- Corbino disk

by Kyrylo Snizhko6 hours ago - Quantum-size electrostatic potential

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

by Prof. Alex Suciu15 Dec 2013 03:22 - General relativity

by Wilson Yu13 Dec 2013 04:40 - High angular resolution

by Prof. Hontas Farmer22 Nov 2013 11:14 - Neutrino Minimal Standard Model

by Prof. Mikhail Shaposhnikov10 Jan 2011 23:58 - Geometric flattening

by Dr. Ganna Ivashchenko05 Dec 2010 22:14 - Gravitational lensing

by Prof. Koen Kuijken05 Dec 2010 22:11 - Minimal Dark Matter

by Dr. Marco Cirelli05 Dec 2010 22:13 - Dzyaloshinskii-Moriya interaction

by Dr. George Jackeli28 Aug 2009 09:41

- Quantum transport through an impurity-free Corbino disk in bilayer graphene is investigated analytically, by the mode-matching method for effective Dirac equation, in the presence of uniform magnetic fields. Similarly as in the monolayer case (see Refs. [1,2]), conductance at the Dirac point shows oscillations with the flux piercing the disk area $\Phi_D$ characterized by the period $\Phi_0=2\,(h/e)\ln(R_{\rm o}/R_{\rm i})$, where $R_{\rm o}$ ($R_{\rm i}$) is the outer (inner) disk radius. The oscillations magnitude depends either on the radii ratio or on the physical disk size, with the condition for maximal oscillations reading $R_{\rm o}/R_{\rm i}\simeq\left[\,R_{\rm i}t_{\perp}/(2\hbar{}v_{F})\,\right]^{4/p}$ (for $R_{\rm o}/R_{\rm i}\gg{}1$), where $t_\perp$ is the interlayer hopping integral, $v_F$ is the Fermi velocity in graphene, and $p$ is an {\em even} integer. {\em Odd}-integer values of $p$ correspond to vanishing oscillations for the normal Corbino setup, or to oscillations frequency doubling for the Andreev-Corbino setup. At higher Landau levels (LLs) magnetoconductance behaves almost identically in the monolayer and bilayer cases. A brief comparison with the Corbino disk in 2DEG is also provided in order to illustrate the role of chiral tunneling in graphene.2D electron gasDirac pointWavefunctionChiralityGrapheneHamiltonianBilayer grapheneElectrostaticsLandau levelInterference...
- We present the results of our study of a volume-limited sample (z <= 0.071) of 101 X-ray galaxy groups and clusters, in which we explore the X-ray cavity energetics. Out of the 101 sources in our parent sample, X-ray cavities are found in 30 of them, all of which have a central cooling time of less than3 Gyr. New X-ray cavities are detected in three sources. We focus on the subset of sources that have a central cooling time of less than 3 Gyr, whose active galactic nucleus (AGN) duty cycle is approximately 61 percent (30/49). This rises to over 80 percent for a central cooling time of less than 0.5 Gyr. When projection effects and central radio source detection rates are considered, the actual duty cycle is probably much higher. In addition, we show that data quality strongly affects the detection rates of X-ray cavities. After calculating the cooling luminosity and cavity powers of each source with cavities, it is evident that the bubbling process induced by the central AGN has to be, on average, continuous, to offset cooling. We find that the radius of the cavities, r, loosely depends on the ambient gas temperature as T^0.5, above about 1.5 keV, with much more scatter below that temperature. Finally, we show that, at a given location in a group or cluster, larger bubbles travel faster than smaller ones. This means that the bubbles seen at larger distances from cluster cores could be the result of the merging of several smaller bubbles, produced in separate AGN cycles.CoolingCluster of galaxiesActive Galactic NucleiIntra-cluster mediumCooling flowLuminosityOptical burstsNGC catalogCluster coreAbundance...
- We examine the spectrum of diffuse emission detected in the 17' by 17' field around Sgr A* during 625 ks of Chandra observations. The spectrum exhibits He-like and H-like lines from Si, S, Ar, Ca, and Fe, that are consistent with originating in a two-temperature plasma, as well as a prominent low-ionization Fe line. The cooler, kT=0.8 keV plasma differs in surface brightness across the image by a factor of 9. This soft plasma is probably heated by supernovae. The radiative cooling rate of the plasma within the inner 20 pc of the Galaxy could be balanced by 1% of the kinetic energy of one supernova every 300,000 y. The hotter, kT=8 keV component is more spatially uniform, ranging over a factor of 2 in surface brightness. The intensity of the hard plasma is correlated with that of the soft, but they are probably only indirectly related, because supernova remnants are not observed to produce thermal plasma hotter than kT=3 keV. Moreover, a kT=8 keV plasma is too hot to be bound to the Galactic center, and therefore would form a slow wind or fountain of plasma. The energy required to sustain such a freely-expanding plasma within the inner 20 pc of the Galaxy is ~10^40 erg/s, which corresponds to the entire kinetic energy of one supernova every 3000 y. This rate is unreasonably high. However, alternative explanations for the kT=8 keV diffuse emission are equally unsatisfying. We are left to conclude that either the diffuse emission is heated by an unanticipated source of energy, or that a population of faint (< 10^31 erg/s), hard X-ray sources that are a factor of 10 more numerous than CVs remains to be discovered. (Abridged)Diffuse emissionPoint sourceGalactic CenterSupernovaGalaxyAbsorptivityInterstellar mediumCoolingX-ray spectrumLuminosity...
- We establish a direct connection between scattering amplitudes in planar four-dimensional theories and a remarkable mathematical structure known as the positive Grassmannian. The central physical idea is to focus on on-shell diagrams as objects of fundamental importance to scattering amplitudes. We show that the all-loop integrand in N=4 SYM is naturally represented in this way. On-shell diagrams in this theory are intimately tied to a variety of mathematical objects, ranging from a new graphical representation of permutations to a beautiful stratification of the Grassmannian G(k,n) which generalizes the notion of a simplex in projective space. All physically important operations involving on-shell diagrams map to canonical operations on permutations; in particular, BCFW deformations correspond to adjacent transpositions. Each cell of the positive Grassmannian is naturally endowed with positive coordinates and an invariant measure which determines the on-shell function associated with the diagram. This understanding allows us to classify and compute all on-shell diagrams, and give a geometric understanding for all the non-trivial relations among them. Yangian invariance of scattering amplitudes is transparently represented by diffeomorphisms of G(k,n) which preserve the positive structure. Scattering amplitudes in (1+1)-dimensional integrable systems and the ABJM theory in (2+1) dimensions can both be understood as special cases of these ideas. On-shell diagrams in theories with less (or no) supersymmetry are associated with exactly the same structures in the Grassmannian, but with a measure deformed by a factor encoding ultraviolet singularities. The Grassmannian representation of on-shell processes also gives a new understanding of the all-loop integrand for scattering amplitudes, presenting all integrands in a novel dLog form which directly reflects the underlying positive structure.GraphPermutationAmplitudeGrassmannianScattering amplitudeDegree of freedomTree amplitudeKinematicsOrientationQuiver...
- A non-trivial, squared helicity amplitude is given for the scattering of an arbitrary number of gluons to lowest order in the coupling constant and to leading order in the number of colors.AmplitudeHelicityGauge fieldCoupling constantScattering amplitudeGluonScattering...
- AmplitudePerturbation theoryWard-Takahashi identityHelicitySupersymmetryQuantum chromodynamicsFeynman diagramGluonCross section...
- We present the first results of our study of a sample of 101 X-ray galaxy groups and clusters, which is volume-limited in each of three X-ray luminosity bins. The aim of this work is to study the properties of the innermost ICM in the cores of our groups and clusters, and to determine the effect of non-gravitational processes, such as active galactic nucleus (AGN) feedback, on the ICM. The entropy of the ICM is of special interest, as it bears the imprint of the thermal history of a cluster, and it also determines a cluster's global properties. Entropy profiles can therefore be used to examine any deviations from cluster self-similarity, as well as the effects of feedback on the ICM. We find that the entropy profiles are well-fitted by a simple powerlaw model, of the form $K(r) = \alpha\times(r/100 \rm{kpc})^{\beta}$, where $\alpha$ and $\beta$ are constants. We do not find evidence for the existence of an "entropy floor", i.e. our entropy profiles do not flatten out at small radii, as suggested by some previous studies.Cluster of galaxiesIntra-cluster mediumCoolingEntropyEntropy profileCooling flowActive Galactic NucleiSelf-similarityX-ray astronomyGalaxy groups and clusters...
- We conduct a joint X-ray and weak-lensing study of four relaxed galaxy clusters (Hydra A, A478, A1689 and A1835) observed by both Suzaku and Subaru out to virial radii, with an aim to understand recently-discovered unexpected feature of the ICM in cluster outskirts. We show that the average hydrostatic-to-lensing total mass ratio for the four clusters decreases from \sim 70% to \sim 40% as the overdensity contrast decreases from 500 to the virial value.The average gas mass fraction from lensing total mass estimates increases with cluster radius and agrees with the cosmic mean baryon fraction within the virial radius, whereas the X-ray-based gas fraction considerably exceeds the cosmic values due to underestimation of the hydrostatic mass. We also develop a new advanced method for determining normalized cluster radial profiles for multiple X-ray observables by simultaneously taking into account both their radial dependence and multivariate scaling relations with weak-lensing masses. Although the four clusters span a range of halo mass, concentration, X-ray luminosity and redshift, we find that the gas entropy, pressure, temperature and density profiles are all remarkably self-similar when scaled with the lensing M_200 mass and r_200 radius.The entropy monotonically increases out to \sim 0.5r_200 following the accretion shock heating model K(r)\propto r^1.1, and flattens at \simgt 0.5r_200.The universality of the scaled entropy profiles indicates that the thermalization mechanism over the entire cluster region (>0.1r_200) is controlled by gravitation in a common to all clusters, although the heating efficiency in the outskirts needs to be modified from the standard law.The bivariate scaling functions of the gas density and temperature reveal that the flattening of the outskirts entropy profile is caused by the steepening of the temperature, rather than the flattening of the gas density.Cluster of galaxiesEntropyEntropy profileWeak lensingOutskirt of a galaxy clusterWeak lensing mass estimateEllipticityIntra-cluster mediumVirial radiusPressure profile...
- Quasars emit more energy than any other objects in the universe, yet are not much bigger than the solar system. We are almost certain that quasars are powered by giant black holes of up to $10^{10}$ times the mass of the Sun, and that black holes of between $10^6$ and $10^{10}$ solar masses---dead quasars---are present at the centers of most galaxies. Our own galaxy contains a black hole of $4.3\times10^6$ solar masses. The mass of the central black hole appears to be closely related to other properties of its host galaxy, such as the total mass in stars, but the origin of this relation and the role that black holes play in the formation of galaxies are still mysteries.Black holeQuasarGalaxyStarSolar massSunParsecEvent horizonAstrophysical jetNearby galaxies...
- Magnetic reconnection is a process that changes magnetic field topology in highly conducting fluids. Traditionally, magnetic reconnection was associated mostly with solar flares. In reality, the process must be ubiquitous as astrophysical fluids are magnetized and motions of fluid elements necessarily entail crossing of magnetic frozen in field lines and magnetic reconnection. We consider magnetic reconnection in realistic 3D geometry in the presence of turbulence. This turbulence in most astrophysical settings is of pre-existing nature, but it also can be induced by magnetic reconnection itself. In this situation turbulent magnetic field wandering opens up reconnection outflow regions, making reconnection fast. We discuss Lazarian \& Vishniac (1999) model of turbulent reconnection, its numerical and observational testings, as well as its connection to the modern understanding of the Lagrangian properties of turbulent fluids. We show that the predicted dependences of the reconnection rates on the level of MHD turbulence make the generally accepted Goldreich \& Sridhar (1995) model of turbulence self-consistent. Similarly, we argue that the well-known Alfv\'en theorem on flux freezing is not valid for the turbulent fluids and therefore magnetic fields diffuse within turbulent volumes. This is an element of magnetic field dynamics that was not accounted by earlier theories. For instance, the theory of star formation that was developing assuming that it is only the drift of neutrals that can violate the otherwise perfect flux freezing, is affected and we discuss the consequences of the turbulent diffusion of magnetic fields mediated by reconnection.TurbulenceMagnetic reconnectionSimulationsMagnetohydrodynamicsMagnetohydrodynamic turbulenceEddyDissipationLundquist numberCompressibilityInstability...
- Recent work has shown that the z~2.5 Lyman-alpha forest on large scales encodes information about the galaxy and quasar populations that keep the intergalactic medium photoionized. We present the first forecasts for constraining the populations with data from current and next-generation surveys. At a minimum the forest should tell us whether galaxies or, conversely, quasars dominate the photon production. The number density and clustering strength of the ionising sources might be estimated to sub-10% precision with a DESI-like survey if degeneracies (e.g., with the photon mean-free-path, small-scale clustering power normalization and potentially other astrophysical effects) can be broken by prior information. We demonstrate that, when inhomogeneous ionisation is correctly handled, constraints on dark energy do not degrade.QuasarCosmologyBaryon acoustic oscillationsGalaxySimulationsTwo-point correlation functionMean free pathLine of sightRadiative transferCovariance matrix...
- We present an extension to the jet area-based pileup subtraction for both jet kinematics and jet shapes. A particle-level approach is explored whereby the jet constituents are corrected or removed using an extension of the methods currently being employed by the LHC experiments. Several jet shapes and nominal jet radii are used to assess the performance in simulated events with pileup levels equivalent to approximately 30 and 100 interactions per bunch crossing, which are characteristic of both the LHC Run I and Run II conditions. An improved performance in removing the pileup contributions is found when using the new subtraction method. The performance of the new procedure is also compared to other existing methods.SimulationsKinematicsHadronizationTop quarkAzimuthPileupLarge Hadron ColliderLHC RunLuminosityLHC 8 TeV run...
- We present a joint estimate of the stellar/dark matter mass fraction in lens galaxies and the average size of the accretion disk of lensed quasars from microlensing measurements of 27 quasar image pairs seen through 19 lens galaxies. The maximum likelihood estimate for the fraction of the surface mass density in the form of stars is $\alpha=0.2^{+0.1}_{-0.1}$ near the Einstein radius of the lenses ($\sim 1 - 2$ effective radii). The estimate for the average accretion disk size is $r_s=6.0^{+3.0}_{-1.1}\sqrt{M/0.3M_\sun}$ light-days. The fraction of mass in stars at these radii is significantly larger than previous estimates from microlensing studies assuming quasars were point-like. The corresponding local dark matter fraction of 80\ is in good agreement with other estimates based on strong lensing or kinematics. The size of the accretion disk inferred in the present study is slightly larger than previous estimates.Gravitational microlensingStarStellar massAccretion diskDark matterQuasarGravitational lens galaxyEinstein radiusStatisticsStrong gravitational lensing...
- We use the Arecibo Legacy Fast ALFA (ALFALFA) 21cm survey to measure the number density of galaxies as a function of their rotational velocity, Vrot,HI (as inferred from the width of their 21cm emission line). Based on the measured velocity function we statistically connect galaxies with their host halos, via abundance matching. In a LCDM cosmology, low-velocity galaxies are expected to be hosted by halos that are significantly more massive than indicated by the measured galactic velocity; allowing lower mass halos to host ALFALFA galaxies would result in a vast overestimate of their number counts. We then seek observational verification of this predicted trend, by analyzing the kinematics of a literature sample of field dwarf galaxies. We find that galaxies with Vrot,HI<25 km/s are kinematically incompatible with their predicted LCDM host halos, in the sense that hosts are too massive to be accommodated within the measured galactic rotation curves. This issue is analogous to the "too big to fail" problem faced by the bright satellites of the Milky Way, but here it concerns extreme dwarf galaxies in the field. Consequently, solutions based on satellite-specific processes are not applicable in this context. Our result confirms the findings of previous studies based on optical survey data, and addresses a number of observational systematics present in these works. Furthermore, we point out the assumptions and uncertainties that could strongly affect our conclusions. We show that the two most important among them, namely baryonic effects on the abundances and rotation curves of halos, do not seem capable of resolving the reported discrepancy.GalaxyRotation CurveALFALFA surveyVector fieldMilky WayInclinationWarm dark matterDwarf galaxySimulationsDark matter subhalo...
- We show that the Lagrangian for interacting nonrelativistic particles can be coupled to an external gauge field and metric tensor in a way that exhibits a nonrelativistic version of general coordinate invariance. We explore the consequences of this invariance on the example of the degenerate Fermi gas at infinite scattering length, where conformal invariance also plays an important role. We find the most general effective Lagrangian consistent with both general coordinate and conformal invariance to leading and next-to-leading orders in the momentum expansion. At the leading order the Lagrangian contains one phenomenological constant and reproduces the results of the Thomas-Fermi theory and superfluid hydrodynamics. At the next-to-leading order there are two additional constants. We express various physical quantities through these constants.Generalized coordinatesEffective LagrangianEffective field theoryUnitary Fermi gasSuperfluidNext-to-leading order computationConformal invariancePhononGalilean invarianceScattering length...
- We present the Early Data Release of the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. The SAMI Galaxy Survey is an ongoing integral field spectroscopic survey of ~3400 low-redshift (z<0.12) galaxies, covering galaxies in the field and in groups within the Galaxy And Mass Assembly (GAMA) survey regions, and a sample of galaxies in clusters. In the Early Data Release, we publicly release the fully calibrated datacubes for a representative selection of 107 galaxies drawn from the GAMA regions, along with information about these galaxies from the GAMA catalogues. All datacubes for the Early Data Release galaxies can be downloaded individually or as a set from the SAMI Galaxy Survey website. In this paper we also assess the quality of the pipeline used to reduce the SAMI data, giving metrics that quantify its performance at all stages in processing the raw data into calibrated datacubes. The pipeline gives excellent results throughout, with typical sky subtraction residuals of 0.9-1.2 per cent, a relative flux calibration uncertainty of 4.1 per cent (systematic) plus 4.3 per cent (statistical), and atmospheric dispersion removed with an accuracy of 0."09, less than a fifth of a spaxel.GalaxyCovarianceLarge scale structure surveyTellurateFull width at half maximumGalaxy And Mass Assembly surveyPoint spread functionField of viewStandard starSloan Digital Sky Survey...
- Pulsar timing arrays (PTAs) are designed to detect gravitational waves (GWs) at nHz frequencies. The expected dominant signal is given by the superposition of all waves emitted by the cosmological population of supermassive black hole (SMBH) binaries. Such superposition creates an incoherent stochastic background, on top of which particularly bright or nearby sources might be individually resolved. In this contribution I describe the properties of the expected GW signal, highlighting its dependence on the overall binary population, the relation between SMBHs and their hosts, and their coupling with the stellar and gaseous environment. I describe the status of current PTA efforts, and prospect of future detection and SMBH binary astrophysics.Binary starSupermassive black holeGravitational wavePulsar timing arrayEccentricityAmplitudePulsarSignal to noise ratioCosmologyMultidimensional Array...
- The matrix valued Berry gauge field strength for the Weyl Hamiltonian in 5+1 dimensions is calculated. In terms of it a symplectic form whose elements are matrices in spin indices is introduced. Definition of the volume form is modified appropriately. A simple method of finding the path integral measure and the chiral current in the presence of external electromagnetic fields is presented. It is shown that within this new approach the chiral anomaly as well as the chiral magnetic effect in 5+1 dimensions are accomplished straightforwardly.Phase spaceChiral magnetic effectChiralityHamiltonianGauge fieldChiral anomalySymplectizationKinetic theoryLiouville's equationTwo-form...
- We present the mid-infrared (IR) star formation rates of 245 X-ray selected, nearby (z<0.1) brightest cluster galaxies (BCGs). A homogeneous and volume limited sample of BCGs was created by X-ray selecting clusters with L_x > 1x10^44 erg/s. The Wide-Field Infrared Survey Explorer (WISE) AllWISE Data Release provides the first measurement of the 12 micron star formation indicator for all BCGs in the nearby Universe. Perseus A and Cygnus A are the only galaxies in our sample to have star formation rates of > 40 M_sol/yr, indicating that these two galaxies are highly unusual at current times. Stellar populations of 99 +/- 0.6 % of local BCGs are (approximately) passively evolving, with star formation rates of <10 M_sol/yr. We find that in general, star formation produces only modest BCG growth at the current epoch.Brightest cluster galaxyStar formation rateGalaxyWide-field Infrared Survey ExplorerStar formationCygnus APhotometryStar formingTwo Micron All Sky SurveyLocal Universe...
- Planet formation scenarios and the observed planetary dynamics in binaries pose a number of theoretical challenges, especially in what concerns circumbinary planetary systems. We explore the dynamical stirring of a planetesimal circumbinary disk in the epoch when the gas component disappears. For this purpose, following theoretical approaches by Heppenheimer (1978) and Moriwaki and Nakagawa (2004), we develop a secular theory for the dynamics of planetesimals in circumbinary disks. If the binary is eccentric and its components have unequal masses, a spiral density wave is generated, engulfing the disk on the secular timescale. This spiral pattern is transient; thus its observed presence may betray system's young age. We explore the pattern both analytically and in numeric experiments. The derived analytical spiral is a modified lituus; it matches the numeric density wave in the gas-free case perfectly. Using the SPH scheme, we explore the effect of residual gas on the wave propagation.PlanetesimalBinary starEccentricitySemimajor axisNumerical simulationDensity WavesPeriastronPlanetAstronomical UnitSimulations...
- Superposition demands that a linear combination of solutions to an electromagnetic problem also be a solution. This paper analyzes some very simple problems: the constructive and destructive interferences of short impulse voltage and current waves along an ideal free-space transmission line. When voltage waves constructively interfere, the superposition has twice the electrical energy of the individual waveforms because current goes to zero, converting magnetic to electrical energy. When voltage waves destructively interfere, the superposition has no electrical energy because it transforms to magnetic energy. Although the impedance of the individual waves is that of free space, a superposition of waves may exhibit arbitrary impedance. Further, interferences of identical waveforms allow no energy transfer between opposite ends of a transmission line. The waves appear to recoil elastically one from another. Although alternate interpretations are possible, these appear less likely. Similar phenomenology arises in waves of arbitrary shape and those propagating in free space as well. We may also interpret this behavior as each wave reflecting from the impedance variations the superposition imparts on free space. This work has practical implications to quantum mechanics, field diversity antenna systems, and near-field electromagnetic ranging.InterferenceElasticityMagnetic energyQuantum mechanicsElectromagnetImpedanceElectrical energyTransformationsImpulseField...
- We propose a simple and computationally fast method for performing N-body simulations for a large class of modified gravity theories with a screening mechanism such as chameleons, symmetrons and galileons. By combining the linear Klein-Gordon equation with a screening factor, calculated from analytical solutions of spherical symmetric configurations, we obtain a modified field equation whose solution is exact in the linear regime while at the same time takes screening into account on non-linear scales. The resulting modified field equation remains linear and can be solved just as quickly as the Poisson equation without any of the convergence problems that can arise when solving the full equation. We test our method with N-body simulations and find that it compares remarkably well with full simulations well into the non-linear regime.SimulationsFifth forceCold dark matterScalar fieldModified gravityCosmologyMass functionShift symmetryNewtonian potentialEffective potential...
- In this paper we show that the Germani-Kehagias model of Higgs inflation (or New Higgs Inflation), where the Higgs boson is kinetically non-minimally coupled to the Einstein tensor is in perfect compatibility with the latest Planck and BICEP2 data. Moreover, we show that the tension between the Planck and BICEP2 data can be relieved within the New Higgs inflation scenario by a negative running of the spectral index. Regarding the unitarity of the model, we argue that it is unitary throughout the evolution of the Universe. Weak couplings in the Higgs-Higgs and Higgs-graviton sectors are provided by a large background dependent cut-off scale during inflation. In the same regime, the W and Z gauge bosons acquire a very large mass, thus decouple. On the other hand, if they are also non-minimally coupled to the Higgs boson, their effective masses can be enormously reduced. In this case, the W and Z bosons are no longer decoupled. After inflation, the New Higgs model is well approximated by a quartic Galileon with a renormalizable potential. We argue that this can unitarily create the right conditions for inflation to eventually start.Higgs bosonPlanck missionBICEP2Higgs inflationSpectral index of power spectrumStandard ModelGravitonNon-minimal couplingLarge Hadron ColliderInflaton...
- We investigate large scale structure formation of collisionless dark matter in the phase-space description based on the Vlasov (or collisionless Boltzmann) equation whose nonlinearity is induced solely by gravitational interaction according to the Poisson equation. Determining the time-evolution of density and peculiar velocity demands solving the full Vlasov hierarchy for the moments of the phase-space distribution function. In the presence of long-range interaction no consistent truncation of the hierarchy is known apart from the pressureless fluid (dust) model which is incapable of describing virialization due to the occurrence of shell-crossing singularities and the inability to generate vorticity and higher cumulants like velocity dispersion. Our goal is to find a phase-space distribution function that is able to describe regions of multi-streaming and therefore can serve as theoretical N-body double. We use the coarse-grained Wigner probability distribution obtained from a wavefunction fulfilling the Schr\"odinger-Poisson equation (SPE) and show that its evolution equation bears strong resemblance to the Vlasov equation but cures the shell-crossing singularities. This feature was already employed in cosmological simulations of large-scale structure formation by Widrow & Kaiser (1993). The coarse-grained Wigner ansatz allows to calculate all higher moments from density and velocity analytically thereby incorporating nonzero higher cumulants in a self-consistent manner. On this basis we are able to show that the Schr\"odinger method (ScM) automatically closes the corresponding hierarchy such that it suffices to solve the SPE in order to directly determine density and velocity and thereby all higher cumulants.Coarse grainingVlasov equationCold dark matterPhase space densityVelocity dispersionPhase spaceEvolution equationLarge scale structureVorticityCosmology...
- Higgs inflation can occur if the Standard Model (SM) is a self-consistent effective field theory up to inflationary scale. This leads to a lower bound on the Higgs boson mass, $M_h \geq M_{\text{crit}}$. If $M_h$ is more than a few hundreds of MeV above the critical value, the Higgs inflation predicts the universal values of inflationary indexes, $r\simeq 0.003$ and $n_s\simeq 0.97$, independently on the Standard Model parameters. We show that in the vicinity of the critical point $M_{\text{crit}}$ the inflationary indexes acquire an essential dependence on the mass of the top quark $m_t$ and $M_h$. Thus the cosmological measurements of $r$ and $n_s$ different from the universal values lead to precise prediction of $M_h$ and $m_t$.Standard ModelHiggs inflationCritical pointHiggs fieldTop quarkEinstein frameHiggs boson massPlanck scaleCERNHiggs boson...
- When measuring the one-dimensional power spectrum of the Ly$\alpha$ forest, it is common to measure the power spectrum in flux fluctuations red-ward of the Ly$\alpha$ emission of quasars and subtract this power from the measurements of the Ly$\alpha$ flux power spectrum. This removes excess power present in the Ly$\alpha$ forest which is believed to be dominated by metal absorption by the low-redshift metals uncorrelated with the neutral hydrogen aborbing in Ly$\alpha$. In this brief report we note that, assuming the contaminants are additive in optical depth, the correction contains a second order term. We estimate the magnitude of this term for two currently published measurements of the 1D Ly$\alpha$ flux power spectrum and show that it is negligible for the current generation of measurements. However, future measurements will have to take this into account when errorbars improve by a factor of two or more.Flux power spectrumQuasarAbsorptivityAbsorbanceNeutral hydrogen gasStatisticsBaryon Oscillation Spectroscopic SurveyIntergalactic mediumProximity effectWave vector...
- We study the finite temperature and density effects on beta decay rates to compute their contributions to nucleosynthesis. QED type corrections to beta decay from the background are studied in the standard model with massless neutrinos. So we re-examine the electron mass contributions and compute the beta decay rate, helium yield, energy density of the universe as well as the change in neutrino temperature, directly from the first order contribution to the selfmass of electrons during these processes. We express nucleosynthesis parameters as a function of temperature and density in different astronomical systems of interest. In this paper, we notice that the helium abundance at T=m of a cooling universe (0.045%) is higher than the helium abundance of a heating universe (0.031%) indicates that the universe started to produce helium at T>m and stopped after some point at T<m. It is also explicitly shown that the chemical potential in the core of supermassive and superdense stars affect beta decay and their helium abundance but the background contributions is still dependent on relative temperature. We calculate this contribution for Temperatures sufficiently smaller than the electron mass which is smaller than the chemical potential. It has been noticed that the acceptable background contribution are obtained for comparatively larger values of T as temperature plays a role of regulating parameter in an extremely dense system.NucleosynthesisElectron massBeta decayQuantum electrodynamicsThe early UniverseAbundanceRenormalizationNeutrinoRadiative correctionCooling...
- We provide an explicit expression for the renormalized expectation value of the stress-energy tensor of a spin-$1/2$ field in a spatially flat FLRW universe. Its computation is based on the extension of the adiabatic regularization method to fermion fields introduced recently in the literature. The tensor is given in terms of UV-finite integrals in momentum space, which involve the mode functions that define the quantum state. As illustrative examples of the method efficiency, we see how to compute the renormalized energy density and pressure in two interesting cosmological scenarios: a de Sitter spacetime and a radiation-dominated universe. In the second case, we explicitly show that the late-time renormalized stress-energy tensor behaves as that of classical cold matter. We also check that, if we obtain the adiabatic expansion of the scalar field mode functions with a similar procedure to the one used for fermions, we recover the well-known WKB-type expansion.RenormalizationFriedmann-Lemaitre-Robertson-Walker metricRegularizationScalar fieldDe Sitter spaceCosmologyVacuum expectation valueExpanding universeScalar mode fluctuationExpectation Value...
- We predict the spatial distribution and number of Milky Way dwarf galaxies to be discovered in the DES and LSST surveys, by completeness correcting the observed SDSS dwarf population. We apply most massive in the past, earliest forming, and earliest infall toy models to a set of dark matter-only simulated Milky Way/M31 halo pairs from Exploring the Local Volume In Simulations (ELVIS). The observed spatial distribution of Milky Way dwarfs in the LSST-era will discriminate between the earliest infall and other simplified models for how dwarf galaxies populate dark matter subhalos. Inclusive of all toy models and simulations, at 90% confidence we predict a total of 37-114 L $\gtrsim 10^3$L$_{\odot}$ dwarfs and 131-782 L $\lesssim 10^3$L$_{\odot}$ dwarfs within 300 kpc. These numbers of L $\gtrsim 10^3$L$_{\odot}$ dwarfs are dramatically lower than previous predictions, owing primarily to our use of updated detection limits and the decreasing number of SDSS dwarfs discovered per sky area. For an effective $r_{\rm limit}$ of 25.8 mag, we predict: 3-13 L $\gtrsim 10^3$L$_{\odot}$ and 9-99 L $\lesssim 10^3$L$_{\odot}$ dwarfs for DES, and 18-53 L $\gtrsim 10^3$L$_{\odot}$ and 53-307 L $\lesssim 10^3$L$_{\odot}$ dwarfs for LSST. These enormous predicted ranges ensure a coming decade of near-field excitement with these next generation surveys.A dwarfsDark matter subhaloMilky WaySimulationsExploring the Local Volume in SimulationsLarge Synoptic Survey TelescopeThe Dark Energy SurveySloan Digital Sky SurveyDwarf galaxyUltra-faint dwarf spheroidal galaxy...
- The renormalization of supersymmetric Yang-Mills theories with soft supersymmetry breaking is presented using spurion fields for introducing the breaking terms. It is proven that renormalization of the fields and parameters in the classical action yields precisely the correct counterterms to cancel all divergences. In the course of the construction of higher orders additional independent parameters appear, but they can be shown to be irrelevant in physics respects. Thus, the only parameters with influence on physical amplitudes are the supersymmetric and the well-known soft breaking parameters.Soft symmetry breakingRenormalizationSupersymmetrySlavnov-Taylor identitiesChiralitySpurionSuper Yang-Mills theoryQuadratic divergenceEffective actionSuperspace...
- We present a complete calculation of the cross section for neutralino annihilation into the two-gluon final state. This channel can be quite important for the phenomenology of neutralino annihilation due to the well-known helicity suppression of neutralino annihilation into light quarks and leptons. In addition, we calculate the cross section for annihilation of neutralinos into a gluon and quark-antiquark pair, and discuss QCD corrections to the tree-level cross sections for neutralino annihilation into quarks. If the neutralino is lighter than the top quark, the effect of these results on high-energy neutrino signals from neutralino annihilation in the Sun and in the Earth can be significant, especially if the neutralino is primarily gaugino. On the other hand, our results should have little effect on calculations of the cosmological abundance of neutralinos. We also briefly discuss implications for cosmic-ray antiprotons from neutralino annihilation in the galactic halo.NeutralinoNeutrinoQuarkNeutralino annihilationQuark massEarthSunAntiprotonCosmic rayBranching ratio...
- The spectrum of photons arising from WIMP annihilation carries a detailed imprint of the structure of the dark sector. In particular, loop-level annihilations into a photon and another boson can in principle lead to a series of lines (a WIMP forest) at energies up to the WIMP mass. A specific model which illustrates this feature nicely is a theory of two universal extra dimensions compactified on a chiral square. Aside from the continuum emission, which is a generic prediction of most dark matter candidates, we find a "forest" of prominent annihilation lines that, after convolution with the angular resolution of current experiments, leads to a distinctive (2-bump plus continuum) spectrum, which may be visible in the near future with the Fermi Gamma-Ray Space Telescope (formerly known as GLAST).Weakly interacting massive particleChiralityStandard ModelWIMP annihilationBosonizationKaluza-Klein modeDark matterUniversal extra dimensionsDark matter candidateFERMI telescope...
- It is proven by explicit construction that regularization by dimensional reduction can be formulated in a mathematically consistent way. In this formulation the quantum action principle is shown to hold. This provides an intuitive and elegant relation between the D-dimensional Lagrangian and Ward or Slavnov-Taylor identities, and it can be used in particular to study to what extent dimensional reduction preserves supersymmetry. We give several examples of previously unchecked cases.SupersymmetrySlavnov-Taylor identitiesRegularizationGreen's functionFeynman diagramsSupersymmetric gauge theoryOne particle irreducibleVertex functionDimensional ReductionCovariance...
- The simplest renormalizable effective field theories with asymmetric dark matter bound states contain two additional gauge singlet fields one being the dark matter and the other a mediator particle that the dark matter annihilates into. We examine the physics of one such model with a Dirac fermion as the dark matter. For a range of parameters the Yukawa coupling of the dark matter to the mediator gives rise to stable asymmetric dark matter bound states. We derive properties of the bound states including nuggets formed from $N\gg1$ dark matter particles. We also consider the formation of bound states in the early universe and direct detection of dark matter bound states. Many of our results also hold for symmetric dark matter.Bound stateDark matterAsymmetric dark matterDark matter particleStandard ModelCosmologyThe early UniverseFreeze-outEffective theoryHiggs boson...
- After two decades of repository development, some conclusions may be drawn as to which type of repository and what kind of service best supports digital scholarly communication, and thus the production of new knowledge. Four types of publication repository may be distinguished, namely the subject-based repository, research repository, national repository system and institutional repository. Two important shifts in the role of repositories may be noted. With regard to content, a well-defined and high quality corpus is essential. This implies that repository services are likely to be most successful when constructed with the user and reader uppermost in mind. With regard to service, high value to specific scholarly communities is essential. This implies that repositories are likely to be most useful to scholars when they offer dedicated services supporting the production of new knowledge. Along these lines, challenges and barriers to repository development may be identified in three key dimensions: a) identification and deposit of content; b) access and use of services; and c) preservation of content and sustainability of service. An indicative comparison of challenges and barriers in some major world regions such as Europe, North America and East Asia plus Australia is offered in conclusion.Communication
- In the present paper, we studied by means of the SIM introduced in Del Popolo (2009), the total and DM density profiles, and the correlations among different quantities, observed by Newman et al. (2012a,b), in seven massive and relaxed clusters, namely MS2137, A963, A383, A611, A2537, A2667, A2390. Similarly to Newman et al. (2012a,b), the total density profile, in the radius range 0.003 - 0.03$r_{200}$, has a mean total density profile in agreement with dissipationless simulations. The slope of the DM profiles of all clusters is flatter than -1. The slope, $\alpha$, has a maximum value (including errors) of $\alpha=-0.88$ in the case of A2390, and minimum value $\alpha=-0.14$ for A2537. The baryonic component dominates the mass distribution at radii $< 5-10$ kpc, while the outer distribution is dark matter dominated. We found an anti-correlation among the slope $\alpha$, the effective radius, $R_e$, and the BCG mass, and a correlation among the core radius $r_{core}$, and $R_e$. Moreover, the mass in 100 kpc (mainly dark matter) is correlated with the mass inside 5 kpc (mainly baryons). The behavior of the total mass density profile, the DM density profile, and the quoted correlations can be understood in a double phase scenario. In the first dissipative phase the proto-BCG forms, and in the second dissipationless phase, dynamical friction between baryonic clumps (collapsing to the center) and the DM halo flattens the inner slope of the density profile. In simple terms, the large scatter in the inner slope from cluster to cluster, and the anti-correlation among the slope, $\alpha$ and $R_e$ is due to the fact that in order to have a total mass density profile which is NFW-like, clusters having more massive BCGs at their centers must contain less DM in their center. Consequently the inner profile has a flatter slope.Cluster of galaxiesDark matterBrightest cluster galaxyDark Matter Density ProfileSimulationsBaryon contentNavarro-Frenk-White profileEllipticityInfall modelAbell 383...
- This paper describes a new algorithm for recovering low-rank matrices from their linear measurements contaminated with Poisson noise: the Poisson noise Maximum Likelihood Singular Value thresholding (PMLSV) algorithm. We propose a convex optimization formulation with a cost function consisting of the sum of a likelihood function and a regularization function which the nuclear norm of the matrix. Instead of solving the optimization problem directly by semi-definite program (SDP), we derive an iterative singular value thresholding algorithm by expanding the likelihood function. We demonstrate the good performance of the proposed algorithm on recovery of solar flare images with Poisson noise: the algorithm is more efficient than solving SDP using the interior-point algorithm and it generates a good approximate solution compared to that solved from SDP.Shot noiseSingular valueRegularizationLikelihood functionMaximum likelihoodIntensitySolar flareRegular functionRankingConvex set...
- The discovery of topological phases in condensed matter systems has changed the modern conception of phases of matter. The global nature of topological ordering makes these phases robust and hence promising for applications. However, the non-locality of this ordering makes direct experimental studies an outstanding challenge, even in the simplest model topological systems, and interactions among the constituent particles adds to this challenge. Here we demonstrate a novel dynamical method to explore topological phases in both interacting and non-interacting systems, by employing the exquisite control afforded by state-of-the-art superconducting quantum circuits. We utilize this method to experimentally explore the well-known Haldane model of topological phase transitions by directly measuring the topological invariants of the system. We construct the topological phase diagram of this model and visualize the microscopic evolution of states across the phase transition, tasks whose experimental realizations have remained elusive. Furthermore, we developed a new qubit architecture that allows simultaneous control over every term in a two-qubit Hamiltonian, with which we extend our studies to an interacting Hamiltonian and discover the emergence of an interaction-induced topological phase. Our implementation, involving the measurement of both global and local textures of quantum systems, is close to the original idea of quantum simulation as envisioned by R. Feynman, where a controllable quantum system is used to investigate otherwise inaccessible quantum phenomena. This approach demonstrates the potential of superconducting qubits for quantum simulation and establishes a powerful platform for the study of topological phases in quantum systems.QubitHamiltonianBerry phaseManifoldMagnetic monopoleGround state manifoldTopological orderGrapheneBrillouin zoneQuantization...
- One of the goals of probabilistic inference is to decide whether an empirically observed distribution is compatible with a candidate Bayesian network. However, Bayesian networks with hidden variables give rise to highly non-trivial constraints on the observed distribution. Here, we propose an information-theoretic approach, based on the insight that conditions on entropies of Bayesian networks take the form of simple linear inequalities. We describe an algorithm for deriving entropic tests for latent structures. The well-known conditional independence tests appear as a special case. While the approach applies for generic Bayesian networks, we presently adopt the causal view, and show the versatility of the framework by treating several relevant problems from that domain: detecting common ancestors, quantifying the strength of causal influence, and inferring the direction of causation from two-variable marginals.Directed acyclic graphCausalityEntropyBayesian networkCausal inferenceStatisticsTest statisticGraphBinary starInformation theory...
- QuarkTransport theoryNuclear matterPlasma oscillationRelativistic plasmaQuark-gluon plasmaFluid dynamicsMean-field approximationParticlesPlasma...
- We investigate the phenomenology of new abelian gauge bosons, which we denote as $X$ bosons, that suffer a mixed anomaly with the Standard Model, but are made self-consistent by the Green-Schwarz mechanism. A distinguishing aspect of the resulting effective theory is the decay of $X$ bosons into Standard Model gauge bosons, $X\to ZZ, WW, \gamma Z$. We compute the production cross-section of the $X$ boson from vector boson fusion at the Large Hadron Collider. We study the $pp\to X\to ZZ\to 4l$ signal, and analyze the prospects of discovery. We argue that such a discovery could indirectly probe high energies, even up to the string scale.Standard ModelVector bosonBosonizationLarge Hadron ColliderChiralityGreen-Schwarz mechanismQuantum anomalyMixed anomalyGauge invarianceEffective theory...
- By considering the kinetic equations for the relic particles and the bath particles supposed in thermal and chemical equilibrium in the early Universe, we show that the problem of finding the present relic abundance is exactly defined by a system of two equations, the usual Boltzmann equation and a new one previously not recognized. The analytical solution of the latter gives the abundance down to a matching temperature that can be identified with freeze out temperature $x_f=m/T_f$, while the usual Boltzmann equation is valid only for $x \ge x_f$. The dependence of the present relic abundance on the abundance at an intermediate temperature is an exact result and not the consequence of the so called freeze out approximation. We also suggest an analytical approximation that furnishes the relic abundance accurate at the level of $1\%-2\%$ in the case of $S$-wave and $P$-wave scattering cross sections.Freeze-outRelic abundanceAbundanceWeakly interacting massive particleStatisticsBoltzmann transport equationChemical equilibriumDegree of freedomEntropyDark matter...
- Minimal Flavor Violation offers an alternative symmetry rationale to R-parity conservation for the suppression of proton decay in supersymmetric extensions of the Standard Model. The naturalness of such theories is generically under less tension from LHC searches than R-parity conserving models. The flavor symmetry can also guarantee the stability of dark matter if it carries flavor quantum numbers. We outline general features of supersymmetric flavored dark matter (SFDM) models within the framework of MFV SUSY. A simple model of top flavored dark matter is presented. If the dark matter is a thermal relic, then nearly the entire parameter space of the model is testable by upcoming direct detection and LHC searches.Dark matterStandard ModelSupersymmetrySuperpotentialSpurionR-parityGluinoPair productionSpin independentSupersymmetry breaking...
- Neutron stars undergoing r-mode oscillation emit gravitational radiation that might be detected on earth. For known millisecond pulsars the observed spindown rate imposes an upper limit on the possible gravitational wave signal of these sources. Taking into account the physics of r-mode evolution, we show that only sources spinning at frequencies above a few hundred Hertz can be unstable to r-modes, and we derive a more stringent universal r-mode spindown limit on their gravitational wave signal, exploiting the fact that the r-mode saturation amplitude is insensitive to the structural properties of individual sources. We find that this refined bound limits the gravitational wave strain from millisecond pulsars to values below the detection sensitivity of next-generation detectors. Young sources are therefore a more promising option for the detection of gravitational waves emitted by r-modes and to probe the interior composition of compact stars in the near future.AmplitudeGravitational waveStarCoolingRadio pulsarMillisecond pulsarPulsarNeutron starInstabilityDissipation...
- In recent years, there have been several successful attempts to constrain the equation of state of neutron star matter using input from low-energy nuclear physics and observational data. We demonstrate that significant further restrictions can be placed by additionally requiring the pressure to approach that of deconfined quark matter at high densities. Remarkably, the new constraints turn out to be highly insensitive to the amount --- or even presence --- of quark matter inside the stars.Quark matterStarPolytropesNeutron starEffective field theoryCompact starChiralitySolar massNuclear matterFirst-order phase transitions...
- We study the symmetries of non-relativistic systems with an emphasis on applications to the fractional quantum Hall effect. A source for the energy current of a Galilean system is introduced and the non-relativistic diffeomorphism invariance studied in previous work is enhanced to a full spacetime symmetry, allowing us to derive a number of Ward identities. These symmetries are smooth in the massless limit of the lowest Landau level. We develop a formalism for Newton-Cartan geometry with torsion to write these Ward identities in a covariant form. Previous results on the connection between Hall viscosity and Hall conductivity are reproduced.CovarianceLowest Landau LevelTorsion tensorDiffeomorphismMassless limitDiffeomorphism invarianceSpacetime symmetriesNon-relativistic diffeomorphismLandau levelRegularization...
- 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...
- Lecture Notes of the 45th IFF Spring School "Computing Solids - Models, ab initio methods and supercomputing" (Forschungszentrum Juelich, 2014).Berry phaseHamiltonianInsulatorsChern numberWavefunctionBrillouin zoneSpin-orbit interactionQuantizationCurvatureWave packet...
- The connection between cosmological observations and neutrino physics is discussed in detail. Neutrinos decouple from thermal contact in the early Universe at a temperature of order 1 MeV which coincides with the temperature where light element synthesis occurs. Observation of light element abundances therefore provides important information on such properties as neutrino energy density and chemical potential. Precision observations of the cosmic microwave background and large scale structure of galaxies can be used to probe neutrino masses with greater precision than current laboratory experiments. In this review I discuss current cosmological bounds on neutrino properties, as well as possible bounds from upcoming measurements.NeutrinoNeutrino massCosmic microwave backgroundLarge scale structureCosmologyBig bang nucleosynthesisMatter power spectrumCold dark matterGalaxyStandard Model...
- The known calculations of the fermion condensate $<\bar{\psi}\psi>$ and the correlator $<\bar{\psi}\psi(x) ~\bar{\psi}\psi(0)>$ have been interpreted in terms of {\em localized} instanton solutions minimizing the {\em effective} action. Their size is of order of massive photon Compton wavelength $\mu^{-1}$. At high temperature, these instantons become quasistatic and present the 2-dimensional analog of the `walls' found recently in 4-dimensional gauge theories. In spite of the static nature of these solutions, they should not be interpreted as `thermal solitons' living in Minkowski space: the mass of these would-be solitons does not display itself in the physical correlators. At small but nonzero fermion mass, the high-T partition function of $QED_2$ is saturated by the rarefied gas of instantons and antiinstantons with density $\propto m~\exp\{-S^{inst.}\}~=~m~\exp\{-\pi T/\mu\}$ to be confronted with the dense strongly correlated instanton-antiinstanton liquid saturating the partition function at $T=0$.InstantonPartition functionSchwinger modelTopological quantum numberZero modeFunctional integrationQuantum fluctuationTorusSolitonLiquids...