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  • Existence of color sextet diquark Higgs fields with TeV masses will indicate a fundamentally different direction for unification than conventional grand unified theories. There is a class of partial unification models based on the gauge group $SU(2)_L\times SU(2)_R\times SU(4)_c$ that implement the seesaw mechanism for neutrino mass with seesaw scale around $10^{11}$ GeV, where indeed such light fields appear naturally despite the high gauge symmetry breaking scale. They couple only to up-type quarks in this model. We discuss phenomenological constraints on these fields and show that they could be detected at LHC via their decay to either $tt$ or single top + jet. We also find that existing Tevatron data gives a lower bound on its mass somewhere in the 400-500 GeV, for reasonable values of its coupling.
    DiquarkLarge Hadron ColliderTop quarkStandard ModelNeutrino massTevatronSeesaw mechanismHiggs fieldYukawa couplingGauge symmetry...
  • 1606.07335  ,  ,  et al.,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  show less
    The characterization of the Galactic foregrounds has been shown to be the main obstacle in the challenging quest to detect primordial B-modes in the polarized microwave sky. We make use of the Planck-HFI 2015 data release at high frequencies to place new constraints on the properties of the polarized thermal dust emission at high Galactic latitudes. Here, we specifically study the spatial variability of the dust polarized spectral energy distribution, and its potential impact on the determination of the tensor-to-scalar ratio. We use the correlation ratio of the $C_\ell^{BB}$ angular power spectra between the 217- and 353-GHz channels as a tracer of these potential variations, computed on different high Galactic latitude regions, ranging from 80% to 20% of the sky. The new insight from Planck data is a departure of the correlation ratio from unity that cannot be attributed to a spurious decorrelation due to the cosmic microwave background, instrumental noise, or instrumental systematics. The effect is marginally detected on each region, but the statistical combination of all the regions gives more than 99% confidence for this variation in polarized dust properties. In addition, we show that the decorrelation increases when there is a decrease in the mean column density of the region of the sky being considered, and we propose a simple power-law empirical model for this dependence, which matches what is seen in the Planck data. We explore the effect that this measured decorrelation has on simulations of the BICEP2-Keck Array/Planck analysis and show that the 2015 constraints from those data still allow a decorrelation between the dust at 150 and 353GHz of the order of the one we measure. Finally we show that either spatial variation of the dust SED or of the dust polarization angle could produce decorrelations between 217- and 353-GHz data similar to those we observe in the data.
    Correlation ratioSpectral energy distributionCosmic microwave backgroundStatisticsPlanck missionHigh Galactic latitudeThermalisationIntensityB-modesGaussian distribution...
  • Dust growth via accretion of gas species has been proposed as the dominant process to increase the amount of dust in galaxies. We show here that this hypothesis encounters severe difficulties that make it unfit to explain the observed UV and IR properties of such systems, particularly at high redshifts. Dust growth in the diffuse ISM phases is hampered by (a) too slow accretion rates; (b) too high dust temperatures, and (c) the Coulomb barrier that effectively blocks accretion. In molecular clouds these problems are largely alleviated. Grains are cold (but not colder than the CMB temperature). However, in dense environments accreted materials form icy water mantles, perhaps with impurities. Mantles are immediately (1 yr) photo-desorbed as grains return to the diffuse ISM at the end of the cloud lifetime, thus erasing any memory of the growth. We conclude that dust attenuating stellar light at high-z must be ready-made stardust largely produced in supernova ejecta.
    AccretionMolecular cloudInterstellar mediumMantleSupernovaDust temperatureThermalisationAbundanceEjectaDust grain...
  • The origin of prompt emission from gamma ray bursts remains to be an open question. Correlated prompt optical and gamma-ray emission observed in a handful of GRBs strongly suggests a common emission region, but failure to adequately fit the broadband GRB spectrum prompted the hypothesis of different emission mechanisms for the low- and high-energy radiations. We demonstrate that our multi-component model for GRB gamma-ray prompt emission provides an excellent fit to GRB 110205A from optical to gamma-ray energies. Our results show that the optical and highest gamma-ray emissions have the same spatial and spectral origin, which is different from the bulk of the X- and softest gamma-ray radiation. Finally, our accurate redshift estimate for GRB 110205A demonstrates promise for using GRBs as cosmological standard candles.
    Prompt emissionStandard candleDissipationCosmologyBATSEMagnetic reconnectionBurst Alert TelescopeGamma ray burstThermalisationObservatories...
  • Galaxies arrive on the red sequences of clusters at high redshift ($z>1$) once their star formation is quenched and evolve passively thereafter. However, we have previously found that cluster red sequence galaxies (CRSGs) undergo significant morphological evolution subsequent to the cessation of star formation, at some point in the past 9-10~Gyr. Through a detailed study of a large sample of cluster red sequence galaxies spanning $0.2<z<1.4$ we elucidate the details of this evolution. Below $z \sim 0.5-0.6$ (in the last 5-6 Gyr) there is little or no morphological evolution in the population as a whole, unlike in the previous 4-5 Gyrs. Over this earlier time (i) disk-like systems with S{\'e}rsic $n < 2$ progressively disappear, as (ii) the range of their axial ratios similarly decreases, removing the most elongated systems (those consistent with thin disks seen at an appreciable inclination angle), and (iii) radial colour gradients (bluer outwards) decrease in an absolute sense from significant age-related gradients to a residual level consistent with the metallicity-induced gradients seen in low redshift cluster members. The distribution of their effective radii shows some evidence of evolution, consistent with growth of {\it at most} a factor $<1.5$ between $z\sim 1.4$ and $z \sim 0.5$, significantly less than for comparable field galaxies, while the distribution of their central ($<1$kpc) bulge surface densities shows no evolution at least at $z<1$. A simple model involving the fading and thickening of a disk component after comparatively recent quenching (after $z\sim 1.5$) around an otherwise passively evolving older spheroid component is consistent with all of these findings.
    LuminosityStar formationQuenchingCluster Lensing And Supernova survey with HubbleEllipticityStellar massStellar populationsHubble Space TelescopeThin stellar diskEarly-type galaxy...
  • The emergence and global adoption of social media has rendered possible the real-time estimation of population-scale sentiment, bearing profound implications for our understanding of human behavior. Given the growing assortment of sentiment measuring instruments, comparisons between them are evidently required. Here, we perform detailed tests of 6 dictionary-based methods applied to 4 different corpora, and briefly examine a further 8 methods. We show that a dictionary-based method will only perform both reliably and meaningfully if (1) the dictionary covers a sufficiently large enough portion of a given text's lexicon when weighted by word usage frequency; and (2) words are scored on a continuous scale.
    GraphTime SeriesSentiment analysisTwitterBinary numberPythonRegular expressionHuman dynamicsAssortativityMeasuring devices...
  • Rapid progress in machine learning and artificial intelligence (AI) has brought increasing attention to the potential impacts of AI technologies on society. In this paper we discuss one such potential impact: the problem of accidents in machine learning systems, defined as unintended and harmful behavior that may emerge from poor design of real-world AI systems. We present a list of five practical research problems related to accident risk, categorized according to whether the problem originates from having the wrong objective function ("avoiding side effects" and "avoiding reward hacking"), an objective function that is too expensive to evaluate frequently ("scalable supervision"), or undesirable behavior during the learning process ("safe exploration" and "distributional shift"). We review previous work in these areas as well as suggesting research directions with a focus on relevance to cutting-edge AI systems. Finally, we consider the high-level question of how to think most productively about the safety of forward-looking applications of AI.
    Machine learningRoboticsOptimizationReinforcement learningRegularizationMass to light ratioArtificial intelligenceMutual informationSecurityCovariance...
  • We use idealized three-dimensional hydrodynamic simulations to study the dynamics and thermal structure of the circumgalactic medium (CGM). Our simulations quantify the role of cooling, galactic winds driven by stellar feedback, and cosmological gas accretion in setting the properties of the CGM in dark matter haloes ranging from $10^{11}-10^{12}$ M$_\odot$. Our simulations support a conceptual picture in which the CGM properties, and the key physics governing it, change markedly with halo mass near $10^{11.5}$ M$_\odot$. As in calculations without feedback, we find that above a critical halo mass of $\sim10^{11.5}$ M$_\odot$ the halo gas is supported by thermal pressure created in the virial shock. The thermal properties of the halo gas at small radii are regulated by feedback triggered when $t_{\rm cool}/t_{\rm ff}\lesssim10$ in the hot halo gas. Below the critical halo mass there is no thermally supported halo and self-regulation at $t_{\rm cool}/t_{\rm ff}\sim10$ does not apply. Instead, the halo gas properties are determined by the interaction between cosmological gas inflow and outflowing galactic winds. The halo gas is not in hydrostatic equilibrium, but is largely supported against gravity by bulk flows (turbulence and coherent inflow/outflow). Its phase structure depends sensitively on both the energy per unit mass and the mass-loading factor of the galaxy outflows. This sensitivity may allow measurements of the thermal state of the CGM in lower mass haloes to constrain the nature of galactic wind feedback. Our idealized simulations can account for some of the properties of the multiphase halo gas inferred from quasar absorption line observations, including the presence of significant mass at a wide range of temperatures, and the characteristic OVI and CIV column densities and kinematics. However, we under-predict the neutral hydrogen content of the $z\sim0$ CGM.
    Circumgalactic mediumThermalisationVirial massCoolingAccretionGalactic windInstabilityCooling timescaleHot gasCosmology...
  • We have recently introduced a new model for the distribution of dark matter (DM) in galaxies, the Ruffini-Arg\"uelles-Rueda (RAR) model, based on a self-gravitating system of massive fermions at finite temperatures. The RAR model, for fermion masses above keV, successfully describes the DM halos in galaxies, and predicts the existence of a denser quantum core towards the center of each configuration. We demonstrate here, for the first time, that the introduction of a cutoff in the fermion phase-space distribution, necessary to account for the finite Galaxy size, defines a new solution with a compact quantum core which represents an alternative to the central black hole (BH) scenario for SgrA*. For a fermion mass in the range $48$~keV$/c^2\lesssim m \lesssim 345$~keV$/c^2$, the DM halo distribution fulfills the most recent data of the Milky Way rotation curves, while harbors a dense quantum core of $4\times10^6 M_\odot$ within the S2 star pericenter. In particular, for a fermion mass of $m\sim 50$~keV$/c^2$ the model is able to explain the DM halos from typical dwarf spheroidal to normal elliptical galaxies, while harboring dark and massive compact objects from $\sim 10^3 M_\odot$ up to $\sim 10^8 M_\odot$ at their respective centers. The model is shown to be in good agreement with different observationally inferred universal relations, such as the ones connecting DM halos with supermassive dark central objects. Finally, the model provides a natural mechanism for the formation of supermassive BHs as heavy as $M_{\rm BH}\sim$ few $10^8 M_\odot$. We argue that larger BH masses ($M_{\rm BH}\sim 10^{9-10} M_\odot$) may be achieved by assuming subsequent accretion processes onto the above heavy seeds, depending on accretion efficiency and environment.
    Dark matter haloDark matterBlack holeFermion massElliptical galaxyDwarf spheroidal galaxyStarAccretionRotation CurveMilky Way...
  • We introduce a decision scheme for optimally choosing a classifier, which segments the cosmic web into different structure types (voids, sheets, filaments, and clusters). Our framework, based on information theory, accounts for the design aims of different classes of possible applications: (i) parameter inference, (ii) model selection, and (iii) prediction of new observations. As an illustration, we use cosmographic maps of web-types in the Sloan Digital Sky Survey to assess the relative performance of the classifiers T-web, DIVA and ORIGAMI for: (i) analyzing the morphology of the cosmic web, (ii) discriminating dark energy models, and (iii) predicting galaxy colors. Our study substantiates a data-supported connection between cosmic web analysis and information theory, and paves the path towards principled design of analysis procedures for the next generation of galaxy surveys. We have made the cosmic web maps, galaxy catalog, and analysis scripts used in this work publicly available.
    Cosmic webMutual informationVoidSloan Digital Sky SurveyEntropyLarge scale structureOptimizationInformation theoryGalaxy colorClassification...
  • The strongest transitions of Zn and CrII are the most sensitive to relative variations in the fine-structure constant ($\Delta\alpha/\alpha$) among the transitions commonly observed in quasar absorption spectra. They also lie within just 40 \AA\ of each other (rest frame), so they are resistant to the main systematic error affecting most previous measurements of $\Delta\alpha/\alpha$: long-range distortions of the wavelength calibration. While Zn and CrII absorption is normally very weak in quasar spectra, we obtained high signal-to-noise, high-resolution echelle spectra from the Keck and Very Large Telescopes of 9 rare systems where it is strong enough to constrain $\Delta\alpha/\alpha$ from these species alone. These provide 12 independent measurements (3 quasars were observed with both telescopes) at redshifts 1.0--2.4, 11 of which pass stringent reliability criteria. These 11 are all consistent with $\Delta\alpha/\alpha=0$ within their individual uncertainties of 3.5--13 parts per million (ppm), with a weighted mean $\Delta\alpha/\alpha = 0.4\pm1.4_{\rm stat}\pm0.9_{\rm sys}$ ppm (1$\sigma$ statistical and systematic uncertainties), indicating no significant cosmological variations in $\alpha$. This is the first statistical sample of absorbers that is resistant to long-range calibration distortions (at the $<$1 ppm level), with a precision comparable to previous large samples of $\sim$150 (distortion-affected) absorbers. Our systematic error budget is instead dominated by much shorter-range distortions repeated across echelle orders of individual spectra.
    AbsorbanceQuasarSystematic errorAbsorptivityUVESHigh resolution échelle spectrometerStatisticsStatistical errorTelescopesCosmology...
  • The EoR 21-cm signal is expected to become highly non-Gaussian as reionization progresses. This severely affects the error-covariance of the EoR 21-cm power spectrum which is important for predicting the prospects of a detection with ongoing and future experiments. Most earlier works have assumed that the EoR 21-cm signal is a Gaussian random field where (1) the error variance depends only on the power spectrum and the number of Fourier modes in the particular $k$ bin, and (2) the errors in the different $k$ bins are uncorrelated. Here we use an ensemble of simulated 21-cm maps to analysis the error-covariance at various stages of reionization. We find that even at the very early stages of reionization ($\bar{x}_{\rm HI} \sim 0.9 $) the error variance significantly exceeds the Gaussian predictions at small length-scales ($k > 0.5 \,{\rm Mpc}^{-1}$) while they are consistent at larger scales. The errors in most $k$ bins (both large and small scales), are however found to be correlated. Considering the later stages ($\bar{x}_{\rm HI} = 0.15$), the error variance shows an excess in all $k$ bins within $k \ge 0.1 \, {\rm Mpc}^{-1}$, and it is around $200$ times larger than the Gaussian prediction at $k \sim 1 \, {\rm Mpc}^{-1}$. The errors in the different $k$ bins are all also highly correlated, barring the two smallest $k$ bins which are anti-correlated with the other bins. Our results imply that the predictions for different 21-cm experiments based on the Gaussian assumption underestimate the errors, and it is ecessary to incorporate the non-Gaussianity for more realistic predictions.
    Epoch of reionizationHydrogen 21 cm lineReionizationNon-GaussianityRandom FieldTrispectrumIonization21-cm power spectrumStatisticsBrightness temperature fluctuations...
  • The birth of the first luminous sources and the ensuing epoch of reionization are best studied via the redshifted 21-cm emission line, the signature of the first two imprinting the last. In this work we present a fully-Bayesian method, \textsc{hibayes}, for extracting the faint, global (sky-averaged) 21-cm signal from the much brighter foreground emission. We show that a simplified (but plausible), Gaussian model of the 21-cm emission from the Cosmic Dawn epoch ($15 \lesssim z \lesssim 30$), parameterized by an amplitude $A_{\rm HI}$, a frequency peak $\nu_{\rm HI}$ and a width $\sigma_{\rm HI}$, can be extracted even in the presence of a structured foreground frequency spectrum (parameterized as a $7^{\rm th}$-order polynomial), provided sufficient signal-to-noise (400~hours of observation with a single dipole). We apply our method to an early, 19-minute long observation from the Large aperture Experiment to detect the Dark Ages, constraining the 21-cm signal amplitude and width to be $-890 < A_{\rm HI} < 0$ mK and $\sigma_{\rm HI} > 6.5$ MHz (corresponding to $\Delta z > 1.9$ at redshift $z \simeq 20$) respectively at the 95-per-cent confidence level in the range $13.2 < z < 27.4$ ($100 > \nu > 50$ MHz).
    Hydrogen 21 cm lineCalibrationIntergalactic mediumReionizationBayesianCosmic microwave backgroundThermalisationDark AgesBayesian posterior probabilityEpoch of reionization...
  • The basic processes of the formation of the first stars in the primordial Universe are outlined and the implications for cosmological structure formation discussed. By employing theoretical and numerical models of cosmic structure evolution embedded within N-body hydrodynamical chemistry simulations, predictions for the production of the first heavy elements in the Universe are given. These results are then compared against measured data of UV luminosities and metal abundances in different kinds of observations in order to draw conclusions on the chemical and thermal state of the cosmic medium at different cosmological epochs.
    Population IIIStar formationStarCosmologyFluid dynamicsGamma ray burstLuminosityStar formation rateLuminosity functionStructure formation...
  • The standard numerical tools for studying non-linear collapse of matter are Newtonian $N$-body simulations. Previous work has shown that these simulations are in accordance with General Relativity (GR) up to first order in perturbation theory, provided that the effects from radiation can be neglected. In this paper we show that the present day matter density receives more than 1% corrections from radiation on large scales if Newtonian simulations are initialised before $z=50$. We provide a relativistic framework in which unmodified Newtonian simulations are compatible with linear GR even in the presence of radiation. Our idea is to use GR perturbation theory to keep track of the evolution of relativistic species and the relativistic spacetime consistent with the Newtonian trajectories computed in $N$-body simulations. If metric potentials are sufficiently small, they can be computed using a first-order Einstein-Boltzmann code such as CLASS. We make this idea rigorous by defining a class of GR gauges, the Newtonian motion gauges, which are defined such that matter particles follow Newtonian trajectories. We construct a simple example of a relativistic space-time within which unmodified Newtonian simulations can be interpreted.
    General relativityGauge conditionGauge transformationRelativistic correctionDark matterBardeen potentialEinstein field equationsAnisotropic stressPerturbation theoryStructure formation...
  • We investigate the spin evolution of dark matter haloes and their dependence on the number of connected filaments from the cosmic web at high redshift (spin-filament relation hereafter). To this purpose, we have simulated $5000$ haloes in the mass range $5\times10^{9}h^{-1}M_{\odot}$ to $5\times10^{11}h^{-1}M_{\odot}$ at $z=3$ in cosmological N-body simulations. We confirm the relation found by Prieto et al. 2015 where haloes with fewer filaments have larger spin. We also found that this relation is more significant for higher halo masses, and for haloes with a passive (no major mergers) assembly history. Another finding is that haloes with larger spin or with fewer filaments have their filaments more perpendicularly aligned with the spin vector. Our results point to a picture in which the initial spin of haloes is well described by tidal torque theory and then gets subsequently modified in a predictable way because of the topology of the cosmic web, which in turn is given by the currently favoured LCDM model. Our spin-filament relation is a prediction from LCDM that could be tested with observations.
    Galaxy filamentCosmic webDark matter haloVirial massDark matterLambda-CDM modelAccretionVorticityN-body simulationSpin-flip...
  • The possibility that the so-called "lithium problem", i.e., the disagreement between the theoretical abundance predicted for primordial $^7 \text{Li}$ assuming standard nucleosynthesis and the value inferred from astrophysical measurements, can be solved through a non-thermal Big Bang Nucleosynthesis (BBN) mechanism has been investigated by several authors. In particular, it has been shown that the decay of a MeV-mass particle, like, e.g., a sterile neutrino, decaying after BBN not only solves the lithium problem, but also satisfies cosmological and laboratory bounds, making such a scenario worth to be investigated in further detail. In this paper, we constrain the parameters of the model with the combination of current data, including Planck 2015 measurements of temperature and polarization anisotropies of the Cosmic Microwave Background (CMB), FIRAS limits on CMB spectral distortions, astrophysical measurements of primordial abundances and laboratory constraints. We find that a sterile neutrino with mass $M_S = 4.35 _{-0.17} ^{+0.13} \, \text{MeV}$ (at $95\%$ c.l.) and decay time $\tau _S = 1.8 _{-1.6} ^{+1.9} \cdot 10^5 \, \text{s}$ (at $95\%$ c.l.) perfectly accounts for the difference between predicted and observed $^7 \text{Li}$ primordial abundance. The same model also predicts an increase of the effective number of relativistic degrees of freedom at the time of CMB decoupling $\Delta N_\text{eff}^\text{cmb}\equiv N_\text{eff}^\text{cmb} -3.046 = 0.34 _{-0.14} ^{+0.16}$ at $95\%$ c.l.. We also provide forecasts for future experiments finding that the combination of measurements from the COrE+ and PIXIE missions will allow to significantly reduce the permitted region for the sterile lifetime and density.
    Sterile neutrinoAbundanceCosmic microwave backgroundBig bang nucleosynthesisMixing angleNeutrinoLithium-7 problemPlanck missionPhotodisintegrationSterile neutrino decay...
  • We experimentally demonstrate the violation of classical physics in a many-atom system using a recently derived criterion [E. Kot et al., Phys. Rev. Lett. 108, 233601 (2013)] that explicitly does not make use of quantum mechanics. We thereby show that the magnetic moment distribution measured by McConnell et al. [R. McConnell et al., Nature 519, 439 (2015)] in a system with a total mass of $2.6\times 10^5$ atomic mass units is inconsistent with classical physics. Notably, the violation of classical physics affects an area in phase space $10^3$ times larger than the Planck quantum $\hbar$.
    Quantum mechanicsMagnetizationPhase space densityPhase spaceInterferencePlanck missionQuantum opticsWigner distribution functionBohr magnetonQuantum theory...
  • It is shown that in semi-classical electrodynamics, which describes how electrically charged particles move according to the laws of quantum mechanics under the influence of a prescribed classical electromagnetic field, only a restricted class of gauge transformations is allowed. This lack of full gauge invariance, in contrast to the situation in classical and quantum electrodynamics which are fully gauge invariant theories, is due to the requirement that the scalar potential in the Hamiltonian of wave mechanics represent a physical potential. Probability amplitudes and energy differences are independent of gauge within this restricted class of gauge transformation.
    ElectrodynamicsGauge invarianceGauge transformationHamiltonianProbability amplitudeQuantum electrodynamicsQuantum mechanicsPotentialParticlesScalar...
  • We propose a method to obtain optimal protocols for adiabatic ground-state preparation near the adiabatic limit, extending earlier ideas from [D. A. Sivak and G. E. Crooks, Phys. Rev. Lett. 108, 190602 (2012)] to quantum non-dissipative systems. The space of controllable parameters of isolated quantum many-body systems is endowed with a Riemannian quantum metric structure, which can be exploited when such systems are driven adiabatically. Here, we use this metric structure to construct optimal protocols in order to accomplish the task of adiabatic ground-state preparation in a fixed amount of time. Such optimal protocols are shown to be geodesics on the parameter manifold, maximizing the local fidelity. Physically, such protocols minimize the average energy fluctuations along the path. Our findings are illustrated on the Landau-Zener model and the anisotropic XY spin chain. In both cases we show that geodesic protocols drastically improve the final fidelity. Moreover, this happens even if one crosses a critical point, where the adiabatic perturbation theory fails.
    GeodesicOptimizationMany-body systemsManifoldHamiltonianExcited stateLandau-Zener transitionInfinitesimalPerturbation theoryGeodesic curvature...
  • We are taught that gauge transformations in classical and quantum mechanics do not change the physics of the problem. Nevertheless here we discuss three broad scenarios where under gauge transformations: (i) conservation laws are not preserved in the usual manner; (ii) non-gauge-invariant quantities can be associated with physical observables; and (iii) there are changes in the physical boundary conditions of the wave function that render it non-single-valued. We give worked examples that illustrate these points, in contrast to general opinions from classic texts. We also give a historical perspective on the development of Abelian gauge theory in relation to our particular points. Our aim is to provide a discussion of these issues at the graduate level.
    Gauge transformationQuantum mechanicsHamiltonianGauge invarianceConserved quantitiesOrientationEigenfunctionElectromagnetismGauge theoryExpectation Value...
  • We study the turbulent regime of chiral (magneto)hydrodynamics for charged and neutral matter with chirality imbalance. We find that the chiral magnetohydrodynamics for charged plasmas possesses a unique scaling symmetry, only without fluid helicity under the local charge neutrality. We also find a different type of unique scaling symmetry in the chiral hydrodynamics for neutral matter with fluid helicity in the inertial range. We show that these symmetries dictate the self-similar inverse cascade of the magnetic and kinetic energies. Our results imply the possible inverse energy cascade in core-collapse supernovae due to the chiral transport of neutrinos.
    ChiralityFluid dynamicsHelicityTurbulenceScaling lawNeutrinoSelf-similarityChiral vorticity effectChiral anomalyCore-collapse supernova...
  • We present a meta-analysis of star-formation rate (SFR) indicators in the GAMA survey, producing 12 different SFR metrics and determining the SFR-M* relation for each. We compare and contrast published methods to extract the SFR from each indicator, using a well-defined local sample of morphologically-selected spiral galaxies, which excludes sources which potentially have large recent changes to their SFR. The different methods are found to yield SFR-M* relations with inconsistent slopes and normalisations, suggesting differences between calibration methods. The recovered SFR-M* relations also have a large range in scatter which, as SFRs of the targets may be considered constant over the different timescales, suggests differences in the accuracy by which methods correct for attenuation in individual targets. We then recalibrate all SFR indicators to provide new, robust and consistent luminosity-to-SFR calibrations, finding that the most consistent slopes and normalisations of the SFR-M* relations are obtained when recalibrated using the radiation transfer method of Popescu et al. These new calibrations can be used to directly compare SFRs across different observations, epochs and galaxy populations. We then apply our calibrations to the GAMA II equatorial dataset and explore the evolution of star-formation in the local Universe. We determine the evolution of the normalisation to the SFR-M* relation from 0 < z < 0.35 - finding consistent trends with previous estimates at 0.3 < z < 1.2. We then provide the definitive z < 0.35 Cosmic Star Formation History, SFR-M* relation and its evolution over the last 3 billion years.
    Star formation rateCalibrationStar formationLuminosityStellar massSpiral galaxyPhotometryStellar populationsRadiative transferObservational error...
  • Massive galaxies at high redshift are predicted to be fed from the cosmic web by narrow, dense, cold streams. These streams penetrate supersonically through the hot medium encompassed by a stable shock near the virial radius of the dark-matter halo. Our long-term goal is to explore the heating and dissipation rate of the streams and their fragmentation and possible breakup, in order to understand how galaxies are fed, and how this affects their star-formation rate and morphology. We present here the first step, where we analyze the linear Kelvin-Helmholtz instability (KHI) of a cold, dense slab or cylinder flowing through a hot, dilute medium in the transonic regime. The current analysis is limited to the adiabatic case with no gravity and assuming equal pressure in the stream and the medium. By analytically solving the linear dispersion relation, we find a transition from a dominance of the familiar rapidly growing surface modes in the subsonic regime to more slowly growing body modes in the supersonic regime. The system is parameterized by three parameters: the density contrast between the stream and the medium, the Mach number of stream velocity with respect to the medium, and the stream width with respect to the halo virial radius. We find that a realistic choice for these parameters places the streams near the mode transition, with the KHI exponential-growth time in the range 0.01-10 virial crossing times for a perturbation wavelength comparable to the stream width. We confirm our analytic predictions with idealized hydrodynamical simulations. Our linear-KHI estimates thus indicate that KHI may in principle be effective in the evolution of streams by the time they reach the galaxy. More definite conclusions await the extension of the analysis to the nonlinear regime and the inclusion of cooling, thermal conduction, the halo potential well, self-gravity and magnetic fields.
    InstabilityMach numberCompressibilitySimulations of structure formationCoolingVirial radiusMarginal stabilityKelvin-Helmholtz instabilityDensity contrastSpeed of sound...
  • With new observational facilities becoming available soon, discovering and characterising supernovae from the first stars will open up alternative observational windows to the end of the cosmic dark ages. Based on a semi-analytical merger tree model of early star formation we constrain Population III supernova rates. We find that our method reproduces the Population III supernova rates of large-scale cosmological simulations very well. Our computationally efficient model allows us to survey a large parameter space and to explore a wide range of different scenarios for Population III star formation. Our calculations show that observations of the first supernovae can be used to differentiate between cold and warm dark matter models and to constrain the corresponding particle mass of the latter. Our predictions can also be used to optimize survey strategies with the goal to maximize supernova detection rates.
    Population IIISupernovaStar formationInitial mass functionMerger treeWarm dark matterCosmologyStar formation rateVirial massStatistics...
  • Excursion Set Theory (EST) is an analytical framework to study the large scale structure of the Universe. EST introduces a procedure to calculate the number density of structures by relating the non-linear structures to cosmological linear perturbation theory. In this work, we introduce a novel approach to re-formulate the EST in Matrix Formalism. It is proposed that the matrix representation of EST will facilitate the the calculations in framework of the large scale structure observables. The method is to discretize the two dimensional plane of variance and density contrast of EST, where the trajectories for each point in the Universe lived there. The probability of having a density contrast in a chosen variance is represented by a probability ket. Naturally the concept of the transition matrix pops up to define the trajectories in EST. We show that in the case of Markovianity of the process, the probability ket, at a specific variance can be constructed by knowing the transition matrix and the initial probability ket. We should note that, in a specific case of Gaussian transitions, the Gaussian profile of density contrast is preserved. In this formalism we define the probability transition rate which is used to obtain the first up-crossing of trajectories and the number count of the structures. The continues limit of the formalism is discussed and the known Fokker-Planck dispersion equation of EST is recovered. Finally we claim and discuss that the Matrix Formalism of EST could be a powerful complimentary approach in non-linear structure formation studies.
    Excursion set modelDensity contrastStructure formationStatisticsPress-Schechter formalismK-spaceLarge scale structureDark matterDark matter haloExpectation Value...
  • Quantum mechanics forces us to reconsider certain aspects of classical causality. The 'central mystery' of quantum mechanics manifests in different ways, depending on the interpretation. This mystery can be formulated as the possibility of selecting part of the initial conditions of the Universe 'retroactively'. This talk aims to show that there is a global, timeless, 'bird's view' of the spacetime, which makes this mystery more reasonable. We will review some well-known quantum effects from the perspective of global consistency.
    Quantum mechanicsCausalityUnitarityPartial differential equationInitial conditions of the universeStanding waveWavefunctionStrangenessMeasuring devicesAlice and Bob...
  • Quantum measurement finds the observed system in a collapsed state, rather than in the state predicted by the Schr\"odinger equation. Yet there is a relatively spread opinion that the wavefunction collapse can be explained by unitary evolution (for instance in the decoherence approach, if we take into account the environment). In this article it is proven a mathematical result which severely restricts the initial conditions for which measurements have definite outcomes, if pure unitary evolution is assumed. This no-go theorem remains true even if we take the environment into account. The result does not forbid a unitary description of the measurement process, it only shows that such a description is possible only for very restricted initial conditions. The existence of such restrictions of the initial conditions can be understood in the four-dimensional block universe perspective, as a requirement of global self-consistency of the solutions of the Schr\"odinger equation.
    Quantum measurementNo-go theoremWavefunction collapseHidden variable theoryPartial differential equationQuantum mechanicsHermitian operatorOrthonormal basisMeasurement problemMeasurement...
  • Landauer's erasure principle exposes an intrinsic relation between thermodynamics and information theory: the erasure of information stored in a system, S, requires an amount of work proportional to the entropy of that system. This entropy, H(S|O), depends on the information that a given observer, O, has about S, and the work necessary to erase a system may therefore vary for different observers. Here, we consider a general setting where the information held by the observer may be quantum-mechanical, and show that an amount of work proportional to H(S|O) is still sufficient to erase S. Since the entropy H(S|O) can now become negative, erasing a system can result in a net gain of work (and a corresponding cooling of the environment).
    EntropyErasureEntanglementQubitInformation theoryQuantum mechanicsALICE experimentVon neumann entropyStatistical mechanicsDissipation...
  • We study an entropy measure for quantum systems that generalizes the von Neumann entropy as well as its classical counterpart, the Gibbs or Shannon entropy. The entropy measure is based on hypothesis testing and has an elegant formulation as a semidefinite program, a type of convex optimization. After establishing a few basic properties, we prove upper and lower bounds in terms of the smooth entropies, a family of entropy measures that is used to characterize a wide range of operational quantities. From the formulation as a semidefinite program, we also prove a result on decomposition of hypothesis tests, which leads to a chain rule for the entropy.
    EntropyVon neumann entropyPositive semi definiteDualityInformation theoryCompressibilityKullback-Leibler divergencePermutationOrthonormal basisRenyi entropy...
  • According to quantum theory, a measurement may have multiple possible outcomes. Single-world interpretations assert that, nevertheless, only one of them "really" occurs. Here we propose a gedankenexperiment where quantum theory is applied to model an experimenter who herself uses quantum theory. We find that, in such a scenario, no single-world interpretation can be logically consistent. This conclusion extends to deterministic hidden-variable theories, such as Bohmian mechanics, for they impose a single-world interpretation.
    Quantum theoryBohmian mechanicsWigner's friendQuantum measurementQuantum mechanicsHidden variable theoryMeasuring devicesIsometryStatisticsBell's theorem...
  • This work presents the foundations of Singular Semi-Riemannian Geometry and Singular General Relativity, based on the author's research. An extension of differential geometry and of Einstein's equation to singularities is reported. Singularities of the form studied here allow a smooth extension of the Einstein field equations, including matter. This applies to the Big-Bang singularity of the FLRW solution. It applies to stationary black holes, in appropriate coordinates (since the standard coordinates are singular at singularity, hiding the smoothness of the metric). In these coordinates, charged black holes have the electromagnetic potential regular everywhere. Implications on Penrose's Weyl curvature hypothesis are presented. In addition, these singularities exhibit a (geo)metric dimensional reduction, which might act as a regulator for the quantum fields, including for quantum gravity, in the UV regime. This opens the perspective of perturbative renormalizability of quantum gravity without modifying General Relativity.
    General relativityEinstein field equationsDimensional ReductionCharged black holeRegularizationQuantum gravityFriedmann-Lemaitre-Robertson-Walker metricBlack holeBig BangWeyl curvature hypothesis...
  • We investigate the scaling of entanglement entropy in both the multi-scale entanglement renormalization ansatz (MERA) and in its generalization, the branching MERA. We provide analytical upper bounds for this scaling, which take the general form of a boundary law with various types of multiplicative corrections, including power-law corrections all the way to a bulk law. For several cases of interest, we also provide numerical results that indicate that these upper bounds are saturated to leading order. In particular we establish that, by a suitable choice of holographic tree, the branching MERA can reproduce the logarithmic multiplicative correction of the boundary law observed in Fermi liquids and spin-Bose metals in $D\geq 2$ dimensions.
    Entanglement entropyCausalityDensity matrixEntropyCoarse grainingEntanglementBranching ratioFree fermionsRegularizationIsometry...
  • We characterize the nonlinear stage of modulational instability (MI) by studying the long-time asymptotics of focusing nonlinear Schrodinger (NLS) equation on the infinite line with initial conditions that tend to constant values at infinity. Asymptotically in time, the spatial domain divides into three regions: a far left field and a far right field, in which the solution is approximately equal to its initial value, and a central region in which the solution has oscillatory behavior and is described by slow modulations of the periodic traveling wave solutions of the focusing NLS equation. These results demonstrate that the asymptotic stage of MI is universal, since the long-time behavior of a large class of perturbations is described by the same asymptotic state.
    Nonlinear Schrodinger equationInstabilityEllipticitySolitonPlane waveReflection coefficientFar-fieldEigenfunctionLax pairContinuous spectrum...
  • We formulate Goldbach type questions for Gaussian, Hurwitz, Octavian and Eisenstein primes. They are different from Goldbach type statements by Takayoshi Mitsui from 1960 for number fields or C.A. Holben and James Jordan from 1968 for Gaussian integers. Here is what we meeasure: 1) Every even Gaussian integer a+ib satisfying a>2, b>2 is a sum of two Gaussian primes with positive coefficients. 2) Every Eisenstein integer a+bw with a>3,b>3 and w=(1+sqrt(-3))/2 is the sum of two Eisenstein primes with positive coefficients. Note that no evenness condition is asked in the Eisenstein case. 3) Every Lipschitz integer quaternion with positive entries is the sum of two Hurwitz primes. 4) There exists a constant K such that every Octavian integer with coefficients larger than K is the sum of two Octavian primes. Except in the Octonion case, where the fewest experiments were done, the statements can be linked to difficult questions like Landau or Bunyakovsky conjectures. We therefore look also more closely and numerically at some Hardy-Littlewood constants following early computations from Daniel Shanks and Marvin Wunderlich from the 50ies and 70ies.
    QuaternionsGoldbach's ConjectureDivision algebraRegularizationComplex planeBinary numberSphere packingStatisticsManifoldQuadratic reciprocity...
  • The quasar mode of Active Galactic Nuclei (AGN) in the high-redshift Universe is routinely observed in gas-rich galaxies together with large-scale AGN-driven winds. It is crucial to understand how photons emitted by the central AGN source couple to the ambient interstellar-medium to trigger large-scale outflows. By means of radiation-hydrodynamical simulations of idealised galactic discs, we study the coupling of photons with the multiphase galactic gas, and how it varies with gas cloud sizes, and the radiation bands included in the simulations, which are ultraviolet (UV), optical, and infrared (IR). We show how a quasar with a luminosity of $10^{46}$ erg/s can drive large-scale winds with velocities of $10^2-10^3$ km/s and mass outflow rates around $10^3$ M$_\odot$/yr for times of order a few million years. Infrared radiation is necessary to efficiently transfer momentum to the gas via multi-scattering on dust in dense clouds. However, IR multi-scattering, despite being extremely important at early times, quickly declines as the central gas cloud expands and breaks up, allowing the radiation to escape through low gas density channels. The typical number of multi-scattering events for an IR photon is only about a quarter of the mean optical depth from the center of the cloud. Our models account for the observed outflow rates of $\sim$500-1000 M$_\odot$/yr and high velocities of $\sim 10^3$ km/s, favouring winds that are energy-driven via extremely fast nuclear outflows, interpreted here as being IR-radiatively-driven winds.
    QuasarLuminosityInterstellar mediumActive Galactic NucleiMomentum transferBlack holeSpeed of lightOpacityMean mass densityTurbulence...
  • The International Symposium on Biomedical Imaging (ISBI) held a grand challenge to evaluate computational systems for the automated detection of metastatic breast cancer in whole slide images of sentinel lymph node biopsies. Our team won both competitions in the grand challenge, obtaining an area under the receiver operating curve (AUC) of 0.925 for the task of whole slide image classification and a score of 0.7051 for the tumor localization task. A pathologist independently reviewed the same images, obtaining a whole slide image classification AUC of 0.966 and a tumor localization score of 0.733. Combining our deep learning system's predictions with the human pathologist's diagnoses increased the pathologist's AUC to 0.995, representing an approximately 85 percent reduction in human error rate. These results demonstrate the power of using deep learning to produce significant improvements in the accuracy of pathological diagnoses.
    ClassificationDeep learningReceiver operating characteristicBinary numberArchitectureFalse positive rateTraining setRegressionRandom forestFeature extraction...
  • We present first results from MMT and Keck spectroscopy for a large sample of $0.1\leq z\leq1$ emission-line galaxies selected from our narrow-band imaging in the Subaru Deep Field. We have measured the weak [OIII]$\lambda$4363 emission line for 164 galaxies (66 with at least 3$\sigma$ detections, and 98 with significant upper limits). The strength of this line is set by the electron temperature for the ionized gas. Since the gas temperature is regulated by the metal content, the gas-phase oxygen abundance is inversely correlated with [OIII]$\lambda$4363 line strength. Our temperature-based metallicity study is the first to span $\approx$8 Gyr of cosmic time and $\approx$3 dex in stellar mass for low-mass galaxies, $\log{\left(M_{\rm star}/M_{\rm sun}\right)}\approx6.0-9.0$. Using extensive multi-wavelength photometry, we measure the evolution of the stellar mass--gas metallicity relation, and its dependence on dust-corrected star formation rate. The latter is obtained from high signal-to-noise Balmer emission-line measurements. Our mass-metallicity relation is consistent with Andrews & Martini at $z\leq0.3$, and evolves toward lower abundances at a given stellar mass, $\log{({\rm O/H})}\propto(1+z)^{-2.32^{+0.52}_{-0.26}}$. We find that galaxies with lower metallicities have higher star formation rates at a given stellar mass and redshift, although the scatter is large ($\approx$0.3 dex), and the trend is weaker than seen in local studies. We also compare our mass--metallicity relation against predictions from high-resolution galaxy formation simulations, and find good agreement with models that adopt energy- and momentum-driven stellar feedback. We have identified 16 extremely metal-poor galaxies with abundances less than a tenth of solar; our most metal-poor galaxy at $z\approx0.84$ is similar to I Zw 18.
    Stellar massStar formation rateAbundanceStar-forming galaxyActive Galactic NucleiIonizationGalaxy FormationSloan Digital Sky SurveyEmission line galaxyLow ionization nuclear emission region...
  • Polarization arising from aligned dust grains presents a unique opportunity to study magnetic fields in the diffuse interstellar medium and molecular clouds. Polarization from circumstellar regions, accretion disks and comet atmospheres can also be related to aligned dust.To reliably trace magnetic fields quantitative theory of grain alignment is required. Formulating the theory that would correspond to observations was one of the longstanding problems in astrophysics. Lately this problem has been successfully addressed, and in this review we summarize some of the most important theoretical advances in the theory of grain alignment by radiative torques (RATs) that act on realistic irregular dust grains. We discuss an analytical model of RATs and the ways to make RAT alignment more efficient, e.g. through paramagnetic relaxation when grains have inclusions with strong magnetic response. For very small grains for which RAT alignment is inefficient, we also discuss paramagnetic relaxation and a process termed resonance relaxation. We provide an extensive analysis of the observational tests of grain alignment theory.
    RelaxationDust grainCometMolecular cloudInterstellar mediumAccretion diskMagnetic fieldResonance...
  • It is still unclear how common the Sun is when compared to other similar stars in regards to some of its physical properties, such as rotation. Considering that gyrochronology relations are widely used today to estimate ages of stars in the main sequence, and that the Sun is used to calibrate it, it is crucial to assess if these procedures are acceptable. We analyze the rotational velocities -- limited by the unknown rotation axis inclination angle -- of an unprecedented large sample of solar twins in order to study the rotational evolution of Sun-like stars, and assess if the Sun is a typical rotator. We use high-resolution ($R = 115000$) spectra obtained with the HARPS spectrograph and ESO's 3.6 m telescope at La Silla Observatory. The projected rotational velocities for 82 solar twins are estimated by line profile fitting with synthetic spectra. Macroturbulence velocities are inferred from a prescription that accurately reflects their dependence with effective temperature and luminosity of the stars. Our sample of solar twins include some spectroscopic binaries with enhanced rotational velocities, and we do not find any non-spectroscopic binaries with unusually high rotation velocities. We verified that the Sun does not have a peculiar rotation, but the solar twins exhibit rotational velocities that depart from the Skumanich relation. The Sun is a regular rotator when compared to solar twins with a similar age. Additionally, we obtain a rotational braking law that better describes the stars in our sample ($v \propto t^{-0.6}$) in contrast to previous, often-used scalings.
    SunStarSpectral lineSpectroscopic binaryHigh accuracy radial velocity planetary searchCompanionChromosphereCross-correlation functionCalibrationMain sequence star...
  • We report on the results of a search for $\gamma$-ray pair halos with a stacking analysis of low-redshift blazars using data from the Fermi Large Area Telescope. For this analysis we used a number of a-priori selection criteria, including the spatial and spectral properties of the Fermi sources. The angular distribution of $\sim$ 1GeV photons around 24 stacked isolated high-synchrotron-peaked BL Lacs with redshift $z<0.5$ shows an excess over that of point-like sources. A statistical analysis yields a Bayes factor of $\mathrm{log}_{10}B_{10}>2$, providing evidence in favor of extended emission against the point-source hypothesis, consistent with expectations for pair halos produced in the IGMF with strength $B_{\mathrm{IGMF}}\sim 10^{-17}-10^{-15}\mathrm{G}$.
    Intergalactic magnetic fieldNull hypothesisFlat spectrum radio quasarBayes factorTest statisticPoint sourceBlazarFERMI telescopePulsarFrequentist approach...
  • Helical intergalactic magnetic fields at the $\sim 10^{-14}~{\rm G}$ level on $\sim 10~{\rm Mpc}$ length scales are indicated by current gamma ray observations. The existence of magnetic fields in cosmic voids and their non-trivial helicity suggest that they must have originated in the early universe and thus have implications for the fundamental interactions. I combine present knowledge of the observational constraints and the dynamics of cosmological magnetic fields to derive characteristics that would need to be explained by the magnetic field generation mechanism. The importance of CP violation and a possible crucial role for chiral effects in the early universe are pointed out.
    HelicityIntergalactic magnetic fieldThe early UniverseDissipationCP violationMagnetic helicityMagnetic field generationChiralityChiral magnetic effectVoid...
  • Time is a parameter playing a central role in our most fundamental modelling of natural laws. Relativity theory shows that the comparison of times measured by different clocks depends on their relative motions and on the strength of the gravitational field in which they are embedded. In standard cosmology, the time parameter is the one measured by fundamental clocks, i.e. clocks at rest with respect to the expanding space. This proper time is assumed to flow at a constant rate throughout the whole history of the Universe. We make the alternative hypothesis that the rate at which cosmological time flows depends on the global geometric curvature the Universe. Using a simple one-parameter model for the relation between proper time and curvature, we build a cosmological model that fits the Type Ia Supernovae data (the best cosmological standard candles) without the need for dark energy nor probably exotic dark matter.
    CosmologyProper timeSupernova Type IaCurvatureDark energyGeneral relativityCosmological modelDark matterGravitational fieldsLambda-CDM model...
  • In view of the projected high number of produced $B$ mesons in Belle II experiment ($\sim 10^{10}$ per year), in addition to the presently ongoing LHC-b, we calculate the rate of decay for the rare decays of $B$ mesons via a sterile on-shell neutrino $N$, which subsequently may decay leptonically or semileptonically within the detector: $B \to (D^{(*)}) \ell_1^{\pm} N$, then $N \to \ell_1^{\pm} \ell_2^{\mp} \nu$ or $N \to \ell^{\pm} \pi^\mp$. Here, $\ell_1 \not= \ell_2$ in order to avoid serious QED background. We account for the possible effects of the strong neutrino lifetime on the observability of the rare decays. If no charmed mesons ($D^{(*)}$) are produced at the first vertex of the sterile neutrino, a strong CKM-suppression becomes effective; this is not true if we consider instead the decays of $B_c$ mesons which can be produced copiously in LHC-b. The production of charmed mesons $D^{(*)}$ at the first vertex offers an attractive possibility because it avoids strong CKM-suppression. Such rare decays of $B$ mesons could be detected at Belle II experiment, with $N$ neutrino either decaying within the detector or manifesting itself as a massive missing momentum.
    NeutrinoDecay widthBranching ratioRare decaySterile neutrinoBELLE IIForm factorCKM suppressionLHCbCharged lepton...
  • Galaxy cluster Abell 3827 hosts the stellar remnants of four almost equally bright elliptical galaxies within a core of radius 10kpc. Such corrugation of the stellar distribution is very rare, and suggests recent formation by several simultaneous mergers. We map the distribution of associated dark matter, using new Hubble Space Telescope imaging and VLT/MUSE integral field spectroscopy of a gravitationally lensed system threaded through the cluster core. We find that each of the central galaxies retains a dark matter halo, but that (at least) one of these is spatially offset from its stars. The best-constrained offset is 1.62+/-0.48kpc, where the 68% confidence limit includes both statistical error and systematic biases in mass modelling. Such offsets are not seen in field galaxies, but are predicted during the long infall to a cluster, if dark matter self-interactions generate an extra drag force. With such a small physical separation, it is difficult to definitively rule out astrophysical effects operating exclusively in dense cluster core environments - but if interpreted solely as evidence for self-interacting dark matter, this offset implies a cross-section sigma/m=(1.7+/-0.7)x10^{-4}cm^2/g x (t/10^9yrs)^{-2}, where t is the infall duration.
    Cluster of galaxiesDark matterCluster coreAbell 3827Statistical errorGravitational lensingStar formationStrong gravitational lensingMass distributionMonte Carlo Markov chain...
  • Over the past century, rooted in the theory of general relativity, cosmology has developed a very successful physical model of the universe: the {\em big-bang model}. Its construction followed different stages to incorporate nuclear processes, the understanding of the matter present in the universe, a description of the early universe and of the large scale structure. This model has been confronted to a variety of observations that allow one to reconstruct its expansion history, its thermal history and the structuration of matter. Hence, what we refer to as the big-bang model today is radically different from what one may have had in mind a century ago. This construction changed our vision of the universe, both on observable scales and for the universe as a whole. It offers in particular physical models for the origins of the atomic nuclei, of matter and of the large scale structure. This text summarizes the main steps of the construction of the model, linking its main predictions to the observations that back them up. It also discusses its weaknesses, the open questions and problems, among which the need for a dark sector including dark matter and dark energy.
    CosmologyBig BangGeneral relativityScalar fieldLarge scale structureHomogenizationThermalisationDark matterInflatonCosmological model...
  • This paper discusses about PSF, an R package for Pattern Sequence based Forecasting (PSF) algorithm used for univariate time series future prediction. The PSF algorithm consists of two major parts: clustering and prediction techniques. Clustering part includes selection of cluster size and then labeling of time series data with reference to various clusters. Whereas, the prediction part include functions like optimum window size selection for specific patterns and prediction of future values with reference to past pattern sequences. The PSF package consists of various functions to implement PSF algorithm. It also contains a function, which automates all other functions to obtain optimum prediction results. The aim of this package is to promote PSF algorithm and to ease its implementation with minimum efforts. This paper describe all the functions in PSF package with their syntax and simple examples. Finally, the usefulness of this package is discussed by comparing it with auto.arima, a well known time series forecasting function available on CRAN repository.
    Cluster analysisTime SeriesSilhouetteK-means clusteringDavies-Bouldin indexElectric vehicleCluster labelingData clusterForecast errorK-means++...
  • An analysis of the physics-rich endgame of reionization at $z=5.7$ is performed, utilizing jointly the observations of the Ly$\alpha$ forest, the mean free path of ionizing photons, the luminosity function of galaxies and new physical insight. We find that an upper limit on ${\rm \tau_e}$ provides a constraint on the minimum mean free path (of ionizing photons) that is primarily due to dwarf galaxies, which in turn yields a new and yet the strongest constraint on the matter power spectrum on $10^6-10^9M_\odot$ scales. With the latest Planck measurements of ${\rm \tau_e = 0.055 \pm 0.009}$, we can place an upper limit of $(8.9\times 10^6, 3.8\times 10^7, 4.2\times 10^8)M_\odot$ on the lower cutoff mass of the halo mass function, or equivalent a lower limit on warm dark matter particle mass ${\rm m_x \ge (15.1, 9.8, 4.6)keV}$ or on sterile neutrino mass ${\rm m_s \ge (161, 90, 33)keV}$, at $(1, 1.4, 2.2)\sigma$ confidence level, respectively.
    Intergalactic mediumIonizing radiationIonizationReionizationMean free pathLyc photonPopulation IIIH II regionLuminosity functionMatter power spectrum...