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01 Nov 2004 |
Scalar-Tensor-Vector Gravity TheoryAuthors: J. W.
Moffat
Comments: 14 pages, Latex file, no figures A covariant scalar-tensor-vector-gravity theory is developed which allows the gravitational constant $G$, a vector field coupling $\omega$ and the vector field mass $\mu$ to vary with space and time. The equations of motion for a test particle lead to a modified gravitational acceleration law that can fit galaxy rotation curves without non-baryonic dark matter. The theory is consistent with solar system and binary pulsar observations. Full-text: PostScript, PDF, or Other formatsGZK Photons as Ultra High Energy Cosmic RaysAuthors: Graciela
Gelmini, Oleg
Kalashev, Dmitry
V. Semikoz
Comments: 20 pages, 31 figures Report-no: UCLA/04/TEP/17 We calculate the flux of "GZK-photons", namely the flux of Ultra High Energy Cosmic Rays (UHECR) consisting of photons produced by extragalactic protons through the resonant photoproduction of pions, the so called Greisen-Zatsepin-Kuzmin (GZK) effect. We show that if the UHECR are mostly protons, depending on the UHECR spectrum, the slope of the proton flux at the source, distribution of sources and intervening backgrounds, between $10^{-4}$ and $10^{-2}$ of the UHECR above $10^{19}$ eV and between $10^{-5}$ and 0.6 of the UHECR above $10^{20}$ eV are photons (the range being much higher for the AGASA than for the HiRes spectrum). Detection of these photons would open the way for UHECR gamma-ray astronomy. Detection of a larger photon flux would imply the emission of photons at the source or new physics. In fact, we find that at energiesclose to $10^{20}$ eV the maximum expected GZK photon fraction is comparable to (for the AGASA spectrum) or much smaller than (for the HiRes spectrum) the minimum photon ratio predicted by Top-Down models which fit the AGASA or the HiRes data, thus, the photon fraction at $10^{20}$ eV is a crucial test for Top-Down models. Full-text: PostScript, PDF, or Other formatsExplaining LSND by a decaying sterile neutrinoComments: 23 pages, 5 figures Report-no: CERN-PH-TH/2005-083, SISSA 34/2005/EP We propose an explanation of the LSND evidence for electron antineutrino appearance based on neutrino decay. We introduce a heavy neutrino, which is produced in pion and muon decays because of a small mixing with muon neutrinos, and then decays into a scalar particle and a light neutrino, predominantly of the electron type. We require values of $g m_4\sim$ few eV, $g$ being the neutrino--scalar coupling and $m_4$ the heavy neutrino mass, e.g. $m_4$ in the range from 1 keV to 1 MeV and $g \sim 10^{-6} - 10^{-3}$. Performing a fit to the LSND data as well as all relevant null-result experiments, we show that all data can be explained within this decay scenario. In the minimal version of the decay model, we predict a signal in the upcoming MiniBooNE experiment corresponding to a transition probability of the same order as seen in LSND. In addition, we show that extending our model to two nearly degenerate heavy neutrinos it is possible to introduce CP violation in the decay, which can lead to a suppression of the signal in MiniBooNE running in the neutrino mode. We briefly discuss signals in future neutrino oscillation experiments, we show that our scenario is compatible with bounds from laboratory experiments, and we comment on implications in astrophysics and cosmology. Full-text: PostScript, PDF, or Other formatsThe Shear TEsting Programme 1: Weak lensing analysis of simulated ground-based observationsAuthors: Catherine
Heymans, Ludovic
Van Waerbeke, David
Bacon, Joel
Berge, Gary
Bernstein, Emmanuel
Bertin, Sarah
Bridle, Michael
L. Brown, Douglas
Clowe, Haakon
Dahle, Thomas
Erben, Meghan
Gray, Marco
Hetterscheidt, Henk
Hoekstra, Patrick
Hudelot, Mike
Jarvis, Konrad
Kuijken, Vera
Margoniner, Richard
Massey, Yannick
Mellier, Reiko
Nakajima, Alexandre
Refregier, Jason
Rhodes, Tim
Schrabback, David
Wittman
Comments: 16 pages, 3 figures, submitted to MNRAS The Shear TEsting Programme, STEP, is a collaborative project to improve the accuracy and reliability of all weak lensing measurements in preparation for the next generation of wide-field surveys. In this first STEP paper we present the results of a blind analysis of simulated ground-based observations of relatively simple galaxy morphologies. The most successful methods are shown to achieve percent level accuracy. From the cosmic shear pipelines that have been used to constrain cosmology, we find weak lensing shear measured to an accuracy that is within the statistical errors of current weak lensing analyses, with shear measurements accurate to better than 7%. The dominant source of measurement error is shown to arise from calibration uncertainties where the measured shear is over or under-estimated by a constant multiplicative factor. This is of concern as calibration errors cannot be detected through standard diagnostic tests. The measured calibration errors appear to result from stellar contamination, false object detection, the shear measurement method itself, selection bias and/or the use of biased weights. Additive systematics (false detections of shear) resulting from residual point-spread function anisotropy are, in most cases, reduced to below an equivalent shear of 0.001, an order of magnitude below cosmic shear distortions on the scales probed by current surveys. Full-text: PostScript, PDF, or Other formatsCharacterizing the Cluster Lens PopulationAuthors: Joseph
F. Hennawi, Neal
Dalal, Paul
Bode, Jeremiah
P. Ostriker
Comments: 19 pages, 15 figures. Submitted to ApJ We present a detailed investigation into which properties of CDM halos make them effective strong gravitational lenses. Strong lensing cross sections of 878 clusters from an N-body simulation are measured by ray tracing through 13,594 unique projections. We measure concentrations, axis ratios, orientations, and the amount of substructure of each cluster, and compare the lensing weighted distribution of each quantity to that of the cluster population as a whole. The concentrations of lensing clusters are on average 34% larger than the typical cluster in the Universe. Despite this bias, the anomalously high concentrations (c >14) recently measured by several groups, appear to be inconsistent with the concentration distribution in our simulations, which predict < 2% of lensing clusters should have concentrations this high. No correlation is found between lensing cross section and the amount of substructure. We introduce several types of simplified dark matter halos, and use them to isolate which properties of CDM clusters make them effective lenses. Projections of halo substructure onto small radii and the large scale mass distribution of clusters do not significantly influence cross sections. The abundance of giant arcs is primarily determined by the mass distribution within an average overdensity of ~ 10,000. A multiple lens plane ray tracing algorithm is used to show that projections of large scale structure increase the giant arc abundance by a modest amount <7%. We revisit the question of whether there is an excess of giant arcs behind high redshift clusters in the RCS survey and find that the number of high redshift (z > 0.6) lenses is in good agreement with LCDM, although our simulations predict more low redshift (z < 0.6) lenses than were observed. (abridged) Full-text: PostScript, PDF, or Other formatsPropagation of Ultra-High Energy Cosmic Rays above $10^{19}$ eV in a Structured Extragalactic Magnetic Field and Galactic Magnetic FieldAuthors: Hajime
Takami, Hiroyuki
Yoshiguchi, Katsuhiko
Sato
Comments: 12 pages, 12 figures, submitted to the Astrophysical Journal We present numerical simulations on propagation of Ultra-High EnergyCosmic Rays (UHECRs) above $10^{19}$ eV in a structured extragalactic magnetic field (EGMF) and simulate their arrival distribution at the earth. We use the IRAS PSCz catalogue in order to construct a model of the EGMF and source model of UHECRs, both of which reproduce the local structures around the Milky Way. We also consider modifications of UHECR arrival directions by the Galactic magnetic field. We follow an inverse process of their propagation from the earth and record the trajectories. This enables us to calculate only trajectories of UHECRs arriving at the earth, which saves the CPU time. We construct arrival distribution of UHECRs from these trajectories and calculate the harmonic amplitudes and the two point correlation functions of their arrival distribution using our source models. We estimate number density of sources which explains the Akeno Ground Air Shower Array observation best. As a result, we find that $\sim 5 \times 10^{-6}$ Mpc$^{-3}$ is the most appropriate number density of source of UHECRs, which constrains the source canditates of UHECRs. We also demonstrate skymaps of their arrival distribution with the event number expected by future experiments and examine how the EGMF affects their arrival distribution. The main result is diffusion of clustering events which are obtained by calculations neglecting the EGMF. Quantitatively, the EGMF weakens the peak of the two point correlation function at small angle scale and we find this fact explains the observational data better. Full-text: PostScript, PDF, or Other formatsRelaxing to Three DimensionsAuthors: Andreas
Karch, Lisa
Randall
Comments: 4 pages Report-no: HUTP-05/A0029, UW/PT-05-14 We propose a new selection principle for distinguishing among possible vacua that we call the "relaxation principle". The idea is that the universe will naturally select among possible vacua through its cosmological evolution, and the configuration with the biggest filling fraction is the likeliest. We apply this idea to the question of the number of dimensions of space. We show that under conventional (but higher-dimensional) FRW evolution, a universe filled with equal numbers of branes and antibranes will naturally come to be dominated by 3-branes and 7-branes. We show why this might help explain the number of dimensions that are experienced in our visible universe. Full-text: PostScript, PDF, or Other formatsOptical and Infrared Signatures of ULX'sAuthors: Christopher
Copperwheat (1), Mark
Cropper (1), Roberto
Soria (1,2), Kinwah
Wu (1) ((1) MSSL/UCL, (2) CfA)
Comments: MNRAS accepted, 11 pages We have constructed a model to describe the optical emission from ultra-luminous X-ray sources (ULXs). We assume a binary model with a black hole accreting matter from a Roche lobe filling companion star. We consider the effects of radiative transport and radiative equilibrium in the irradiated surfaces of both the star and a thin accretion disk. We have developed this model as a tool with which to positively identify the optical counterparts of ULXs, and subsequently derive parameters such as the black hole mass and the luminosity class and spectral type of the counterpart. We examine the dependence of the optical emission on these and other variables. We extend our model to examine the magnitude variation at infrared wavelengths, and we find that observations at these wavelengths may have more diagnostic power than in the optical. We apply our model to existing HST observations of the candidates for the optical counterpart of ULX X-7 in NGC 4559. All candidates could be consistent with an irradiated star alone, but we find that a number of them are too faint to fit with an irradiated star and disk together. Were one of these the optical counterpart to X-7, it would display a significant temporal variation. Full-text: PostScript, PDF, or Other formatsGRAPE-SPH Chemodynamical Simulation of Elliptical Galaxies II: Scaling Relations and the Fundamental PlaneAuthors: Chiaki Kobayashi (MPA)Comments: Accepted for publication in MNRAS. 13 pages mpeg simulations available at this http URL We simulate the formation and chemodynamical evolution of 128 elliptical galaxies using a GRAPE-SPH code that includes various physical processes that are associated with the formation of stellar systems: radiative cooling, star formation, feedback from Type II and Ia supernovae and stellar winds, and chemical enrichment. We find that the star formation timescale controls when and where stars form in the contracting gas cloud, determines the effective radius at given mass, and is constrained by observation to be ten times longer than the local dynamical timescale. We succeed in reproducing the observed global scaling relations under our CDM-based scenario, e.g., the Faber-Jackson relation, the Kormendy relation, and the fundamental plane. An intrinsic scatter exists along the fundamental plane, and the origin of this scatter lies in differences in merging history. Galaxies that undergo major merger events tend to have larger effective radii and fainter surface brightnesses, which result in larger masses, smaller surface brightnesses, and larger mass-to-light ratios. We can also reproduce the observed colour-magnitude and mass-metallicity relations, although the scatter is larger than observed. The scatter arises because feedback is not very effective and star formation does not terminate completely in our simulations. ~25% of accreted baryons are blown away in the simulations, independent of the assumed star formation timescale and initial mass function. Most heavy elements end up locked into stars in the galaxy. The ejected metal fraction depends only on the star formation timescale, and is ~2% even to rapid star formation. Full-text: PostScript, PDF, or Other formats |
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