- Quadrature

by Nicolas Guarin Zapata11 Oct 2014 01:22 - Transitive reduction

by James Clough23 Sep 2014 16:14 - Corbino disk

by Kyrylo Snizhko25 Jul 2014 16:42 - Quantum-size electrostatic potential

by Prof. Michael V. Moskalets06 May 2014 17:44 - Dwyer-Fried invariant

by Prof. Alex Suciu15 Dec 2013 03:22 - Wigner transform

by Dr. Claude Becker06 Apr 2011 14:04 - Fermi surface

by Dr. Vadim Cheianov05 Dec 2010 22:11 - Universal Conductance Fluctuations

by Prof. Carlo Beenakker08 Dec 2010 13:33 - Minimal Dark Matter

by Dr. Marco Cirelli05 Dec 2010 22:13 - Kaluza-Klein dark matter

by Dr. Geraldine Servant05 Dec 2010 22:13

- We have made core-collapse supernova simulations that allow oscillations between electron neutrinos (or their anti particles) with right-handed sterile neutrinos. We have considered a range of mixing angles and sterile neutrino masses including those consistent with sterile neutrinos as a dark matter candidate. We examine whether such oscillations can impact the core bounce and shock reheating in supernovae. We identify the optimum ranges of mixing angles and masses that can dramatically enhance the supernova explosion by efficiently transporting electron anti-neutrinos from the core to behind the shock where they provide additional heating leading to much larger explosion kinetic energies. We show that this effect can cause stars to explode that otherwise would have collapsed. We find that an interesting periodicity in the neutrino luminosity develops due to a cycle of depletion of the neutrino density by conversion to sterile neutrinos that shuts off the conversion, followed by a replenished neutrino density as neutrinos transport through the core.NeutrinosphereProto-neutron starAntineutrinoForward scatteringNeutrino flavorMikheev-Smirnov-Wolfenstein effectThermalisationCoolingActive neutrinoFree streaming...
- The Standard Model calculation of $H\rightarrow\gamma\gamma$ has the curious feature of being finite but regulator-dependent. While dimensional regularization yields a result which respects the electromagnetic Ward identities, additional terms which violate gauge invariance arise if the calculation is done setting $d=4$. This discrepancy between the $d=4-\epsilon$ and $d=4$ results is recognized as a true ambiguity which must be resolved using physics input; as dimensional regularization respects gauge invariance, the $d=4-\epsilon$ calculation is accepted as the correct SM result. However, here we point out another possibility; working in analogy with the gauge chiral anomaly, we note that it is possible that the individual diagrams do violate the electromagnetic Ward identities, but that the gauge-invariance-violating terms cancel when all contributions to $H\rightarrow\gamma\gamma$, both from the SM and from new physics, are included. We thus examine the consequences of the hypothesis that the $d=4$ calculation is valid, but that such a cancellation occurs. We work in general renormalizable gauge, thus avoiding issues with momentum routing ambiguities. We point out that the gauge-invariance-violating terms in $d=4$ arise not just for the diagram containing a SM $W^{\pm}$ boson, but also for general fermion and scalar loops, and relate these terms to a lack of shift invariance in Higgs tadpole diagrams. We then derive the analogue of "anomaly cancellation conditions", and find consequences for solutions to the hierarchy problem. In particular, we find that supersymmetry obeys these conditions, even if it is softly broken at an arbitrarily high scale.Standard ModelGauge invarianceQuadratic divergenceTadpoleHierarchy problemDimensional regularizationSelf-energyBeyond the Standard ModelAxial anomalyChiral anomaly...
- In light of recent successes in measuring baryon acoustic oscillations in quasar absorption using the Lyman $\alpha$ (Ly$\alpha$) transition, I explore the possibility of using the 1548\AA\ transition of triply ionized carbon (C IV) as a tracer. While the Ly-alpha forest is a more sensitive tracer of intergalactic gas, it is limited by the fact that it can only be measured in the optical window at redshifts $z > 2$. Quasars are challenging to identify and observe at these high-redshifts, but the C IV forest can be probed down to redshifts $z \approx 1.3$, taking full advantage of the peak in the redshift distribution of quasars that can be targeted with high efficiency. I explore the strength of the C IV absorption signal and show that the absorbing population on the red side of the Ly-alpha emission line is dominated by C IV (and so will dominate over the potential BAO signal of other metals). As a consequence, I argue that forthcoming surveys may have a sufficient increase in quasar number density to offset the lower sensitivity of the C IV forest and provide competitive precision using both the C IV autocorrelation and the C IV-quasar cross-correlation at $< z > \approx 1.6$.QuasarCosmologyLarge scale structureBaryon acoustic oscillationsAbsorptivityIntergalactic mediumLyman-alpha forestExpansion of the UniverseAbsorption lineLine of sight...
- We investigate the distribution of dark matter in galaxies by solving the equations of equilibrium of a self-gravitating system of massive fermions (`inos') at selected temperatures and degeneracy parameters within general relativity. The most general solutions present, as a function of the radius, a segregation of three physical regimes: 1) an inner core of almost constant density governed by degenerate quantum statistics; 2) an intermediate region with a sharply decreasing density distribution followed by an extended plateau, implying quantum corrections; 3) a decreasing density distribution $\rho\propto r^{-2}$ leading to flat rotation curves fulfilling the classical Boltzmann statistics. The mass of the inos is determined as an eigenfunction of the mass of the inner quantum cores. We compare and contrast this mass value with the lower limit on the particle mass by Tremaine and Gunn (1979), and show that the latter is approached for the less degenerate quantum cores in agreement with the fixed halo observables. Consequences of this alternative approach to the massive core in SgrA* and to dwarf galaxies are outlined.Active Galactic NucleiGalaxyDark matterGraphClimateBoxicityStar formation rateStellar massRenormalonStar...
- Magnetotransport measurements on two-dimensional electrons confined to wide GaAs quantum wells reveal a remarkable evolution of the ground state at filling factor $\nu=1/2$ as we tilt the sample in the magnetic field. Starting with a compressible state at zero tilt angle, a strong $\nu=1/2$ fractional quantum Hall state appears at intermediate angles. At higher angles an insulating phase surrounds this state and eventually engulfs it at the highest angles. This evolution occurs because the parallel component of the field renders the charge distribution increasingly bilayer-like.Fractional Quantum Hall EffectGaAs QWsPhase diagramWigner crystalReciprocal spaceFractional quantum Hall stateMoore-Read Pfaffian wavefunctionSuperconductivityLandau levelCompressibility...
- The study of galaxy cluster outskirts has emerged as one of the new frontiers in extragalactic astrophysics and cosmology with the advent of new observations in X-ray and microwave. However, the thermodynamic properties and chemical enrichment of this diffuse and azimuthally asymmetric component of the intracluster medium (ICM) are still not well understood. This work, for the first time, systematically explores potential observational biases in these regions. To assess X-ray measurements of galaxy cluster properties at large radii ($>{R}_{500c}$), we use mock Chandra analyses of cosmological galaxy cluster simulations. The pipeline is identical to that used for Chandra observations, but the biases discussed in this paper are relevant for all X-ray observations outside of ${R}_{500c}$. We find the following from our analysis: (1) filament regions can contribute as much as $50\%$ at $R_{200c}$ to the emission measure; (2) X-ray temperatures and metal abundances from model fitted mock X-ray spectra in a multi-temperature ICM respectively vary to the level of $10\%$ and $50\%$; (3) resulting density profiles vary to within $10\%$ out to $R_{200c}$, and gas mass, total mass, and baryon fractions all vary to within a few percent; (4) the bias from a metal abundance extrapolated a factor of five higher than the true metal abundance results in total mass measurements biased high by $20\%$ and total gas measurements biased low by $10\%$; and (5) differences in projection and dynamical state of a cluster can lead to gas density slope measurements that differ by a factor of $15\%$ and $30\%$, respectively. The presented results can partially account for some of the recent gas profile measurements in cluster outskirts by, e.g., Suzaku. Our findings are pertinent to future X-ray cosmological constraints from cluster outskirts.AbundanceLine of sightTemperature profileAccretionX-ray spectrumHydrostatic massSystematic errorOutskirt of a galaxy clusterCoolingRelaxation...
- Understanding the relationship between galaxies hosting active galactic nuclei (AGN) and the dark matter halos in which they reside is key to constraining how black-hole fueling is triggered and regulated. Previous efforts have relied on simple halo mass estimates inferred from clustering, weak gravitational lensing, or halo occupation distribution modeling. In practice, these approaches remain uncertain because AGN, no matter how they are identified, potentially live a wide range of halo masses with an occupation function whose general shape and normalization are poorly known. In this work, we show that better constraints can be achieved through a rigorous comparison of the clustering, lensing, and cross-correlation signals of AGN hosts to a fiducial stellar-to-halo mass relation (SHMR) derived for all galaxies. Our technique exploits the fact that the global SHMR can be measured with much higher accuracy than any statistic derived from AGN samples alone. Using 382 moderate luminosity X-ray AGN at z<1 from the COSMOS field, we report the first measurements of weak gravitational lensing from an X-ray selected sample. Comparing this signal to predictions from the global SHMR, we find that, contrary to previous results, most X-ray AGN do not live in medium size groups ---nearly half reside in relatively low mass halos with Mh~10^12.5 Msun. The AGN occupation function is well described by the same form derived for all galaxies but with a lower normalization---the fraction of halos with AGN in our sample is a few percent. By highlighting the relatively "normal" way in which moderate luminosity X-ray AGN hosts occupy halos, our results suggest that the environmental signature of distinct fueling modes for luminous QSOs compared to moderate luminosity X-ray AGN is less obvious than previously claimed.Halo Occupation DistributionMock catalogWeak lensingLensing signalAccretionHost galaxyGalaxy galaxy lensingDark matterBlack holeObscured AGN...
- Ebola virus disease is a lethal human and primate disease that currently requires a particular attention from the national and international health authorities due to important outbreaks concurring in some Western African countries and possible spread to other continents, which has already occurred in the USA and Spain. Regarding the emergency of this situation, there is a need of development of decision tools to help the authorities to focus their efforts in important factors that can help to eradicate Ebola. Mathematical modeling and, more precisely, epidemiological modeling can help to predict the possible evolution of the Ebola outbreaks and to give some recommendations in the region to be prioritized for surveillance. In this work, we present a first formulation of a new spatial-temporal epidemiological model, called Be-CoDiS (Between-COuntries Disease Spread), based on the combination of a deterministic Individual-Based model (modelling the interaction between countries, considered as individual) for between country spread with a deterministic compartmental model, based on ordinary differential equations, for within-country spread. The goal is to simulate the spread of a particular disease and identify risk zones worldwide. This model is a particular adaptation of a previous epidemiological software, called Be-FAST, used to predict the spatial spread of animal diseases. The main interesting characteristics of Be-CoDiS are the consideration of migratory flux between countries, control measure effects and time dependent coefficients adapted to each country. First, we focus on the mathematical formulation of each component of the model. Next, to validate our approach, we consider various numerical experiments regarding the 2014 Ebola epidemic. The results are compared to current data and other models outputs found in literature. Finally, a parameter sensitivity analysis is done.HorizonLeast squaresClimateEbola VirusHuman diseasesEpidemiological modelingBetweenness centralityNumerical simulationClassificationNonlinear regression...
- JavaScript engines inside modern browsers are capable of running sophisticated multi-player games, rendering impressive 3D scenes, and supporting complex, interactive visualizations. Can this processing power be harnessed for information retrieval? This paper explores the feasibility of building a JavaScript search engine that runs completely self-contained on the client side within the browser---this includes building the inverted index, gathering terms statistics for scoring, and performing query evaluation. The design takes advantage of the IndexDB API, which is implemented by the LevelDB key-value store inside Google's Chrome browser. Experiments show that although the performance of the JavaScript prototype falls far short of the open-source Lucene search engine, it is sufficiently responsive for interactive applications. This feasibility demonstration opens the door to interesting applications in offline and private search across multiple platforms as well as hybrid split-execution architectures whereby clients and servers collaboratively perform query evaluation. One possible future scenario is the rise of an online search marketplace in which commercial search engine companies and individual users participate as rational economic actors, balancing privacy, resource usage, latency, and other factors based on customizable utility profiles.CompressibilityTwitterTerm frequencyKeyphraseRankingMarketArchitectureMultidimensional ArrayRanking algorithmPrivacy...
- We present the first public release of our Bayesian inference tool, Bayes-X, for the analysis of X-ray observations of galaxy clusters. We illustrate the use of Bayes-X by analysing a set of four simulated clusters at z=0.2-0.9 as they would be observed by a Chandra-like X-ray observatory. In both the simulations and the analysis pipeline we assume that the dark matter density follows a spherically-symmetric Navarro, Frenk and White (NFW) profile and that the gas pressure is described by a generalised NFW (GNFW) profile. We then perform four sets of analyses. By numerically exploring the joint probability distribution of the cluster parameters given simulated Chandra-like data, we show that the model and analysis technique can robustly return the simulated cluster input quantities, constrain the cluster physical parameters and reveal the degeneracies among the model parameters and cluster physical parameters. We then analyse Chandra data on the nearby cluster, A262, and derive the cluster physical profiles. To illustrate the performance of the Bayesian model selection, we also carried out analyses assuming an Einasto profile for the matter density and calculated the Bayes factor. The results of the model selection analyses for the simulated data favour the NFW model as expected. However, we find that the Einasto profile is preferred in the analysis of A262. The Bayes-X software, which is implemented in Fortran 90, is available at http://www.mrao.cam.ac.uk/facilities/software/bayesx/.TelescopesPressure profilePrior probabilityCluster of galaxiesBayesian evidenceNavarro-Frenk-White profileAbundanceLine emissionEffective areaContinuum emission...
- Word clouds are a popular tool for visualizing documents, but they are not a good tool for comparing documents, because identical words are not presented consistently across different clouds. We introduce the concept of word storms, a visualization tool for analysing corpora of documents. A word storm is a group of word clouds, in which each cloud represents a single document, juxtaposed to allow the viewer to compare and contrast the documents. We present a novel algorithm that creates a coordinated word storm, in which words that appear in multiple documents are placed in the same location, using the same color and orientation, in all of the corresponding clouds. In this way, similar documents are represented by similar-looking word clouds, making them easier to compare and contrast visually. We evaluate the algorithm in two ways: first, an automatic evaluation based on document classification; and second, a user study. The results confirm that unlike standard word clouds, a coordinated word storm better allows for visual comparison of documents.ClassificationPolymersTerm frequencyCosine similarityInformation and communication technologiesDimensional ReductionSubcategorySupport vector machineOverfittingOrientation...
- Transformation of CMB photons into light pseudoscalar particles at post big bang nucleosynthesis epoch is considered. Using the present day value of a large scale magnetic field to estimate it at earlier cosmological epochs, the oscillation probability of photons into light pseudoscalar particles with an account of coherence breaking in cosmological plasma is calculated. Demanding that the photon transformation does not lead to an exceedingly large CMB spectral distortion and temperature anisotropy, the constraints on the coupling constant of axion like particles to photons, $ g_{\phi\gamma} B \lesssim (10^{-15} - 10^{-12}) \textrm{nG}\times \textrm{GeV}^{-1}$, are found for the axion like particle mass in the interval $10^{-25}$ eV $\lesssim m_{\phi}\lesssim 10^{-5}$ eV, where $B$ is the strength of the large scale magnetic field at the present time. Our results update the previously obtained ones since we use the density matrix formalism which is more accurate than the wave function approximation for the description of oscillations with an essential coherence breaking. In the axion like particle mass range $10^{-25}$ eV $\lesssim m_{\phi}\lesssim 10^{-14}$ eV, weaker limits, by at least 2 orders of magnitude $g_{\phi\gamma} B \lesssim 10^{-11}\textrm{nG}\times \textrm{GeV}^{-1}$, are obtained in comparison with the wave function approximation. In the mass range $10^{-14}$ eV $\lesssim m_{\phi}\lesssim 10^{-5}$ eV, on the other hand, limits that are stronger, by more than an order of magnitude are obtained. Our results are derived by using upper limits on spectral distortion parameter $\mu$ and temperature anisotropy $\Delta T/T$ found by COBE and expected sensitivities by PIXIE/PRISM.Axion-like particleIndex of refractionALP parameter spaceCompton scatteringIonization fractionAbsorptivityAxionKinetic equationQuantum electrodynamicsBig bang nucleosynthesis...
- We study implications of exact conformal invariance of scalar quantum field theories at the critical point in non-integer dimensions for the evolution kernels of the light-ray operators in physical (integer) dimensions. We demonstrate that all constraints due the conformal symmetry are encoded in the form of the generators of the collinear sl(2) subgroup. Two of them, S_- and S_0, can be fixed at all loops in terms of the evolution kernel, while the generator of special conformal transformations, S_+, receives nontrivial corrections which can be calculated order by order in perturbation theory. Provided that the generator S_+ is known at the k-1 loop order, one can fix the evolution kernel in physical dimension to the k-loop accuracy up to terms that are invariant with respect to the tree-level generators. The invariant parts can easily be restored from the anomalous dimensions. The method is illustrated on two examples: The O(n)-symmetric phi^4 theory in d=4 to the three-loop accuracy, and the su(n) matrix phi^3 theory in d=6 to the two-loop accuracy. We expect that the same technique can be used in gauge theories e.g. in QCD.Anomalous dimensionEvolution equationConformal invarianceSubgroupPerturbation theorySpecial conformal transformationCritical pointConformal symmetryQuantum field theoryGauge theory...
- We present a variational principle for relativistic hydrodynamics with gauge-anomaly terms for a fluid coupled to an Abelian background gauge field. For this we utilize the Clebsch parametrization of the velocity field. We also set up the Hamiltonian formulation and the canonical framework for the theory. While the equations of motion only involve the density and velocity fields, i.e., the Clebsch potentials only appear in the combination which is the velocity field, the generators of symmetry transformations (including the Hamiltonian) depend explicitly on one of the Clebsch potentials, if the background field is time-dependent. For the special case of time-independent background fields, this feature is absent.Quantum anomalyGauge transformationPoisson bracketConstitutive relationGauge invarianceQuantum field theoryPerfect fluidPoisson algebraHamiltonian reductionDiffeomorphism...
- The properties of the extremely strong magnetic fields of neutron stars affect in a unique way their evolution and the associated phenomenology. Due to the lack of constraints from direct observations, our understanding of the magnetic field configuration in neutron star interiors depends on the progress in theoretical modelling. Here we discuss the effort in building models of magnetized neutron stars focussing on some of the recent results. In particular, we comment on the instability of purely poloidal and purely toroidal magnetic field configurations and on the evidence in favour of the so-called twisted-torus solutions. We conclude with an outlook on the present status of the field and future directions.Neutron starMagnetized neutron starGravitational waveMagnetic energyMagnetohydrodynamicsStarEllipticityDissipationMagnetarDifferential rotation...
- Since reionization prevents star formation in most halos below 3 x 10^9 solar masses, dwarf galaxies only populate a fraction of existing dark matter halos. We use hydrodynamic cosmological simulations of the Local Group to study the discriminating factors for galaxy formation in the early Universe and connect them to the present-day properties of galaxies and halos. A combination of selection effects related to reionization, and the subsequent evolution of halos in different environments, introduces strong biases between the population of halos that host dwarf galaxies, and the total halo population. Halos that host galaxies formed earlier and are more concentrated. In addition, halos more affected by tidal stripping are more likely to host a galaxy for a given mass or maximum circular velocity, vmax, today. Consequently, satellite halos are populated more frequently than field halos, and satellite halos of 10^8 - 10^9 solar masses or vmax of 12 - 20 km/s, similar to the Local Group dwarf spheroidals, have experienced a greater than average reduction in both mass and vmax after infall. They are on closer, more radial orbits with higher infall velocities and earlier infall times. Together, these effects make dwarf galaxies highly biased tracers of the underlying dark matter distribution.StarHydrodynamical simulationsDark matter haloMilky WayMass ratioLocal Group dwarf galaxyCoolingIntergalactic mediumVirial massPhotoevaporation...
- If a primordial magnetic field in the universe has non-zero helicity, the violation of parity symmetry results in non-zero correlations between cosmic microwave background temperature and B-mode polarization. In this paper we derive approximations to the relevant microwave background power spectra arising from a helical magnetic field. Using the cross-power spectrum between temperature and B-mode polarization from the WMAP nine-year data, we set a 95\% confidence level upper limit on the helicity amplitude to be 10 nG$^2$ Gpc for helicity spectral index $n_H = -1.9$, for a cosmological magnetic field with effective field strength of 3 nG and a power-law index $n_B = -2.9$ near the scale-invariant value. Future microwave background polarization maps with greater sensitivity will be able to detect the helicity of an inflationary magnetic field well below the maximum value allowed by microwave background constraints on the magnetic field amplitude.Power spectrumVorticityCosmologyParity violationCosmological modelHelicityCosmic microwave backgroundDiffusion dampingCutoff scaleAngular power spectrum...
- Force-Free Electrodynamics (FFE) describes magnetically dominated relativistic plasma via non-linear equations for the electromagnetic field alone. Such plasma is thought to play a key role in the physics of pulsars and active black holes. Despite its simple covariant formulation, FFE has primarily been studied in 3+1 frameworks, where spacetime is split into space and time. In this article we systematically develop the theory of force-free magnetospheres taking a spacetime perspective. Using a suite of spacetime tools and techniques (notably exterior calculus) we cover 1) the basics of the theory, 2) exact solutions that demonstrate the extraction and transport of the rotational energy of a compact object (in the case of a black hole, the Blandford-Znajek mechanism), 3) the behavior of current sheets, 4) the general theory of stationary, axisymmetric magnetospheres and 5) general properties of pulsar and black hole magnetospheres. We thereby synthesize, clarify and generalize known aspects of the physics of force-free magnetospheres, while also introducing several new results.HorizonStarRegularizationTwo-formDifferential formInclinationDifferential form of degree threeOrientationSpinning Black HoleConserved quantities...
- The soft X-ray flux produced by solar axions in the Earth's magnetic field is evaluated in the context of ESA's XMM-Newton observatory. Recent calculations of the scattering of axion-conversion X-rays suggest that the sunward magnetosphere could be an observable source of 0.2-10 keV photons. For XMM-Newton, any conversion X-ray intensity will be seasonally modulated by virtue of the changing visibility of the sunward magnetic field region. A simple model of the geomagnetic field is combined with the ephemeris of XMM-Newton to predict the seasonal variation of the conversion X-ray intensity. This model is compared with stacked XMM-Newton blank sky datasets from which point sources have been systematically removed. Remarkably, a seasonally varying X-ray background signal is observed. The EPIC count rates are in the ratio of their X-ray grasps, indicating a non-instrumental, external photon origin, with significances of 11(pn), 4(MOS1) and 5(MOS2) sigma. After examining the constituent observations spatially, temporally and in terms of the cosmic X-ray background, we conclude that this variable signal is consistent with the conversion of solar axions in the Earth's magnetic field. The spectrum is consistent with a solar axion spectrum dominated by bremsstrahlung- and Compton-like processes, i.e. axion-electron coupling dominates over axion-photon coupling and the peak of the axion spectrum is below 1 keV. A value of 2.2e-22 /GeV is derived for the product of the axion-photon and axion-electron coupling constants, for an axion mass in the micro-eV range. Comparisons with limits derived from white dwarf cooling may not be applicable, as these refer to axions in the 0.01 eV range. Preliminary results are given of a search for axion-conversion X-ray lines, in particular the predicted features due to silicon, sulphur and iron in the solar core, and the 14.4 keV transition line from 57Fe.Solar axionIntensityXMM-Newton EPIC cameraXMM-NewtonMoS2ThermalisationSolar axion fluxBlank sky datasetAxion massHigh Earth orbit...
- We identify a weak line at $E \sim 3.5$ keV in X-ray spectra of the Andromeda galaxy and the Perseus galaxy cluster -- two dark matter-dominated objects, for which there exist deep exposures with the XMM-Newton X-ray observatory. Such a line was not previously known to be present in the spectra of galaxies or galaxy clusters. Although the line is weak, it has a clear tendency to become stronger towards the centers of the objects; it is stronger for the Perseus cluster than for the Andromeda galaxy and is absent in the spectrum of a very deep "blank sky" dataset. Although for individual objects it is hard to exclude the possibility that the feature is due to an instrumental effect or an atomic line of anomalous brightness, it is consistent with the behavior of a line originating from the decay of dark matter particles. Future detections or non-detections of this line in multiple astrophysical targets may help to reveal its nature.Andromeda galaxyDark matterPerseus ClusterCluster of galaxiesXMM-NewtonDark matter decayEPIC PN cameraXMM-Newton MOS cameraDM decay lineNGC 1275...
- Assuming that mass scales arise in nature only via dimensional transmutation, we extend the dimension-less Standard Model by adding vector-like fermions charged under a new strong gauge interaction. Their non-perturbative dynamics generates a mass scale that is transmitted to the elementary Higgs boson by electro-weak gauge interactions. In its minimal version the model has the same number of parameters as the Standard Model, predicts that the electro-weak symmetry gets broken, predicts new-physics in the multi-TeV region and is compatible with all existing bounds, provides two Dark Matter candidates stable thanks to accidental symmetries: a composite scalar in the adjoint of SU(2)_L and a composite singlet fermion; their thermal relic abundance is predicted to be comparable to the measured cosmological DM abundance. Some models of this type allow for extra Yukawa couplings; DM candidates remain even if explicit masses are added.Higgs boson massStandard ModelTechnicolorCondensationElectroweak interactionQuadratic divergenceVector mesonYukawa interactionVacuum expectation valueHiggs boson...
- We consider some implications of X-ray lines from certain astronomical objects as potential effects of dark matter decay in the context of the scotogenic model, where neutrinos acquire mass radiatively via one-loop interactions with dark matter. As an example, we focus on the 3.5 keV line recently detected in the X-ray spectra of galaxy clusters, assuming that it stands future scrutiny. We explore the scenario in which the line originates from the slow decay of fermionic dark matter in the model. After obtaining a number of benchmark points representing the parameter space consistent with the new data and various other constraints, we make predictions on several observables in leptonic processes. They include the effective Majorana mass in neutrinoless double-beta decay, the sum of neutrino masses, and the rate of flavor-changing decay mu -> e gamma, as well as the cross sections of e+e- collisions into final states containing nonstandard particles in the model. These are testable in ongoing or future experiments and thus offer means to probe the scotogenic scenario studied.Dark matterStandard ModelYukawa couplingNeutrino oscillationsBranching ratioBaryon acoustic oscillationsCosmic microwave backgroundVacuum expectation valueHiggs bosonAbundance...
- Massive gravitons in effective field theories can be recovered by extending General Relativity and taking into account generic functions of the curvature invariants not necessarily linear in the Ricci scalar R. In particular, adopting the minimal extension of f(R) gravity, an effective field theory with a massive state is straightforwardly recovered. This approach allows to evade shortcomings like ghosts and discontinuities if a suitable choice of expansion parameters is performed. We show that the massive state can be identified with a massive graviton.GravitonEffective LagrangianGeneral relativityEffective field theoryDegree of freedomDark energyEffective theoryGravitational interactionCosmological constantScalar field...
- I briefly review the conceptual developments that led to the Standard Model and discuss some of its remarkable qualitative features. On the way, I draw attention to several puzzling aspects that are beyond the reach of our present understanding of the basic laws of physics.QuarkGauge fieldStrong interactionsWeak interactionQuantum chromodynamicsCondensationQuantum electrodynamicsGauge invarianceFlavourQuantum field theory...
- Landau's Fermi-liquid theory is the standard model for metals, characterized by the existence of electron quasiparticles near a Fermi surface as long as Landau's interaction parameters lie below critical values for instabilities. Recently, this fundamental paradigm has been challenged by physics of strong spin-orbit coupling although the concept of electron quasiparticles remains valid near the Fermi surface, where the Landau's Fermi-liquid theory fails to describe electromagnetic properties of this novel metallic state, referred to as Weyl metal. A novel ingredient is that such a Fermi surface encloses a Weyl point with definite chirality, referred to as a chiral Fermi surface, which can arise from breaking of either time reversal or inversion symmetry in systems with strong spin-orbit coupling, responsible for both Berry curvature and chiral anomaly. As a result, electromagnetic properties of the Weyl metallic state are described not by conventional Maxwell equations but by axion electrodynamics, where Maxwell equations are modified with a topological-in-origin spatially modulated $\theta(\bm{r}) \bm{E} \cdot \bm{B}$ term. This novel metallic state has been realized recently in Bi$_{1-x}$Sb$_{x}$ around $x \sim 3%$ under magnetic fields, where the Dirac spectrum appears around the critical point between the normal semiconducting ($x < 3%$) and topological semiconducting phases ($x > 3%$) and the time reversal symmetry breaking perturbation causes the Dirac point to split into a pair of Weyl points along the direction of the applied magnetic field for such a strong spin-orbit coupled system. In this review article, we discuss how the topological structure of both the Berry curvature and chiral anomaly (axion electrodynamics) gives rise to anomalous transport phenomena in Bi$_{1-x}$Sb$_{x}$ around $x \sim 3%$ under magnetic fields, modifying the Drude model of Landau's Fermi liquids.Boltzmann transport equationBerry phaseWeak antilocalizationMomentum spaceGrapheneQuantum electrodynamicsEffective field theoryTransport theoryAnomalous Hall EffectChern number...
- This review aims at a theoretical discussion of Dirac points in two-dimensional systems. Whereas Dirac points and Dirac fermions are prominent low-energy electrons in graphene (two-dimensional graphite), research on Dirac fermions in low-energy physics has spread beyond condensed-matter systems. In these alternative systems, a large versatility in the manipulation of the relevant band parameters can be achieved. This allows for a systematic study of the motion and different possible fusions of Dirac points, which are beyond the physical limits of graphene. We introduce the basic properties of Dirac fermions and the motion of Dirac points here and aim at a topological classification of these motions. The theoretical concepts are illustrated in particular model systems.HamiltonianWinding numberTime-reversal symmetryLandau levelTopological quantum numberWave vectorBrillouin zoneReciprocal spaceQuantum mechanicsTight-binding model...
- Motivated by the possibility of explaining the 3.5 keV line through dark matter decaying to axion-like particles that subsequently convert to photons, we study ALP-photon conversion for sightlines passing within 50 pc of the galactic centre. Conversion depends on the galactic centre magnetic field which is highly uncertain. For fields at low or mid-range of observational estimates (10--100 $\mu$G), no observable signal is possible. For fields at the high range of observational estimates (a pervasive poloidal mG field over the central 150 pc) it is possible to generate sufficient signal to explain recent observations of a 3.5 keV line in the galactic centre. In this scenario, the galactic centre line signal comes predominantly from the region with $z > 20$ pc, reconciling the results from the Chandra and XMM-Newton X-ray telescopes. The dark matter to ALP to photon scenario also naturally predicts the non-observation of the 3.5 keV line in stacked galaxy spectra. We further explore predictions for the line flux in galaxies and suggest a set of galaxies that is optimised for observing the 3.5 keV line in this model.Field of viewElectronic densityCluster of galaxiesMilky WayRegularizationAndromeda galaxyLine of sightDark matter decaySagittarius A*Dwarf spheroidal galaxy...
- The scalar averaging approach to cosmology interprets dark energy as the growth of average, void-dominated, negative spatial curvature during the virialisation epoch, leaving the metric a priori unspecified, while models with a Friedmann-Lemaitre-Robertson-Walker (FLRW) metric assume comoving spatial rigidity of metrical properties. The former predicts that voids are hyperbolic and that superclusters occupy positively curved space, and that a best-fit metric should be close to the void case modelled as a constant-curvature metric on a given time slice. Thus, comoving separations near superclusters should be compressed in comparison to the homogeneous case. We demonstrate this by measuring the two-point auto-correlation function on comoving scales in order to detect shifts in the baryonic acoustic oscillation (BAO) peak location for Large Red Galaxy (LRG) pairs of the Sloan Digital Sky Survey Data Release 7. In tangential directions, subsets of pairs overlapping with superclusters or voids show the BAO peak. The tangential BAO peak location for overlap with Nadathur & Hotchkiss superclusters is 4.3\pm1.6 Mpc/h less than that for LRG pairs unselected for supercluster overlap, and 6.6\pm2.8 Mpc/h less than that of the complementary pairs. Liivamagi et al. superclusters give corresponding differences of 3.7\pm2.9 Mpc/h and 6.3\pm2.6 Mpc/h, respectively. We have found moderately significant evidence (Kolmogorov-Smirnov tests suggest very significant evidence) that the BAO peak location for supercluster-overlapping pairs is compressed by about 6% compared to that of the complementary sample, providing a potential challenge to FLRW models and a benchmark for predictions from backreaction models.Two-point correlation functionSloan Digital Sky SurveyLambda-CDM modelPeculiar velocityLine of sightStatisticsSuperclusterBaryon acoustic oscillationsCold dark matterComoving distance...
- This paper introduces a new publicly available numerical library for cosmology, Cosmo++. The library has been designed using object-oriented programming techniques, and fully implemented in C++. Cosmo++ introduces a unified interface for using most of the frequently used numerical methods in cosmology. Most of the features are implemented in Cosmo++ itself, while a part of the functionality is implemented by linking to other publicly available libraries. The most important features of the library are Cosmic Microwave Background anisotropies power spectrum and transfer function calculations, likelihood calculations, parameter space sampling tools, sky map simulations, and mask apodization. Cosmo++ also includes a few mathematical tools that are frequently used in numerical research in cosmology and beyond. A few simple examples are included in Cosmo++ to help the user understand the key features. The library has been fully tested, and we describe some of the important tests in this paper. Cosmo++ is publicly available at http://cosmo.grigoraslanyan.comPlanck missionCosmological parametersPower spectrum of primordial density perturbationsCovariance matrixCovarianceCosmic microwave backgroundLikelihood functionDegree of freedomCMB power spectraWhite noise...
- We performed a deep search for radio synchrotron emissions induced by weakly interacting massive particles (WIMPs) annihilation or decay in six dwarf spheroidal (dSph) galaxies of the Local Group. Observations were conducted with the Australia Telescope Compact Array (ATCA) at 16 cm wavelength, with an rms sensitivity better than 0.05 mJy/beam in each field. In this work, we first discuss the uncertainties associated with the modeling of the expected signal, such as the shape of the dark matter (DM) profile and the dSph magnetic properties. We then investigate the possibility that point-sources detected in the proximity of the dSph optical center might be due to the emission from a DM cuspy profile. No evidence for an extended emission over a size of few arcmin (which is the DM halo size) has been detected. We present the associated bounds on the WIMP parameter space for different annihilation/decay final states and for different astrophysical assumptions. If the confinement of electrons and positrons in the dSph is such that the majority of their power is radiated within the dSph region, we obtain constraints on the WIMP annihilation rate which are well below the thermal value for masses up to few TeV. On the other hand, for conservative assumptions on the dSph magnetic properties, the bounds can be dramatically relaxed. We show however that, within the next 10 years and regardless of the astrophysical assumptions, it will be possible to progressively close in on the full parameter space of WIMPs by searching for radio signals in dSphs with SKA and its precursors.Dark Matter Density ProfileNavarro-Frenk-White profileDiffuse emissionRadio telescopeCarina DwarfTelescopesDark matter annihilationInverse ComptonHercules ConstellationMultidimensional Array...
- We simulate the adiabatic contraction of a dark matter (DM) distribution during the process of the star formation, paying particular attention to the phase space distribution of the DM particles after the contraction. Assuming the initial uniform density and Maxwellian distribution of DM velocities, we find that the number $n(r)$ of DM particles within the radius $r$ scales like $n(r) \propto r^{1.5}$, leading to the DM density profile $\rho\propto r^{-1.5}$, in agreement with the Liouville theorem and previous numerical studies. At the same time, the number of DM particles $\nu(r)$ with periastra smaller than $r$ is parametrically larger, $\nu(r) \propto r$, implying that many particles contributing at any given moment into the density $\rho(r)$ at small $r$ have very elongated orbits and spend most of their time at distances larger than $r$. This has implications for the capture of DM by stars in the process of their formation. As a concrete example we consider the case of primordial black holes (PBH). We show that accounting for very eccentric orbits boosts the amount of captured PBH by a factor of up to $2\times 10^3$ depending on the PBH mass, improving correspondingly the previously derived constraints on the PBH abundance.Compact starNeutron starVelocity dispersionPre-stellar coreWhite dwarfDwarf spheroidal galaxyGiant Molecular CloudPrimordial black holeMain sequence starProtostar...
- We propose a mechanism for baryogenesis from particle decays or annihilations that can work at the TeV scale. Some heavy particles annihilate or decay into a heavy sterile neutrino N (with M > 0.5 TeV) and a "light" one \nu (with m << 100 GeV), generating an asymmetry among the two helicity degrees of freedom of \nu. This asymmetry is partially transferred to Standard Model leptons via fast Yukawa interactions and reprocessed into a baryon asymmetry by the electroweak sphalerons. We illustrate this mechanism in a WIMPy baryogenesis model where the helicity asymmetry is generated in the annihilation of dark matter. This model connects the baryon asymmetry, dark matter, and neutrino masses. Moreover it also complements previous studies on general requirements for baryogenesis from dark matter annihilation. Finally we discuss other possible realizations of this helicitogenesis mechanism.Dark matterStandard ModelBaryon asymmetry of the UniverseYukawa couplingLepton numberFreeze-outDark matter annihilationCP violationThermalisationCP asymmetry...
- A tight-binding approach based on the Chebyshev-Bogoliubov-de Gennes method is used to describe disordered single-layer graphene Josephson junctions. Scattering by vacancies, ripples or charged impurities is included. We compute the Josephson current and investigate the nature of multiple Andreev reflections, which induce bound states appearing as peaks in the density of states for energies below the superconducting gap. In the presence of single atom vacancies, we observe a strong suppression of the supercurrent that is a consequence of strong inter-valley scattering. Although lattice deformations should not induce inter-valley scattering, we find that the supercurrent is still suppressed, which is due to the presence of pseudo-magnetic barriers. For charged impurities, we consider two cases depending on whether the average doping is zero, i.e. existence of electron-hole puddles, or finite. In both cases, short range impurities strongly affect the supercurrent, similar to the vacancies scenario.Density of statesBumpingDirac pointHamiltonianGreen's functionCritical currentTime-reversal symmetryFermi levelLocal density of statesInterference...
- Ultra-light axions (ULAs) with masses in the range 10^{-33} eV <m <10^{-20} eV are motivated by string theory and might contribute to either the dark-matter or dark-energy density of the Universe. ULAs could suppress the growth of structure on small scales, or lead to an enhanced integrated Sachs-Wolfe effect on large-scale cosmic microwave-background (CMB) anisotropies. In this work, cosmological observables over the full ULA mass range are computed, and then used to search for evidence of ULAs using CMB data from the Wilkinson Microwave Anisotropy Probe (WMAP), Planck satellite, Atacama Cosmology Telescope, and South Pole Telescope, as well as galaxy clustering data from the WiggleZ galaxy-redshift survey. In the mass range 10^{-32} eV < m <10^{-25.5} eV, the axion relic-density \Omega_{a} (relative to the total dark-matter relic density \Omega_{d}) must obey the constraints \Omega_{a}/\Omega_{d} < 0.05 and \Omega_{a}h^{2} < 0.006 at 95%-confidence. For m> 10^{-24} eV, ULAs are indistinguishable from standard cold dark matter on the length scales probed, and are thus allowed by these data. For m < 10^{-32} eV, ULAs are allowed to compose a significant fraction of the dark energy.Cold dark matterDark matterDark energyMatter power spectrumNeutrinoIntegrated Sachs-Wolfe effectScalar fieldQCD axionLarge scale structureAxion mass...
- In this talk we explore the possibility that the smallness of the observed neutrino masses is naturally understood in a modified version of the standard model with N extra generations of fermions and N right-handed neutrinos, in which light neutrino masses are generated at two loops. We find that with N = 1 it is not possible to fit the observed spectrum of masses and mixings while with N = 2 it is. Within this extension, we analyse the parameters which are allowed and the possible phenomenological signals of the model in future experiments. Contribution to the proceedings of Les Rencontres de Moriond EW 2011, Young Scientist Forum.NeutrinoStandard ModelMajorana massCharged leptonColumn vectorSterile neutrinoMajorana neutrinoFlavourInverted hierarchyNormal hierarchy...
- In this short review, I present some of the recent progresses on the pending questions of solar physics. These questions let us revisit the solar wind, the solar dynamo problem, the dynamics of the photosphere and finally have a glimpse at other solar type stars. Discussing the use of direct numerical simulations in solar physics, I show that the full numerical calculation of the flow in a single supergranule would require more electric power than the luminosity of the sun itself with present computer technology.StarMagnetic helicityCoronaGranuleNumerical simulationEarthMagnetohydrodynamicsTurbulence modelingIntensityChromosphere...
- Our understanding of the state of the universe between the end of inflation and big bang nucleosynthesis (BBN) is incomplete. The dynamics at the end of inflation are rich and a potential source of observational signatures. Reheating, the energy transfer between the inflaton and Standard Model fields (possibly through intermediaries) and their subsequent thermalization, can provide clues to how inflation fits in with known high-energy physics. We provide an overview of our current understanding of the nonperturbative, nonlinear dynamics at the end of inflation, some salient features of realistic particle physics models of reheating, and how the universe reaches a thermal state before BBN. In addition, we review the analytical and numerical tools available in the literature to study preheating and reheating and discuss potential observational signatures from this fascinating era.Big bang nucleosynthesisThermalisationStandard Model fieldPreheatingReheatingInflationInflatonUniversePotentialParticle physics...
- Given a finite simple graph G=(V,E) with chromatic number c and chromatic polynomial C(x). Every vertex graph coloring f of G defines an index i_f(x) satisfying the Poincare-Hopf theorem sum_x i_f(x)=chi(G). As a variant to the index expectation result we prove that E[i_f(x)] is equal to curvature K(x) satisfying Gauss-Bonnet sum_x K(x) = \chi(G), where the expectation is the average over the finite probability space containing the C(c) possible colorings with c colors, for which each coloring has the same probability.GraphEuler characteristicLinear functionalPlanar graphManifoldRiemannian metricChromatic polynomialWheel graphPermutationIsomorphism...
- We explore relations between various variational problems for graphs like Euler characteristic chi(G), characteristic length mu(G), mean clustering nu(G), inductive dimension iota(G), edge density epsilon(G), scale measure sigma(G), Hilbert action eta(G) and spectral complexity xi(G). A new insight in this note is that the local cluster coefficient C(x) in a finite simple graph can be written as a relative characteristic length L(x) of the unit sphere S(x) within the unit ball B(x) of a vertex. This relation L(x) = 2-C(x) will allow to study clustering in more general metric spaces like Riemannian manifolds or fractals. If eta is the average of scalar curvature s(x), a formula mu ~ 1+log(epsilon)/log(eta) of Newman, Watts and Strogatz relates mu with the edge density epsilon and average scalar curvature eta telling that large curvature correlates with small characteristic length. Experiments show that the statistical relation mu ~ log(1/nu) holds for random or deterministic constructed networks, indicating that small clustering is often associated to large characteristic lengths and lambda=mu/log(nu) can converge in some graph limits of networks. Mean clustering nu, edge density epsilon and curvature average eta therefore can relate with characteristic length mu on a statistical level. We also discovered experimentally that inductive dimension iota and cluster-length ratio lambda correlate strongly on Erdos-Renyi probability spaces.GeodesicClustering coefficientArboricityLine graphTorusManifoldGraph theoryEigenvalueCohomologyGeneral relativity...
- The interaction induced chiral asymmetry is calculated in cold QED plasma beyond the weak-field approximation. By making use of the recently developed Landau-level representation for the fermion self-energy, the chiral shift and the parity-even chiral chemical potential function are obtained with the help of numerical methods. The results are used to quantify the chiral asymmetry of the Fermi surface in dense QED matter. Because of the weakness of the QED interactions, the value of the asymmetry appears to be rather small even in the strongest magnetic fields and at the highest stellar densities. However, the analogous asymmetry can be substantial in the case of dense quark matter.Lowest Landau LevelChiral separation effectChiral magnetic effectFermion propagatorCoupling constantMonte Carlo methodTranslational invarianceRadiative correctionGamma distributionMagnetic field strength...
- We study here the interaction of $D \bar D^*$ in the isospin $I=1$ channel in the light of recent theoretical advances that allow to combine elements of the local hidden gauge approach with heavy quark spin symmetry. We find that the exchange of light $q \bar q$ is OZI suppressed and, thus, we concentrate on the exchange of heavy vectors and of two pion exchange. The latter is found to be small compared to the exchange of heavy vectors, which then determines the strength of the interaction. A barely $D\bar{D}^*$ bound state decaying into $\eta_c\rho$ and $\pi J/\psi$ is found. At the same time we reanalyze the data of the BESIII experiment on $e^+ e^- \to \pi^{\pm} (D \bar D^*)^\mp$, from where a $Z_c(3885)$ state was claimed, associated to a peak in the $(D \bar D^*)^\mp$ invariant mass distribution close to threshold, and we find the data compatible with a resonance with mass around $3875$ MeV and width around $30$ MeV. We discuss the possibility that this and the $Z_c(3900)$ state found at BESIII, reconfirmed at 3896 MeV at Belle, or 3885 MeV at CLEO, could all be the same state and correspond to the one that we find theoretically.Vector mesonPseudoscalarCharmed baryonsPseudoscalar mesonRegularizationX(3872)Form factorTetraquarkQuarkPolarization vector...
- The ratio of branching fractions of the radiative B decays B0 -> K*0 gamma and Bs0 phi gamma has been measured using an integrated luminosity of 1.0 fb-1 of pp collision data collected by the LHCb experiment at a centre-of-mass energy of sqrt(s)=7 TeV. The value obtained is BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma) = 1.23 +/- 0.06(stat.) +/- 0.04(syst.) +/- 0.10(fs/fd), where the first uncertainty is statistical, the second is the experimental systematic uncertainty and the third is associated with the ratio of fragmentation fractions fs/fd. Using the world average value for BR(B0 -> K*0 gamma), the branching fraction BR(Bs0 -> phi gamma) is measured to be (3.5 +/- 0.4) x 10^{-5}. The direct CP asymmetry in B0 -> K*0 gamma decays has also been measured with the same data and found to be A(CP)(B0 -> K*0 gamma) = (0.8 +/- 1.7(stat.) +/- 0.9(syst.))%. Both measurements are the most precise to date and are in agreement with the previous experimental results and theoretical expectations.Branching ratioInvariant massVector mesonStandard ModelIntegrated luminosityCrystal BallCharm quarkPionKinematicsMass distribution...
- We extend the notion of simplicial set with effective homology to diagrams of simplicial sets. Further, for a given finite diagram of simplicial sets $X \colon \mathcal{I} \to \mathsf{sSet}$ such that each simplicial set $X(i)$ has effective homology, we present an algorithm computing the homotopy colimit $\mathsf{hocolim} X$ as a simplicial set with effective homology. We also give an algorithm computing the cofibrant replacement $X^\mathsf{cof}$ of $X$ as a diagram with effective homology. This is applied to computing of equivariant cohomology operations.Chain complexMorphismModel structureSimplicial setHomomorphismFibrationEquivariant mapIsomorphismTensor productPerturbation theory...
- We propose a method for inferring human attributes (such as gender, hair style, clothes style, expression, action) from images of people under large variation of viewpoint, pose, appearance, articulation and occlusion. Convolutional Neural Nets (CNN) have been shown to perform very well on large scale object recognition problems. In the context of attribute classification, however, the signal is often subtle and it may cover only a small part of the image, while the image is dominated by the effects of pose and viewpoint. Discounting for pose variation would require training on very large labeled datasets which are not presently available. Part-based models, such as poselets and DPM have been shown to perform well for this problem but they are limited by flat low-level features. We propose a new method which combines part-based models and deep learning by training pose-normalized CNNs. We show substantial improvement vs. state-of-the-art methods on challenging attribute classification tasks in unconstrained settings. Experiments confirm that our method outperforms both the best part-based methods on this problem and conventional CNNs trained on the full bounding box of the person.ClassificationDeep learningTraining setDAMA/LIBRAArchitectureCrowdsourcingGlassStatisticsBinary starClassification systems...
- A large fraction of this thesis is dedicated to the study of the information content of random fields with heavy tails, in particular the lognormal field, a model for the matter density fluctuation field. It is well known that in the nonlinear regime of structure formation, the matter fluctuation field develops such large tails. It has also been suggested that fields with large tails are not necessarily well described by the hierarchy of $N$-point functions. In this thesis, we are able to make this last statement precise and with the help of the lognormal model to quantify precisely its implications for inference on cosmological parameters : we find as our main result that only a tiny fraction of the total Fisher information of the field is still contained in the hierarchy of $N$-point moments in the nonlinear regime, rendering parameter inference from such moments very inefficient. We show that the hierarchy fails to capture the information that is contained in the underdense regions, which at the same time are found to be the most rich in information. We find further our results to be very consistent with numerical analysis using $N$-body simulations. We also discuss these issues with the help of explicit families of fields with the same hierarchy of $N$-point moments defined in this work. A similar analysis is then applied to the convergence field, the weighted projection of the matter density fluctuation field along the line of sight, with similar conclusions. We also show how simple mappings can correct for this inadequacy, consistently with previous findings in the literature (Abridged) .EntropyFisher informationFisher information matrixCosmologyGalaxyCovariance matrixStatisticsWeak lensingOrthogonal polynomialsTwo-point correlation function...
- The low energy dynamics of QCD is investigated with special attention paid to the matching between QCD and chiral perturbation theory(ChPT), and also to some useful algebraic chiral operator relations which survive even when we include chiral loop corrections. It then allows us to evaluate the hadronic matrix elements below the energy scale $\Lambda_{\chi} \simeq 1$ GeV. Based on the new analyzes, we present a consistent prediction for both direct CP-violating parameter $\epsilon'/\epsilon$ and $\Delta I =1/2$ rule in the kaon decays. In the leading $1/N_c$ approximation, the isospin amplitudes $A_0$ and $A_2$ are found to agree well with the data, and the direct CP-violating parameter $\epsilon'/\epsilon$ is predicted to be large, which also confirms our early conclusion. Its numerical value is $\epsilon'/\epsilon = 23.6^{+12.4}_{-7.8}\times 10^{-4}(Im\lambda_t/1.2\times 10^{-4})$ which is no longer sensitive to the strange quark mass due to the matching conditions. Taking into account a simultaneous consistent analysis on the isospin amplitudes $A_0$ and $A_2$, the ratio $\epsilon'/\epsilon$ is in favor of the values $\epsilon'/\epsilon = (20\pm 9)\times 10^{-4}$.ChiralityQuantum chromodynamicsCP violationIsospinQuarkRenormalizationPerturbative QCDCoupling constantHadronizationQuark mass...
- Through defining irreducible loop integrals (ILIs), a set of consistency conditions for the regularized (quadratically and logarithmically) divergent ILIs are obtained to maintain the generalized Ward identities of gauge invariance in non-Abelian gauge theories. Overlapping UV divergences are explicitly shown to be factorizable in the ILIs and be harmless via suitable subtractions. A new regularization and renormalization method is presented in the initial space-time dimension of the theory. The procedure respects unitarity and causality. Of interest, the method leads to an infinity free renormalization and meanwhile maintains the symmetry principles of the original theory except the intrinsic mass scale caused conformal scaling symmetry breaking and the anomaly induced symmetry breaking. Quantum field theories (QFTs) regularized through the new method are well defined and governed by a physically meaningful characteristic energy scale (CES) $M_c$ and a physically interesting sliding energy scale (SES) $\mu_s$ which can run from $\mu_s \sim M_c$ to a dynamically generated mass gap $\mu_s=\mu_c$ or to $\mu_s =0$ in the absence of mass gap and infrared (IR) problem. It is strongly indicated that the conformal scaling symmetry and its breaking mechanism play an important role for understanding the mass gap and quark confinement.RegularizationGraphGauge invarianceQuantum field theoryDimensional regularizationLoop integralLoop momentumRenormalizationQuadratic divergenceVacuum polarization...
- A star collapsing gravitationally into a black hole emits a flux of radiation, knowns as Hawking radiation. When the initial state of a quantum field on the background of the star, is placed in the Unruh vacuum in the far past, then Hawking radiation corresponds to a flux of positive energy radiation travelling outwards to future infinity. The evaporation of the collapsing star can be equivalently described as a negative energy flux of radiation travelling radially inwards towards the center of the star. Here, we are interested in the evolution of the star during its collapse. Thus we include the backreaction of the negative energy Hawking flux in the interior geometry of the collapsing star and solve the full 4-dimensional Einstein and hydrodynamical equations numerically. We find that Hawking radiation emitted just before the star passes through its Schwarzschild radius slows down the collapse of the star and substantially reduces its mass thus the star bounces before reaching the horizon. The area radius starts increasing after the bounce. Beyond this point our program breaks down due to shell crossing. We find that the star stops collapsing at a finite radius larger than its horizon, turns around and its core explodes. This study provides a more realistic investigation of the backreaction of Hawking radiation on the collapsing star, that was first presented in [1].LuminosityThermalisationEvolution equationCausalityFinite differenceUnitarityStencilEinstein field equationsCollapsed starsNull geodesic...