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    • Advances in theoretical ideas on how galaxies formed have not been strongly influenced by the advances in observations of what might be in the voids between the concentrations of ordinary optically selected galaxies. The theory and observations are maturing, and the search for a reconciliation offers a promising opportunity to improve our understanding of cosmic evolution. I comment on the development of this situation and present an update of a nearest neighbor measure of the void phenomenon that may be of use in evaluating theories of galaxy formation.
      VoidGalaxyGalaxy FormationStatisticsLow surface brightness galaxyTwo-point correlation functionLambda-CDM modelRedshift spaceSpiral galaxyGas clouds...
    • We consider a possibility to naturally explain tiny neutrino masses without the lepton number violation. We study a simple model with SU(2)_L singlet charged scalars (s_1^+, s_2^+) as well as singlet right-handed neutrino (nu_R). Yukawa interactions for Dirac neutrinos, which are forbidden at the tree level by a softly-broken Z_2 symmetry, are induced at the one-loop level via the soft-breaking term in the scalar potential. Consequently neutrinos obtain small Dirac masses after the electroweak symmetry breaking. It is found that constrains from neutrino oscillation measurements and lepton flavor violation search results (especially for mu to e gamma) can be satisfied. We study the decay pattern of the singlet charged scalars, which could be tested at the LHC and the ILC. We discuss possible extensions also, e.g. to introduce dark matter candidate.
      Majorana massCoupling constantStandard ModelCharged leptonLepton flavour violationHiggs bosonDark matterBosonizationTri Bimaximal mixingScalar field...
    • We extend the scalar sector of the neutrinophilic two Higgs doublet model, where small masses of Dirac neutrinos are obtained via a small vacuum expectation value v_nu of the neutrinophilic SU(2)_L-doublet scalar field which has a Yukawa interaction with only right-handed neutrinos. A global U(1)_X symmetry is used for the neutrinophilic nature of the second SU(2)_L-doublet scalar field and also for eliminating Majorana mass terms of neutrinos. By virtue of an appropriate assignment of the U(1)_X-charges to new particles, our model has an unbroken Z_2 symmetry, under which the lightest Z_2-odd scalar boson can be a dark matter candidate. In our model, v_nu is generated by the one-loop diagram to which Z_2-odd particles contribute. We briefly discuss a possible signature of our model at the LHC.
      Vacuum expectation valueNeutrinoNeutrino massScalar fieldDark matter candidateScalar bosonStandard ModelDark matterMass eigen stateYukawa interaction...
    • Warm dark matter (WDM) has been proposed as an alternative to cold dark matter (CDM), to resolve issues such as the apparent lack of satellites around the Milky Way. Even if WDM is not the answer to observational issues, it is essential to constrain the nature of the dark matter. The effect of WDM on haloes has been extensively studied, but the small-scale initial smoothing in WDM also affects the present-day cosmic web and voids. It suppresses the cosmic "sub-web" inside voids, and the formation of both void haloes and subvoids. In N-body simulations run with different assumed WDM masses, we identify voids with the zobov algorithm, and cosmic-web components with the origami algorithm. As dark-matter warmth increases, the initial-conditions smoothing increases, and the number of voids and subvoids is suppressed. Also, void density profiles change, their shapes become flatter inside the void radius, while edges of the voids remain unchanged. Also, filaments and walls become cleaner, as the sub-structures in between have been smoothed out; this leads to a clear, mid-range peak in the density PDF. These distinct features of voids make them possible observational indicators of the warmth of dark matter.
      Dark matterWDM particlesGalaxyWarm dark matterThermalisationAbundanceCosmologyStructure formationRedshift-space distortionLambda-CDM model...
    • This paper presents a systematic treatment of the linear theory of scalar gravitational perturbations in the synchronous gauge and the conformal Newtonian (or longitudinal) gauge. It differs from others in the literature in that we give, in both gauges, a complete discussion of all particle species that are relevant to any flat cold dark matter (CDM), hot dark matter (HDM), or CDM+HDM models (including a possible cosmological constant). The particles considered include CDM, baryons, photons, massless neutrinos, and massive neutrinos (an HDM candidate), where the CDM and baryons are treated as fluids while a detailed phase-space description is given to the photons and neutrinos. Particular care is applied to the massive neutrino component, which has been either ignored or approximated crudely in previous works. Isentropic initial conditions on super-horizon scales are derived. The coupled, linearized Boltzmann, Einstein and fluid equations that govern the evolution of the metric and density perturbations are then solved numerically in both gauges for the standard CDM model and two CDM+HDM models with neutrino mass densities $\onu=0.2$ and 0.3, assuming a scale-invariant, adiabatic spectrum of primordial fluctuations. We also give the full details of the cosmic microwave background anisotropy, and present the first accurate calculations of the angular power spectra in the two CDM+HDM models including photon polarization, higher neutrino multipole moments, and helium recombination. The numerical programs for both gauges are available at http://arcturus.mit.edu/cosmics/ .
      HorizonMetric perturbationBoltzmann transport equationPhase space densityThomson scatteringIonizationEinstein field equationsRadiation-dominated epochEvolution equationScalar mode fluctuation...
    • We consider some aspects of the perturbation to the luminosity distance $d(z)$ that are of relevance for SN1a cosmology and for future peculiar velocity surveys at non-negligible redshifts. 1) Previous work has shown that the correction to the lowest order perturbation $\delta d / d = -\delta v / c z$ has the peculiar characteristic that it appears to depend on the absolute state of motion of sources, rather than on their motion relative to that of the observer. The resolution of this apparent violation of the equivalence principle is that it is necessary to allow for evolution of the velocities with time, and also, when considering perturbations on the scale of the observer-source separation, to include the gravitational redshift effect. We provide an expression for $\delta d / d$ that provides a physically consistent way to compute the impact of peculiar motions for SN1a cosmology and peculiar velocity surveys. 2) We then calculate the perturbation to the redshift as a function of source flux density, which has been proposed as an alternative probe of large-scale motions. We show how the inclusion of surface brightness modulation modifies the relation between $\delta z(m)$ and the peculiar velocity, and that, while the noise properties of this method might appear promising, the velocity signal is swamped by the effect of galaxy clustering for most scales of interest. 3) We show how, in linear theory, peculiar velocity measurements are biased downwards by the effect of smaller scale motions or by measurement errors (such as in photometric redshifts). Our results nicely explain the effects seen in simulations by Koda et al.\ 2013. We critically examine the prospects for extending peculiar velocity studies to larger scales with near-term future surveys.
      GalaxyRedshift spaceVelocity dispersionLine of sightPrimordial density perturbationThe Dark Energy SurveyWeak lensingCosmic microwave backgroundLuminosityTully-Fisher relation...
    • We continue the study of the impact of baryon physics on the small scale problems of the $\Lambda$CDM model, based on a semi-analytical model (Del Popolo, 2009). Withsuch model, we show how the cusp/core, missing satellite (MSP), Too Big to Fail (TBTF) problems and the angular momentum catastrophe can be reconciled with observations, adding parent-satellite interaction. Such interaction between darkmatter (DM) and baryons through dynamical friction (DF) can sufficiently flattenthe inner cusp of the density profiles to solve the cusp/core problem. Combining, in our model, a Zolotov et al. (2012)-like correction, similarly to Brooks et al. (2013), and effects of UV heating and tidal stripping, the number of massive, luminous satellites, as seen in the Via Lactea 2 (VL2) subhaloes,is in agreement with the numbers observed in the MW, thus resolving the MSP and TBTF problems. The model also produces a distribution of the angular spin parameter and angular momentum in agreement with observations of the dwarfs studied by van den Bosch, Burkert, \\& Swaters (2001).
      EllipticityCircular velocitySmoothed-particle hydrodynamicsN-body simulationStellar massCold dark matterStarHost galaxyStar formationGalaxy...
    • The Higgs field mass term, being superrenomalizable, has a unique status within the standard model. Through the opening it affords, $SU(3) \times SU(2) \times U(1)$ singlet fields can have renormalizable couplings to standard model fields. We present examples that are neither grotesque nor unnatural. A possible consequence is to spread the Higgs particle resonance into several weaker ones, or to afford it additional, effectively invisible decay channels.
      Hidden sectorStandard ModelHiggs fieldHiggs bosonStandard Model fieldQuarkGauge fieldNucleosynthesisChiral symmetry breakingVacuum expectation value...
    • 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.
      ParsecEvent horizonAstrophysical jetNearby galaxiesMilky WayAccretion diskMassive black holeGround telescopesGravitational fieldsAccretion...
    • 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.
      MagnetohydrodynamicsEddyRichardson diffusionDissipationLundquist numberCompressibilityInstabilityNumerical simulationMagnetosphere of a starSolar wind...
    • The rotation curve, the total mass and the gravitational potential of the Galaxy are sensitive measurements of the dark matter halo profile. In this publication cuspy and cored DM halo profiles are analysed with respect to recent astronomical constraints in order to constrain the shape of the Galactic DM halo and the local DM density. All Galactic density components (luminous matter and DM) are parametrized. Then the total density distribution is constrained by astronomical observations: 1) the total mass of the Galaxy, 2) the total matter density at the position of the Sun, 3) the surface density of the visible matter, 4) the surface density of the total matter in the vicinity of the Sun, 5) the rotation speed of the Sun and 6) the shape of the velocity distribution within and above the Galactic disc. The mass model of the Galaxy is mainly constrained by the local matter density (Oort limit), the rotation speed of the Sun and the total mass of the Galaxy from tracer stars in the halo. It is shown from a statistical chi^2 fit to all data that the local DM density is strongly positively (negatively) correlated with the scale length of the DM halo (baryonic disc). Since these scale lengths are poorly constrained the local DM density can vary from 0.2 to 0.4 GeV/cm^3 (0.005 - 0.01 M_sun/pc^3) for a spherical DM halo profile and allowing total Galaxy masses up to 2 * 10^12 M_sun. For oblate DM halos and dark matter discs, as predicted in recent N-body simulations, the local DM density can be increased significantly.
      Globular clusterScale heightMass distributionMilky WayNavarro-Frenk-White profileThin stellar diskDark Matter Density ProfileDark matter haloLocal dark matter densityCircular velocity...
    • 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.
      CosmologyBaryon acoustic oscillationsTwo-point correlation functionLine of sightRadiative transferCovariance matrixRedshift-space distortionCosmological parametersUltraviolet sourcesFisher information matrix...
    • 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.
      Stellar massStatisticsStellar dynamicsStellar surfacesExtinctionMass distributionAccretion diskQuasarPierre Auger ObservatoryMass profile...
    • 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.
      Vector fieldRotation CurveToo big to fail problemInclinationMilky WayDark matter subhaloWDM particlesTHINGS surveyWarm dark matterVelocity Width Function...
    • We have compiled a new sample of 240 halo objects with accurate distance and radial velocity measurements, including globular clusters, satellite galaxies, field blue horizontal branch stars and red giant stars from the Spaghetti survey. The new data lead to a significant increase in the number of known objects for Galactocentric radii beyond 50 kpc, which allows a reliable determination of the radial velocity dispersion profile out to very large distances. The radial velocity dispersion shows an almost constant value of 120 km/s out to 30 kpc and then continuously declines down to 50 km/s at about 120 kpc. This fall-off puts important constraints on the density profile and total mass of the dark matter halo of the Milky Way. For a constant velocity anisotropy, the isothermal profile is ruled out, while both a dark halo following a truncated flat model of mass $1.2^{+1.8}_{-0.5}\times 10^{12}$ M_sun and an NFW profile of mass $0.8^{+1.2}_{-0.2}\times 10^{12}$ M_sun and c=18 are consistent with the data. The significant increase in the number of tracers combined with the large extent of the region probed by these has allowed a more precise determination of the Milky Way mass in comparison to previous works. We also show how different assumptions for the velocity anisotropy affect the performance of the mass models.
      Navarro-Frenk-White profileCircular velocityVelocity dispersionStellar haloProper motionVirial massThomas-Fermi modelGalaxyCore radiusA giants...
    • We present a simple method for fitting parametrized mass models of the Milky Way to observational constraints. We take a Bayesian approach which allows us to take into account input from photometric and kinematic data, and expectations from theoretical modelling. This provides us with a best-fitting model, which is a suitable starting point for dynamical modelling. We also determine a probability density function on the properties of the model, which demonstrates that the mass distribution of the Galaxy remains very uncertain. For our choices of parametrization and constraints, we find disc scale lengths of 3.00 \pm 0.22 kpc and 3.29 \pm 0.56 kpc for the thin and thick discs respectively; a Solar radius of 8.29 \pm 0.16 kpc and a circular speed at the Sun of 239 \pm 5 km/s; a total stellar mass of 6.43 \pm 0.63 * 10^10 M_sun; a virial mass of 1.26 \pm 0.24 * 10^12 M_sun and a local dark matter density of 0.40 \pm 0.04 GeV/cm^3. We find some correlations between the best-fitting parameters of our models (for example, between the disk scale lengths and the Solar radius), which we discuss. The chosen disc scale-heights are shown to have little effect on the key properties of the model.
      GalaxyKinematicsMilky WayScale heightVirial massStellar massSunCold dark matterThin stellar diskThick stellar disk...
    • We derive the mass model of the Milky Way (MW) using a cored dark matter (DM) halo profile and recent data. The method used consists in fitting a spherically symmetric model of the Galaxy with a Burkert DM halo profile to available data: MW terminal velocities in the region inside the solar circle, circular velocity as recently estimated from maser star forming regions at intermediate radii, and velocity dispersions of stellar halo tracers for the outermost Galactic region. The latter are reproduced by integrating the Jeans equation for every modeled mass distribution, and by allowing for different velocity anisotropies for different tracer populations. For comparison we also consider a Navarro-Frenk-White profile. We find that the cored profile is the preferred one, with a shallow central density of rho_H~4x10^7M_s/kpc^3 and a large core radius R_H~10 kpc, as observed in external spirals and in agreement with the mass model underlying the Universal Rotation Curve of spirals. We describe also the derived model uncertainties, which are crucially driven by the poorly constrained velocity dispersion anisotropies of halo tracers. The emerging cored DM distribution has implications for the DM annihilation angular profile, which is much less boosted in the Galactic center direction with respect to the case of the standard \Lambda CDM, NFW profile. Using the derived uncertainties we discuss finally the limitations and prospects to discriminate between cored and cusped DM profile with a possible observed diffuse DM annihilation signal. The present mass model aims to characterize the present-day description of the distribution of matter in our Galaxy, which is needed to frame current crucial issues of Cosmology, Astrophysics and Elementary Particles.
      Navarro-Frenk-White profileSunKinematicsDark Matter Density ProfileThin stellar diskStellar diskBlue horizontal-branch starMilky WayRotation CurveProper motion...
    • We derive new constraints on the mass of the Milky Way's dark matter halo, based on a set of halo stars from SDSS as kinematic tracers. Our sample comprises 2401 rigorously selected Blue Horizontal-Branch (BHB) halo stars drawn from SDSS DR-6. To interpret these distributions, we compare them to matched mock observations drawn from two different cosmological galaxy formation simulations designed to resemble the Milky Way, which we presume to have an appropriate orbital distribution of halo stars. We then determine which value of $\rm V_{cir}(r)$ brings the observed distribution into agreement with the corresponding distributions from the simulations. This procedure results in an estimate of the Milky Way's circular velocity curve to $\sim 60$ kpc, which is found to be slightly falling from the adopted value of $\rm 220 km s^{-1}$ at the Sun's location, and implies M$(<60 \rm kpc) = 4.0\pm 0.7\times 10^{11}$M$_\odot$. The radial dependence of $\rm V_{cir}(r)$, derived in statistically independent bins, is found to be consistent with the expectations from an NFW dark matter halo with the established stellar mass components at its center. If we assume an NFW halo profile of characteristic concentration holds, we can use the observations to estimate the virial mass of the Milky Way's dark matter halo, M$_{\rm vir}=1.0^{+0.3}_{-0.2} \times 10^{12}$M$_\odot$, which is lower than many previous estimates. This estimate implies that nearly 40% of the baryons within the virial radius of the Milky Way's dark matter halo reside in the stellar components of our Galaxy. A value for M$_{\rm vir}$ of only $\sim 1\times10^{12}$M$_\odot$ also (re-)opens the question of whether all of the Milky Way's satellite galaxies are on bound orbits.
      StarBlue horizontal-branch starRadial velocityGalaxyMilky Way haloJeans equationNavarro-Frenk-White profileVelocity dispersionAbsolute magnitudeVirial mass...
    • Several groups have identified an extended excess of gamma rays over the modeled foreground and background emissions towards the Galactic center (GC) based on observations with the Fermi Large Area Telescope. This excess emission is compatible in morphology and spectrum with a telltale sign from dark matter (DM) annihilation. Here, we present a critical reassessment of DM interpretations of the GC signal in light of the foreground and background uncertainties that some of us recently outlaid in Calore et al. 2014. We find that a much larger number of DM models fits the gamma-ray data than previously noted. In particular: (1) In the case of DM annihilation into $\bar{b}b$, we find that even large DM masses up to $m_\chi \simeq$ 74 GeV are allowed with a $p$-value $> 0.05$. (2) Surprisingly, annihilation into non-relativistic hh gives a good fit to the data. (3) The inverse Compton emission from $\mu^+\mu^-$ with $m_\chi\sim$ 60-70 GeV can also account for the excess at higher latitudes, $|b|>2^\circ$, both in its spectrum and morphology. We also present novel constraints on a large number of mixed annihilation channels, including cascade annihilation involving hidden sector mediators. Finally, we show that the current limits from dwarf spheroidal observations are not in tension with a DM interpretation when uncertainties on the DM halo profile are accounted for.
      Inverse ComptonIntensityDiffuse emissionCosmic rayQuarkBranching ratioStandard ModelPositronBremsstrahlungDwarf spheroidal galaxy...
    • We report the discovery of two dwarf galaxies, Pisces A and B, from a blind 21 cm HI search. These were the only two galaxies found via optical imaging and spectroscopy of 22 HI clouds identified in the GALFA-HI survey as dwarf galaxy candidates. They have properties consistent with being in the Local Volume ($<10$ Mpc), and one has resolved stellar populations such that it may be on the outer edge of the Local Group ($\sim 1 \, {\rm Mpc}$ from M31). While the distance uncertainty makes interpretation ambiguous, these may be among the faintest starforming galaxies known. Additionally, rough estimates comparing these galaxies to $\Lambda$CDM dark matter simulations suggest consistency in number density, implying that dark matter halos likely to host these galaxies are primarily HI-rich. The galaxies may thus be indicative of a large population of dwarfs at the limit of detectability that are comparable to the faint satellites of the Local Group. Because they are outside the influence of a large dark matter halo to alter their evolution, these galaxies can provide critical anchors to dwarf galaxy formation models.
      Point sourceStarSloan Digital Sky SurveyTelescopesGalaxyExploring the Local Volume in SimulationsStar formingObservatoriesHubble flowHertzsprung-Russell diagram...
    • Methods.There are no experimental data about the background experienced by microcalorimeters in the L2 orbit, and thus the particle background levels were calculated by means of Monte Carlo simulations: we considered the original design configuration and an improved configuration aimed to reduce the unrejected background, and tested them in the L2 orbit and in the low Earth orbit, comparing the results with experimental data reported by other X-ray instruments.To show the results obtainable with the improved configuration we simulated the observation of a faint, high-redshift, point source (F[0.5-10 keV]~6.4E-16 erg cm-2 s-1, z=3.7), and of a hot galaxy cluster at R200 (Sb[0.5-2 keV]=8.61E-16 erg cm-2 s-1 arcmin-2,T=6.6 keV). Results.First we confirm that implementing an active cryogenic anticoincidence reduces the particle background by an order of magnitude and brings it close to the required level.The implementation and test of several design solutions can reduce the particle background level by a further factor of 6 with respect to the original configuration.The best background level achievable in the L2 orbit with the implementation of ad-hoc passive shielding for secondary particles is similar to that measured in the more favorable LEO environment without the passive shielding, allowing us to exploit the advantages of the L2 orbit.We define a reference model for the diffuse background and collect all the available information on its variation with epoch and pointing direction.With this background level the ATHENA mission with the X-IFU instrument is able to detect ~4100 new obscured AGNs with F>6.4E-16 erg cm-2 s-1 during three years, to characterize cluster of galaxies with Sb(0.5-2 keV)>9.4E-16 erg cm-2 s-1 sr-1 on timescales of 50 ks (500 ks) with errors <40% (<12%) on metallicity,<16% (4.8%) on temperature,2.6% (0.72%) on the gas density, and several single-element abundances.
      Cluster of galaxiesObscured AGNAbundanceAthena+ missionLow Earth orbitMicrocalorimeterVirial radiusPoint sourceMonte Carlo methodOrbit...
    • It has been a notably elusive task to find a remotely sensical ansatz for a calculation of Sommerfeld's electrodynamic fine-structure constant alpha_QED ~ 1/137.036 based on first principles. However, this has not prevented a number of researchers to invest considerable effort into the problem, despite the formidable challenges, and a number of attempts have been recorded in the literature. Here, we review a possible approach based on the quantum electrodynamic (QED) beta function, and on algebraic identities relating alpha_QED to invariant properties of "internal" symmetry groups, as well as attempts to relate the strength of the electromagnetic interaction to the natural cut-off scale for other gauge theories. Conjectures based on both classical as well as quantum-field theoretical considerations are discussed. We point out apparent strengths and weaknesses of the most prominent attempts that were recorded in the literature. This includes possible connections to scaling properties of the Einstein-Maxwell Lagrangian which describes gravitational and electromagnetic interactions on curved space-times. Alternative approaches inspired by string theory are also discussed. A conceivable variation of the fine-structure constant with time would suggest a connection of alpha_QED to global structures of the Universe, which in turn are largely determined by gravitational interactions.
      Renormalization groupQuantum fluctuationQuantizationCoupling constantCasimir energyClassical electron radiusPhase transitionsGravitonThe age of the UniverseElectron-positron pair...
    • We analyze the dynamical evolution of a perturbed force-free magnetosphere of a rotating black hole, which is described by the Blandford-Znajek solution in the stationary limit. We find that the electromagnetic field perturbations can be classified into two categories: "trapped modes" and "traveling waves". The trapped modes are analogous to the vacuum (without plasma) electromagnetic quasinormal modes in rotating black hole spacetimes, but with different eigenfrequencies and wave functions, due to their coupling with the background electromagnetic field and current. The traveling waves propagate freely to infinity or the black hole horizon along specific null directions, and they are closely related to the no-scattering Poynting flux solutions discovered by Brennan, Gralla and Jacobson. Our results suggest that the Blandford-Znajek solution is mode stable, and more importantly we expect this study to illuminate the dynamical behavior of force-free magnetospheres as well as to shed light on the path to new exact solutions.
      Black holeWave equationDifferential formBlack hole spinKerr black holeHamiltonianHorizonEvolution equationSchwarzschild black holesMagnetosphere of a star...
    • In this paper, we investigate the twisted algebra of the fermionic oscillators associated with Dirac field defined in $\kappa$-Minkowski space-time. Starting from $\kappa$-deformed Dirac theory, which is invariant under the undeformed $\kappa$-Poincare algebra, using the twisted flip operator, we derive the deformed algebra of the creation and annihilation operators corresponding to the Dirac field quanta in $\kappa$-Minkowski space-time. In the limit $a\rightarrow 0$, the deformed algebra reduces to the commutative result.
      Symmetry algebraStatisticsHopf algebraFermionic fieldSymmetry groupStar productQ-deformed oscillator algebraDirac fieldQuantum gravityQuantization...
    • We consider a gas of free chiral fermions trapped inside a uniform rotating spherical shell. Once the shell becomes transparent the fermions are emitted along the axis of rotation due to the chiral and mixed anomaly. In return, owing to momentum conservation, the shell is propelled forward. We study the dependence of the magnitude of this effect on the shell parameters in a controlled setting and find that it is sensitive to the formation of an ergosphere around the rotating shell. A brief discussion on a possible relation to pulsar kicks is provided.
      Proto-neutron starNeutron starConstitutive relationVorticityStarNeutrinoThermalisationCoolingSchwarzschild radiusDecay rate...
    • In a model independent framework, the effects of new physics at the electroweak scale can be parametrized in terms of an effective Lagrangian expansion. Assuming the $SU(2)_L x U(1)_Y$ gauge symmetry is linearly realized, the expansion at the lowest order span dimension--six operators built from the observed Standard model (SM) particles, in addition to a light scalar doublet. After a proper choice of the operator basis we present a global fit to all the updated available data related to the electroweak symmetry breaking sector: triple gauge boson vertex (TGV) collider measurements, electroweak precision tests and Higgs searches. In this framework modifications of the interactions of the Higgs field to the electroweak gauge bosons are related to anomalous TGV's, and given the current experimental precision, we show that the analysis of the latest Higgs boson data at the LHC and Tevatron gives rise to strong bounds on TGV's that are complementary to those from direct TGV measurements. Interestingly, we present how this correlated pattern of deviations from the SM predictions could be different for theories based on a non--linear realization of the $SU(2)_L x U(1)_Y$ symmetry, characteristic of for instance composite Higgs models. Furthermore, anomalous TGV signals expected at first order in the non--linear realization may appear only at higher orders of the linear one, and viceversa. Their study could lead to hints on the nature of the observed boson.
      Tri-Linear Gauge Boson CouplingsChiralityReachabilityHiggs bosonComplementarityStandard ModelEffective theoryElectroweak precision testGauge coupling constantElectroweak symmetry breaking...
    • We present new upper limits on the volume-weighted neutral hydrogen fraction, <xHI>, at z~5-6 derived from spectroscopy of bright quasars. The fraction of the Lyman-alpha and Lyman-beta forests that is "dark" (with zero flux) provides the only model-independent upper limit on <xHI>, requiring no assumptions about the physical conditions in the intergalactic medium or the quasar's unabsorbed UV continuum. In this work we update our previous results using a larger sample (22 objects) of medium-depth (~ few hours) spectra of high-redshift quasars obtained with the Magellan, MMT, and VLT. This significantly improves the upper bound on <xHI> derived from dark pixel analysis to <xHI> <= 0.06 + 0.05 (1{\sigma}) at z=5.9, and <xHI> <= 0.04 + 0.05 (1{\sigma}) at z=5.6. These results provide robust constraints for theoretical models of reionization, and provide the strongest available evidence that reionization has completed (or is very nearly complete) by z~6.
      StatisticsIntergalactic mediumRedshift binsAbsorptivityEffective optical depthTelescopesInverse-variance weightingSpectrographsQuasarCosmology...
    • We present a high order one-step ADER-WENO finite volume scheme with space-time adaptive mesh refinement (AMR) for the solution of the special relativistic hydrodynamic and magnetohydrodynamic equations. By adopting a local discontinuous Galerkin predictor method, a high order one-step time discretization is obtained, with no need for Runge--Kutta sub-steps. This turns out to be particularly advantageous in combination with space-time adaptive mesh refinement, which has been implemented following a "cell-by-cell" approach. As in existing second order AMR methods, also the present higher order AMR algorithm features time-accurate local time stepping (LTS), where grids on different spatial refinement levels are allowed to use different time steps. We also compare two different Riemann solvers for the computation of the numerical fluxes at the cell interfaces. The new scheme has been validated over a sample of numerical test problems in one, two and three spatial dimensions, exploring its ability in resolving the propagation of relativistic hydrodynamical and magnetohydrodynamical waves in different physical regimes. The astrophysical relevance of the new code for the study of the Richtmyer--Meshkov instability is briefly discussed in view of future applications.
      InstabilityStencilShock waveLorentz factorRiemann problemRelativistic magnetohydrodynamicsAlfvén waveContact discontinuityAdaptive mesh refinementExact solution...
    • This paper presents a brief, semi-technical comparison of the essential features of the frequentist and Bayesian approaches to statistical inference, with several illustrative examples implemented in Python. The differences between frequentism and Bayesianism fundamentally stem from differing definitions of probability, a philosophical divide which leads to distinct approaches to the solution of statistical problems as well as contrasting ways of asking and answering questions about unknown parameters. After an example-driven discussion of these differences, we briefly compare several leading Python statistical packages which implement frequentist inference using classical methods and Bayesian inference using Markov Chain Monte Carlo.
      Confidence intervalMonte Carlo Markov chainFrequentist approachNuisance parameterMaximum likelihoodPoint estimationStarBayesian approachPythonAlice and Bob...
    • Galaxy clusters exhibit remarkable self-similar behavior which allows us to establish simple scaling relationships between observable quantities and cluster masses, making galaxy clusters useful cosmological probes. Recent X-ray observations suggest that self-similarity may be broken in the outskirts of galaxy clusters. In this work, we analyze a mass-limited sample of massive galaxy clusters from the Omega500 cosmological hydrodynamic simulation to investigate the self-similarity of the diffuse X-ray emitting intracluster medium (ICM) in the outskirts of galaxy clusters. We find that the self-similarity of the outer ICM profiles is better preserved if they are normalized with respect to the mean density of the universe, while the inner profiles are more self-similar when normalized using the critical density. However, the outer ICM profiles as well as the location of accretion shock around clusters are sensitive to their mass accretion rate, which causes the apparent breaking of self-similarity in cluster outskirts. We also find that the collisional gas does not follow the distribution of collisionless dark matter perfectly in the infall regions of galaxy clusters, leading to 10% departures in the gas-to-dark matter density ratio from the cosmic mean value. Our results have a number implications for interpreting observations of galaxy clusters in X-ray and through the Sunyaev-Zel'dovich effect and their application to cluster cosmology.
      Dark matterEntropy profileEntropyRadial velocityThermalisationGalaxy filamentPressure profileRadial velocity profileCluster of galaxiesCluster sampling...
    • Theoretical models for the production of relativistic jets from active galactic nuclei predict that jet power arises from the spin and mass of the central black hole, as well as the magnetic field near the event horizon. The physical mechanism mechanism underlying the contribution from the magnetic field is the torque exerted on the rotating black hole by the field amplified by the accreting material. If the squared magnetic field is proportional to the accretion rate, then there will be a correlation between jet power and accretion luminosity. There is evidence for such a correlation, but inadequate knowledge of the accretion luminosity of the limited and inhomogeneous used samples prevented a firm conclusion. Here we report an analysis of archival observations of a sample of blazars (quasars whose jets point towards Earth) that overcomes previous limitations. We find a clear correlation between jet power as measured through the gamma-ray luminosity, and accretion luminosity as measured by the broad emission lines, with the jet power dominating over the disk luminosity, in agreement with numerical simulations. This implies that the magnetic field threading the black hole horizon reaches the maximum value sustainable by the accreting matter.
      Flat spectrum radio quasarAccretionAstrophysical jetEGRETMagnetic energyLorentz factorBlack hole spinBroad-line regionSpectral energy distributionActive Galactic Nuclei...
    • The measurement of the Higgs mass at the LHC has confirmed that the Standard Model electroweak vacuum is a shallow local minimum and is not absolutely stable. In addition to a probable unacceptably fast tunneling to the deep true minimum, it is not clear how the observable present-day vacuum could be reached from the early Universe particularly following inflation. In this note it is shown that these problems can be alleviated if the Higgs field is non-minimally coupled to a higher-curvature theory of gravity which is effective in deriving inflation a la Starobinsky. Moreover, it implies that the Higgs self-coupling could be enhanced and have an observable effect at the next generation of particle colliders.
      Standard ModelPlanck scaleEinstein frameHiggs potentialPlanck missionHiggs bosonMixing angleE-foldingScalar fieldHiggs quartic coupling...
    • Bayesian inference provides a flexible way of combining data with prior information. However, quantile regression is not equipped with a parametric likelihood, and therefore, Bayesian inference for quantile regression demands careful investigation. This paper considers the Bayesian empirical likelihood approach to quantile regression. Taking the empirical likelihood into a Bayesian framework, we show that the resultant posterior from any fixed prior is asymptotically normal; its mean shrinks toward the true parameter values, and its variance approaches that of the maximum empirical likelihood estimator. A more interesting case can be made for the Bayesian empirical likelihood when informative priors are used to explore commonality across quantiles. Regression quantiles that are computed separately at each percentile level tend to be highly variable in the data sparse areas (e.g., high or low percentile levels). Through empirical likelihood, the proposed method enables us to explore various forms of commonality across quantiles for efficiency gains. By using an MCMC algorithm in the computation, we avoid the daunting task of directly maximizing empirical likelihood. The finite sample performance of the proposed method is investigated empirically, where substantial efficiency gains are demonstrated with informative priors on common features across several percentile levels. A theoretical framework of shrinking priors is used in the paper to better understand the power of the proposed method.
      Bayesian approachClimateFrequentist approachStatisticsEstimating equationsCoverage probabilityIndicator functionUniform convergenceWettingCovariance...
    • I apply FDR -- a recently introduced Four Dimensional Regularization approach to quantum field theories -- to compute the NLO QCD corrections to H -> gg in the large top mass limit. The calculation involves all key ingredients of massless QCD, namely ultraviolet, infrared and collinear divergences, besides alpha_s renormalization. I show in detail how the correct result emerges in FDR, and discuss the translation rules to dimensional regularization.
      Dimensional ReductionQuantum field theoryPhase spaceFDRStrong coupling constantPartonInfrared divergenceGauge invarianceFeynman rulesTransition rule...
    • The Standard Model of particle physics is still lacking an understanding of the generation and nature of neutrino masses. A favorite theoretical scenario (the see-saw mechanism) is that both Dirac and Majorana mass terms are present, leading to the existence of heavy partners of the light neutrinos, presumably massive and nearly sterile. These heavy neutrinos can be searched for at high energy lepton colliders of very high luminosity, such as the Future electron-positron e+e- Circular Collider, FCC-ee (TLEP), presently studied within the Future Circular Collider design study at CERN, as a possible first step. A first look at sensitivities, both from neutrino counting and from direct search for heavy neutrino decay, are presented. The number of neutrinos should be measurable with a precision between 0.001 - 0.0004, while the direct search appears very promising due to the long lifetime of heavy neutrinos for small mixing angles. A sensitivity down to a heavy-light mixing of 10^{-12} is obtained, covering a large phase-space for heavy neutrino masses between 10 and 80 GeV/c2.
      Sterile neutrinoNeutrinoColliderTLEP experimentMixing angleCERNNeutrino massStandard ModelLuminosityMajorana mass...
    • Observations of the redshifted 21 cm line from neutral hydrogen will open a new window on the early Universe. By influencing the thermal and ionization history of the intergalactic medium (IGM), annihilating dark matter (DM) can leave a detectable imprint in the 21 cm signal. Building on the publicly available 21cmFAST code, we compute the 21 cm signal for a 10 GeV WIMP DM candidate. The most pronounced role of DM annihilations is in heating the IGM earlier and more uniformly than astrophysical sources of X-rays. This leaves several unambiguous, qualitative signatures in the redshift evolution of the large-scale ($k\approx0.1$ Mpc$^{-1}$) 21 cm power amplitude: (i) the local maximum (peak) associated with IGM heating can be lower than the other maxima; (ii) the heating peak can occur while the IGM is in emission against the cosmic microwave background (CMB); (iii) there can be a dramatic drop in power (a global minimum) corresponding to the epoch when the IGM temperature is comparable to the CMB temperature. These signatures are robust to astrophysical uncertainties, and will be easily detectable with second generation interferometers. We also briefly show that decaying warm dark matter has a negligible role in heating the IGM.
      GalaxyIntergalactic mediumCoolingCosmologyAbsorptivityAstronomical X-ray sourceKinetic temperatureDark AgesReionizationHydrogen 21 cm line...
    • The oscillation of the CMB photons into axions can cause CMB spectral distortion in the presence of large scale magnetic field. With the COBE limit on the $\mu$ parameter and a homogeneous magnetic field with strength $B\lesssim 3.2$ nG at the horizon scale, stronger lower limit on the axion mass in comparison with the limit of the ADMX experiment is found to be, $4.8\times 10^{-5}$ eV $\lesssim m_a$ for the KSVZ axion model. On the other hand, using the experimental limit on the axion mass $3.5\times 10^{-6}$ eV $\lesssim m_a$ from the ADMX experiment together with the COBE bound on $\mu$, is found $B\lesssim 53$ nG for the KSVZ axion model and $B\lesssim 141$ nG for DFSZ axion model, for a homogeneous magnetic field with coherence length at the present epoch $\lambda_B\sim 1.3$ Mpc. Limits on $B$ and $m_a$ for PIXIE/PRISM expected sensitivity on $\mu$ are derived. If CMB $\mu$ distortion would be detected by the future space missions PIXIE/PRISM and assuming that the strength of the large scale magnetic field is close to its canonical value, $B\sim 1-3$ nG, axions in the mass range $2\, \mu$eV - $3\, \mu$eV would be potential candidates of CMB $\mu$-distortion.
      Magnetic field strengthFaraday rotationIndex of refractionCMB temperature anisotropyCosmologyAxion modelCoupling constantQuantum electrodynamicsAxionFaraday effect...
    • Evidence of a heavy neutrino, $\nu_H$, in the $K^+\to\mu^+\nu_H$ decays was sought using the E949 experimental data with an exposure of $1.70\times 10^{12}$ stopped kaons. With the major background from the radiative $K^+\to\mu^+\nu_\mu\gamma$ decay understood and suppressed, upper limits (90% C.L.) on the neutrino mixing matrix element between muon and heavy neutrino, $|U_{\mu H}|^2$, were set at the level of $10^{-7}$ to $10^{-9}$ for the heavy neutrino mass region 175 to 300 MeV/$c^2$.
      PionKaonBranching ratioStatisticsMonte Carlo methodScintillationStandard ModelKinematicsKaon decayBig bang nucleosynthesis...
    • Both observations and modelling of magnetic fields in the diffuse interstellar gas of spiral galaxies are well developed but the theory has been confronted with observations for only a handful of individual galaxies. There is now sufficient data to consider statistical properties of galactic magnetic fields. We have collected data from the literature on the magnetic fields and interstellar media (ISM) of 20 spiral galaxies, and tested for various physically motivated correlations between magnetic field and ISM parameters. Clear correlations emerge between the total magnetic field strength and molecular gas density as well as the star formation rate. The magnetic pitch angle exhibits correlations with the total gas density, the star formation rate and the strength of the axisymmetric component of the mean magnetic field. The total and mean magnetic field strengths exhibit noticeable degree of correlation, suggesting a universal behaviour of the degree of order in galactic magnetic fields. We also compare the predictions of galactic dynamo theory to observed magnetic field parameters and identify directions in which theory and observations might be usefully developed.
      Mean fieldSteady stateTurbulenceSpiral armHelicityAzimuthDifferential rotationMagnetic helicityCompressibilityIntensity...
    • NeutrinoInterferenceGauge fieldLepton numberWeak neutral current interactionLeptonic model of particle accelerationCharged currentSterile neutrinoElectronParticles...
    • Semileptonic decayTau leptonParity violationChiralityChiral modelDalitz plotMassLeptonsP-symmetryVector...
    • The spectral functions of the vector current and the axial-vector current have been measured in hadronic tau decays using the OPAL detector at LEP. Within the framework of the Operator Product Expansion a simultaneous determination of the strong coupling constant alpha_s, the non-perturbative operators of dimension 6 and 8 and of the gluon condensate has been performed. Different perturbative descriptions have been compared to the data. The Contour Improved Fixed Order Perturbation Theory gives alpha_s(mtau**2) = 0.348 +- 0.009 +- 0.019 at the tau-mass scale and alpha_s(mz**2) = 0.1219 +- 0.0010 +- 0.0017 at the Z-mass scale. The values obtained for alpha_s(mz**2) using Fixed Order Perturbation Theory or Renormalon Chain Resummation are 2.3% and 4.1% smaller, respectively. The running of the strong coupling between s_0 ~1.3 GeV**2 and s_0 = mtau**2 has been tested from direct fits to the integrated differential hadronic decay rate R_tau. A test of the saturation of QCD sum rules at the tau-mass scale has been performed.
      Monte Carlo methodRegularizationBranching ratioStatisticsSystematic errorQuantum chromodynamicsPionRenormalization schemeQuark massPerturbative QCD...
    • 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.
      Dark matter subhaloMilky WayA dwarfsUltra-faint dwarf spheroidal galaxyGalaxyAzimuthStatisticsStarAndromeda galaxyInfall model...
    • 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.
      Baryon contentNavarro-Frenk-White profileCluster of galaxiesAbell 383GalaxyStarVirial massAdiabatic contraction of dark matterN-body simulationDM mass...
    • 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.
      Weakly interacting massive particleStatisticsRelic abundanceDegree of freedomFreeze-outEntropyDark matterAbundanceStandard ModelBoltzmann transport equation...
    • Observations of interstellar clouds that cast shadows in the soft X-ray background can be used to separate the background Galactic halo emission from the local emission due to solar wind charge exchange (SWCX) and/or the Local Bubble (LB). We present an XMM-Newton observation of a shadowing cloud, G225.60-66.40, that is sufficiently compact that the on- and off-shadow spectra can be extracted from a single field of view (unlike previous shadowing observations of the halo with CCD-resolution spectrometers, which consisted of separate on- and off-shadow pointings). We analyzed the spectra using a variety of foreground models: one representing LB emission, and two representing SWCX emission. We found that the resulting halo model parameters (temperature $T_h \approx 2 \times 10^6$ K, emission measure $E_h \approx 4 \times 10^{-3}$ cm$^{-6}$ pc) were not sensitive to the foreground model used. This is likely due to the relative faintness of the foreground emission in this observation. However, the data do favor the existence of a foreground. The halo parameters derived from this observation are in good agreement with those from previous shadowing observations, and from an XMM-Newton survey of the Galactic halo emission. This supports the conclusion that the latter results are not subject to systematic errors, and can confidently be used to test models of the halo emission.
      Solar windSurface brightnessSoft X-ray backgroundAbundanceThermalisationIntensityScience analysis systemCollisional ionization equilibriumAtomDBSpectral analysis...
    • This is a review of particle-theory models of inflation, and of their predictions for the primordial density perturbation that is thought to be the origin of structure in the Universe. It contains mini-reviews of the relevant observational cosmology, of elementary field theory and of supersymmetry, that may be of interest in their own right. The spectral index $n(k)$, specifying the scale-dependence of the spectrum of the curvature perturbation, will be a powerful discriminator between models, when it is measured by Planck with accuracy $\Delta n\sim 0.01$. The usual formula for $n$ is derived, as well as its less familiar extension to the case of a multi-component inflaton; in both cases the key ingredient is the separate evolution of causally disconnected regions of the Universe. Primordial gravitational waves will be an even more powerful discriminator if they are observed, since most models of inflation predict that they are completely negligible. We treat in detail the new wave of models, which are firmly rooted in modern particle theory and have supersymmetry as a crucial ingredient. The review is addressed to both astrophysicists and particle physicists, and each section is fairly homogeneous regarding the assumed background knowledge.
      HorizonInflatonSlow rollSlow-roll inflationCosmic Background ExplorerSupergravityGravitational waveVacuum expectation valueScalar fieldHubble time...
    • 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.
      StarCoolingRadio pulsarPulsarInstabilityDissipationLaser Interferometer Gravitational-Wave ObservatorySteady stateAccretionMode coupling...
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