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  • The formation of the disk and feedback from supernova winds impacts the distribution of dark matter in galaxies. Recently, Di Cintio et al. (2014b) characterized the halo response from baryonic processes in hydrodynamical simulations via a dependence on the ratio of stellar-to-halo mass ($M_{\star}/M_{{\rm halo}}$). The (stellar) mass dependent halo profile links together the local and global properties of the halo (e.g. inner slope and $M_{{\rm halo}}$) which allows for measurements of $M_{{\rm halo}}$ without virial tracers. We compile a large sample of rotation curves from the literature to test this halo profile. We find that this halo profile can explain rotation curve observations over a wide range of $M_{\star}$. However, the global results from our sample are inconsistent with a $\Lambda$ cold dark matter universe. We do not find the expected correlation between the halo concentration and $M_{{\rm halo}}$ and there is significantly larger scatter than expected. Furthermore, a large portion of galaxies below $M_{\star} \sim 10^{9}\,M_{\odot}$ are found to be hosted by smaller halos than expectations from the abundance matching technique. We find our results are robust to statistical priors and systematic effects such as inclination angle, asymmetric drift correction, data source, and uncertainties in stellar mass-to-light ratios. This suggests either a mischaracterization of the halo response due to baryonic processes or additional non-standard dark matter physics.
    Rotation CurveDark matterHydrodynamical simulationsInner slopeCosmologyHalo abundance matchingAsymmetric driftCold dark matterCircular velocityPressure support...
  • We report on a numerical study of real-time dynamics of electromagnetically interacting chirally imbalanced lattice Dirac fermions within the classical statistical field theory approach. Namely, we perform exact simulations of the real-time quantum evolution of fermionic fields coupled to classical electromagnetic fields, which are in turn coupled to the vacuum expectation value of the fermionic electric current. We use Wilson-Dirac Hamiltonian for fermions, and non-compact action for the gauge field. In general, we observe that the backreaction of fermions on the electromagnetic field prevents the system from acquiring chirality imbalance. In the case of chirality pumping in parallel electric and magnetic fields, electric field is screened by the produced on-shell fermions and the accumulation of chirality is hence stopped. In the case of evolution with initially present chirality imbalance, axial charge tends to transform to helicity of electromagnetic field. By performing simulations on large lattices we show that in most cases this decay process is accompanied by the inverse cascade phenomenon which transfers energy from short-wavelength to long-wavelength electromagnetic fields. In some simulations, however, we observe a very clear signature of inverse cascade for the helical magnetic fields which is not accompanied by the axial charge decay. This suggests that the relation between inverse cascade and axial charge decay is not as straightforward as predicted by the simplest form of anomalous Maxwell equations.
    Axial chargeChiralityHelicityHamiltonianChiral plasma instabilityInverse cascadeElectricity and magnetismAnomalous Maxwell equationsGauge fieldChirality imbalance...
  • 1605.06795  ,  ,  et al.,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  show less
    The main physical results on the registration of solar neutrinos and the search for rare processes obtained by the Borexino collaboration to date are presented.
    BorexinoSolar neutrinoNeutrinoScintillationSolar axionLaboratori Nazionali del Gran SassoSunStandard solar modelCNO cycleAxion...
  • 1605.03507  ,  ,  et al.,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  show less
    We investigate constraints on cosmic reionization extracted from the Planck cosmic microwave background (CMB) data. We combine the Planck CMB anisotropy data in temperature with the low-multipole polarization data to fit {\Lambda}CDM models with various parameterizations of the reionization history. We obtain a Thomson optical depth {\tau}=0.058 +/- 0.012 for the commonly adopted instantaneous reionization model. This confirms, with only data from CMB anisotropies, the low value suggested by combining Planck 2015 results with other data sets and also reduces the uncertainties. We reconstruct the history of the ionization fraction using either a symmetric or an asymmetric model for the transition between the neutral and ionized phases. To determine better constraints on the duration of the reionization process, we also make use of measurements of the amplitude of the kinetic Sunyaev-Zeldovich (kSZ) effect using additional information from the high resolution Atacama Cosmology Telescope and South Pole Telescope experiments. The average redshift at which reionization occurs is found to lie between z=7.8 and 8.8, depending on the model of reionization adopted. Using kSZ constraints and a redshift-symmetric reionization model, we find an upper limit to the width of the reionization period of {\Delta}z < 2.8. In all cases, we find that the Universe is ionized at less than the 10% level at redshifts above z~10. This suggests that an early onset of reionization is strongly disfavoured by the Planck data. We show that this result also reduces the tension between CMB-based analyses and constraints from other astrophysical sources.
    Planck missionReionizationHistory of the reionizationReionization modelsCMB temperature anisotropyIonizationCosmic microwave backgroundPlanck dataIonization fractionKinetic Sunyaev-Zel'dovich effect...
  • The intrinsic escape fraction of ionizing Lyman continuum photons ($f_{esc}$) is crucial to understand whether galaxies are capable of reionizing the neutral hydrogen in the early universe at z>6. Unfortunately, it is not possible to access $f_{esc}$ at z>4 with direct observations and the handful of measurements from low redshift galaxies consistently find $f_{esc}$ < 10%, while at least $f_{esc}$ ~ 10% is necessary for galaxies dominate reionization. Here, we present the first empirical prediction of $f_{esc}$ at z>6 by combining the (sparsely populated) relation between [OIII]/[OII] and $f_{esc}$ with the redshift evolution of [OIII]/[OII] as predicted from local high-z analogs selected by their H$\alpha$ equivalent-width. We find $f_{esc}$ = $5.7_{-3.3}^{+8.3}$% at z=6 and $f_{esc}$ = $10.4_{-6.3}^{+15.5}$% at z=9 for galaxies with log(M/M$_{sun}$) ~ 9.0 (errors given as 1$\sigma$). However, there is a negative correlation with stellar mass and we find up to 50% larger $f_{esc}$ per 0.5 dex decrease in stellar mass. The population averaged escape fraction increases according to $f_{esc}$ = $f_{esc,0} ((1+z)/3)^a$, with $f_{esc,0} = 2.3 \pm 0.05$% and $a=1.17 \pm 0.02$ at z > 2 for log(M/M$_{sun}$) ~ 9.0. With our empirical prediction of $f_{esc}$ (thus fixing an important previously unknown variable) and further reasonable assumption on clumping factor and the production efficiency of Lyman continuum photons, we conclude that the average population of galaxies is just capable to reionize the universe by z ~ 6.
    Stellar massExtended stellar componentsLyman recombination continuaReionizationIonizationHigh-redshift galaxyLuminosity functionIntergalactic mediumThe early UniverseSloan Digital Sky Survey...
  • We constrain the internal dynamics of a stack of 10 clusters from the GCLASS survey at 0.87<z<1.34. We determine the stack cluster mass profile M(r) using the MAMPOSSt algorithm of Mamon et al., the velocity anisotropy profile beta(r) from the inversion of the Jeans equation, and the pseudo-phase-space density profiles Q(r) and Qr(r), obtained from the ratio between the mass density profile and the third power of the (total and, respectively, radial) velocity dispersion profiles of cluster galaxies. Several M(r) models are statistically acceptable for the stack cluster (Burkert, Einasto, Hernquist, NFW). The total mass distribution has a concentration c=r200/r-2=4.0-0.6+1.0, in agreement with theoretical expectations, and is less concentrated than the cluster stellar-mass distribution. The stack cluster beta(r) is similar for passive and star-forming galaxies and indicates isotropic galaxy orbits near the cluster center and increasingly radially elongated with increasing cluster-centric distance. Q(r) and Qr(r) are almost power-law relations with slopes similar to those predicted from numerical simulations of dark matter halos. Combined with results obtained for lower-z clusters we determine the dynamical evolution of galaxy clusters, and compare it with theoretical predictions. We discuss possible physical mechanisms responsible for the differential evolution of total and stellar mass concentrations, and of passive and star-forming galaxy orbits [abridged].
    Stellar massAnisotropyNavarro-Frenk-White profileCluster of galaxiesBrightest cluster galaxyJeans equationCosmologyMass profileNumerical simulationVelocity dispersion profile...
  • Using a sample of dwarf irregular galaxies selected from the ALFALFA blind HI-survey and observed using the VIMOS IFU, we investigate the relationship between H$\alpha$ emission and Balmer optical depth ($\tau_{\text{b}}$). We find a positive correlation between H$\alpha$ luminosity surface density and Balmer optical depth in 8 of 11 at $\geq$ 0.8$\sigma$ significance (6 of 11 at $\geq$ 1.0$\sigma$) galaxies. Our spaxels have physical scales ranging from 30 to 80 pc, demonstrating that the correlation between these two variables continues to hold down to spatial scales as low as 30 pc. Using the Spearman's rank correlation coefficient to test for correlation between $\Sigma_{\text{H}\alpha}$ and $\tau_{\text{b}}$ in all the galaxies combined, we find $\rho = 0.39$, indicating a positive correlation at 4$\sigma$ significance. Our low stellar-mass galaxy results are in agreement with observations of emission line regions in larger spiral galaxies, indicating that this relationship is independent of the size of the galaxy hosting the emission line region. The positive correlation between H$\alpha$ luminosity and Balmer optical depth within spaxels is consistent with the hypothesis that young star-forming regions are surrounded by dusty birth-clouds.
    Star formation rateDwarf irregular galaxyLuminositySmall Magellanic CloudReddeningALFALFA surveyDwarf galaxyCalibrationStar-forming regionStellar mass...
  • We present an argument that radio galaxies (active galaxies with mis-aligned jets) are likely to be the primary sources of the high-energy astrophysical neutrinos observed by IceCube. In particular, if the gamma-ray emission observed from radio galaxies is generated through the interactions of cosmic-ray protons with gas, these interactions can also produce a population of neutrinos with a flux and spectral shape similar to that measured by IceCube. We present a simple physical model in which high-energy cosmic rays are confined within the volumes of radio galaxies, where they interact with gas to generate the observed diffuse fluxes of neutrinos and gamma rays. In addition to simultaneously accounting for the observations of Fermi and IceCube, radio galaxies in this model also represent an attractive class of sources for the highest energy cosmic rays.
    Radio galaxyIceCube Neutrino ObservatoryNeutrinoNeutrino fluxCosmic rayUltra-high-energy cosmic rayActive galaxyCentaurus AElectromagnetic cascadeCosmic ray protons...
  • We investigate the process of reionisation in a model in which the dark matter is a warm elementary particle such as a sterile neutrino. We focus on models that are consistent with the dark matter decay interpretation of the recently detected line at 3.5 keV in the X-ray spectra of galaxies and clusters. In warm dark matter models the primordial spectrum of density perturbations has a cut-off on the scale of dwarf galaxies. Structure formation therefore begins later than in the standard cold dark matter (CDM) model and very few objects form below the cut-off mass scale. To calculate the number of ionising photons, we use the Durham semi-analytic model of galaxy formation, GALFORM. We find that even the most extreme 7 keV sterile neutrino we consider is able to reionise the Universe early enough to be compatible with the bounds on the epoch of reionisation from Planck. This, perhaps surprising, result arises from the rapid build-up of high redshift galaxies in the sterile neutrino models which is also reflected in a faster evolution of their far-UV luminosity function between $10>z>7$ than in CDM. The dominant sources of ionising photons are systematically more massive in the sterile neutrino models than in CDM. As a consistency check on the models, we calculate the present-day luminosity function of satellites of Milky Way-like galaxies. When the satellites recently discovered in the DES survey are taken into account, strong constraints are placed on viable sterile neutrino models.
    Sterile neutrinoCold dark matterReionizationLuminosity functionIonizing radiationGalaxy FormationWarm dark matterKeV sterile neutrinosDark matterCosmology...
  • We investigate the region around the Planck-detected z=3.26 gravitationally lensed galaxy HATLAS J114637.9-001132 (hereinafter HATLAS12-00) using both archival Herschel data from the H-ATLAS survey and using submm data obtained with both LABOCA and SCUBA2. The lensed source is found to be surrounded by a strong overdensity of both Herschel-SPIRE sources and submm sources. We detect 17 bright (S_870 >~7 mJy) sources at >4sigma closer than 5 arcmin to the lensed object at 850/870 microns. Ten of these sources have good cross-identifications with objects detected by Herschel-SPIRE which have redder colours than other sources in the field, with 350 micron flux > 250 micron flux, suggesting that they lie at high redshift. Submillimeter Array (SMA) observations localise one of these companions to ~1 arcsecond, allowing unambiguous cross identification with a 3.6 and 4.5 micron Spitzer source. The optical/near-IR spectral energy distribution (SED) of this source is measured by further observations and found to be consistent with z>2, but incompatible with lower redshifts. We conclude that this system may be a galaxy cluster/protocluster or larger scale structure that contains a number of galaxies undergoing starbursts at the same time.
    Spectral energy distributionCalibrationCompanionProtoclustersPhotometryStar-forming galaxySubmillimeter ArrayAtacama Pathfinder ExperimentFull width at half maximumLuminosity...
  • We present two new examples of galaxies undergoing transformation in the Shapley supercluster core. These low-mass (stellar mass from 0.4E10 to 1E10 Msun) galaxies are members of the two clusters SC-1329-313 (z=0.045) and SC-1327-312 (z=0.049). Integral-field spectroscopy complemented by imaging in ugriK bands and in Halpha narrow-band are used to disentangle the effects of tidal interaction (TI) and ram-pressure stripping (RPS). In both galaxies, SOS-61086 and SOS-90630, we observe one-sided extraplanar ionized gas extending respectively 30kpc and 41kpc in projection from their disks. The galaxies' gaseous disks are truncated and the kinematics of the stellar and gas components are decoupled, supporting the RPS scenario. The emission of the ionized gas extends in the direction of a possible companion for both galaxies suggesting a TI. The overall gas velocity field of SOS-61086 is reproduced by ad hoc N-body/hydrodynamical simulations of RPS acting almost face-on and starting about 250Myr ago, consistent with the age of the young stellar populations. A link between the observed gas stripping and the cluster-cluster interaction experienced by SC-1329-313 and A3562 is suggested. Simulations of ram pressure acting almost edge-on are able to fully reproduce the gas velocity field of SOS-90630, but cannot at the same time reproduce the extended tail of outflowing gas. This suggests that an additional disturbance from a TI is required. This study adds a piece of evidence that RPS may take place in different environments with different impacts and witnesses the possible effect of cluster-cluster merger on RPS.
    Star formationRam pressureIntra-cluster mediumShapley SuperclusterKinematicsStellar populationsSignal to noise ratioRam pressure strippingTidal interactionStellar mass...
  • The study of carbon and oxygen abundances yields information on the time evolution and nucleosynthetic origins of these elements, yet remains relatively unexplored. At low metallicities (12+log(O/H) < 8.0), nebular carbon measurements are limited to rest-frame UV collisionally excited emission lines. Therefore, we present UV spectrophotometry of 12 nearby, low-metallicity, high-ionization HII regions in dwarf galaxies obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope. We present the first analysis of the C/O ratio in local galaxies based solely on simultaneous significant detections of the UV O^+2 and C^+2 collisionally excited lines in seven of our targets and five objects from the literature, to create a final sample of 12 significant detections. Our sample is complemented by optical SDSS spectra, from which we measured the nebular physical conditions and oxygen abundances using the direct method. At low metallicity (12+log(O/H) < 8.0), no clear trend is evident in C/O vs. O/H for the present sample given the large dispersion observed. When combined with recombination line observations at higher values of O/H, a general trend of increasing C/O with increasing O/H is also viable, but with some significant outliers. Additionally, we find the C/N ratio appears to be constant (but with significant scatter) over a large range in oxygen abundance, indicating carbon is predominantly produced by similar nucleosynthetic mechanisms as nitrogen. If true, and our current understanding of nitrogen production is correct, this would indicate that primary production of carbon (a flat trend) dominates at low metallicity, but quasi-secondary production (an increasing trend) becomes prominent at higher metallicities. A larger sample will be needed to determine the true nature and dispersion of the relation.
    AbundanceStarSloan Digital Sky SurveyDwarf galaxyIonizationInitial mass functionMassive starsElectron temperatureReddeningHubble Space Telescope...
  • The dust emissivity spectral index, $\beta$, is a critical parameter for deriving the mass and temperature of star-forming structures, and consequently their gravitational stability. The $\beta$ value is dependent on various dust grain properties, such as size, porosity, and surface composition, and is expected to vary as dust grains evolve. Here we present $\beta$, dust temperature, and optical depth maps of the star-forming clumps in the Perseus Molecular Cloud determined from fitting SEDs to combined Herschel and JCMT observations in the 160 $\mu$m, 250 $\mu$m, 350 $\mu$m, 500 $\mu$m, and 850 $\mu$m bands. Most of the derived $\beta$, and dust temperature values fall within the ranges of 1.0 - 2.7 and 8 - 20 K, respectively. In Perseus, we find the $\beta$ distribution differs significantly from clump to clump, indicative of grain growth. Furthermore, we also see significant, localized $\beta$ variations within individual clumps and find low $\beta$ regions correlate with local temperature peaks, hinting at the possible origins of low $\beta$ grains. Throughout Perseus, we also see indications of heating from B stars and embedded protostars, as well evidence of outflows shaping the local landscape.
    Spectral energy distributionYoung stellar objectStar formationNGC 1333Dust grainB starIC 348Dust emissionLine of sightCalibration...
  • We present optical and near-infrared photometric and spectroscopic observations of SN 2013ej, in galaxy M74, from 1 to 450 days after the explosion. SN 2013ej is a hydrogen-rich supernova, classified as a Type IIL due to its relatively fast decline following the initial peak. It has a relatively high peak luminosity (absolute magnitude M$_\rm{V}$ = -17.6) but a small $^{56}$Ni production of ~0.023 M$_\odot$. Its photospheric evolution is similar to other Type II SNe, with shallow absorption in the H{\alpha} profile typical for a Type IIL. During transition to the radioactive decay tail at ~100 days, we find the SN to grow bluer in B - V colour, in contrast to some other Type II supernovae. At late times, the bolometric light curve declined faster than expected from $^{56}$Co decay and we observed unusually broad and asymmetric nebular emission lines. Based on comparison of nebular emission lines most sensitive to the progenitor core mass, we find our observations are best matched to synthesized spectral models with a M$_\rm{ZAMS}$ = 12 - 15 M$_\odot$ progenitor. The derived mass range is similar to but not higher than the mass estimated for Type IIP progenitors. This is against the idea that Type IIL are from more massive stars. Observations are consistent with the SN having a progenitor with a relatively low-mass envelope.
    SupernovaLight curveNear-infraredEjectaPhotometryCalibrationTelescopesPhotosphereAbsorptivityZero-age main sequence stars...
  • Phosphorus is a crucial element in biochemistry, especially the P-O bond, which is key for the formation of the backbone of the deoxyribonucleic acid. So far, PO has only been detected towards the envelope of evolved stars, and never towards star-forming regions. We report the first detections of PO towards two massive star-forming regions, W51 e1/e2 and W3(OH), using data from the IRAM 30m telescope. PN has also been detected towards the two regions. The abundance ratio PO/PN is 1.8 and 3 for W51 and W3(OH), respectively. Our chemical model indicates that the two molecules are chemically related and are formed via gas-phase ion-molecule and neutral-neutral reactions during the cold collapse. The molecules freeze out onto grains at the end of the collapse and desorb during the warm-up phase once the temperature reaches 35 K. Similar abundances of the two species are expected during a period of 5x10^{4} yr at the early stages of the warm-up phase, when the temperature is in the range 35-90 K. The observed molecular abundances of 10^{-10} are predicted by the model if a relatively high initial abundance of 5x10^{-9} of depleted phosphorus is assumed.
    AbundanceStar-forming regionTelescopesInterstellar mediumPrebioticIRAM 30-mIntensityEvolved starsFreeze-outOpacity...
  • The set-up of the initial conditions in cosmological N-body simulations is usually implemented by rescaling the desired low-redshift linear power spectrum to the required starting redshift consistently with the Newtonian evolution of the simulation. The implementation of this practical solution requires more care in the context of massive neutrino cosmologies, mainly because of the non-trivial scale-dependence of the linear growth that characterises these models. In this work we consider a simple two-fluid, Newtonian approximation for cold dark matter and massive neutrinos perturbations that can reproduce the cold matter linear evolution predicted by Boltzmann codes such as CAMB or CLASS with a 0.1% accuracy or below for all redshift relevant to nonlinear structure formation. We use this description, in the first place, to quantify the systematic errors induced by several approximations often assumed in numerical simulations, including the typical set-up of the initial conditions for massive neutrino cosmologies adopted in previous works. We then take advantage of the flexibility of this approach to rescale the late-time linear power spectra to the simulation initial redshift, in order to be as consistent as possible with the dynamics of the N-body code and the approximations it assumes. We implement our method in a public code providing the initial displacements and velocities for cold dark matter and neutrino particles that will allow accurate, i.e. one-percent level, numerical simulations for this cosmological scenario.
    NeutrinoMassive neutrinoCosmologyBoltzmann codeN-body simulationSystematic errorCold dark matterMatter power spectrumNumerical simulationNeutrino mass...
  • Cold dark matter (CDM) is a well established paradigm to describe cosmological structure formation, and works extraordinarily well on large, linear, scales. Progressing further in dark matter physics requires being able to understand structure formation in the non-linear regime, both for CDM and its alternatives. This short note describes a calculation, and accompanying code, WarmAndFuzzy, incorporating the popular models of warm and fuzzy dark matter (WDM and FDM) into the standard halo model to compute the non-linear matter power spectrum. The FDM halo model power spectrum has not been computed before. The FDM implementation models ultralight axions and other scalar fields with $m_a\approx 10^{-22}\text{ eV}$. The WDM implementation models thermal WDM with mass $m_X\approx 1\text{ keV}$. The halo model shows that differences between WDM, FDM, and CDM survive at low redshifts in the quasi-linear and fully non-linear regimes. The code uses analytic transfer functions for the linear power spectrum, modified collapse barriers in the halo mass function, and a modified concentration-mass relationship for the halo density profiles. Modified halo density profiles (for example, cores) are not included, but are under development. Cores are expected to have very minor effects on the power spectrum on observable scales. Applications of this code to the Lyman-$\alpha$ forest flux power spectrum and the cosmic microwave background lensing power spectrum will be discussed in companion papers. \textsc{WarmAndFuzzy} is available online at \url{https://github.com/DoddyPhysics/HMcode}, where collaboration in development is welcomed.
    Warm dark matterCold dark matterHalo modelHalo mass functionTransfer functionHalo density profileMessier 15Dark matterNavarro-Frenk-White profileVirial mass...
  • In this work, we consider the cosmological constant model $\Lambda\propto\alpha^{-6}$, which is well motivated from three independent approaches. As is well known, the evidence of varying fine structure constant $\alpha$ was found in 1998. If $\Lambda\propto\alpha^{-6}$ is right, it means that the cosmological constant $\Lambda$ should be also varying. In this work, we try to develop a suitable framework to model this varying cosmological constant $\Lambda\propto\alpha^{-6}$, in which we view it from an interacting vacuum energy perspective. We propose two types of models to describe the evolutions of $\Lambda$ and $\alpha$. Then, we consider the observational constraints on these models, by using the 293 $\Delta\alpha/\alpha$ data from the absorption systems in the spectra of distant quasars, and the data of type Ia supernovae (SNIa), cosmic microwave background (CMB), baryon acoustic oscillation (BAO). We find that the model parameters can be tightly constrained to the narrow ranges of ${\cal O}(10^{-5})$ typically. In particular, 3 of 4 models considered in this work favor the varying $\Lambda$ and $\alpha$, while $\Lambda$CDM model and $\alpha=const.$ deviate from the best fit beyond $2\sigma$ or at least $1\sigma$. On the other hand, we can also view the varying cosmological constant model $\Lambda\propto\alpha^{-6}$ from another perspective, namely it can be equivalent to a model containing "dark energy" (whose equation-of-state parameter (EoS) $w_{de}\not=-1$) and "warm dark matter" (whose EoS $w_{dm}\not=0$), but there is no interaction between them. We derive the effective EoS of "warm dark matter" and "dark energy", and find that they are fully consistent with the observational constraints on warm dark matter. We consider that the varying cosmological constant model $\Lambda\propto\alpha^{-6}$ is viable and deserves further studies.
    Cosmological constantWarm dark matterFine structure constantVacuum energyCosmic microwave backgroundBaryon acoustic oscillationsSupernova Type IaLambda-CDM modelDark energyAbsorptivity...
  • Recent reports of a weak unidentified emission line at ~3.5 keV found in spectra of several matter-dominated objects may give a clue to resolve the long-standing problem of dark matter. One of the best physically motivated particle candidate able to produce such an extra line is sterile neutrino with the mass of ~7 keV. Previous works show that sterile neutrino dark matter with parameters consisting with the new line measurement modestly affects structure formation compared to conventional cold dark matter scenario. In this work, we concentrate on contribution of the sterile neutrino dark matter to the process of reionization. By incorporating dark matter power spectra for ~7 keV sterile neutrinos into extended semi-analytical 'bubble' model of reionization we obtain that such a dark matter would produce significantly sharper reionization compared to widely used cold dark matter models, impossible to 'imitate' within the cold dark matter scenario under any reasonable choice of our model parameters, and would have a clear tendency of lowering both the redshift of reionization and the electron scattering optical depth (although the difference is still below the existing model uncertainties). Further dedicated studies of reionization (such as 21 cm measurements or studies of kinetic Sunyaev-Zeldovich effect) will thus be essential for reconstruction of particle candidate responsible the ~3.5 keV line.
    ReionizationSterile neutrino DMDark matterCold dark matterSterile neutrinoRecombinationIonizing radiationIonizationStarKeV sterile neutrinos...
  • Deep observations of galaxies reveal faint extended stellar components (hereafter ESCs) of streams, shells, and halos. These are a natural prediction of hierarchical galaxy formation, as accreted satellite galaxies are tidally disrupted by their host. We investigate whether or not global properties of the ESC could be used to test of dark matter, reasoning that they should be sensitive to the abundance of low-mass satellites, and therefore the underlying dark matter model. Using cosmological simulations of galaxy formation in the favoured Cold Dark Matter (CDM) and Warm Dark Matter (WDM) models ($m_{\rm WDM}$=0.5,1,2 keV/$c^2$), which suppress the abundance of low-mass satellites, we find that the kinematics and orbital structure of the ESC is consistent across models. However, we find striking differences in its spatial structure, as anticipated -- a factor of $\sim$10 drop in spherically averaged mass density between $\sim$10% and $\sim$75% of the virial radius in the more extreme WDM runs ($m_{\rm WDM}$=0.5, 1 keV/$c^2$) relative to the CDM run. These differences are consistent with the mass assembly histories of the different components, and are present across redshifts. However, even the least discrepant of the WDM models is incompatible with current observational limits on $m_{\rm WDM}$. Importantly, the differences we observe when varying the underlying dark matter are comparable to the galaxy-to-galaxy variation we expect within a fixed dark matter model. This suggests that it will be challenging to place limits on dark matter using only the unresolved spatial structure of the the ESC.
    Extended stellar componentsDark matterWarm dark matterCold dark matterDark matter modelAbundanceGalaxy FormationWDM particlesDark matter subhaloStar...
  • Cosmic reionization and dark matter decay can impact observations of the cosmic microwave sky in a similar way. A simultaneous study of both effects is required to constrain unstable dark matter from cosmic microwave background observations. We compare two reionization models with and without dark matter decay. We find that a reionization model that fits also data from quasars and star forming galaxies results in tighter constraints on the reionization optical depth $\tau_{\text{reio}}$, but weaker constraints on the spectral index $n_{\text{s}}$ than the conventional parametrization. We use the Planck 2015 data to constrain the effective decay rate of dark matter to $\Gamma_{\rm eff} < 2.9 \times 10^{-25}/$s at $95$\% C.L. This limit is robust and model independent. It holds for any type of decaying dark matter and it depends only weakly on the chosen parametrization of astrophysical reionization. For light dark matter particles that decay exclusively into electromagnetic components this implies a limit of $\Gamma < 5.3 \times 10^{-26}/$s at $95$\% C.L. Specifying the decay channels, we apply our result to the case of keV-mass sterile neutrinos as dark matter candidates and obtain constraints on their mixing angle and mass, which are comparable to the ones from the diffuse X-ray background.
    ReionizationDark matter decayCode for Anisotropies in the Microwave BackgroundIonizationDark matterCosmic microwave backgroundDecay rateRecombinationQuasarHistory of the reionization...
  • Using a Bayesian framework, we quantify what current observations imply about the history of the epoch of reionisation (EoR). We use a popular, three-parameter EoR model, flexible enough to accommodate a wide range of physically-plausible reionisation histories. We study the impact of various EoR observations: (i) the optical depth to the CMB measured by Planck 2016; (ii) the dark fraction in the Lyman $\alpha$ and $\beta$ forests; (iii) the redshift evolution of galactic Ly$\alpha$ emission (so-called "Ly$\alpha$ fraction"); (iv) the clustering of Ly$\alpha$ emitters; (v) the IGM damping wing imprint in the spectrum of QSO ULASJ1120+0641; (vi) and the patchy kinetic Sunyaev-Zel'dovich signal. Combined, (i) and (ii) already place interesting constraints on the reionisation history, with the epochs corresponding to an average neutral fraction of (75, 50, 25) per cent, constrained at 1$\sigma$ to $z= (9.21\substack{+1.22 \\ -1.15}, 8.14\substack{+1.08 \\ -1.00}, 7.26\substack{+1.13 \\ -0.96})$. Folding-in more model-dependent EoR observations [(iii--vi)], strengthens these constraints by tens of per cent, at the cost of a decrease in the likelihood of the best-fit model, driven mostly by (iii). The tightest constraints come from (v). Unfortunately, no current observational set is sufficient to break degeneracies and constrain the astrophysical EoR parameters. However, model-dependent priors on the EoR parameters themselves can be used to set tight limits by excluding regions of parameter space with strong degeneracies. Motivated by recent observations of $z\sim7$ faint, lensed galaxies, we show how a conservative upper limit on the virial temperature of haloes which host reionising galaxies can constrain the escape fraction of ionising photons to $f_{\rm esc} = 0.14\substack{+0.26 \\ -0.09}$
    Epoch of reionizationReionizationIonization history of the UniverseIntergalactic mediumQuasarDamping Wing of Gunn-Peterson TroughIonizing radiationVirial temperatureCluster of galaxiesLuminosity function...
  • Understanding the formation and evolution of the first stars and galaxies represents one of the most exciting frontiers in astronomy. Since the universe was filled with hydrogen atoms at early times, the most promising probe of the epoch of the first stars is the prominent 21-cm spectral line of hydrogen. Current observational efforts are focused on the cosmic reionization era, but observations of the pre-reionization cosmic dawn are also promising. While observationally unexplored, theoretical studies predict a rich variety of observational signatures from cosmic dawn. As the first stars formed, their radiation (plus that from stellar remnants) produced significant cosmic events including Lyman-alpha coupling at z~25, and early X-ray heating. Much focus has gone to studying the angle-averaged power spectrum of 21-cm fluctuations. Additional probes include the global (sky-averaged) 21-cm spectrum, and the line-of-sight anisotropy of the 21-cm power spectrum. A particularly striking signature may result from the recently recognized effect of a supersonic relative velocity between the dark matter and gas. Work in this field, focused on understanding the whole era of reionization and cosmic dawn with analytical models and numerical simulations, is likely to grow in intensity and importance, as the theoretical predictions are finally expected to confront 21-cm observations in the coming years. [Abridged]
    Hydrogen 21 cm lineReionizationCosmologyNumerical simulationStar formationPopulation IIIStarCosmic microwave background21-cm power spectrumIonization...
  • We present first results from radio observations with the Murchison Widefield Array seeking to constrain the power spectrum of 21 cm brightness temperature fluctuations between the redshifts of 11.6 and 17.9 (113 and 75 MHz). Three hours of observations were conducted over two nights with significantly different levels of ionospheric activity. We use these data to assess the impact of systematic errors at low frequency, including the ionosphere and radio-frequency interference, on a power spectrum measurement. We find that after the 1-3 hours of integration presented here, our measurements at the Murchison Radio Observatory are not limited by RFI, even within the FM band, and that the ionosphere does not appear to affect the level of power in the modes that we expect to be sensitive to cosmology. Power spectrum detections, inconsistent with noise, due to fine spectral structure imprinted on the foregrounds by reflections in the signal-chain, occupy the spatial Fourier modes where we would otherwise be most sensitive to the cosmological signal. We are able to reduce this contamination using calibration solutions derived from autocorrelations so that we achieve an sensitivity of $10^4$ mK on comoving scales $k\lesssim 0.5 h$Mpc$^{-1}$. This represents the first upper limits on the $21$ cm power spectrum fluctuations at redshifts $12\lesssim z \lesssim 18$ but is still limited by calibration systematics. While calibration improvements may allow us to further remove this contamination, our results emphasize that future experiments should consider carefully the existence of and their ability to calibrate out any spectral structure within the EoR window.
    IonosphereCalibrationEpoch of reionizationAutocorrelationIntergalactic mediumReionizationX-ray heatingSystematic errorCosmologyThermalisation...
  • We statistically study the physical properties of a sample of narrow absorption line (NAL) systems looking for empirical evidences to distinguish between intrinsic and intervening NALs without taking into account any a priori definition or velocity cut-off. We analyze the spectra of 100 quasars with 3.5 < z$\rm_{em}$ < 4.5, observed with X-shooter/VLT in the context of the XQ-100 Legacy Survey. We detect a $\sim$ 8 $\sigma$ excess in the number density of absorbers within 10,000 km/s of the quasar emission redshift with respect to the random occurrence of NALs. This excess does not show a dependence on the quasar bolometric luminosity and it is not due to the redshift evolution of NALs. It extends far beyond the standard 5000 km/s cut-off traditionally defined for associated absorption lines. We propose to modify this definition, extending the threshold to 10,000 km/s when also weak absorbers (equivalent width < 0.2 \AA) are considered. We infer NV is the ion that better traces the effects of the quasar ionization field, offering the best statistical tool to identify intrinsic systems. Following this criterion we estimate that the fraction of quasars in our sample hosting an intrinsic NAL system is 33 percent. Lastly, we compare the properties of the material along the quasar line of sight, derived from our sample, with results based on close quasar pairs investigating the transverse direction. We find a deficiency of cool gas (traced by CII) along the line of sight associated with the quasar host galaxy, in contrast with what is observed in the transverse direction.
    QuasarAbsorbanceAbsorptivityEquivalent widthAbsorption lineIonizationStatisticsHost galaxyActive Galactic NucleiLine of sight...
  • The spatial distribution of the satellite populations of the Milky Way and Andromeda are puzzling in that they are nearly perpendicular to the disks of their central galaxies. To understand the origin of such configurations we study the alignment of the central galaxy, satellite system and dark matter halo in the largest of the "Evolution and Assembly of GaLaxies and their Environments" (EAGLE) simulation. We find that centrals and their satellite systems tend to be well aligned with their haloes, with a median misalignment angle of $33^{\circ}$ in both cases. While the centrals are better aligned with the inner $10$ kpc halo, the satellite systems are better aligned with the entire halo indicating that satellites preferentially trace the outer halo. The central - satellite alignment is weak (median misalignment angle of $52^{\circ}$) and we find that around $20\%$ of systems have a misalignment angle larger than $78^{\circ}$, which is the value for the Milky Way. The central - satellite alignment is a consequence of the tendency of both components to align with the dark matter halo. As a consequence, when the central is parallel to the satellite system, it also tends to be parallel to the halo. In contrast, if the central is perpendicular to the satellite system, as in the case of the Milky Way and Andromeda, then the central - halo alignment is much weaker. Dispersion-dominated (spheroidal) centrals have a stronger alignment with both their halo and their satellites than rotation-dominated (disk) centrals. We also found that the halo, the central galaxy and the satellite system tend to be aligned with the surrounding large-scale distribution of matter, with the halo being the better aligned of the three.
    Milky WayLarge scale structureDark matter haloAndromeda galaxyOrientationBetweenness centralityDark matterAccretionSatellite galaxyLocal group...
  • Cosmic voids found in galaxy surveys are defined based on the galaxy distribution in redshift space. We show that the large scale distribution of voids in redshift space traces the fluctuations in the dark matter density field \delta(k) (in Fourier space with \mu being the line of sight projected k-vector): \delta_v^s(k) = (1 + \beta_v \mu^2) b^s_v \delta(k), with a beta factor that will be in general different than the one describing the distribution of galaxies. Only in case voids could be assumed to be quasi-local transformations of the linear (Gaussian) galaxy redshift space field, one gets equal beta factors \beta_v=\beta_g=f/b_g with f being the growth rate, and b_g, b^s_v being the galaxy and void bias on large scales defined in redshift space. Indeed, in our mock void catalogs we measure void beta factors being in good agreement with the galaxy one. Further work needs to be done to confirm the level of accuracy of the beta factor equality between voids and galaxies, but in general the void beta factor needs to be considered as a free parameter for RSD studies.
    VoidRedshift spaceDark matterRedshift-space distortionTwo-point correlation functionBaryon acoustic oscillationsQuadrupoleDensity contrastCross-correlationLine of sight...
  • We provide new exact solutions to the Einstein-Maxwell system of equations for matter configurations with anisotropy and charge. The spacetime is static and spherically symmetric. A quadratic equation of state is utilised for the matter distribution. By specifying a particular form for one of the gravitational potentials and the electric field intensity we obtain new exact solutions in isotropic coordinates. In our general class of models, an earlier model with a linear equation of state is regained. For particular choices of parameters we regain the masses of the stars PSR J1614-2230, 4U 1608-52, PSR J1903+0327, EXO 1745-248 and SAX J1808.4-3658. A comprehensive physical analysis for the star PSR J1903+0327 reveals that our model is reasonable.
    Exact solutionPSR J1903+0327Compact starEquation of statePSR J1614-2230IntensityRegularizationSAX J1808.4-3658StarStellar surfaces...
  • The existence of critical points for the peculiar velocity field is a natural feature of the correlated vector field. These points appear at the junctions of velocity domains with different orientations of their averaged velocity vectors. Since peculiar velocities are the important cause of the scatter in the Hubble expansion rate, we propose that a more precise determination of the Hubble constant can be made by restricting analysis to a subsample of observational data containing only the zones around the critical points of the peculiar velocity field, associated with voids and saddle points. On large-scales the critical points, where the first derivative of the gravitational potential vanishes, can easily be identified using the density field and classified by the behavior of the Hessian of the gravitational potential. We use high-resolution N-body simulations to show that these regions are stable in time and hence are excellent tracers of the initial conditions. Furthermore, we show that the variance of the Hubble flow can be substantially minimized by restricting observations to the subsample of such regions of vanishing velocity instead of aiming at increasing the statistics by averaging indiscriminately using the full data sets, as is the common approach.
    Peculiar velocityCritical pointHubble constantHubble parameterHubble flowStatisticsVoidCosmic microwave backgroundHigh resolution N-body simulationHomogenization...
  • Finding the electromagnetic (EM) counterpart is critically important for a gravitational wave event. Although many efforts have been made to search for the purported EM counterpart of GW150914, the first gravitational wave event detected by LIGO, only Fermi/GBM reported an excess above background (i.e. GW150914-GBM) at 0.4 s after the LIGO trigger time, that is possibly associated with this GW event (Connaughton et al. 2016). However, since there is no significant detection by the INTEGRAL/SPI-ACS around the time of GW150914-GBM, a great debate has been raised about whether GW150914-GBM is of astrophysical origin and associated with the GW150914 (Savchenko et al. 2016). In order to answer this question, we re-analyzed the GBM data with a straightforward but sophisticated method. We find that the excess of GW150914-GBM mostly comes from those detectors with bad viewing angles to the GW event, whereas the good viewing detectors see nothing significant beyond background fluctuation around the trigger time of GW150914. This finding suggests that GW150914-GBM is very unlikely associated with the GW150914. Given that GW150914-GBM is the only event found by GBM that is possibly associated with this GW event in a comprehensive search, we conclude that GBM did not detect any electromagnetic radiation from the GW150914.
    LIGO GW150914 eventGravitational waveLaser Interferometer Gravitational-Wave ObservatoryElectron microscopyFermi/GBMGamma ray burstLight curveBlack holeEarthField of view...
  • Plausibility measures are structures for reasoning in the face of uncertainty that generalize probabilities, unifying them with weaker structures like possibility measures and comparative probability relations. So far, the theory of plausibility measures has only been developed for classical sample spaces. In this paper, we generalize the theory to test spaces, so that they can be applied to general operational theories, and to quantum theory in particular. Our main results are two theorems on when a plausibility measure agrees with a probability measure, i.e. when its comparative relations coincide with those of a probability measure. For strictly finite test spaces we obtain a precise analogue of the classical result that the Archimedean condition is necessary and sufficient for agreement between a plausibility and a probability measure. In the locally finite case, we prove a slightly weaker result that the Archimedean condition implies almost agreement.
    Hahn-Banach theoremVector spaceQuantum theoryGleason's theoremOperator theoryArtificial intelligenceQuantum gravityProjection operatorSecurityStatistical mechanics...
  • Algebraic quantum field theory provides a general, mathematically precise description of the structure of quantum field theories, and then draws out consequences of this structure by means of various mathematical tools -- the theory of operator algebras, category theory, etc.. Given the rigor and generality of AQFT, it is a particularly apt tool for studying the foundations of QFT. This paper is a survey of AQFT, with an orientation towards foundational topics. In addition to covering the basics of the theory, we discuss issues related to nonlocality, the particle concept, the field concept, and inequivalent representations. We also provide a detailed account of the analysis of superselection rules by S. Doplicher, R. Haag, and J. E. Roberts (DHR); and we give an alternative proof of Doplicher and Roberts' reconstruction of fields and gauge group from the category of physical representations of the observable algebra. The latter is based on unpublished ideas due to Roberts and the abstract duality theorem for symmetric tensor *-categories, a self-contained proof of which is given in the appendix.
    Von Neumann algebraCommutantIsomorphismSuperselectionAlgebraic quantum field theoryMorphismIsometryPermutationDualityAutomorphism...
  • Through investigating history, evolution of the concept, and development in the theories of electrons, I am convinced that what was missing in our understanding of the electron is a structure, into which all attributes of the electron could be incorporated in a self-consistent way. It is hereby postulated that the topological structure of the electron is a closed two-turn Helix (a so-called Hubius Helix) that is generated by circulatory motion of a mass-less particle at the speed of light. A formulation is presented to describe an isolated electron at rest and at high speed. It is shown that the formulation is capable of incorporating most (if not all) attributes of the electron, including spin, magnetic moment, fine structure constant, anomalous magnetic moment, and charge quantization into one concrete description of the Hubius Helix. The equations for the description emerge accordingly. Implications elicited by the postulate are elaborated. Inadequacy of the formulation is discussed.
  • A full one-loop calculation of neutralino S-wave annihilation into the $Z\gamma$ final state is performed in the minimal supersymmetric extension of the Standard Model. This process, like the similar one with two photons in the final state, may be of importance for the indirect detection of supersymmetric dark matter through the very narrow $\gamma$ ray line that would result from neutralino annihilations in the galactic halo. We give the complete analytical formulas for this loop-induced process and treat the case of a pure Higgsino as a first application of our expressions. Predictions for the gamma line flux are given for the halo model which is of the form suggested by Kravtsov et al. and for the profile proposed by Navarro, Frenk and White. For heavy neutralinos, the lines from $2\gamma$ and $Z\gamma$ would have indistiguishable energy in a realistic detector, making the fluxes add and facilitating discovery. For lighter neutralinos, the positions and relative strengths of the two lines would give valuable information on the nature of the supersymmetric dark matter particles.
  • For the first time, a full one-loop calculation of the process $\chi\chi\to 2\gamma$ is performed, where $\chi$ is the lightest neutralino in the minimal supersymmetric extension of the Standard Model. This process is of interest for dark matter detection, since it would give a sharp $\gamma$ ray line with $E_\gamma=m_\chi$. We improve upon and correct published formulas, and give cross sections for supersymmetric models with $\chi$ masses between 30 GeV and several TeV. We find a new contribution, previously neglected, which enhances the $2\gamma$ rate for TeV higgsinos by up to an order of magnitude. As a byproduct, we obtain a new expression for the related process $\chi\chi\to 2 gluons$, which on the other hand is generally smaller than previously calculated. There has been a recent claim that evidence for a 3.5 TeV higgsino annihilating into a $\gamma$ line may already exist from balloon emulsion and Air Cherenkov Telescope data. We comment on attractive features and problems with this interpretation.
    NeutralinoHiggsinoDark matterGalactic CenterGalactic haloHalo modelCherenkov telescopeBosonizationEarthSun...
  • In this article, I discuss how the AI community views concerns about the emergence of superintelligent AI and related philosophical issues.
    Artificial intelligenceComputational scienceDeep learningSchedulingMachine learningOptimizationDecision makingClimateAsteroidsOrientation...
  • Scientists pursue collective knowledge, but they also seek personal recognition from their peers. When scientists decide whether or not to work on a big new problem, they weigh the potential rewards of a major discovery against the costs of setting aside other projects. These self-interested choices can potentially spread researchers across problems in an efficient manner, but efficiency is not guaranteed. We use simple economic models to understand such decisions and their collective consequences. Academic science differs from industrial R&D in that academics often share partial solutions to gain reputation. This convention of Open Science is thought to accelerate collective discovery, but we find that it need not do so. The ability to share partial results influences which scientists work on a particular problem; consequently, Open Science can slow down the solution of a problem if it deters entry by important actors.
    Risk dominanceOptimizationSubgameSecurityBest response strategyEconomic modelsNash equilibriumGeneMutationMolecular biology...
  • Mach-Zehnder interferometry has been proposed as a probe for detecting the statistics of anyonic quasiparticles in fractional quantum Hall (FQH) states. Here we focus on interferometers made of multimode edge states with upstream modes. We find that the interference visibility is suppressed due to downstream-upstream mode entanglement; the latter serves as a "which path" detector to the downstream interfering trajectories. Our analysis tackles a concrete realization of filling factor 2/3, but its applicability goes beyond that specific case, and encompasses the recent observation of ubiquitous emergence of upstream neutral modes in FQH states. The latter, according to our analysis, goes hand in hand with the failure to observe Mach-Zehnder anyonic interference in fractional states. We point out how charge-neutral mode disentanglement will resuscitate the interference signal.
    InterferenceNeutral edge modeAnyonElectronic Mach-Zehnder interferometerInterferometersQuantum Hall EffectFractional quantum Hall stateTunneling amplitudesBranch pointInterferometry...
  • Microblogging platforms such as Twitter provide active communication channels during mass convergence and emergency events such as earthquakes, typhoons. During the sudden onset of a crisis situation, affected people post useful information on Twitter that can be used for situational awareness and other humanitarian disaster response efforts, if processed timely and effectively. Processing social media information pose multiple challenges such as parsing noisy, brief and informal messages, learning information categories from the incoming stream of messages and classifying them into different classes among others. One of the basic necessities of many of these tasks is the availability of data, in particular human-annotated data. In this paper, we present human-annotated Twitter corpora collected during 19 different crises that took place between 2013 and 2015. To demonstrate the utility of the annotations, we train machine learning classifiers. Moreover, we publish first largest word2vec word embeddings trained on 52 million crisis-related tweets. To deal with tweets language issues, we present human-annotated normalized lexical resources for different lexical variations.
    TwitterHuman annotatorsComputational linguisticsWord embeddingMachine learningEarthquakeClassificationCrowdsourcingSupport vector machineLatent Semantic Analysis...
  • The increasing power of computer technology does not dispense with the need to extract meaningful in- formation out of data sets of ever growing size, and indeed typically exacerbates the complexity of this task. To tackle this general problem, two methods have emerged, at chronologically different times, that are now commonly used in the scientific community: data mining and complex network theory. Not only do complex network analysis and data mining share the same general goal, that of extracting information from complex systems to ultimately create a new compact quantifiable representation, but they also often address similar problems too. In the face of that, a surprisingly low number of researchers turn out to resort to both methodologies. One may then be tempted to conclude that these two fields are either largely redundant or totally antithetic. The starting point of this review is that this state of affairs should be put down to contingent rather than conceptual differences, and that these two fields can in fact advantageously be used in a synergistic manner. An overview of both fields is first provided, some fundamental concepts of which are illustrated. A variety of contexts in which complex network theory and data mining have been used in a synergistic manner are then presented. Contexts in which the appropriate integration of complex network metrics can lead to improved classification rates with respect to classical data mining algorithms and, conversely, contexts in which data mining can be used to tackle important issues in complex network theory applications are illustrated. Finally, ways to achieve a tighter integration between complex networks and data mining, and open lines of research are discussed.
    Data miningComplex networkClassificationSupport vector machineGraphStatisticsBig dataFeature selectionGeneCausality...
  • We present a unified treatment of the quantum mechanics of B-factory and neutrino oscillation experiments. While our approach obtains the usual phenomenological predictions for these experiments, it does so without having to invoke perplexing Einstein-Podolsky-Rosen correlations or non-intuitive kinematical assumptions.
    Neutrino oscillationsB mesonB-factoryKinematicsQuantum mechanics...
  • We study mass distributions within and beyond 5~effective radii ($R_{\rm e}$) in 23 early-type galaxies from the SLUGGS survey, using their globular cluster (GC) kinematic data. The data are obtained with Keck/DEIMOS spectrograph, and consist of line-of-sight velocities for ~$3500$ GCs, measured with a high precision of ~15 $\rm km\ s^{-1}$ per GC and extending out to $~13 R_{\rm e}$. We obtain the mass distribution in each galaxy using the tracer mass estimator of Watkins et al. and account for kinematic substructures, rotation of the GC systems and galaxy flattening in our mass estimates. The observed scatter between our mass estimates and results from the literature is less than 0.2 dex. The dark matter fraction within $5R_{\rm e}$ ($f_{\rm DM}$) increases from ~$0.6$ to ~$0.8$ for low- and high-mass galaxies, respectively, with some intermediate-mass galaxies ($M_*{\sim}10^{11}M_\odot$) having low $f_{\rm DM}\sim0.3$, which appears at odds with predictions from simple galaxy models. We show that these results are independent of the adopted orbital anisotropy, stellar mass-to-light ratio, and the assumed slope of the gravitational potential. However, the low $f_{\rm DM}$ in the ~$10^{11}M_\odot$ galaxies agrees with the cosmological simulations of Wu et al. where the pristine dark matter distribution has been modified by baryons during the galaxy assembly process. We find hints that these $M_*\sim10^{11}M_\odot$ galaxies with low $f_{\rm DM}$ have very diffuse dark matter haloes, implying that they assembled late. Beyond $5R_{\rm e}$, the $M/L$ gradients are steeper in the more massive galaxies and shallower in both low and intermediate mass galaxies.
    Globular clusterStellar massKinematicsEllipticityDark matterAnisotropyMass distributionDark matter haloMilky WayMassive galaxies...
  • Cosmological N-body simulations predict dark matter (DM) haloes with steep central cusps (e.g. NFW), which contradicts observations of gas kinematics in low mass galaxies that imply the existence of shallow DM cores. Baryonic processes such as adiabatic contraction and gas outflows can, in principle, alter the initial DM density profile, yet their relative contributions to the halo transformation remain uncertain. Recent high resolution, cosmological hydrodynamic simulations (Di Cintio et al. 2014, DC14) predict that inner density profiles depend systematically on the ratio of stellar to DM mass (M$_*$/M$_{\rm halo}$). Using a Markov Chain Monte Carlo approach, we test the NFW and the M$_*$/M$_{\rm halo}$-dependent DC14 halo models against a sample of 147 galaxy rotation curves from the new SPARC data set. These galaxies all have extended HI rotation curves from radio interferometry as well as accurate stellar mass density profiles from near-infrared photometry. The DC14 halo profile provides markedly better fits to the data than does the NFW profile. Unlike NFW, the DC14 halo parameters found in our rotation curve fits naturally recover both the mass-concentration relation predicted by $\Lambda$CDM and the stellar mass-halo mass relation inferred from abundance matching. Halo profiles modified by baryonic processes are therefore more consistent with expectations from $\Lambda$CDM cosmology and provide better fits to galaxy rotation curves across a wide range of galaxy properties than do halo models which neglect baryonic physics. Our results reconcile observations of galaxies with $\Lambda$CDM expectations, offering a solution to the decade long cusp-core discrepancy.
    Rotation CurveNavarro-Frenk-White profileDark matter haloMonte Carlo Markov chainDark matterHalo modelLambda-CDM modelCosmologyConcentration-mass relationHalo abundance matching...
  • We revisit AdS$_2$ holography with the Sachdev-Ye-Kitaev models in mind. Our main result is to rewrite a generic theory of gravity near an AdS$_2$ throat as a novel hydrodynamics coupled to the correlation functions of a conformal quantum mechanics. This gives a prescription for the computation of $n$-point functions in the dual quantum mechanics. We thereby find that the dual is maximally chaotic.
    Anti de Sitter spaceDilatonFluid dynamicsQuantum mechanicsEntropyRenormalizationThermalisationConformal invarianceChaosPartition function...
  • We present an exact RG analysis of O(N)-invariant scalar field theory about the Gaussian fixed point. We prove a series of statements that taken together show that the non-polynomial eigen-perturbations found in the local potential approximation at the linearised level, do not lead to new interactions (enlarge the universality class). Non-perturbatively, their RG flow does not emanate from the fixed point. For the equivalent Wilsonian effective action they can be re-expressed in terms of the usual couplings to polynomial interactions, which can furthermore be tuned to be as small as desired for all finite RG time. For the infrared cutoff Legendre effective action, this can also be done for the infrared evolution. We explain why this is nevertheless consistent with the fact that the large field behaviour is fixed by these perturbations.
    Renormalization groupGaussian fixed pointScalar field theoryMean fieldInfinitesimalEffective actionScaling dimensionExact solutionUniversality classPerturbation theory...
  • We present how the thermal geometry emerges from CFT at finite temperature by using the truncated entanglement renormalization network, the cMERA. For the case of $2d$ CFT, the reduced geometry is the BTZ black hole or the thermal AdS as expectation. In order to determine which spacetimes prefer to form, we propose a cMERA description of the Hawking-Page phase transition. Our proposal is in agreement with the picture of the recent proposed surface/state correspondence.
    ThermalisationRenormalizationEntanglementPhase transitionsEmergent spacetimeBTZ black holeMixed statesAdS black holeBlack holeIsometry...
  • Entanglement spectrum of the reduced density matrix contains information beyond the von Neumann entropy and provides unique insights into exotic orders or critical behavior of electronic and quantum spin systems. Here we show that strongly-disordered systems in the many-body localized phase have universal power-law entanglement spectra, arising from the presence of extensively many local integrals of motion. The power-law entanglement spectrum distinguishes many-body localized systems from ergodic systems, as well as from ground states of gapped integrable models or systems in the vicinity of scale-invariant critical points. We confirm our results using large-scale exact diagonalization. In addition, we develop a matrix-product state algorithm which allows us to access the eigenstates of large systems close to the localization transition, and discuss general implications of our results for variational studies of highly excited eigenstates in many-body localized systems.
    Entanglement spectrumReduced density matrixVon neumann entropyEntanglementMatrix product statesErgodicityScale invarianceCritical pointUniverseAlgorithms...
  • We present a theory of the anomalous Hall effect in a topological Weyl superconductor with broken time reversal symmetry. Specifically, we consider a ferromagnetic Weyl metal with two Weyl nodes of opposite chirality near the Fermi energy. In the presence of inversion symmetry, such a metal experiences a weak-coupling Bardeen-Cooper-Schrieffer (BCS) instability, with pairing of parity-related eigenstates. Due to the nonzero topological charge, carried by the Weyl nodes, such a superconductor is necessarily topologically nontrivial, with Majorana surface states coexisting with the Fermi arcs of the normal Weyl metal. We demonstrate that, surprisingly, the anomalous Hall conductivity of such a superconducting Weyl metal coincides with that of a nonsuperconducting one, under certain conditions, in spite of the nonconservation of charge in a superconductor. We relate this to the existence of an extra (nearly) conserved quantity in a Weyl metal, the chiral charge.
    Weyl semimetalSuperconductivityHall conductanceSuperconductorChiral chargeBardeen Cooper SchriefferTime-reversal symmetryAnomalous Hall EffectMomentum spaceHamiltonian...