Munch

We calculate the CMB angular trispectrum, spherical harmonic transform of the four-point correlation function, from primordial non-Gaussianity in primordial curvature perturbations characterized by a constant non-linear coupling parameter, $f_{\rm NL}$. We fully take into account the effect of the radiation transfer function, and thus provide the most accurate estimate of the signal-to-noise ratio of the angular trispectrum of CMB temperature anisotropy. We find that the predicted signal-to-noise ratio of the trispectrum summed up to a given $l$ is approximately a power-law, $(S/N)(<l)\sim 2.2\times 10^{-9}f^2_{\rm NL}l^2$, up to the maximum multipole that we have reached in our numerical calculation, $l=1200$, assuming that the error is dominated by cosmic variance. Our results indicate that the signal-to-noise ratio of the temperature trispectrum exceeds that of the bispectrum at the critical multipole, $l_c \sim 1500~(50/|f_{\rm NL}|)$. Therefore, the trispectrum of the Planck data is more sensitive to primordial non-Gaussianity than the bispectrum for $|f_{\rm NL}|\gtrsim 50$. We also report the predicted constraints on the amplitude of trispectrum, which may be useful for other non-Gaussian models such as curvaton models.

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The shape of high order correlation functions in CMB anisotropy maps

Authors: T. Brunier, F. Bernardeau
Comments: 31 pages, 17 figures, submitted to Phys. Rev. D
Report-no: SPhT-T06/004

We present a phenomenological investigation of non-Gaussian effects that could be seen on CMB temperature maps. Explicit expressions for the temperature correlation functions are given for different types of primordial mode couplings. We argue that a simplified description of the radial transfer function for the temperature anisotropies allows to get insights into the general properties of the bi and tri-spectra. The accuracy of these results is explored together with the use of the small scale approximation to get explicit expressions of high order spectra. The bi-spectrum is found to have alternate signs for the successive acoustic peaks. Sign patterns for the trispectra are more complicated and depend specifically on the type of metric couplings. Local primordial couplings are found to give patterns that are different from those expected from weak lensing effects.

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Non-gaussianity and cosmic uncertainty in curvaton-type models

Authors: D. H. Lyth
Comments: 18 pages

In curvaton-type models, observable non-gaussianity of the curvature perturbation would come from a contribution of the form $(\delta\sigma)^2$, where $\delta\sigma$ is gaussian. I analyse this situation allowing $\delta\sigma$ to be scale-dependent. The actual curvaton model is considered in more detail than before, including its cosmic uncertainty and anthropic status.

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Does the Fornax dwarf spheroidal have a central cusp or core?

Authors: Tobias Goerdt (1), Ben Moore (1), J. I. Read (1), Joachim Stadel (1), Marcel Zemp (1,2), ((1) University of Zürich, (2) ETH Zürich)
Comments: 6 pages, 5 figures, accepted for publication in MNRAS, high resolution simulations included

The dark matter dominated Fornax dwarf spheroidal has five globular clusters orbiting at ~1 kpc from its centre. In a cuspy CDM halo the globulars would sink to the centre from their current positions within a few Gyrs, presenting a puzzle as to why they survive undigested at the present epoch. We show that a solution to this timing problem is to adopt a cored dark matter halo. We use numerical simulations and analytic calculations to show that, under these conditions, the sinking time becomes many Hubble times; the globulars effectively stall at the dark matter core radius. We conclude that the Fornax dwarf spheroidal has a shallow inner density profile with a core radius constrained by the observed positions of its globular clusters. If the phase space density of the core is primordial then it implies a warm dark matter particle and gives an upper limit to its mass of ~0.5 keV, consistent with that required to significantly alleviate the substructure problem.

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Galaxy cluster mass profiles

Authors: L.M. Voigt, A.C. Fabian (Institute of Astronomy, Cambridge, UK)
Comments: 16 pages, 10 figures, 4 tables, accepted for publication in MNRAS

Accurate measurements of the mass distribution in galaxy and cluster halos are essential to test the cold dark matter (CDM) paradigm. The cosmological model predicts a universal shape for the density profile in all halos, independent of halo mass. Its profile has a `cuspy' centre, with no evidence for the constant density core. In this paper we carry out a careful analysis of twelve galaxy clusters, using Chandra data to compute the mass distribution in each system under the assumption of hydrostatic equilibrium. Due to their low concentration, clusters provide ideal objects for studying the central cusps in dark matter halos. The majority of the systems are consistent with the CDM model, but 4 objects exhibit flat inner density profiles. We suggest that the flat inner profile found for these clusters is due to an underestimation of the mass in the cluster centre (rather than any problem with the CDM model), since these objects also have a centrally peaked gas mass fraction. We discuss possible causes for erroneously low mass measurements in the cores of some systems.

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Likelihood Functions for Galaxy Cluster Surveys

Authors: Gilbert Holder (McGill University)
Comments: 6 pages, 3 figures, updated key reference

Galaxy cluster surveys offer great promise for measuring cosmological parameters, but survey analysis methods have not been widely studied. Using methods developed decades ago for galaxy clustering studies, it is shown that nearly exact likelihood functions can be written down for galaxy cluster surveys. The sparse sampling of the density field by galaxy clusters allows simplifications that are not possible for galaxy surveys. An application to counts in cells is explicitly tested using cluster catalogs from numerical simulations and it is found that the calculated probability distributions are very accurate at masses above several times 10^{14}h^{-1} solar masses at z=0 and lower masses at higher redshift.

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Supernova Ia and Galaxy Cluster Gas Mass Fraction Constraints on Dark Energy

Authors: Kyle M. Wilson, Gang Chen, Bharat Ratra
Comments: 13 pages, 4 figures

We use the Riess et al.(2004) supernova Ia apparent magnitude versus redshift data and the Allen et al.(2004) galaxy cluster gas mass fraction versus redshift data to constrain dark energy models. These data provide complementary constraints that when combined together ignificantly restrict model parameters and favor lowly-evolving dark energy density models, close to the Einstein cosmological constant limit of dark energy.

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Local dark matter clumps and the cosmic ray positron excess

Authors: Daniel T. Cumberbatch, Joseph Silk
Comments: submitted to MNRAS

It has been proposed that the excess in cosmic ray positrons, at approximately 8 GeV, observed on both flights of the HEAT balloon experiment may be associated with the annihilation of supersymmetric (SUSY) dark matter particles in the Milky Way halo. In this paper we show how the presence of local dark matter substructure could account for this excess. Specifically, we concentrate on dark matter clumps, with uniform density, located at distances much less than 1 kpc. We use results from simulations of the local dark matter distribution to place limits on the clump mass and radius as well as the annihilation rate per particle, for a range of representative SUSY dark matter scenarios.

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Population III Star Formation in a Lambda WDM Universe

Authors: Brian W. O'Shea, Michael L. Norman
Comments: 30 pages, 9 figures (2 color). Astrophysical Journal, submitted. Comments welcome
Report-no: LA-UR-06-0237

In this paper we examine aspects of primordial star formation in a gravitino warm dark matter universe with a cosmological constant. We compare a set of simulations using a single cosmological realization but with a wide range of warm dark matter particle masses which have not yet been conclusively ruled out by observations. The addition of a warm dark matter component to the initial power spectrum results in a delay in the collapse of high density gas at the center of the most massive halo in the simulation and, as a result, an increase in the virial mass of this halo at the onset of baryon collapse. Both of these effects become more pronounced as the warm dark matter particle mass becomes smaller. A cosmology using a gravitino warm dark matter power spectrum assuming a particle mass of m_{WDM} ~ 40keV is effectively indistinguishable from the cold dark matter case, whereas the m_{WDM} ~ 15 keV case delays star formation by approx. 10^8 years. There is remarkably little scatter between simulations in the final properties of the primordial protostar which forms at the center of the halo, possibly due to the overall low rate of halo mergers which is a result of the WDM power spectrum. The detailed evolution of the collapsing halo core in two representative WDM cosmologies is described. At low densities (n_{b} <= 10^5 cm^{-3}), the evolution of the two calculations is qualitatively similar, but occurs on significantly different timescales, with the halo in the lower particle mass calculation taking much longer to evolve over the same density range and reach runaway collapse. Once the gas in the center of the halo reaches relatively high densities (n_{b} >= 10^5 cm^{-3}) the overall evolution is essentially identical in the two calculations.

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Right-handed Sneutrinos as Nonthermal Dark Matter

Authors: Shrihari Gopalakrishna, Andre de Gouvea, Werner Porod
Comments: 17 pages v.2: References added
Report-no: IFIC/06-01, NUHEP-TH/06-01

When the minimal supersymmetric standard model is augmented by three right-handed neutrino superfields, one generically predicts that the neutrinos acquire Majorana masses. We postulate that all supersymmetry (SUSY) breaking masses as well as the Majorana masses of the right-handed neutrinos are around the electroweak scale and, motivated by the smallness of neutrino masses, assume that the lightest supersymmetric particle (LSP) is an almost-pure right-handed sneutrino. We discuss the conditions under which this LSP is a successful dark matter candidate. In general, such an LSP has to be nonthermal in order not to overclose the universe, and we find the conditions under which this is indeed the case by comparing the Hubble expansion rate with the rates of the relevant thermalizing processes, including self-annihilation and co-annihilation with other SUSY and standard model particles.

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511 keV line and diffuse gamma rays from moduli

Authors: Shinta Kasuya, Masahiro Kawasaki
Comments: 6 pages, 5 figures

We obtain the spectrum of gamma ray emissions from the moduli whose decay into $e^+ e^-$ accounts for the 511 keV line observed by SPI/INTERGRAL. The moduli emit gamma rays through internal bremsstrahlung, and also decay directly into two gammas via tree and/or one-loop diagrams. We show that the internal bremsstahlung constrains the mass of the moduli below $\sim 40$ MeV model-independently. On the other hand, the flux of two gammas directly decayed from the moduli through one loop diagrams will exceed the observed galactic diffuse gamma-ray background if the moduli mass exceeds $\sim 20$ MeV in the typical situation. Moreover, forthcoming analysis of SPI data in the range of 1-8 MeV may detect the line emisson with the energy half the moduli mass in the near future, which confirms the decaying moduli scenario.

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Constraints on the Evolution of the Primordial Magnetic Field from the Small Scale CMB Angular Anisotropy

Authors: D. Yamazaki, K. Ichiki, T. Kajino, G. J. Mathews
Comments: 27 pages, 4 figures, submitted to ApJ

Recent observations of the cosmic microwave background (CMB) have extended measured the power spectrum to higher multipoles $l\gtrsim$1000, and there appears to be possible evidence for excess power on small angular scales. The primordial magnetic field (PMF) can strongly affect the CMB power spectrum and the formation of large scale structure. In this paper, we calculate the CMB temperature anisotropies generated by including a power-law magnetic field at the photon last scattering surface (PLSS). We then deduce an upper limit on the primordial magnetic field based upon our theoretical analysis of the power excess on small angular scales. We have taken into account several important effects such as reionization and the modified matter sound speed in the presence of a magnetic field. An upper limit to the field strength of $|B_\lambda|\lesssim$ 4.7 nG at the present scale of 1 Mpc is deduced. This is obtained by comparing the calculated theoretical result including the Sunyaev-Zeldovich (SZ) effect with recent observed data on the small scale CMB anisotropies from the Wilkinson Microwave Anisotropy Probe (WMAP), the Cosmic Background Imager (CBI) and the Arcminute Cosmology Bolometer Array Receiver (ACBAR). We discuss several possible mechanisms for the generation and evolution of the PMF.

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MOND habitats within the solar system

Authors: Jacob Bekenstein, Joao Magueijo

MOdified Newtonian Dynamics (MOND) is an interesting alternative to dark matter in extragalactic systems. We here examine the possibility that mild or even strong MOND behavior may become evident well inside the solar system, in particular near saddle points of the total gravitational potential. Whereas in Newtonian theory tidal stresses are finite at saddle points, they are expected to diverge in MOND, and to remain distinctly large inside a sizeable oblate ellipsoid around the saddle point. We work out the MOND effects using the nonrelativistic limit of the T$e$V$e$S theory, both in the perturbative nearly Newtonian regime and in the deep MOND regime. While strong MOND behavior would be a spectacular ``backyard'' vindication of the theory, pinpointing the MOND-bubbles in the setting of the realistic solar system may be difficult. Space missions, such as the LISA Pathfinder, equipped with sensitive accelerometers, may be able to explore the larger perturbative region.

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