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  • Intergalactic space is filled with a pervasive medium of ionized gas, the Intergalactic Medium (IGM). A residual neutral fraction is detected in the spectra of Quasi-Stellar Objects at both low and high redshifts, revealing a highly fluctuating medium with temperatures characteristic of photoionized gas. The statistics of the fluctuations are well-reproduced by numerical gravity-hydrodynamics simulations within the context of standard cosmological structure formation scenarios. As such, the study of the IGM offers an opportunity to probe the nature of the primordial density fluctuations on scales unavailable to other methods. The simulations also suggest the IGM is the dominant reservoir of baryons produced by the Big Bang, and so the principal source of the matter from which galaxies formed. The detection of metal systems within the IGM shows that it was enriched by evolved stars early in its history, demonstrating an intimate connection between galaxy formation and the IGM. The author presents a comprehensive review of the current understanding of the structure and physical properties of the IGM and its relation to galaxies, concluding with comments on prospects for furthering the study of the IGM using future ground-based facilities and space-based experiments.
    QuasarAbsorptivityReionizationAbsorbanceRecombinationDamped Lyman-alpha systemAbsorption featureLine of sightUltraviolet backgroundLuminosity...
  • We review the hadro-production data presently available on open charm and beauty absolute production cross-sections, collected by experiments at CERN, DESY and Fermilab. The published charm production cross-section values are updated, in particular for the "time evolution" of the branching ratios. These measurements are compared to LO pQCD calculations, as a function of the collision energy, using recent parametrisations of the parton distribution functions. We then estimate, including nuclear effects of the parton densities, the charm and beauty production cross-sections relevant for measurements at SPS and RHIC energies, in proton-proton, proton-nucleus and nucleus-nucleus collisions. The calculations are also compared with measurements of single D and B kinematical distributions, and DDbar pair correlations. We finish with two brief comments, concerning the importance of beauty production as a feed-down source of J/psi production, and open charm measurements performed using leptonic decays.
    D mesonParton distribution functionHadronizationPhase spaceMuonPionSystematic errorCollider Detector at FermilabQuarkNeutral D mesons...
  • X-ray surface brightness fluctuations in the core of the Perseus Cluster are analyzed, using deep observations with the Chandra observatory. The amplitude of gas density fluctuations on different scales is measured in a set of radial annuli. It varies from 8 to 12 per cent on scales of ~10-30 kpc within radii of 30-160 kpc from the cluster center and from 9 to 7 per cent on scales of ~20-30 kpc in an outer, 60-220 kpc annulus. Using a statistical linear relation between the observed amplitude of density fluctuations and predicted velocity, the characteristic velocity of gas motions on each scale is calculated. The typical amplitudes of the velocity outside the central 30 kpc region are 90-140 km/s on ~20-30 kpc scales and 70-100 km/s on smaller scales ~7-10 kpc. The velocity power spectrum is consistent with cascade of turbulence and its slope is in a broad agreement with the slope for canonical Kolmogorov turbulence. The gas clumping factor estimated from the power spectrum of the density fluctuations is lower than 7-8 per cent for radii ~30-220 kpc from the center, leading to a density bias of less than 3-4 per cent in the cluster core. Uncertainties of the analysis are examined and discussed. Future measurements of the gas velocities with the Astro-H, Athena and Smart-X observatories will directly measure the gas density-velocity perturbation relation and further reduce systematic uncertainties in these quantities.
    Point sourceShot noiseIntra-cluster mediumDissipationCluster of galaxiesPerseus Cluster coreNumerical simulationMean free pathCalibrationFactorisation...
  • Bohmian mechanics is a theory about point particles moving along trajectories. It has the property that in a world governed by Bohmian mechanics, observers see the same statistics for experimental results as predicted by quantum mechanics. Bohmian mechanics thus provides an explanation of quantum mechanics. Moreover, the Bohmian trajectories are defined in a non-conspiratorial way by a few simple laws.
    Bohmian mechanicsQuantum mechanicsStatisticsQuantum field theoryManifoldQuantum measurementPermutationSelf-adjoint operatorIdentical particlesContinuity equation...
  • Isolated neutron stars show a diversity in timing and spectral properties, which has historically led to a classification in different sub-classes. The magnetic field plays a key role in many aspects of the neutron star phenomenology: it regulates the braking torque responsible for their timing properties and, for magnetars, it provides the energy budget for the outburst activity and high quiescent luminosities (usually well above the rotational energy budget). We aim at unifying this observational variety by linking the results of the state-of-the-art 2D magneto-thermal simulations with observational data. The comparison between theory and observations allows to place two strong constraints on the physical properties of the inner crust. First, strong electrical currents must circulate in the crust, rather than in the star core. Second, the innermost part of the crust must be highly resistive, which is in principle in agreement with the presence of a novel phase of matter so-called nuclear pasta phase.
    Neutron starThermalisationDissipationPulsarCoolingX-ray pulsarCooling curveKinematicsJouleMagnetic field strength...
  • We explore the possibility of employing e+e- colliders to probe the scotogenic model, in which neutrinos get mass radiatively via one-loop interactions involving dark matter. Assuming the lightest one of the new particles in the model to be fermionic cold dark matter and taking into account various constraints, including those from LHC Higgs experiments, we show that LEP II data on e+e- scattering into a pair of charged leptons plus missing energy can place significant extra restrictions on the parameter space which contains sufficiently low masses of the charged scalars in the model. On the other hand, LEP II data on e+e- collisions into a photon plus missing energy do not yield strong constraints. The allowed parameter space can still accommodate Higgs exotic decays into the nonstandard particles and thus is testable at the LHC. We also consider using future measurements of these two types of e+e- scattering at the International Linear Collider to examine the scenario of interest further and find that they can provide complementary information whether or not they reveal scotogenic effects.
    International Linear ColliderDark matterLarge Hadron ColliderStandard ModelNeutrinoHiggs bosonCharged leptonBranching ratioYukawa couplingCold dark matter...
  • The search for new physics in single- and multi-photon final states with large missing energy at LEP and future e^+ e^- colliders requires precise predictions for the Standard Model irreducible background. While at LEP1 the theoretical situation is under control, going to LEP2 (and beyond) some improvements are necessary. To approach the aimed $O(1%)$ theoretical accuracy, the tree-level matrix elements for the processes $e^+ e^- \to \nu \bar\nu n\gamma$, with n=1,2,3, are exactly computed in the Standard Model, including the possibility of anomalous couplings for single-photon production. Due to the presence of observed photons in the final state, particular attention is paid to the treatment of higher-order QED corrections. Comparisons with existing calculations are shown and commented. An improved version of the event generator NUNUGPV is presented.
    Standard ModelRadiative correctionNeutrinoMissing massPhase spacePYTHIASoft photonsBosonizationDegree of freedomLarge Electron-Positron Collider...
  • The Tribimaximal (TBM) ansatz for neutrino mixing has recently been invalidated. Since the TBM ansatz yielded a vanishing determinant for the neutrino propagation matrix, $\mathscr{P}$, the door is now open for a non-vanishing determinant, i.e., for an invertible $\mathscr{P}$, which would allow an inference of flavor ratios at cosmic sources directly from measurements at Earthly observatories. However, we show that the determinant of $\mathscr{P}$ can still vanish if the CP-violating phase $\delta$ is equal to a unique value determined by the three leptonic mixing angles. Validation of this result would beg for a new symmetry in the three-neutrino sector. Neutrino flavor ratios evolve according to this $\mathscr{P}$ matrix. The evolved flavor ratios are best exhibited in a triangular flavor diagram. We prove a theorem, that the area of this Earthly flavor triangle is proportional to the determinant of the $\mathscr{P}$ matrix. This theorem therefore relates the triangle's area to the invertiblity of $\mathscr{P}$. The triangle is thin. We relate this thinness to the small deviations of the two angles $\theta_{32}$ and $\theta_{13}$ from their TBM values. Finally, we consider ramifications of the expected lack of $\nu_\tau$ injection at cosmic sources. With the use of the Earthly flavor triangle, some tests of this "no $\nu_\tau$ injection" hypothesis are given.
    Neutrino telescopeUnitarityQuarkIceCube Neutrino ObservatoryEarthNeutrino interactionsNormal hierarchyUnitary transformationNeutrino flavorNeutrino oscillation experiments...
  • Finding new collective electronic states in materials is one of the fundamental goals of condensed matter physics. Atomic-scale superlattices formed from transition metal oxides are a particularly appealing hunting ground for new physics. In bulk form, transition metal oxides exhibit a remarkable range of magnetic, superconducting, and multiferroic phases that are of great scientific interest and are potentially capable of providing innovative energy, security, electronics and medical technology platforms. In superlattices new states may emerge at the interfaces where dissimilar materials meet. Here we illustrate the essential features that make transition metal oxide-based heterostructures an appealing discovery platform for emergent properties with a few selected examples, showing how charge redistributes, magnetism and orbital polarization arises and ferroelectric order emerges from heterostructures comprised of oxide components with nominally contradictory behavior with the aim providing insight into the creation and control of novel behavior at oxide interfaces by suitable mechanical, electrical or optical boundary conditions and excitations.
    Unit cellFerromagnetismInsulatorsCopper oxideDopingSemiconductorDegree of freedomCompressibilityThin filmsChemical bond...
  • These are lecture notes of an introduction to quantum integrability given at the Tenth Modave Summer School in Mathematical Physics, 2014, aimed at PhD candidates and junior researchers in theoretical physics. We introduce spin chains and discuss the coordinate Bethe Ansatz (CBA) for a representative example: the Heisenberg XXZ model. The focus lies on the structure of the CBA and on its main results, deferring a detailed treatment of the CBA for the general $M$-particle sector of the XXZ model to an appendix. Subsequently the transfer-matrix method is discussed for the six-vertex model, uncovering a relation between that model and the XXZ spin chain. Equipped with this background the quantum inverse-scattering method (QISM) and algebraic Bethe Ansatz (ABA) are treated. We emphasize the use of graphical notation for algebraic quantities as well as computations. Finally we turn to quantum integrability in the context of theoretical high-energy physics. We discuss factorized scattering in two-dimensional QFT, and conclude with a qualitative introduction to one current research topic relating quantum integrability to theoretical high-energy physics: the Bethe/gauge correspondence.
    XXZ modelBethe ansatzXXZ spin chainQuantum inverse scattering methodTransfer-matrix methodAlgebraScatteringParticlesSpin...
  • This is a slightly edited version of my talk on Mathematische Arbeitstagung 2011, Bonn. I present a result relating noncommutative Laurent polynomials with algebraic functions, and show examples of integrability and Laurent phenomenon for free noncommutative variables.
    AutomorphismDiscrete symmetryLine bundleLaurent polynomialConjugacy classFormal power seriesOne-parameter groupLinear functionalFree independenceCyclic permutation...
  • Few independent detections of a weak X-ray emission line at an energy of ~3.5 keV seen toward a number of astrophysical sites have been reported. If this signal will be confirmed to be the signature of decaying DM sterile neutrino with a mass of ~7.1 keV, then the cosmological observables should be consistent with its properties. We compute the radiation and matter perturbations including the full resonance sweep solution for active - sterile neutrino flavor conversion and place constraints on the cosmological parameters and sterile neutrino properties by using most of the present cosmological measurements. We find the sterile neutrino upper limits for mass and mixing angle of 7.86 keV (equivalent to 2.54 keV thermal mass) and 9.41 x 10^{-9} (at 95% CL) respectively, for a lepton number per flavor of 0.0042, that is significantly higher than that inferred in Abazajian (2014) from the linear large scale structure constraints. This reflects the sensitivity of the high precision CMB anisotropies to the helium abundance yield which in turn is set by the electron neutrino lepton number and the non-thermal active neutrino spectra. Other cosmological parameters are in agreement with the predictions of the minimal extension of the base LambdaCDM model except for the active neutrino total mass uper limit that is decreased to 0.21 eV (95% CL).
    NeutrinoDark matterLepton asymmetryPhase space densitySterile neutrino DMBig bang nucleosynthesisThermalisationSterile neutrino massRP sterile neutrinosStandard Model...
  • The structure and dark matter halo core properties of dwarf spheroidal galaxies (dSphs) are investigated. A double-isothermal model of an isothermal stellar system, embedded in an isothermal dark halo core provides an excellent fit to the various observed stellar surface density distributions. The stellar system can be well characterised by King profiles with a broad distribution of concentration parameters c. The core scale length of the stellar system a_* is sensitive to the central dark matter density rho_0. In contrast to single-component systems, the cut-off radius of the stellar system, rs_t, however does not trace the tidal radius but the core radius r_c of its dark matter halo. c is therefore sensitive to the ratio of the stellar to the dark matter velocity dispersion, sigma_*/sigma_0. Simple empirical relationships are derived that allow to calculate the dark halo core parameters rho_0, r_c and sigma_0, given the observable quantities sigma_*, a_* and c. The DIS model is applied to the Milky Way's dSphs. Their halo velocity dispersions lie in a narrow range of 10km/s <= sigma_0 <= 18km/s with halo core radii of 280pc <= r_c <= 1.3kpc and r_c=2a_*. All dSphs follow closely the same universal dark halo core scaling relation rho_0*r_c=75 Msolar/pc^2 that characterises the cores of more massive galaxies over several orders of magnitude in mass. The dark matter core mass is a strong function of core radius. Inside a fixed radius r_u, with r_u the logarithmic mean of the dSph's core radii, the total enclosed mass M_u is however roughly constant, although outliers should exist. For our dSphs we find r_u=400pc and M_u=2.6*10^7 Msolar. The core densities of the Galaxy's dSphs are very high, with rho_0=0.2 Msolar/pc^3. They should therefore be tidally undisturbed. Observational evidence for tidal effects might then provide a serious challenge for the cold dark matter scenario.
    StarKing modelKinematicsCold dark matterRotation CurveMilky WayStar systemsStellar velocity dispersionHost galaxyCarina Dwarf...
  • Superradiance is a radiation enhancement process that involves dissipative systems. With a 60 year-old history, superradiance has played a prominent role in optics, quantum mechanics and especially in relativity and astrophysics. In General Relativity, black-hole superradiance is permitted by dissipation at the event horizon, that allows for energy and angular momentum extraction from the vacuum, even at the classical level. Black-hole superradiance is intimately connected to the black-hole area theorem, Penrose process, tidal forces and even Hawking radiation, which can be interpreted as a quantum version of black-hole superradiance. Various mechanisms (as diverse as massive fields, magnetic fields, anti-de Sitter boundaries, nonlinear interactions, etc...) can confine the amplified radiation and give rise to strong instabilities. These "black-hole bombs" have applications in searches of dark matter and of physics beyond the Standard Model, are associated to the threshold of formation of new black hole solutions that evade the no-hair theorems, can be studied in the laboratory by devising analog models of gravity, and even provide a holographic description of spontaneous symmetry breaking and superfluidity through the gauge-gravity duality. This work is meant to provide a unified picture of this multifaceted subject, which was missing in the literature. We focus on the recent developments in the field, and work out a number of novel examples and applications, ranging from fundamental physics to astrophysics.
    Black holeHorizonGravitational waveKerr black holeStarScalar fieldBosonizationAccretionSpinning Black HoleGeneral relativity...
  • Path integral Monte Carlo (PIMC) simulations have become an important tool for the investigation of the statistical mechanics of quantum systems. I discuss some of the history of applying the Monte Carlo method to non-relativistic quantum systems in path-integral representation. The principle feasibility of the method was well established by the early eighties, a number of algorithmic improvements have been introduced in the last two decades.
    StatisticsAutocorrelationPartition functionQuantum mechanicsDensity matrixHarmonic oscillatorStatistical errorSystematic errorMarkov chainMonte Carlo method...
  • The IceCube Neutrino Observatory has observed highly energetic neutrinos in excess of the expected atmospheric neutrino background. It is intriguing to consider the possibility that such events are probing physics beyond the standard model of particle physics. In this context, $\mathcal{O}$(PeV) dark matter (DM) particles decaying to neutrinos have been considered while DM annihilation has been dismissed invoking the unitarity bound as a limiting factor for the annihilation rate. However, the latter claim was done ignoring the contribution from DM substructure, which in a PeV Cold DM scenario, would extend down to a free streaming mass of $\mathcal{O}$($10^{-18}$M$_\odot$). Since the unitarity bound is less stringent at low velocities, ($\sigma_{\rm ann}$v)$\leq4\pi/m_\chi^2v$, then, it is possible that these cold subhalos would contribute dominantly to a DM-induced neutrino flux and easily account for the events observed by IceCube. A DM model where annihilations are enhanced by a Sommerfeld mechanism can naturally support such scenario. Interestingly, the spatial distribution of the events shows features that are expected in a DM interpretation. Although not conclusive, 7 of the 28 events appear to be clustered around the Galactic Center region while 5 others spatially coincide, within the reported angular errors, with 4 of 26 Milky Way satellites. However, a simple estimate of the probability of the latter occurring by chance is $\sim30%$. More events are needed to statistically test this hypothesis. PeV DM particles are massive enough that their abundance as thermal relics would overclose the Universe. This issue can be solved in alternative scenarios, for instance if the decay of new massive unstable particles generates significant entropy reheating the Universe to a slightly lower temperature than the freeze-out temperature, $T_{\rm RH} \lesssim T_{\rm f}\sim4\times10^4$GeV.
    NeutrinoDark matterDark matter subhaloDark matter particleDark matter annihilationUnitaritySommerfeld enhancementIceCube Neutrino ObservatoryGalactic CenterAbundance...
  • We report new calculations of the cross sections for deeply inelastic neutrino-nucleon scattering at neutrino energies between $10^{9}\ev$ and $10^{21}\ev$. We compare with results in the literature and assess the reliability of our predictions. For completeness, we briefly review the cross sections for neutrino interactions with atomic electrons, emphasizing the role of the $W$-boson resonance in $\bar{\nu}_{e}e$ interactions for neutrino energies in the neighborhood of $6.3\pev$. Adopting model predictions for extraterrestrial neutrino fluxes from active galactic nuclei, gamma-ray bursters, and the collapse of topological defects, we estimate event rates in large-volume water \v{C}erenkov detectors and large-area ground arrays.
    Charged currentPartonEarthMuonActive Galactic NucleiCosmic rayObservatoriesParton distribution functionUltra-high energy neutrinoPierre Auger Observatory...
  • In the light of the new IceCube data on the (yet unidentified) astrophysical neutrino flux in the PeV and sub-PeV range, we present an update on the status of decaying dark matter interpretation of the events. In particular, we develop further the angular distribution analysis and discuss the perspectives for diagnostics. By performing various statistical tests (maximum likelihood, Kolmogorov-Smirnov and Anderson-Darling tests) we conclude that currently the data show a mild preference (below the two sigma level) for the angular distribution expected from dark matter decay vs. the isotropic distribution foreseen for a conventional astrophysical flux of extragalactic origin. Also, we briefly develop some general considerations on heavy dark matter model building and on the compatibility of the expected energy spectrum of decay products with the IceCube data, as well as with existing bounds from gamma-rays. Alternatively, assuming that the IceCube data originate from conventional astrophysical sources, we derive bounds on both decaying and annihilating dark matter for various final states. The lower limits on heavy dark matter lifetime improve by up to an order of magnitude with respect to existing constraints, definitively making these events---even if astrophysical in origin---an important tool for astroparticle physics studies.
    Dark matterNeutrinoDark matter decayDecaying dark matterKolmogorov-Smirnov testGalactic CenterInverted hierarchyNormal hierarchyDM massBranching ratio...
  • The announcement by the IceCube Collaboration of the observation of 28 cosmic neutrino candidates has been greeted with a great deal of justified excitement. The data reported so far depart by 4.3\sigma from the expected atmospheric neutrino background, which raises the obvious question: "Where in the Cosmos are these neutrinos coming from?" We review the many possibilities which have been explored in the literature to address this question, including origins at either Galactic or extragalactic celestial objects. For completeness, we also briefly discuss new physics processes which may either explain or be constrained by IceCube data.
    NeutrinoIceCube Neutrino ObservatoryCosmic rayGamma ray burstNeutrino fluxActive Galactic NucleiMuonGalaxyLuminosityEarth...
  • It is assumed that neutrino-nucleon scattering at ultra-high energies effectively proceeds through excitations of leptoquarks in neutrino-quark subprocesses. This approach reproduces the behavior of the energy dependence of the ultra-high energy neutrino-nucleon cross sections and allows to estimate masses as well as the decay widths of the involved leptoquarks. For instance, this leads to the leptoquark mass $1353\pm230$ GeV in a way independent on the leptoquark quantum numbers. The discovery potential of the LHC for the leptoquarks is evaluated.
    LeptoquarkQuarkNeutrinoUltra-high energy neutrinoParton distribution functionStandard ModelCharged leptonCharged currentLuminosityWeak neutral current interaction...
  • The radiative decay of sterile neutrinos with typical masses of 10 keV is investigated in the presence of a strong magnetic field and degenerate plasma. Full account is taken of the strongly modified photon dispersion relation relative to vacuum. The limiting cases of relativistic and non-relativistic plasma are analyzed. The decay rate in a strongly magnetized plasma as a function of the electron number density is compared with the un-magnetized case. We find that a strong magnetic field suppresses the catalyzing influence of the plasma on the decay rate.
    NeutrinoKinematicsPlasma frequencyPolarization vectorEigenvalueElectronic densityPhoton dispersion relation in mediumLowest Landau LevelActive neutrinoDegenerate electron gas...
  • Sterile neutrinos in the mass range of a few keV are candidates for both cold and warm dark matter. An ad-mixture of a heavy neutrino mass eigenstate to the electron neutrino would result in a minuscule distortion - a 'kink' - in a $\beta$-decay spectrum. In this paper we show that a wavelet transform is a very powerful shape analysis method to detect this signature. For a tritium source strength, similar to what is expected from the KATRIN experiment, a statistical sensitivity to active-to-sterile neutrino mixing down to $\sin^2 \theta= 10^{-6}$ ($90\%$ CL) can be obtained after 3 years of measurement time. It is demonstrated that the wavelet approach is largely insensitive to systematic effects that result in smooth spectral modifications. To make full use of this analysis technique a high resolution measurement (FWHM of $\sim100$~eV) of the tritium $\beta$-decay spectrum is required.
    SpectrometersKATRIN experimentMixing angleSterile neutrino massNeutrino mass eigenstatesNeutrino massWarm dark matterStandard ModelSterile neutrinoCold dark matter...
  • 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...
  • We study the system of massive and mixed neutrinos interacting with background matter moving with an acceleration. We start with the derivation of the Dirac equation for a single neutrino in the noninertial frame where matter is at rest. A particular case of matter rotating with a constant angular velocity is considered. The Dirac equation is solved and the neutrino energy levels are found for ultrarelativistic particles propagating in rotating matter. Then we generalize our results to include several neutrino generations and consider mixing between them. Using the relativistic quantum mechanics approach we derive the effective Schr\"{o}dinger equation for the description of neutrino flavor oscillations in rotating matter. We obtain the resonance condition for neutrino oscillations and examine how it can be affected by the matter rotation. We also compare our results with the findings of other authors who studied analogous problem previously.
    PulsarNeutrino mass eigenstatesGamma matricesEffective potentialNeutrino flavorPeculiar velocityNeutrinosphereMass eigen stateNeutrinoEffective Lagrangian...
  • 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...
  • Relativistic, spherically symmetric configurations consisting of a gravitating magnetized anisotropic fluid are studied. For such configurations, we obtain static equilibrium solutions with an axisymmetric, poloidal magnetic field produced by toroidal electric currents. The presence of such a field results in small deviations of the shape of the configuration from spherical symmetry. This in turn leads to the modification of an equation for the current and correspondingly to changes in the structure of the internal magnetic field for the systems supported by the anisotropic fluid, in contrast to the case of an isotropic fluid, where such deviations do not affect the magnetic field.
    PolytropesRegularizationNeutron matterEinstein field equationsStarNeutron starUltra-strong magnetic fieldMagnetic field strengthTolman-Oppenheimer-Volkoff equationDipole magnet...
  • 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...
  • Design is a critical to the successful development of any interactive learning environment (ILE). Moreover, in technology enhanced learning (TEL), the design process requires input from many diverse areas of expertise. As such, anyone undertaking tool development is required to directly address the design challenge from multiple perspectives. We provide a motivation and rationale for design approaches for learning technologies that draws upon Simon's seminal proposition of Design Science (Simon, 1969). We then review the application of Design Experiments (Brown, 1992) and Design Patterns (Alexander et al., 1977) and argue that a patterns approach has the potential to address many of the critical challenges faced by learning technologists.
    Potential
  • Angle resolved photoemission spectroscopy (ARPES) enables direct observation of the Fermi surface and underlying electronic structure of crystals---the basic concepts to describe all the electronic properties of solids and to understand the key electronic interactions involved. The method is the most effective to study quasi-2D metals, to which the subjects of almost all hot problems in modern condensed matter physics have happened to belong. This has forced incredibly the development of the ARPES method which we face now. The aim of this paper is to introduce to the reader the state-of-the-art ARPES, reviewing the results of its application to such topical problems as high temperature superconductivity in cuprates and iron based superconductors, and electronic ordering in the transition metal dichalcogenides and manganites.
    Angle resolved photoemission spectroscopyHigh-Tc superconductivityIron based superconductorsCondensed matter physicsFermi surfaceElectronMetalsForce...
  • A term first coined by Mott back in 1968 a `pseudogap' is the depletion of the electronic density of states at the Fermi level, and pseudogaps have been observed in many systems. However, since the discovery of the high temperature superconductors (HTSC) in 1986, the central role attributed to the pseudogap in these systems has meant that by many researchers now associate the term pseudogap exclusively with the HTSC phenomenon. Recently, the problem has got a lot of new attention with the rediscovery of two distinct energy scales (`two-gap scenario') and charge density waves patterns in the cuprates. Despite many excellent reviews on the pseudogap phenomenon in HTSC, published from its very discovery up to now, the mechanism of the pseudogap and its relation to superconductivity are still open questions. The present review represents a contribution dealing with the pseudogap, focusing on results from angle resolved photoemission spectroscopy (ARPES) and ends up with the conclusion that the pseudogap in cuprates is a complex phenomenon which includes at least three different `intertwined' orders: spin and charge density waves and preformed pairs, which appears in different parts of the phase diagram. The density waves in cuprates are competing to superconductivity for the electronic states but, on the other hand, should drive the electronic structure to vicinity of Lifshitz transition, that could be a key similarity between the superconducting cuprates and iron based superconductors. One may also note that since the pseudogap in cuprates has multiple origins there is no need to recoin the term suggested by Mott.
    Charge density waveDopingFermi surfaceIncommensurateSuperconductorSpin density waveDensity of statesShort Term MemoryStripe phasesInsulators...
  • We consider the local molecular field (LMF) theory for the effects of solute attractive forces on hydrophobic interactions. The principal result of LMF theory is outlined, then tested by obtaining radial distribution functions (rdfs) for Ar atoms in water, with and without attractive interactions distinguished by the Weeks-Chandler-Andersen (WCA) separation. Change from purely repulsive atomic solute interactions to include realistic attractive interactions substantially \emph{diminishes} the strength of hydrophobic bonds. Since attractions make a big contribution to hydrophobic interactions, Pratt-Chandler theory, which did not include attractions, should not be simply comparable to computer simulation results with general physical interactions, including attractions. The rdfs permit evaluation of osmotic second virial coefficients $B_2$. Those $B_2$ are consistent with the conclusion that incorporation of attractive interactions leads to more positive (repulsive) values. In all cases here, $B_2$ becomes more attractive with increasing temperature below $T$ = 360K. Ultimately, LMF theory does not accurately describe the numerical results for the effects of solute attractive forces on hydrophobic interactions in this case. This is due to the incomplete evaluation within LMF theory of the mean hydration energy of the second Ar atom joining the Ar pair.
    Statistical mechanicsHard sphereMean fieldThermalisationSecond Virial CoefficientField theoryStatisticsElectrostaticsInteratomic forceChemical potential...
  • In this paper we present a simple method for deriving an alternative form of the functional equation for Riemann's Zeta function. The connections between some functional equations obtained implicitly by Leonhard Euler in his work "Remarques sur un beau rapport entre les series des puissances tant directes que reciproques" in Memoires de l'Academie des Sciences de Berlin 17, (1768), permit to define a special function, named A(s), which is fully symmetric and is similar to Riemann's "XI" function. To be complete we find several integral representations of the A(s) function and as a direct consequence of the second integral representation we obtain also an analytic continuation of the same function using an identity of Ramanujan.
    Riemann zeta functionAnalytic continuationSpecial function
  • Conformal cyclic cosmology (CCC) posits the existence of an aeon preceding our Big Bang 'B', whose conformal infinity 'I' is identified, conformally, with 'B', now regarded as a spacelike 3-surface. Black-hole encounters, within bound galactic clusters in that previous aeon, would have the observable effect, in our CMB sky, of families of concentric circles over which the temperature variance is anomalously low, the centre of each such family representing the point of 'I' at which the cluster converges. These centres appear as fairly randomly distributed fixed points in our CMB sky. The analysis of Wilkinson Microwave Background Probe's (WMAP) cosmic microwave background 7-year maps does indeed reveal such concentric circles, of up to 6{\sigma} significance. This is confirmed when the same analysis is applied to BOOMERanG98 data, eliminating the possibility of an instrumental cause for the effects. These observational predictions of CCC would not be easily explained within standard inflationary cosmology.
    Cosmic microwave backgroundWilkinson Microwave Anisotropy ProbeBig BangCosmologyConformal Cyclic CosmologyBlack holeTemperature...
  • 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.
    HorizonMagnetic monopoleStarRegularizationTwo-formDifferential formInclinationDifferential form of degree threeOrientationSpinning Black Hole...
  • 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 CloudMain sequence starProtostarPrimordial black hole...
  • 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...
  • After a comment on the performance of LEP some highlights of the LEP1 and LEP2 physics programmes are reviewed. The talk concentrates on the precision measurements at the Z resonance, two fermion production above the Z, W+W- production, ZZ production, indirect limits on the Higgs mass, LEP contributions to the exploration of the CKM matrix, and on the LEP measurements of alpha_s.
    Standard ModelQuarkQCD jetHadronizationLarge Electron-Positron ColliderForward-backward asymmetrySystematic errorALEPHStatisticsRadiative correction...
  • Recent works of [1402.2301,1402.4119], claiming the detection of extra emission line with energy ~3.5 keV in X-ray spectra of certain clusters of galaxies and nearby Andromeda galaxy, have raised considerable interest in astrophysics and particle physics communities. A number of new observational studies claim detection or non-detection of the extra line in X-ray spectra of various cosmic objects. In this review I summarize existing results of these studies, overview possible interpretations of the extra line, including intriguing connection with radiatively decaying dark matter, and show future directions achievable with existing and planned X-ray cosmic missions.
    Dark matterKeV lineCluster of galaxiesPerseus galaxy clusterIntensityAtomDBDark matter particleGalactic CenterAndromeda galaxyExtensions of the standard model...
  • We propose a class of models with gauge mediation of supersymmetry breaking, inspired by simple brane constructions, where R-symmetry is very weakly broken. The gauge sector has an extended N=2 supersymmetry and the two electroweak Higgses form an N=2 hypermultiplet, while quarks and leptons remain in N=1 chiral multiplets. Supersymmetry is broken via the D-term expectation value of a secluded U(1) and it is transmitted to the Standard Model via gauge interactions of messengers in N=2 hypermultiplets: gauginos thus receive Dirac masses. The model has several distinct experimental signatures with respect to ordinary models of gauge or gravity mediation realizations of the Minimal Supersymmetric Standard Model (MSSM). First, it predicts extra states as a third chargino that can be observed at collider experiments. Second, the absence of a D-flat direction in the Higgs sector implies a lightest Higgs behaving exactly as the Standard Model one and thus a reduction of the `little' fine-tuning in the low tan(beta) region. This breaking of supersymmetry can be easily implemented in string theory models
    Standard ModelSuperfieldVacuum expectation valueHiggs boson massGravitinoGravitational interactionStack of D-branesSuperpotentialTorusElectroweak symmetry breaking...
  • It is becoming increasingly clear that metastable vacua may play a prominent role in supersymmetry-breaking. To date, however, this idea has been realized only in models where non-perturbative dynamics complicates the analysis of metastability. In this paper, we present a simple construction in which metastable vacua occur classically, i.e., at tree-level, and in which supersymmetry-breaking is sourced by both D-terms and F-terms. All relevant dynamics is perturbative, and hence calculations of vacuum energies and lifetimes can be performed explicitly. Moreover, we find that our construction can even give rise to multiple non-supersymmetric vacua which are degenerate. The non-trivial vacuum structure of such models therefore suggests that they can provide a rich arena for future studies of vacuum metastability in supersymmetric field theories. Our results may also have important consequences for Z' phenomenology and the string landscape.
    Metastable vacuumSupersymmetryGauge coupling constantEigenvalueSuperpotentialVacuum stateQuantum mechanicsVacuum expectation valueCosmological mirror symmetryChiral superfield...
  • We present the first fully self-consistent three-dimensional model of a neutron star's magnetic field, generated by electric currents in the star's crust via the Hall effect. We find that the global-scale field converges to a Hall-attractor state, as seen in recent axisymmetric models, but that small-scale features in the magnetic field survive even on much longer timescales. These small-scale features propagate toward the dipole equator, where the crustal electric currents organize themselves into a strong equatorial jet. By calculating the distribution of magnetic stresses in the crust, we predict that neutron stars with fields stronger than $10^{14}$G can still be subject to starquakes more than $10^5$yr after their formation.
    Neutron star magnetic fieldAttractorPulsarMagnetohydrodynamicsSpeed of lightGamma-ray flaresLight yearOptical burstsStrong magnetic fieldNeutron star crust...
  • Mindful of the anomalous perihelion precession of Mercury discovered by U. Le Verrier in the second half of the nineteenth century and its successful explanation by A. Einstein with his General Theory of Relativity in the early years of the twentieth century, discrepancies among observed effects in our Solar system and their theoretical predictions on the basis of the currently accepted laws of gravitation applied to known bodies have the potential of paving the way for remarkable advances in fundamental physics. This is particularly important now more than ever, given that most of the Universe seems to be made of unknown substances dubbed Dark Matter and Dark Energy. Should this not be directly the case, Solar system's anomalies could anyhow lead to advancements in cumulative science, as shown to us by the discovery of Neptune in the first half of the nineteenth century. Moreover, investigations in one of such directions can serendipitously enrich the other one as well. The current status of some alleged gravitational anomalies in the Solar system is critically reviewed. They are: a) Possible anomalous advances of planetary perihelia; b) Unexplained orbital residuals of a recently discovered moon of Uranus (Mab); c) The lingering unexplained secular increase of the eccentricity of the orbit of the Moon; d) The so-called Faint Young Sun Paradox; e) The secular decrease of the mass parameter of the Sun; f) The Flyby Anomaly; g) The Pioneer Anomaly; and h) The anomalous secular increase of the astronomical unit
    EphemeridesPlanetEarthUranusPerihelion precessionPlutoThermalisationCosmologyStatistical significanceOrbital motion...
  • Based on the s-d interaction model for dilute magnetic alloys we have calculated the scattering probability of the conduction electrons to the second Born approximation. Because of the dynamical character of the localized spin system, the Pauli principle should be taken into account in the intermediate states of the second order terms. Thus the effect of the Fermi sphere is involved in the scattering probability and gives rise to a singular term in the resistivity which involves c log T as a factor, where c is the concentration of impurity atoms. When combined with the lattice resistivity, this gives rise to a resistance minimum, provided the s-d exchange integral J is negative. The temperature at which the minimum ccurs is proportional to c1/5 and the depth of the minimum to c, as is observed. The predicted log T dependence is tested with available experiments and is confirmed. The value of J to have fit with experiments is about -0.2 ev, which is of reasonable magnitude. Our conclusion is that J should be negative in alloys which show a resistance minimum. It is argued that the resistance minimum is a result of the sharp Fermi surface.
    Born approximationFermi surfaceScatteringProbabilityAtomTemperatureSpinElectronMagneticsResist...
  • During the last decade, many exciting phenomena have been experimentally observed and theoretically predicted for ultracold atoms in optical lattices. This paper reviews these rapid developments concentrating mainly on the theory. Different types of the bosonic systems in homogeneous lattices of different dimensions as well as in the presence of harmonic traps are considered. An overview of the theoretical methods used for these investigations as well as of the obtained results is given. Available experimental techniques are presented and discussed in connection with theoretical considerations. Eigenstates of the interacting bosons in homogeneous lattices and in the presence of harmonic confinement are analysed. Their knowledge is essential for understanding of quantum phase transitions at zero and finite temperature.
    HamiltonianSuperfluidQuantum Monte CarloEigenvalueSolitonMean field theoryLasersTwo-point correlation functionCompressibilityPhase diagram...
  • Full manifold of the complex Bloch-Floquet eigenfunctions is investigated for the ground level of the purely magnetic 2D Pauli operators (equal to zero because of supersymmetry). Deep connection of it with the 2D analog of the "Burgers Nonlinear Hierarchy" plays fundamental role here. Everything is completely calculated for the broad class of Algebro-Geometric operators found in this work for this case. For the case of nonzero flux the ground states were found by Aharonov-Casher (1979) for the rapidly decreasing fields, and by Dubrovin-Novikov (1980) for the periodic fields. No Algebro-Geometric operators where known in the case of nonzero flux. For genus $g=1$ we found periodic operators with zero flux, singular magnetic fields and Bohm-Aharonov phenomenon. Our arguments imply that the delta-term really does not affect seriously the spectrum nearby of the ground state. For $g>1$ our theory requires to use only algebraic curves with selected point leading to the solutions elliptic in the variable $x$ for KdV and KP in order to get periodic magnetic fields. The algebro-geometric case of genus zero leads, in particular, to the slowly decreasing lump-like magnetic fields with especially interesting variety of ground states in the Hilbert Space $\cL_2(\bR^2)$.
    QuasiperiodicityInstantonGenerating functionalSegmentationHolomorphLaplace transformRiemann surfaceSolitonGauge transformationBloch wave...