Recently bookmarked papers

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  • Context: The cosmological concordance model ($\Lambda$CDM) matches the cosmological observations exceedingly well. This model has become the standard cosmological model with the evidence for an accelerated expansion provided by the type Ia supernovae (SNIa) Hubble diagram. However, the robustness of this evidence has been addressed recently with somewhat diverging conclusions. Aims: The purpose of this paper is to assess the robustness of the conclusion that the Universe is indeed accelerating if we rely only on low-redshift (z$\lesssim$2) observations, that is to say with SNIa, baryonic acoustic oscillations, measurements of the Hubble parameter at different redshifts, and measurements of the growth of matter perturbations. Methods: We used the standard statistical procedure of minimizing the $\chi^2$ function for the different probes to quantify the goodness of fit of a model for both $\Lambda$CDM and a simple nonaccelerated low-redshift power law model. In this analysis, we do not assume that supernovae intrinsic luminosity is independent of the redshift, which has been a fundamental assumption in most previous studies that cannot be tested. Results: We have found that, when SNIa intrinsic luminosity is not assumed to be redshift independent, a nonaccelerated low-redshift power law model is able to fit the low-redshift background data as well as, or even slightly better, than $\Lambda$CDM. When measurements of the growth of structures are added, a nonaccelerated low-redshift power law model still provides an excellent fit to the data for all the luminosity evolution models considered. Conclusions: Without the standard assumption that supernovae intrinsic luminosity is independent of the redshift, low-redshift probes are consistent with a nonaccelerated universe.
    LuminosityBaryon acoustic oscillationsNuisance parameterLambda-CDM modelCosmologySupernovaCosmological parametersGoodness of fitCosmological modelAccelerated expansion of the Universe...
  • Chiral anomaly induces a new kind of macroscopic quantum behavior in relativistic magnetohydrodynamics, including the chiral magnetic effect. In this talk we present two new quantum effects present in fluids that contain charged chiral fermions: 1) the turbulent inverse cascade driven by the chiral anomaly; 2) quantized chiral magnetic current induced by the reconnections of magnetic flux. We also discuss the implications for the evolution of the quark-gluon plasma produced in heavy ion collisions.
    Chiral magnetic effectChiral anomalyRelativistic magnetohydrodynamicsInverse cascadeChiral fermionMagnetic helicityHelicityQuark-gluon plasmaChirality imbalanceChirality...
  • Emission of fullerenes in their infrared vibrational bands has been detected in space near hot stars. The proposed attribution of the diffuse interstellar bands at 9577 and 9632 \AA\ to electronic transitions of the buckminsterfullerene cation (i.e. C$_{60}^+$ ) was recently supported by new laboratory data, confirming the presence of this species in the diffuse interstellar medium (ISM). In this letter, we present the detection, also in the diffuse ISM, of the 17.4 and 18.9 $\mu$m emission bands commonly attributed to vibrational bands of neutral C$_{60}$. According to classical models that compute the charge state of large molecules in space, C$_{60}$ is expected to be mostly neutral in the diffuse ISM. This is in agreement with the abundances of diffuse C$_{60}$ we derive here from observations. We also find that C$_{60}$ is less abundant in the diffuse ISM than in star forming regions, supporting the proposal that C$_{60}$ can be formed in these regions.
    Interstellar mediumLine of sightAbundanceFullereneBuckminsterfullereneStar-forming regionElectronic transitionDiffuse interstellar bandEvolved starsUltraviolet background...
  • A human-robotic "Moon Village" would offer significant scientific opportunities by providing an infrastructure on the lunar surface. An analogy would be the way in which human outposts in Antarctica facilitate research activities across multiple scientific disciplines on that continent. Scientific fields expected to benefit from a Moon Village will include: planetary science, astronomy, astrobiology, life sciences, and fundamental physics. In addition, a Moon Village will help develop the use of lunar resources, which will yield additional longer-term scientific benefits.
    XenobiologyPlanetary scienceRoboticsAstronomyField...
  • We present a suite of cosmological zoom-in simulations at z>5 from the Feedback In Realistic Environments project, spanning a halo mass range M_halo~10^8-10^12 M_sun at z=5. We predict the stellar mass-halo mass relation, stellar mass function, and luminosity function in several bands from z=5-12. The median stellar mass-halo mass relation does not evolve strongly at z=5-12. The faint-end slope of the luminosity function steepens with increasing redshift, as inherited from the halo mass function at these redshifts. Below z~6, the stellar mass function and ultraviolet (UV) luminosity function slightly flatten below M_star~10^4.5 M_sun (fainter than M_1500~-14), owing to the fact that star formation in low-mass halos is suppressed by the ionizing background by the end of reionization. Such flattening does not appear at higher redshifts. We provide redshift-dependent fitting functions for the SFR-M_halo, SFR-M_star, and broad-band magnitude-stellar mass relations. We derive the star formation rate density and stellar mass density at z=5-12 and show that the contribution from very faint galaxies becomes more important at z>8. Furthermore, we find that the decline in the z~6 UV luminosity function brighter than M_1500~-20 is largely due to dust attenuation. Approximately 37% (54%) of the UV luminosity from galaxies brighter than M_1500=-13 (-17) is obscured by dust at z~6. Our results broadly agree with current data and can be tested by future observations.
    GalaxyStellar massVirial massStellar mass functionLuminosity functionStar formationStarFIRE simulationsReionizationDust attenuation curve...
  • For one decade, the spectral-type and age of the $\rho$ Oph object IRS-48 were subject to debates and mysteries. Modelling its disk with mid-infrared to millimeter observations led to various explanations to account for the complex intricacy of dust-holes and gas-depleted regions. We present multi-epoch high-angular-resolution interferometric near-infrared data of spatially-resolved emissions in its first 15AU, known to have very strong Polycyclic Aromatic Hydrocarbon (PAH) emissions within this dust-depleted region. We make use of new Sparse-Aperture-Masking data to instruct a revised radiative-transfer model where SED fluxes and interferometry are jointly fitted. Neutral and ionized PAH, Very Small Grains (VSG) and classical silicates are incorporated into the model; new stellar parameters and extinction laws are explored. A bright (42L$_{\odot}$) central-star with A$_v$=12.5mag and R$_v$=6.5 requires less near-infrared excess: the inner-most disk at $\approx$1AU is incompatible with the data. The revised stellar parameters place this system on a 4 Myr evolutionary track, 4 times younger than previous estimations, in better agreement with the surrounding $\rho$ Oph region and disk-lifetimes observations. The disk-structure converges to a classical-grains outer-disk from 55AU combined with a fully resolved VSG\&PAH-ring, at 11-26 AU. We find two over-luminosities in the PAH-ring at color-temperatures consistent with the radiative transfer simulations; one follows a Keplerian circular orbit at 14AU. We show a depletion of a factor $\approx$5 of classical dust grains compared to VSG\&PAH: the IRS-48 disk is nearly void of dust-grains in the first 55 AU. A 3.5M$_{Jup}$ planet on a 40AU orbit qualitatively explains the new disk-structure.
    Astronomical UnitStarInfrared Spectrometer on SpitzerPoint sourceSpectral energy distributionNear-infraredSilicateExtinctionCompanionRadiative transfer...
  • We construct certain Rajchman measures by using integrability properties of the Fourier and Fourier-Stieltjes transforms. In particular, we state a problem and prove that it is equivalent to the known and still unsolved question posed by R. Salem (Trans. Amer. Math. Soc. 53 (3) (1943), p. 439) whether Fourier-Stieltjes coefficients of the Minkowski's question mark function vanish at infinity.
    Minkowski's question mark functionModified Bessel FunctionRiemann-Lebesgue lemmaMonotonic functionMinkowski functionalElementary theoryRiemann-Stieltjes integralSingular measureFubini's theoremRegularization...
  • We show that the scaling dimensions of lowest operators in conformal field theories (CFTs) can be isolated in small and closed regions from single correlator bootstrap. We find the conserved currents play crucial roles in bootstrapping the crossing equation. By imposing a mild gap between the scaling dimensions of the conserved current and its next operator, the scaling dimensions of lowest operators are forced to lie in small isolated regions, i.e., these CFTs can be almost fixed by few lowest operators in certain channels. For CFTs with extended supersymmetry, the single correlator crossing equation involves several conserved or shorted operators and by imposing gaps in these sectors it is possible to isolate different CFTs. Specifically, we bootstrap the isolated regions corresponding to the 3D Ising model, $O(N)$ vector model, $N=1,2$ supersymmetric Ising models by introducing mild gaps in certain sectors with conserved or shorted operators.
    Conformal field theorySupersymmetric CFTScaling dimensionConformal Bootstrap3D Ising modelGlobal symmetryOperator product expansionIsing modelExtended supersymmetryWess-Zumino model...
  • Newton's Principia, when it appeared in 1687, was received with the greatest admiration, not only by the foremost mathematicians and astronomers in Europe, but also by philosophers like Voltaire and Locke and by members of the educated public. In this account I describe some of the controversies that it provoked, and the impact it had during the next century on the development of celestial mechanics, and the theory of gravitation.
    PlanetGravitational forceEarthSunNatural satelliteOrbital motionEllipticityCurvatureVorticityElliptical orbit...
  • This paper provides a unified account of two schools of thinking in information retrieval modelling: the generative retrieval focusing on predicting relevant documents given a query, and the discriminative retrieval focusing on predicting relevancy given a query-document pair. We propose a game theoretical minimax game to iteratively optimise both models. On one hand, the discriminative model, aiming to mine signals from labelled and unlabelled data, provides guidance to train the generative model towards fitting the underlying relevance distribution over documents given the query. On the other hand, the generative model, acting as an attacker to the current discriminative model, generates difficult examples for the discriminative model in an adversarial way by minimising its discrimination objective. With the competition between these two models, we show that the unified framework takes advantage of both schools of thinking: (i) the generative model learns to fit the relevance distribution over documents via the signals from the discriminative model, and (ii) the discriminative model is able to exploit the unlabelled data selected by the generative model to achieve a better estimation for document ranking. Our experimental results have demonstrated significant performance gains as much as 23.96% on Precision@5 and 15.50% on MAP over strong baselines in a variety of applications including web search, item recommendation, and question answering.
    Information retrievalRankingGenerative modelDiscriminative modelGenerative Adversarial NetRankMinimaxLearning to rankConvolutional neural networkFactorisation...
  • The main purposes of this paper are (i) to illustrate explicitly by a number of examples the gauge functions chi(x, t) whose spatial and temporal derivatives transform one set of electromagnetic potentials into another equivalent set; and (ii) to show that, whatever propagation or non-propagation characteristics are exhibited by the potentials in a particular gauge, the electric and magnetic fields are always the same and display the experimentally verified properties of causality and propagation at the speed of light. The example of the transformation from the Lorenz gauge (retarded solutions for both scalar and vector potential) to the Coulomb gauge (instantaneous, action-at-a-distance, scalar potential) is treated in detail. A transparent expression is obtained for the vector potential in the Coulomb gauge, with a finite nonlocality in time replacing the expected spatial nonlocality of the transverse current. A class of gauges (v-gauge) is described in which the scalar potential propagates at an arbitrary speed v relative to the speed of light. The Lorenz and Coulomb gauges are special cases of the v-gauge. The last examples of gauges and explicit gauge transformation functions are the Hamiltonian or temporal gauge, the nonrelativistic Poincare or multipolar gauge, and the relativistic Fock-Schwinger gauge.
    Gauge transformationCoulomb gaugeSpeed of lightHamiltonianCausalityElectricity and magnetismPotentialScalarTransformationsVector...
  • While question answering (QA) with neural network, i.e. neural QA, has achieved promising results in recent years, lacking of large scale real-word QA dataset is still a challenge for developing and evaluating neural QA system. To alleviate this problem, we propose a large scale human annotated real-world QA dataset WebQA with more than 42k questions and 556k evidences. As existing neural QA methods resolve QA either as sequence generation or classification/ranking problem, they face challenges of expensive softmax computation, unseen answers handling or separate candidate answer generation component. In this work, we cast neural QA as a sequence labeling problem and propose an end-to-end sequence labeling model, which overcomes all the above challenges. Experimental results on WebQA show that our model outperforms the baselines significantly with an F1 score of 74.69% with word-based input, and the performance drops only 3.72 F1 points with more challenging character-based input.
    Sequence labelingEmbeddingClassificationRankingF1 scoreNeural networkWord embeddingTraining setRankPart-of-speech...
  • Hamiltonian Truncation (a.k.a. Truncated Spectrum Approach) is an efficient numerical technique to solve strongly coupled QFTs in d=2 spacetime dimensions. Further theoretical developments are needed to increase its accuracy and the range of applicability. With this goal in mind, here we present a new variant of Hamiltonian Truncation which exhibits smaller dependence on the UV cutoff than other existing implementations, and yields more accurate spectra. The key idea for achieving this consists in integrating out exactly a certain class of high energy states, which corresponds to performing renormalization at the cubic order in the interaction strength. We test the new method on the strongly coupled two-dimensional quartic scalar theory. Our work will also be useful for the future goal of extending Hamiltonian Truncation to higher dimensions d >= 3.
    HamiltonianNext-to-leading order computationRenormalizationQuantum field theoryVacuum energyConformal field theoryIsing modelPerturbation theoryMass gapRenormalization group...
  • As a case study to understand the coevolution of Brightest Cluster Galaxies (BCGs) and their host clusters, we investigate the BCGs in dynamically young and old clusters, Abell 1139 (A1139) and Abell 2589 (A2589). We analyze the pixel color-magnitude diagrams (pCMDs) using deep g- and r-band images, obtained from the Canada-France-Hawaii Telescope observations. After masking foreground/background objects and smoothing pixels in consideration of the observational seeing size, detailed pCMD features are compared between the two BCGs. (1) While the overall shapes of the pCMDs are similar to those of typical early-type galaxies, the A2589-BCG tends to have redder mean pixel color and smaller pixel color deviation at given surface brightness than the A1139-BCG. (2) The mean pixel color distribution as a function of pixel surface brightness (pCMD backbone) indicates that the A2589-BCG formed a larger central body (~ 2.0 kpc in radius) by major dry mergers at an early epoch than the A1139-BCG (a central body ~ 1.3 kpc in radius), while they have grown commonly by subsequent minor mergers. (3) The spatial distributions of the pCMD outliers reveal that the A1139-BCG experienced considerable tidal events more recently than the A2589-BCG, whereas the A2589-BCG has an asymmetric compact core possibly resulting from major dry merger at an early epoch. (4) The A2589-BCG shows a very large faint-to-bright pixel number ratio compared to early-type non-BCGs, whereas the ratio for the A1139-BCG is not distinctively large. These results are consistent with the idea that the BCG in the dynamically older cluster (A2589) formed earlier and is relaxed better.
    Brightest cluster galaxyGalaxyStellar populationsSurface brightnessHertzsprung-Russell diagramEarly-type galaxyMilky WayCanada-France-Hawaii TelescopeBright galaxiesElliptical galaxy...
  • We perform numerical simulations of the merging galaxy cluster 1E 0657-56 (the Bullet Cluster), including the effects of elastic dark matter scattering. In a similar manner to the stripping of gas by ram pressure, dark matter self-interactions would transfer momentum between the two galaxy cluster dark matter haloes, causing them to lag behind the collisionless galaxies. The absence of an observed separation between the dark matter and stellar components in the Bullet Cluster has been used to place upper limits on the cross-section for dark matter scattering. We emphasise the importance of analysing simulations in an observationally-motivated manner, finding that the way in which the positions of the various components are measured can have a larger impact on derived constraints on dark matter's self-interaction cross-section than reasonable changes to the initial conditions for the merger. In particular, we find that the methods used in previous studies to place some of the tightest constraints on this cross-section do not reflect what is done observationally, and overstate the Bullet Cluster's ability to constrain the particle properties of dark matter. We introduce the first simulations of the Bullet Cluster including both self-interacting dark matter and gas. We find that as the gas is stripped it introduces radially-dependent asymmetries into the stellar and dark matter distributions. As the techniques used to determine the positions of the dark matter and galaxies are sensitive to different radial scales, these asymmetries can lead to erroneously measured offsets between dark matter and galaxies even when they are spatially coincident.
    Dark matterBullet ClusterSelf-interacting dark matterDark matter haloStarDark matter particleMerging galaxy clusterSoftening lengthWeak lensingNavarro-Frenk-White profile...
  • Initial conditions for (Newtonian) cosmological N-body simulations are usually set by re-scaling the present-day power spectrum obtained from linear (relativistic) Boltzmann codes to the desired initial redshift of the simulation. This back-scaling method can account for the effect of inhomogeneous residual thermal radiation at early times, which is absent in the Newtonian simulations. We analyse this procedure from a fully relativistic perspective, employing the recently-proposed Newtonian motion gauge framework. We find that N-body simulations for LambdaCDM cosmology starting from back-scaled initial conditions can be self-consistently embedded in a relativistic space-time with first-order metric potentials calculated using a linear Boltzmann code. This space-time coincides with a simple "N-body gauge" for z<50 for all observable modes. Care must be taken, however, when simulating non-standard cosmologies. As an example, we analyse the back-scaling method in a cosmology with decaying dark matter, and show that metric perturbations become large at early times in the back-scaling approach, indicating a breakdown of the perturbative description. We suggest a suitable "forwards approach" for such cases.
    N-body simulationCold dark matterBoltzmann codeDark matterCosmologyDecaying dark matterMetric perturbationSynchronous gaugeGauge conditionThe early Universe...
  • We explore the phenomenology of Elastically Decoupling Relic (ELDER) dark matter. ELDER is a thermal relic whose present density is determined primarily by the cross-section of its elastic scattering off Standard Model (SM) particles. Assuming that this scattering is mediated by a kinetically mixed dark photon, we argue that the ELDER scenario makes robust predictions for electron-recoil direct-detection experiments, as well as for dark photon searches. These predictions are independent of the details of interactions within the dark sector. Together with the closely related Strongly-Interacting Massive Particle (SIMP) scenario, the ELDER predictions provide a physically motivated, well-defined target region, which will be almost entirely accessible to the next generation of searches for sub-GeV dark matter and dark photons. We provide useful analytic approximations for various quantities of interest in the ELDER scenario, and discuss two simple renormalizable toy models which incorporate the required strong number-changing interactions among the ELDERs, as well as explicitly implement the coupling to electrons via the dark photon portal.
    Standard ModelDark matterHidden photonDark sectorStrongly Interacting Massive ParticleElastic scatteringFreeze-outDark matter particleDegree of freedomKinetic decoupling...
  • We explore the sensitivity of displaced vertex searches at LHCb for testing sterile neutrino extensions of the Standard Model towards explaining the observed neutrino masses. We derive estimates for the constraints on sterile neutrino parameters from a recently published displaced vertex search at LHCb based on run 1 data. They yield the currently most stringent limit on active-sterile neutrino mixing in the sterile neutrino mass range between 4.5 GeV and 10 GeV. Furthermore, we present forecasts for the sensitivities that could be obtained from the run 2 data and also for the high-luminosity phase of the LHC.
    Sterile neutrinoLHCbDisplaced verticesSterile neutrino massActive-sterile neutrino mixingLuminosityNeutrinoLarge Hadron ColliderStandard ModelExclusion limit...
  • We determine within lattice QCD, the nucleon spin carried by valence and sea quarks, and gluons. The calculation is performed using an ensemble of gauge configurations with two degenerate light quarks with mass fixed to approximately reproduce the physical pion mass. We find that the total spin carried by the quarks in the nucleon is $J_{u+d+s}{=}0.408(61)_{\rm stat.}(48)_{\rm syst.}$ and the gluon contribution is $J_g =0.133(11)_{\rm stat.}(14)_{\rm syst.}$ giving a total of $J_N=0.54(6)_{\rm stat.}(5)_{\rm syst.}$ consistent with the spin sum. For the quark intrinsic spin contribution we obtain $\frac{1}{2}\Delta\Sigma_{u+d+s}=0.201(17)_{\rm stat.}(5)_{\rm syst.}$. All quantities are given in the $\overline{\textrm{MS}}$ scheme at 2 GeV. The quark and gluon momentum fractions are also computed and add up to $\langle x\rangle_{u+d+s}+\langle x\rangle_g=0.804(121)_{\rm stat.}(95)_{\rm syst.}+0.267(12)_{\rm stat.}(10)_{\rm syst.}=1.07(12)_{\rm stat.}(10)_{\rm syst.}$ satisfying the momentum sum.
    RenormalizationLattice QCDPion massStrange quarkExcited stateAxial chargeLight quarkDown quarkPropagatorQuark mass...
  • The N = 2, 4 superconformal symmetry constraints in d = 4 for four point functions of chiral primary 1/2-BPS operators are derived. The operators are described by symmetric traceless tensors of the internal R-symmetry group. A substantial simplification is achieved by introduction of null vectors. Two variable polynomials corresponding to different R-symmetry representations are constructed. The Ward identities for superconformal symmetry are obtained as simple differential equations. The general solution is presented in terms of a constant, a single variable function and a two variable function. An interpretation in terms of the operator product expansion is given for the case of fields of equal dimension and for the so called (next-to)extremal cases. The result is shown to accommodate long multiplets, semishort and short multiplets with protected dimension. Generically also non-unitary multiplets can appear. It is shown how to remove them to obtain a unitary theory. Implications of crossing symmetry for the four point functions studied are derived and discussed. It is shown that crossing symmetry fixes the single variable function in the general solution to be of free field form using singularity arguments. For a restricted set of next-to-extremal correlation functions with S3 symmetry amongst the first three fields it is shown that the amplitude is fixed up to normalization to free field form. We compute the conformal partial wave expansion of all representations in this amplitude and compute an averaged value of the anomalous dimensions for long multiplets given spin and twist in each relevant representation at first order in 1/N. Finally assuming the universal singularity structure we derive the general large N amplitude of four identical 1/2-BPS operators in the [0, p, 0] representation in terms of D functions. Explicit expressions for all coefficients are given.
    Operator product expansionTwo-point correlation functionAnomalous dimensionScaling dimensionSuperconformal symmetrySupermultipletSupersymmetryEigenfunctionShort supermultipletUnitarity...
  • gPhoton is a new database product and software package that enables analysis of GALEX ultraviolet data at the photon level. The project's stand-alone, pure-Python calibration pipeline reproduces the functionality of the original mission pipeline to reduce raw spacecraft data to lists of time-tagged, sky-projected photons, which are then hosted in a publicly available database by the Mikulski Archive at Space Telescope (MAST). This database contains approximately 130 terabytes of data describing approximately 1.1 trillion sky-projected events with a timestamp resolution of five milliseconds. A handful of Python and command line modules serve as a front-end to interact with the database and to generate calibrated light curves and images from the photon-level data at user-defined temporal and spatial scales. The gPhoton software and source code are in active development and publicly available under a permissive license. We describe the motivation, design, and implementation of the calibration pipeline, database, and tools, with emphasis on divergence from prior work, as well as challenges created by the large data volume. We summarize the astrometric and photometric performance of gPhoton relative to the original mission pipeline. For a brief example of short time domain science capabilities enabled by gPhoton, we show new flares from the known M dwarf flare star CR Draconis. The gPhoton software has permanent object identifiers with the ASCL (ascl:1603.004) and DOI (doi:10.17909/T9CC7G). This paper describes the software as of version v1.27.2.
    Galaxy Evolution ExplorerCalibrationPhotometryEclipsesLight curvePythonCountingData archiveM dwarfsAstrometry...
  • When a large feedforward neural network is trained on a small training set, it typically performs poorly on held-out test data. This "overfitting" is greatly reduced by randomly omitting half of the feature detectors on each training case. This prevents complex co-adaptations in which a feature detector is only helpful in the context of several other specific feature detectors. Instead, each neuron learns to detect a feature that is generally helpful for producing the correct answer given the combinatorially large variety of internal contexts in which it must operate. Random "dropout" gives big improvements on many benchmark tasks and sets new records for speech and object recognition.
    ArchitectureBackpropagationHyperparameterHidden Markov modelFilter bankNeural networkGeneMarketClassificationRegularization...
  • The recently introduced dropout training criterion for neural networks has been the subject of much attention due to its simplicity and remarkable effectiveness as a regularizer, as well as its interpretation as a training procedure for an exponentially large ensemble of networks that share parameters. In this work we empirically investigate several questions related to the efficacy of dropout, specifically as it concerns networks employing the popular rectified linear activation function. We investigate the quality of the test time weight-scaling inference procedure by evaluating the geometric average exactly in small models, as well as compare the performance of the geometric mean to the arithmetic mean more commonly employed by ensemble techniques. We explore the effect of tied weights on the ensemble interpretation by training ensembles of masked networks without tied weights. Finally, we investigate an alternative criterion based on a biased estimator of the maximum likelihood ensemble gradient.
    ArithmeticHyperparameterRegularizationActivation functionTraining setNeural networkMaximum likelihoodStochastic gradient descentLearning ruleMonte Carlo method...
  • Galaxy clusters are thought to grow by accreting mass through large-scale, strong, structure-formation shocks. Such a shock is expected to accelerate relativistic electrons, thus generating a spectrally flat leptonic virial ring. However, until now, only the nearby Coma cluster has shown evidence for a $\gamma$-ray virial ring. We stack Fermi-LAT data for the 112 most massive, high latitude, extended clusters, enhancing the ring sensitivity by rescaling clusters to their virial radii and utilizing the expected flat spectrum. In addition to a central unresolved, hard signal (detected at the $\sim 6\sigma$ confidence level), probably dominated by AGN, we identify ($>4.5\sigma$ isolated; $5.9\sigma$ for our nominal model) a bright, spectrally flat $\gamma$-ray ring at the expected virial shock position. It implies that the shock deposits $\sim 0.5\%$ of the thermal energy in relativistic electrons over a Hubble time. This result, consistent with the Coma signal, supports and calibrates the virial shock model, and indicates that the cumulative emission from such shocks significantly contributes to the diffuse extragalactic $\gamma$-ray and low-frequency radio backgrounds.
    Point sourceActive Galactic NucleiCluster of galaxiesPoint spread functionMock catalogCluster samplingTest statisticVERITASGalactic planeComa Cluster...
  • In this thesis we want to introduce the first steps towards realising a new method to investigate the cosmological parameters and conduct a detailed analysis of the galaxy cluster MACS J0416. Toward this end, we use the current model from Grillo et al. (2015) as a template and the publicly available lensing code Lenstool. This code has previously been used by Jauzac et al. (2014), Richard et al. (2014), Jauzac et al. (2015) and Caminha et al. (2016) to model MACS J0416 (Grillo et al. (2015) used GLEE). We created $10$ different models to cover a reasonable set of different approaches. In addition to the replication of the Grillo et al. (2015) models, with two cluster scale halos and 175 circular cluster member mass-density profiles, we created models using elliptical mass-density profiles for the cluster members and models where we optimize the cluster member scaling relation slopes. In order to investigate the viability of using the projected total mass estimate from different cosmological models to estimate the cosmological parameter values, we created 49 models each representing a different set of cosmological parameters.
    GalaxyStrong gravitational lensingCosmological parametersPhase space causticOptimizationVelocity dispersionMass distributionCluster Lensing And Supernova survey with HubbleDeflection angleCluster of galaxies...
  • Big Bang Nucleosynthesis (BBN) explores the first few minutes of nuclei formation after the Big Bang. We present updates that result in new constraints at the 2{\sigma} level for the abundances of the four primary light nuclides - D,3He,4He, and 7Li - in BBN. A modified standard BBN code was used in a Monte Carlo analysis of the nucleosynthesis uncertainty as a function of baryon-to-photon ratio. Reaction rates were updated to those of NACRE and REACLIB, and R-Matrix calculations. The results are then used to derive a new constraint on the effective number of neutrinos.
    Big bang nucleosynthesisAbundanceMonte Carlo methodBig BangEffective number of neutrinosExpansion of the UniverseNucleosynthesisGaussian distributionNeutron lifetimeLight element abundances...
  • To date, the LIGO collaboration has detected three gravitational wave (GW) events appearing in both its Hanford and Livingston detectors. In this article we reexamine the LIGO data with regard to correlations between the two detectors. With special focus on GW150914, we report correlations in the detector noise which, at the time of the event, happen to be maximized for the same time lag as that found for the event itself. Specifically, we analyze correlations in the calibration lines in the vicinity of 35\,Hz as well as the residual noise in the data after subtraction of the best-fit theoretical templates. The residual noise for the two more recent events, GW151226 and GW170104, exhibits equivalent behavior with respect to each of their time lags. A clear distinction between signal and noise therefore remains to be established in order to determine the contribution of gravitational waves to the detected signals.
    Gravitational waveLaser Interferometer Gravitational-Wave ObservatoryLIGO GW150914 eventCalibrationTime delayCross-correlationLIGO GW151226 eventInterferenceTwo-point correlation functionFast Fourier transform...
  • We present a study of AGN feedback at higher redshifts ($0.3<z<1.2$) using Sunyaev-Zel'dovich (SZ) selected samples of clusters from the South-Pole Telescope and Atacama Cosmology Telescope surveys. In contrast to studies of nearby systems, we do not find a separation between cooling flow clusters and non-cooling flow clusters based on the radio luminosity of the central radio source. This lack may be due to the increased incidence of galaxy-galaxy mergers at higher redshift that triggers AGN activity. In support of this scenario, we find evidence for evolution in the radio luminosity function of the central radio source: while the lower-luminosity sources do not evolve much, the higher-luminosity sources show a strong increase in the frequency of their occurrence at higher redshifts. We interpret this evolution as an increase in high-excitation radio galaxies (HERGs) in massive clusters at $z>0.6$, implying a transition from HERG-mode accretion to lower-power low-excitation radio galaxy (LERG)-mode accretion at intermediate redshifts. Additionally, we use local radio-to-jet power scaling relations to estimate feedback power and find that half of the cooling flow systems in our sample probably have enough heating to balance cooling. However, we postulate that the local relations are likely not well suited to predict feedback power in high-luminosity HERGs, as they are derived from samples composed mainly of lower-luminosity LERGs.
    LuminosityCoolingRadio sourcesCooling timescaleAGN feedbackHigh-Excitation Radio GalaxiesCooling flowLow-Excitation Radio GalaxiesRadio luminosity functionActive Galactic Nuclei...
  • We explore the origin of fast molecular outflows that have been observed in Active Galactic Nuclei (AGN). Previous numerical studies have shown that it is difficult to create such an outflow by accelerating existing molecular clouds in the host galaxy, as the clouds will be destroyed before they can reach the high velocities that are observed. In this work, we consider an alternative scenario where molecules form in-situ within the AGN outflow. We present a series of hydro-chemical simulations of an isotropic AGN wind interacting with a uniform medium. We follow the time-dependent chemistry of 157 species, including 20 molecules, to determine whether molecules can form rapidly enough to produce the observed molecular outflows. We find H$_2$ outflow rates up to 140 M$_\odot$ yr$^{-1}$, which is sensitive to density, AGN luminosity, and metallicity. We compute emission and absorption lines of CO, OH and warm (a few hundred to a few thousand K) H$_2$ from the simulations in post-processing. The CO-derived outflow rates and OH absorption strengths at solar metallicity agree with observations, although the maximum line of sight velocities from the model CO spectra are a factor $\approx$2 lower than is observed. We derive a CO (1-0) to H$_2$ conversion factor of $\alpha_{\rm{CO} (1-0)}$ = 0.15 M$_\odot$ (K km s$^{-1}$ pc$^2$)$^{-1}$, 5 times lower than is commonly assumed in observations of such systems. We find strong emission from the mid-infrared lines of H$_2$, which traces at least 70 per cent of the total H$_2$ mass. This H$_2$ emission may be observable by JWST.
    Active Galactic NucleiMolecular outflowLuminosityMetallicityCoolingInterstellar mediumAbundanceDust grainUltraluminous infrared galaxyQuasar...
  • Deep Learning has revolutionized vision via convolutional neural networks (CNNs) and natural language processing via recurrent neural networks (RNNs). However, success stories of Deep Learning with standard feed-forward neural networks (FNNs) are rare. FNNs that perform well are typically shallow and, therefore cannot exploit many levels of abstract representations. We introduce self-normalizing neural networks (SNNs) to enable high-level abstract representations. While batch normalization requires explicit normalization, neuron activations of SNNs automatically converge towards zero mean and unit variance. The activation function of SNNs are "scaled exponential linear units" (SELUs), which induce self-normalizing properties. Using the Banach fixed-point theorem, we prove that activations close to zero mean and unit variance that are propagated through many network layers will converge towards zero mean and unit variance -- even under the presence of noise and perturbations. This convergence property of SNNs allows to (1) train deep networks with many layers, (2) employ strong regularization, and (3) to make learning highly robust. Furthermore, for activations not close to unit variance, we prove an upper and lower bound on the variance, thus, vanishing and exploding gradients are impossible. We compared SNNs on (a) 121 tasks from the UCI machine learning repository, on (b) drug discovery benchmarks, and on (c) astronomy tasks with standard FNNs and other machine learning methods such as random forests and support vector machines. SNNs significantly outperformed all competing FNN methods at 121 UCI tasks, outperformed all competing methods at the Tox21 dataset, and set a new record at an astronomy data set. The winning SNN architectures are often very deep. Implementations are available at: github.com/bioinf-jku/SNNs.
    Singular valueNeural networkContraction mappingArchitectureConvolutional neural networkRecurrent neural networkMachine learningDeep learningActivation functionHyperparameter...
  • Weakly Interacting Massive Particles (WIMPs) are among the best-motivated dark matter candidates. In light of no conclusive detection signal yet despite an extensive search program that combines, often in a complementary way, direct, indirect, and collider probes, we find it timely to give a broad overview of the WIMP paradigm. In particular, we review here the theoretical foundations of the WIMP paradigm, discuss status and prospects of various detection strategies, and explore future experimental challenges and opportunities.
    Dark matterWeakly interacting massive particleStandard ModelHiggs bosonStandard Model fermionDark matter particle massColliderSpin independentLaboratory dark matter searchPseudoscalar...
  • The precise measurement of neutrino properties is among the highest priorities in fundamental particle physics, involving many experiments worldwide. Since the experiments rely on the interactions of neutrinos with bound nucleons inside atomic nuclei, the planned advances in the scope and precision of these experiments requires a commensurate effort in the understanding and modeling of the hadronic and nuclear physics of these interactions, which is incorporated as a nuclear model in neutrino event generators. This model is essential to every phase of experimental analyses and its theoretical uncertainties play an important role in interpreting every result. In this White Paper we discuss in detail the impact of neutrino-nucleus interactions, especially the nuclear effects, on the measurement of neutrino properties using the determination of oscillation parameters as a central example. After an Executive Summary and a concise Overview of the issues, we explain how the neutrino event generators work, what can be learned from electron-nucleus interactions and how each underlying physics process - from quasi-elastic to deep inelastic scattering - is understood today. We then emphasize how our understanding must improve to meet the demands of future experiments. With every topic we find that the challenges can be met only with the active support and collaboration among specialists in strong interactions and electroweak physics that include theorists and experimentalists from both the nuclear and high energy physics communities.
    NeutrinoPionKinematicsForm factorDeep inelastic scatteringCharged currentFinal state interactionsWeak neutral current interactionElectron scatteringT2K experiment...
  • We use the LHC Higgs data to derive updated constraints on electroweak-scale sterile neutrinos that naturally occur in many low-scale seesaw extensions of the Standard Model to explain the neutrino masses. We also analyze the signal sensitivity for a new final state involving a single charged lepton and two jets with missing energy, which arises from the decay of sterile neutrinos produced through the Higgs and $W,Z$ boson mediated processes at the LHC. Future prospects of these sterile neutrino signals in precision Higgs measurements, as well as at a future 100 TeV collider, are also discussed.
    Sterile neutrinoHiggs bosonLarge Hadron ColliderStandard ModelColliderPrecision Higgs measurementsHiggs boson decaySterile neutrino massDecay widthYukawa coupling...
  • Understanding how QSO's UV radiation affects galaxy formation is vital to our understanding of reionization era. Using a custom made narrow-band filter, $NB906$, on Subaru/Suprime-Cam, we investigated the number density of Ly$\alpha$ emitters (LAE) around a QSO at z=6.4. To date, this is the highest redshift narrow-band observation, where LAEs around a luminous QSO are investigated. Due to the large field-of-view of Suprime-Cam, our survey area is $\sim$5400~cMpc$^2$, much larger than previously studies at z=5.7 ($\sim$200 cMpc$^2$). In this field, we previously found a factor of 7 overdensity of Lyman break galaxies (LBGs). Based on this, we expected to detect $\sim$100 LAEs down to $NB906$=25 ABmag. However, our 6.4 hour exposure found none. The obtained upper limit on the number density of LAEs is more than an order lower than the blank fields. Furthermore, this lower density of LAEs spans a large scale of 10 $p$Mpc across. A simple argument suggests a strong UV radiation from the QSO can suppress star-formation in halos with $M_{vir}<10^{10}M_{\odot}$ within a $p$Mpc from the QSO, but the deficit at the edge of the field (5 $p$Mpc) remains to be explained.
    QuasarLyman alpha emitterLyman break galaxySuprime-CamGalaxyStar formationSubaru telescopeField of viewFull width at half maximumCompleteness...
  • Self-interacting dark matter may have striking astrophysical signatures, such as observable offsets between galaxies and dark matter in merging galaxy clusters. Numerical N-body simulations used to predict such observables typically treat the galaxies as collisionless test particles, a questionable assumption given that each galaxy is embedded in its own dark matter halo. To enable a more accurate treatment we develop an effective description of small dark matter haloes taking into account the two major effects due to dark matter self-scatterings: deceleration and evaporation. We point out that self-scatterings can have a sizeable impact on the trajectories of galaxies, diminishing the separation between galaxies and dark matter in merging clusters. This effect depends sensitively on the underlying particle physics, in particular the angular dependence of the self-scattering cross section, and cannot be predicted from the momentum transfer cross section alone.
    GalaxySelf-interacting dark matterDark matter haloDark matterMilky WayEvaporationDark matter particleMerging galaxy clusterCluster of galaxiesEscape velocity...
  • The dominant sequence transduction models are based on complex recurrent or convolutional neural networks in an encoder-decoder configuration. The best performing models also connect the encoder and decoder through an attention mechanism. We propose a new simple network architecture, the Transformer, based solely on attention mechanisms, dispensing with recurrence and convolutions entirely. Experiments on two machine translation tasks show these models to be superior in quality while being more parallelizable and requiring significantly less time to train. Our model achieves 28.4 BLEU on the WMT 2014 English-to-German translation task, improving over the existing best results, including ensembles by over 2 BLEU. On the WMT 2014 English-to-French translation task, our model establishes a new single-model state-of-the-art BLEU score of 41.0 after training for 3.5 days on eight GPUs, a small fraction of the training costs of the best models from the literature. We show that the Transformer generalizes well to other tasks by applying it successfully to English constituency parsing both with large and limited training data.
    TransductionArchitectureRecurrent neural networkConvolutional neural networkHidden layerEmbeddingPath lengthHidden stateInferenceHyperparameter...
  • For the first time, Kataoka \& Stawarz reported a clear detection of a hard X-ray excess, above $\gtrsim$20 keV, in the high-synchrotron-peaked BL Lac object Mrk 421. We find that this feature may not be produced by the low-energy part of the same electron population that produced the {\it Fermi}/LAT $\gamma$-ray. Because of that it is required that the power-law electron energy go down to $\gamma_{\rm min}\approx19$, which predicts a very strong radio emission (radio flux larger than the observed) even considering the synchrotron self-absorption effect. We investigate the possibility of this excess being produced from the spine/layer jet structure, which has been clearly detected in Mrk 421. We find that (1) similar to one-zone modeling, the spine emissions provide good modeling of the broadband spectral energy distribution, except for the hard X-ray excess; and (2) the hard X-ray excess can be well represented by the synchrotron photons (from the layer) being inverse Compton scattered by the spine electrons.
    Hard X-rayAstrophysical jetSpectral energy distributionInverse ComptonSynchrotronMarkarian 421Synchrotron Self-Compton radiationBlazarBL LacertaeSynchrotron radiation...
  • The discovery of the Planck's relation is generally regarded as the starting point of quantum physics. The Planck's constant h is now regarded as one of the most important universal constants. The physical nature of h, however, has not been well understood. It was originally suggested as a fitting constant to explain the black-body radiation. Although Planck had proposed a theoretical justification of h, he was never satisfied with that. To solve this outstanding problem, we used the Maxwell theory to directly calculate the energy and momentum of a radiation wave packet. We found the energy of the wave packet is indeed proportional to its oscillation frequency. This allows us to derive the value of the Planck's constant. Furthermore, we showed that the emission and transmission of a photon follows the principle of all-or-none. The "strength" of the wave packet can be characterized by zeta, which represents the integrated strength of the vector potential along a transverse axis. We reasoned that zeta should have a fixed cut-off value for all photons. Our results suggest that a wave packet can behave like a particle. This offers a simple explanation to the recent satellite observations that the cosmic microwave background follows closely the black-body radiation as predicted by the Planck's law.
    Planck's constantWave packetPlanck missionCosmic microwave backgroundPlanck lawTheoryPhotonEnergyBlack bodyParticles...
  • We introduce a stable, well tested Python implementation of the affine-invariant ensemble sampler for Markov chain Monte Carlo (MCMC) proposed by Goodman & Weare (2010). The code is open source and has already been used in several published projects in the astrophysics literature. The algorithm behind emcee has several advantages over traditional MCMC sampling methods and it has excellent performance as measured by the autocorrelation time (or function calls per independent sample). One major advantage of the algorithm is that it requires hand-tuning of only 1 or 2 parameters compared to $\sim N^2$ for a traditional algorithm in an N-dimensional parameter space. In this document, we describe the algorithm and the details of our implementation and API. Exploiting the parallelism of the ensemble method, emcee permits any user to take advantage of multiple CPU cores without extra effort. The code is available online at http://dan.iel.fm/emcee under the MIT License.
    Monte Carlo Markov chainAutocorrelationNuisance parameterBayesian posterior probabilityHyperparameterCovarianceMarkov chainStatisticsBayesianExpectation Value...
  • The four point functions of chiral primary BPS operators in ${\cal N}=4$ superconformal Yang Mills are expressed in a form manifestly satisfying the superconformal Ward identities. They are subsequently expanded in terms of conformal partial waves. Correlation functions of two pairs of identical chiral primaries, one pair having the lowest possible scale dimension, are considered. Crossing symmetries determine their free field value up to numeric constants. The contributions from different supermultiplets to the partial wave expansion is analysed, and determined in the case of the free fields and compared with established results at strong and weak coupling. In the large $N$, strong coupling limit, non-trivial cancellations are found between the free field values and results from supergravity. In the perturbative case values are obtained for the anomalous dimensions of lowest twist operators and the correction to the coupling by analysing the conformal wave expansions of certain hypergeometric and logarithmic functions. Next, we attempt to count shortened ${\cal N}=4$ SYM operators, beginning by constructing from fundamental fields the most general operators belonging to certain $SU(4)_R$ representations at low twists. The number of independent solutions to the conditions imposed on such operators is found via a combinatoric approach. Generating functions for the number of operators with spin $\ell=0,1,2,\dotsc$ are derived. Explicit values are obtained for specific $R$-symmetry representations at low twist in various sectors of the theory. The asymptotic behaviour at large twist is also considered. Finally the conformal field theory operator product expansion is analysed. Solutions in terms of series expansions are found, initially for scalar operators in two dimensions, and then more generally.
    Super Yang-Mills theoryFree fieldAnomalous dimensionScaling dimensionSupermultipletOperator product expansionTwo-point correlation functionConformal field theorySupergravitySymmetry...
  • We propose a simple method to extract the community structure of large networks. Our method is a heuristic method that is based on modularity optimization. It is shown to outperform all other known community detection method in terms of computation time. Moreover, the quality of the communities detected is very good, as measured by the so-called modularity. This is shown first by identifying language communities in a Belgian mobile phone network of 2.6 million customers and by analyzing a web graph of 118 million nodes and more than one billion links. The accuracy of our algorithm is also verified on ad-hoc modular networks. .
    ModularityCommunity detectionOptimizationCommunity structureSocial networkMobile phone networksWeighted networkMobile phoneComplex networkGraph...
  • We report the discovery of 11 very faint (r< 23), low surface brightness ({\mu}_r< 27 mag/arcsec^2) dwarf galaxies in one deep field in the Virgo cluster, obtained by the prime focus cameras (LBC) at the Large Binocular Telescope (LBT). These extend our previous sample to reach a total number of 27 galaxies in a field of just of 0.17 deg^2 located at a median distance of 390 kpc from the cluster center. Their association with the Virgo cluster is supported by their separate position in the central surface brightness - total magnitude plane with respect to the background galaxies of similar total magnitude. For a significant fraction (26\%) of the sample the association to the cluster is confirmed by spectroscopic follow-up. We show that the mere abundance of satellite galaxies corresponding to our observed number in the target field provides extremely tight constraints on Dark Matter models with suppressed power spectrum compared to the Cold Dark Matter case, independently of the galaxy luminosity distribution. In particular, requiring the observed number of satellite galaxies not to exceed the predicted abundance of Dark Matter sub-halos yields a limit m_X >3 keV at 1-{\sigma} and m_X > 2.3 keV at 2-{\sigma} confidence level for the mass of thermal Warm Dark Matter particles. Such a limit is competitive with other limits set by the abundance of ultra-faint satellite galaxies in the Milky Way, is completely independent of baryon physics involved in galaxy formation, and has the potentiality for appreciable improvements with next observations. We extend our analysis to Dark Matter models based on sterile neutrinos, showing that our observations set tight constraints on the combination of sterile neutrino mass m_{\nu} and mixing parameter sin^2(2{\theta}). We discuss the robustness of our results with respect to systematics.
    GalaxyAbundanceDark matter modelDark matterVirgo ClusterCold dark matterMilky WayThermal WDMDwarf galaxyWarm dark matter...
  • We study the propagation of ultra-high-energy cosmic rays in the magnetised cosmic web. We focus on the particular case of highly magnetised voids ($B \sim \text{nG}$), using the upper bounds from the Planck satellite. The cosmic web was obtained from purely magnetohydrodynamical cosmological simulations of structure formation considering different power spectra for the seed magnetic field in order to account for theoretical uncertainties. We investigate the impact of these uncertainties on the propagation of cosmic rays, showing that they can affect the measured spectrum and composition by up to $\simeq 80\%$ and $\simeq 5\%$, respectivelly. In our scenarios, even if magnetic fields in voids are strong, deflections of 50 EeV protons from sources closer than $\sim\;$50 Mpc are less than $15^\circ$ in approximately 10-50% of the sky, depending on the distribution of sources and magnetic power spectrum. Therefore, UHECR astronomy might be possible in a significant portion of the sky depending on the primordial magnetic power spectrum, provided that protons constitute a sizeable fraction of the observed UHECR flux.
    Ultra-high-energy cosmic rayVoidCosmic rayCosmic webHydrodynamical simulationsEarthCentaurus AFilling fractionIntergalactic magnetic fieldExtragalactic magnetic field...
  • We present new limits on the amplitude of potential primordial magnetic fields (PMFs) using temperature and polarization measurements of the cosmic microwave background (CMB) from Planck, BICEP2/Keck Array, Polarbear, and SPTpol. We reduce twofold the 95% CL upper limit on the CMB anisotropy power due to PMFs, from $A_{PMF}$ < 0.76 for Planck alone to $A_{PMF}$ < 0.36 for the combined dataset. We also forecast the expected limits from soon-to-deploy CMB experiments (like SPT-3G, Adv. ACTpol, or the Simons Array) and the proposed CMB-S4 experiment. Future CMB experiments should dramatically reduce the current uncertainties, by one order of magnitude for the near-term experiments and two orders of magnitude for the CMB-S4 experiment. The constraints from CMB-S4 have the potential to rule out much of the parameter space for PMFs.
    Cosmological magnetic fieldCMB-S4B-modesCosmic microwave backgroundCosmological modelCosmic microwave background experimentFull width at half maximumCalibrationTelescopesInflationary gravitational wave...
  • The transverse stratification of active galactic nuclei (AGN) jets is suggested by observations and theoretical arguments, as a consequence of intrinsic properties of the central engine (accretion disc + black hole) and external medium. On the other hand, the one-component jet approaches are heavily challenged by the various observed properties of plasmoids in radio jets (knots), often associated with internal shocks. Given that such a transverse stratification plays an important role on the jets acceleration, stability, and interaction with the external medium, it should also induce internal shocks with various strengths and configurations, able to describe the observed knots behaviours. By establishing a relation between the transverse stratification of the jets, the internal shock properties, and the multiple observed AGN jet morphologies and behaviours, our aim is to provide a consistent global scheme of the various AGN jet structures. Working on a large sample of AGN radio jets monitored in very long baseline interferometry (VLBI) by the MOJAVE collaboration, we determined the consistency of a systematic association of the multiple knots with successive re-collimation shocks. We then investigated the re-collimation shock formation and the influence of different transverse stratified structures by parametrically exploring the two relativistic outflow components with the specific relativistic hydrodynamic (SRHD) code AMRVAC. We were able to link the different spectral classes of AGN with specific stratified jet characteristics, in good accordance with their VLBI radio properties and their accretion regimes.
    Astrophysical jetCollimationMach numberVery long baseline interferometryBlazarLorentz factorRarefaction waveAGN jetsShock waveActive Galactic Nuclei...
  • We develop and apply new techniques in order to uncover galaxy rotation curves (RC) systematics. Considering that an ideal dark matter (DM) profile should yield RCs that have no bias towards any particular radius, we find that the Burkert DM profile satisfies the test, while the Navarro-Frenk-While (NFW) profile has a tendency of better fitting the region between one and two disc scale lengths than the inner disc scale length region. Our sample indicates that this behaviour happens to more than 75% of the galaxies fitted with an NFW halo. Also, this tendency does not weaken by considering "large" galaxies, for instance those with $M_*\gtrsim 10^{10} M_\odot$. Besides the tests on the homogeneity of the fits, we also use a sample of 62 galaxies of diverse types to perform tests on the quality of the overall fit of each galaxy, and to search for correlations with stellar mass, gas mass and the disc scale length. In particular, we find that only 13 galaxies are better fitted by the NFW halo; and that even for the galaxies with $M_* \gtrsim 10^{10} M_\odot$ the Burkert profile either fits as good as, or better than, the NFW profile. This result is relevant since different baryonic effects important for the smaller galaxies, like supernova feedback and dynamical friction from baryonic clumps, indicate that at such large stellar masses the NFW profile should be preferred over the Burkert profile. Hence, our results either suggest a new baryonic effect or a change of the dark matter physics.
    GalaxyNavarro-Frenk-White profileMilky WayRotation CurveBurkert profileDark matterDark Matter Density ProfileStellar massDark matter haloBaryonic Tully-Fisher relation...
  • We perform numerical simulations of Cold Electroweak Baryogenesis, including for the first time in the Bosonic sector the full electroweak gauge group SU(2)$\times$U(1) and CP-violation. We find that the maximum generated baryon asymmetry is reduced by a factor of three relative to the SU(2)-only model, but that the quench time dependence is very similar. In addition, we compute the magnitude of the helical magnetic fields, and find that it is proportional to the strength of CP-violation and dependent on quench time, but is not proportional to the magnitude of the baryon asymmetry as proposed in the literature. Astrophysical signatures of primordial magnetic helicity can therefore not in general be used as evidence that electroweak baryogenesis has taken place.
    QuenchingChern-Simons numberCP violationCP-oddHiggs fieldBaryon asymmetry of the UniverseHyperchargeGauge fieldHiggs bosonHelical magnetic field...
  • We present the first results from the ongoing LAGER project (Lyman Alpha Galaxies in the Epoch of Reionization), which is the largest narrowband survey for $z \sim$ 7 galaxies to date. Using a specially built narrowband filter NB964 for the superb large-area Dark-Energy Camera (DECam) on the NOAO/CTIO 4m Blanco telescope, LAGER has collected 34 hours NB964 narrowband imaging data in the 3 deg$^2$ COSMOS field. We have identified 23 Lyman Alpha Emitter (LAE) candidates at $z$ = 6.9 in the central 2-deg$^2$ region, where DECam and public COSMOS multi-band images exist. The resulting luminosity function can be described as a Schechter function modified by a significant excess at the bright end (4 galaxies with $L_{Ly\alpha} \sim $ 10$^{43.4\pm0.2}$ erg s$^{-1}$). The number density at $L_{Ly\alpha}\sim$ 10$^{43.4\pm0.2}$ erg s$^{-1}$ is little changed from z= 6.6, while at fainter $L_{Ly\alpha}$ it is substantially reduced. Overall, we see a fourfold reduction in Ly$\alpha$ luminosity density from $z$ = 5.7 to 6.9. Combined with a more modest evolution of the continuum UV luminosity density, this suggests a factor of $\sim 3$ suppression of Ly$\alpha$ by radiative transfer through the $z \sim$ 7 intergalactic medium (IGM). It indicates an IGM neutral fraction $x_{HI}$ $\sim$ 0.4--0.6 (assuming Ly$\alpha$ velocity offsets of 100-200 km s$^{-1}$). The changing shape of the Ly$\alpha$ luminosity function between $z\lesssim 6.6$ and $z=6.9$ supports the hypothesis of ionized bubbles in a patchy reionization at $z\sim$ 7.
    Lyman alpha emitterLuminosity functionLyman Alpha Galaxies in the Epoch of ReionizationLuminosityGalaxyIntergalactic mediumReionizationCOSMOS surveySchechter functionSubaru telescope...