBH mergers by aLIGO.
    Binary black hole systemBinary starBlack holeShort gamma-ray burstDouble Neutron StarStarNeutron starLIGO GW150914 eventLIGO GW151226 eventHertzsprung gap...
  • The gravitational-wave (GW) asteroseismology is a powerful technique for extracting interior information of compact objects. In this work, we focus on spacetime modes, the so-called $w$-modes, of GWs emitted from a proto-neutron star (PNS) in the postbounce phase of core-collapse supernovae. Using results from recent three-dimensional supernova models, we study how to infer the properties of the PNS based on a quasi-normal mode analysis in the context of the GW asteroseismology. We find that the $w_1$-mode frequency multiplied by the PNS radius is expressed as a linear function with respect to the ratio of the PNS mass to the PNS radius. This relation is insensitive to the nuclear equation of state (EOS) employed in this work. Combining with another universal relation of the $f$-mode oscillations, we point out that the time dependent mass-radius relation of the PNS can be obtained by observing both the $f$- and $w_1$-mode GWs simultaneously. Our results suggest that the simultaneous detection of the two modes could provide a new probe into finite-temperature nuclear EOS that predominantly determines the PNS evolution.
    Proto-neutron starGravitational waveNeutron starAsteroseismologyDamping rateCore-collapse supernovaStationary accretion shock instabilityStarCompact starSupernova...
  • The structure of interactions in most of animals and human societies can be best represented by complex hierarchical networks. In order to maintain close to optimal functioning both stability and adaptability are necessary. Here we investigate the stability of hierarchical networks that emerge from the simulations of an organization-type having an efficiency function reminiscent of the Hamiltonian of spin-glasses. Using this quantitative approach we find a number of expected (from everyday observations) and highly non-trivial results for the obtained locally optimal networks, including such as: i) stability increases with growing efficiency and level of hierarchy, ii) the same perturbation results in a larger change for more efficient states, iii) networks with a lower level of hierarchy become more efficient after perturbation, iv) due to the huge number of possible optimal states only a small fraction of them exhibits resilience and, finally, v) "attacks" targeting the nodes selectively (regarding their position in the hierarchy) can result in paradoxical outcomes.
    HamiltonianSpin glassNetworksSimulations...
  • In the merging-compression method of plasma start-up, two flux-ropes with parallel toroidal current are formed around in-vessel poloidal field coils, before merging to form a spherical tokamak plasma. This start-up method, used in the Mega-Ampere Spherical Tokamak (MAST), is studied as a high Lundquist number and low plasma-beta magnetic reconnection experiment. In this paper, 2D fluid simulations are presented of this merging process in order to understand the underlying physics, and better interpret the experimental data. These simulations examine the individual and combined effects of tight-aspect ratio geometry and two-fluid physics on the merging. The ideal self-driven flux-rope dynamics are coupled to the diffusion layer physics, resulting in a large range of phenomena. For resistive MHD simulations, the flux-ropes enter the sloshing regime for normalised resistivity eta < 1E-5. In Hall-MHD three regimes are found for the qualitative behaviour of the current sheet, depending on the ratio of the current sheet width to the ion-sound radius. These are a stable collisional regime, an open X-point regime, and an intermediate regime that is highly unstable to tearing-type instabilities. In toroidal axisymmetric geometry, the final state after merging is a MAST-like spherical tokamak with nested flux-surfaces. It is also shown that the evolution of simulated 1D radial density profiles closely resembles the Thomson scattering electron density measurements in MAST. An intuitive explanation for the origin of the measured density structures is proposed, based upon the results of the toroidal Hall-MHD simulations.
    Mega Ampere Spherical TokamakHall-MHD simulationHydrodynamical simulationsTokamakResistive MHD simulationCurrent densityViscosityDissipationInstabilityElectron temperature...
  • Many real world tasks such as reasoning and physical interaction require identification and manipulation of conceptual entities. A first step towards solving these tasks is the automated discovery of distributed symbol-like representations. In this paper, we explicitly formalize this problem as inference in a spatial mixture model where each component is parametrized by a neural network. Based on the Expectation Maximization framework we then derive a differentiable clustering method that simultaneously learns how to group and represent individual entities. We evaluate our method on the (sequential) perceptual grouping task and find that it is accurately able to recover the constituent objects. We demonstrate that the learned representations are useful for predictive coding.
    Expectation maximizationRecurrent neural networkNeural networkInferenceBernoulli distributionMixture modelArchitectureMaximum likelihood estimateGround truthAutoencoder...
  • We identify a new contribution to the chiral magnetic conductivity at finite frequencies -- the magnetization current. This allows to quantitatively reproduce the known field-theoretic time-dependent (AC) chiral magnetic response in terms of kinetic theory. We evaluate the corresponding AC chiral magnetic conductivity in two flavor QCD plasma at weak coupling. The magnetization current results from the spin response of chiral quasiparticles to magnetic field, and is thus proportional to the quasiparticle's $g$-factor. In condensed matter systems, where the chiral quasi-particles are emergent and the $g$-factor can significantly differ from 2, this opens the possibility to tune the AC chiral magnetic response.
    Chiral magnetic conductivityChiral magnetic effectBerry phaseMagnetizationFree streaming of particlesKinetic theoryEquilibrium CMEKinematicsHydrodynamic regimeAnatomy...
  • When combining cosmological and oscillations results to constrain the neutrino sector, the question of the propagation of systematic uncertainties is often raised. We address this issue in the context of the derivation of an upper bound on the sum of the neutrino masses ($\Sigma m_\nu$) with recent cosmological data. This work is performed within the ${{\mathrm{\Lambda{CDM}}}}$ model extended to $\Sigma m_\nu$, for which we advocate the use of three mass-degenerate neutrinos. We focus on the study of systematic uncertainties linked to the foregrounds modelling in CMB data analysis, and on the impact of the present knowledge of the reionisation optical depth. This is done through the use of different likelihoods built from Planck data. Limits on $\Sigma m_\nu$ are derived with various combinations of data, including the latest Baryon Acoustic Oscillations (BAO) and Type Ia Supernovae (SN) results. We also discuss the impact of the preference for current CMB data for amplitudes of the gravitational lensing distortions higher than expected within the ${{\mathrm{\Lambda{CDM}}}}$ model, and add the Planck CMB lensing. We then derive a robust upper limit: $\Sigma m_\nu< 0.17\hbox{ eV at }95\% \hbox{CL}$, including 0.01 eV of foreground systematics. We also discuss the neutrino mass repartition and show that today's data do not allow one to disentangle normal from inverted hierarchy. The impact on the other cosmological parameters is also reported, for different assumptions on the neutrino mass repartition, and different high and low multipole CMB likelihoods.
    NeutrinoNeutrino massProfile likelihoodSystematic errorCosmic microwave backgroundCosmological parametersMassive neutrinoForeground residualsInverted hierarchyBaryon acoustic oscillations...
  • Supermassive black hole binaries (SMBHBs) in the 10 million to 10 billion $M_\odot$ range form in galaxy mergers, and live in galactic nuclei with large and poorly constrained concentrations of gas and stars. There are currently no observations of merging SMBHBs--- it is in fact possible that they stall at their final parsec of separation and never merge. While LIGO has detected high frequency GWs, SMBHBs emit GWs in the nanohertz to millihertz band. This is inaccessible to ground-based interferometers, but possible with Pulsar Timing Arrays (PTAs). Using data from local galaxies in the 2 Micron All-Sky Survey, together with galaxy merger rates from Illustris, we find that there are on average $91\pm7$ sources emitting GWs in the PTA band, and $7\pm2$ binaries which will never merge. Local unresolved SMBHBs can contribute to GW background anisotropy at a level of $\sim20\%$, and if the GW background can be successfully isolated, GWs from at least one local SMBHB can be detected in 10 years.
    Pulsar timing arrayGalaxyPulsarSupermassive black holeGalaxy mergerTwo Micron All Sky SurveyWhite noiseGravitational waveRed noiseMilky Way...
  • We show how the model of pseudo-complex general relativity can be tested using gravitational wave signals from coalescing compact objects. The model, which agrees with Einstein gravity in the weak-field limit, diverges dramatically in the near-horizon regime, with certain parameter ranges excluding the existence of black holes. We show that simple limits can be placed on the model in both the inspiral and ringdown phase of coalescing compact objects. We discuss further how these bounds relate to current observational limits. In particular, for minimal scenarios previously considered in the literature, gravitational wave observations are able to constrain pseudo-complex general relativity parameters to values that require the existence of black hole horizons.
    Gravitational waveGeneral relativityHorizonInspiralLaser Interferometer Gravitational-Wave ObservatoryBlack holeCompact starLIGO GW150914 eventGeodesicCircular orbit...
  • We describe a general mathematical framework for $\chi^2$ discriminators in the context of the compact binary coalescence search. We show that with any $\chi^2$ is associated a vector bundle over the signal manifold, that is, the manifold traced out by the signal waveforms in the function space of data segments. The $\chi^2$ is then defined as the square of the $L_2$ norm of the data vector projected onto a finite dimensional subspace (the fibre) of the Hilbert space of data trains and orthogonal to the signal waveform - any such fibre leads to a $\chi^2$ discriminator and the full vector bundle comprising the subspaces and the base manifold constitute the $\chi^2$ discriminator. We show that the $\chi^2$ discriminators used so far in the CBC searches correspond to different fiber structures constituting different vector bundles on the same base manifold, namely, the parameter space. The general formulation indicates procedures to formulate new $\chi^2$s which could be more effective in discriminating against commonly occurring glitches in the data. It also shows that no $\chi^2$ with a reasonable degree of freedom is foolproof. It could also shed light on understanding why the traditional $\chi^2$ works so well. As an example, we propose a family of ambiguity $\chi^2$ discriminators that is an alternative to the traditional one. Any such ambiguity $\chi^2$ makes use of the filtered output of the template bank, thus adding negligible cost to the overall search. We test teh performance of ambiguity $\chi^2$ on simulated data using spinless TaylorF2 waveforms. We show that the ambiguity $\chi^2$ essentially gives a clean separation between glitches and signals. Finally, we investigate the effects of mismatch between signal and templates on the $\chi^2$ and also further indicate how the ambiguity $\chi^2$ can be generalized to detector networks for coherent observations.
    Pulsar glitchManifoldVector bundleStatisticsDegree of freedomGaussian noiseMatched filterGravitational waveOrthonormal basisCovariance matrix...
  • We present an analytical waveform family describing gravitational waves (GWs) from the inspiral, merger and ringdown of non-spinning black-hole binaries including the effect of several non-quadrupole modes [($\ell = 2, m = \pm 1), (\ell = 3, m = \pm 3), (\ell = 4, m = \pm 4)$ apart from $(\ell = 2, m=\pm2)$]. We first construct spin-weighted spherical harmonics modes of hybrid waveforms by matching numerical-relativity simulations (with mass ratio $1-10$) describing the late inspiral, merger and ringdown of the binary with post-Newtonian/effective-one-body waveforms describing the early inspiral. An analytical waveform family is constructed in frequency domain by modeling the Fourier transform of the hybrid waveforms making use of analytical functions inspired by perturbative calculations. The resulting highly accurate, ready-to-use waveforms are highly faithful (unfaithfulness $\simeq 10^{-4} - 10^{-2}$) for observation of GWs from non-spinning black hole binaries and are extremely inexpensive to generate.
    InspiralGravitational waveSpinning Black HoleMass ratioOrientationNumerical relativityQuadrupoleGeneral relativityBinary black hole systemSpin-weighted spherical harmonics...
  • We investigate constraints on scalar dark matter (DM) by analyzing the Lyman-alpha forest, which probes structure formation at medium and small scales, and also by studying its cosmological consequences at high and low redshift. For scalar DM that constitutes more than 30% of the total DM density, we obtain a lower limit m >~ 10^{-21} eV for the mass of scalar DM. This implies an upper limit on the initial field displacement (or the decay constant for an axion-like field) of phi <~ 10^{16} GeV. We also derive limits on the energy scale of cosmic inflation and establish an upper bound on the tensor-to-scalar ratio of r < 10^{-3} in the presence of scalar DM. Furthermore, we show that there is very little room for ultralight scalar DM to solve the "small-scale crisis" of cold DM without spoiling the Lyman-alpha forest results. The constraints presented in this paper can be used for testing generic theories that contain light scalar fields.
    Scalar DMDark matterCold dark matterLyman-alpha forestScalar fieldLight scalarUltralight scalar DMInflationMatter power spectrumJeans length...
  • We use a cosmological simulation of the formation of the Local Group of Galaxies to identify a mechanism that enables the removal of baryons from low-mass halos without appealing to feedback or reionization. As the Local Group forms, matter bound to it develops a network of filaments and pancakes. This moving web of gas and dark matter drifts and sweeps a large volume, overtaking many halos in the process. The dark matter content of these halos is unaffected but their gas can be efficiently removed by ram-pressure. The loss of gas is especially pronounced in low-mass halos due to their lower binding energy and has a dramatic effect on the star formation history of affected systems. This "cosmic web stripping" may help to explain the scarcity of dwarf galaxies compared with the numerous low-mass halos expected in \Lambda CDM and the large diversity of star formation histories and morphologies characteristic of faint galaxies. Although our results are based on a single high-resolution simulation, it is likely that the hydrodynamical interaction of dwarf galaxies with the cosmic web is a crucial ingredient so far missing from galaxy formation models.
    GalaxyCosmic webDwarf galaxyStar formationLocal groupStarDark matterA dwarfsRam pressureCold dark matter...
  • The scaling of disk galaxy rotation velocity with baryonic mass (the "Baryonic Tully-Fisher" relation, BTF) has long confounded galaxy formation models. It is steeper than the M ~ V^3 scaling relating halo virial masses and circular velocities and its zero point implies that galaxies comprise a very small fraction of available baryons. Such low galaxy formation efficiencies may in principle be explained by winds driven by evolving stars, but the tightness of the BTF relation argues against the substantial scatter expected from such vigorous feedback mechanism. We use the APOSTLE/EAGLE simulations to show that the BTF relation is well reproduced in LCDM simulations that match the size and number of galaxies as a function of stellar mass. In such models, galaxy rotation velocities are proportional to halo virial velocity and the steep velocity-mass dependence results from the decline in galaxy formation efficiency with decreasing halo mass needed to reconcile the CDM halo mass function with the galaxy luminosity function. Despite the strong feedback, the scatter in the simulated BTF is smaller than observed, even when considering all simulated galaxies and not just rotationally-supported ones. The simulations predict that the BTF should become increasingly steep at the faint end, although the velocity scatter at fixed mass should remain small. Observed galaxies with rotation speeds below ~40 km/s seem to deviate from this prediction. We discuss observational biases and modeling uncertainties that may help to explain this disagreement in the context of LCDM models of dwarf galaxy formation.
    GalaxyBaryonic Tully-Fisher relationMilky WayVirial massGalaxy FormationCircular velocityRotation CurveGalaxy massVirial velocityStellar mass...
  • We calculate the solar neutrino and antineutrino flux in the keV energy range. The dominant thermal source processes are photoproduction ($\gamma e\to e \nu\bar\nu$), bremsstrahlung ($e+Ze\to Ze+e+\nu\bar\nu$), plasmon decay ($\gamma\to\nu\bar\nu$), and $\nu\bar\nu$ emission in free-bound and bound-bound transitions of partially ionized elements heavier than hydrogen and helium. These latter processes dominate in the energy range of a few keV and thus carry information about the solar metallicity. To calculate their rate we use libraries of monochromatic photon radiative opacities in analogy to a previous calculation of solar axion emission. Our overall flux spectrum and many details differ significantly from previous works. While this low-energy flux is not measurable with present-day technology, it could become a significant background for future direct searches for keV-mass sterile neutrino dark matter.
    NeutrinoPlasmonBremsstrahlungNeutrino fluxOpacitySolar neutrinoEarthAxionSunPhase space...
  • The majority of stars are now thought to support exoplanets. Many of those exoplanets discovered thus far are categorized as rocky objects with an atmosphere. Most of these objects are however hot due to their short orbital period. Models suggest that water is the dominant species in their atmospheres. The hot temperatures are expected to turn these atmospheres into a (high pressure) steam bath containing remains of melted rock. The spectroscopy of these hot rocky objects will be very different from that of cooler objects or hot gas giants. Molecules suggested to be important for the spectroscopy of these objects are reviewed together with the current status of the corresponding spectroscopic data. Perspectives of building a comprehensive database of linelist/cross sections applicable for atmospheric models of rocky super-Earths as part of the ExoMol project are discussed. The quantum-mechanical approaches used in linelist productions and their challenges are summarized.
    Extrasolar planetSuper-earthPlanetEarthCoolingMeltingIntensityOpacityStarJames Webb Space Telescope...