Munch

Authors: M.I. Wilkinson, J.T. Kleyna, N.W. Evans, G.F. Gilmore, J.I. Read, A. Koch, E.K. Grebel, M.J. Irwin
Comments: 8 pages, 5 figs. Invited review in Proceedings of XXIst IAP Colloquium, "Mass Profiles & Shapes of Cosmological Structures" (Paris, 4-9 July 2005), eds G.A. Mamon, F. Combes, C. Deffayet, B. Fort (Paris: EDP Sciences)

The status of kinematic observations in Local Group dwarf spheroidal galaxies (dSphs) is reviewed. Various approaches to the dynamical modelling of these data are discussed and some general features of dSph dark matter haloes based on simple mass models are presented.

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Likelihood Methods for Cluster Dark Energy Surveys

Authors: Wayne Hu, J.D. Cohn
Comments: 4 pages

Galaxy cluster counts at high redshift, binned into spatial pixels and binned into ranges in an observable proxy for mass, contain a wealth of information on both the dark energy equation of state and the mass selection function required to extract it. The likelihood of the number counts follows a Poisson distribution whose mean fluctuates with the large-scale structure of the universe. We develop a joint likelihood method that accounts for these distributions. Maximization of the likelihood over a theoretical model that includes both the cosmology and the observable-mass relations allows for a joint extraction of dark energy and cluster structural parameters.

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A new bound on the neutrino mass from the SDSS baryon acoustic peak

Authors: Ariel Goobar, Steen Hannestad, Edvard Mortsell, Huitzu Tu
Comments: 12 pages, 3 figures, JCAP format

We have studied bounds on the neutrino mass using new data from the Sloan Digital Sky Survey measurement of the baryon acoustic peak. We find that even in models with a running spectral index where the number of neutrinos and the dark energy equation of state are allowed to vary, the bound on the sum of neutrino masses is robustly below 0.5 eV. Using the SDSS Lyman-alpha constraint on the amplitude of the matter power spectrum at small scales pushes the bound to \sum m_nu < 0.30 eV (95% C.L.).

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Right-handed Sneutrinos as Nonthermal Dark Matter

Authors: Shrihari Gopalakrishna, Andre de Gouvea, Werner Porod
Comments: 21 pages

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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Right-handed neutrinos as the source of density perturbations

Authors: Lotfi Boubekeur, Paolo Creminelli
Comments: 14 pages, 2 figures
Report-no: IC/2006/004

We study the possibility that cosmological density perturbations are generated by the inhomogeneous decay of right-handed neutrinos. This will occur if a scalar field whose fluctuations are created during inflation is coupled to the neutrino sector. Robust predictions of the model are a detectable level of non-Gaussianity and, if standard leptogenesis is the source of the baryon asymmetry, a baryon isocurvature perturbations at the level of the present experimental constraints.

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Detecting neutrino mass difference with cosmology

Authors: Anze Slosar
Comments: 5 pages, 4 figures

Cosmological parameter estimation exercises usually make the approximation that the three standard neutrinos have degenerate mass, which is at odds with recent terrestrial measurements of the difference in the square of neutrino masses. In this paper we examine whether the use of this approximation is justified for the cosmic microwave background (CMB) spectrum, matter power spectrum and the CMB lensing potential power spectrum. We find that, assuming delta m^2_{23} ~ 2.5 x 10^-3eV^2 in agreement with recent Earth based measurements of atmospheric neutrino oscillations, the correction due to nondegeneracy is of the order of precision of present numerical codes and undetectable for the foreseeable future for the CMB and matter power spectra. An ambitious experiment that could reconstruct the lensing potential power spectrum to the cosmic variance limit up to l ~ 1000 has the potential to detect neutrino mass difference to high significance in some parts of the parameter space. If the restriction on the mass squared difference is relaxed, the corrections due to non-degeneracy could become important for all the cosmological probes discussed here.

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Deciphering Inflation with Gravitational Waves: Cosmic Microwave Background Polarization vs. Direct Detection with Laser Interferometers

Authors: Tristan L. Smith (Caltech), Hiranya V. Peiris (KICP/EFI, U. Chicago), Asantha Cooray (U.C. Irvine)
Comments: 4 pages, 2 color figures, submitted to PRL; comments are welcome. Full resolution figures are available at this http URL

A detection of the primordial gravitational wave background is considered to be the ``smoking-gun '' evidence for inflation. While super-horizon waves are probed with cosmic microwave background (CMB) polarization, the relic background will be studied with laser interferometers. The long lever arm spanned by the two techniques improves constraints on the inflationary potential and validation of consistency relations expected under inflation. If gravitational waves with a tensor-to-scalar amplitude ratio greater than 0.01 are detected by the CMB, then a direct detection experiment with a sensitivity consistent with current concept studies should be pursued vigorously. If no primordial tensors are detected by the CMB, a direct detection experiment to understand the simplest form of inflation must have a sensitivity improved by two to three orders of magnitude over current plans.

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Gravitino Production from Heavy Moduli Decay and Cosmological Moduli Problem Revived

Authors: Shuntaro Nakamura (Tohoku U.), Masahiro Yamaguchi (Tohoku U.)
Comments: 14 pages, 1 figure
Report-no: TU-765

The cosmological moduli problem for relatively heavy moduli fields is reinvestigated. For this purpose we examine the decay of a modulus field at a quantitative level. The modulus dominantly decays into gauge bosons and gauginos, provided that the couplings among them are not suppressed in the gauge kinetic function. Remarkably the modulus decay into a gravitino pair is unsuppressed generically, with a typical branching ratio of order 0.01. Such a large gravitino yield after the modulus decay causes cosmological difficulties. The constraint from the big-bang nucleosynthesis pushes up the gravitino mass above 10^5 GeV. Furthermore to avoid the over-abundance of the stable neutralino lightest superparticles (LSPs), the gravitino must weigh more than about 10^6 GeV for the wino-like LSP, and even more for other neutralino LSPs. This poses a stringent constraint on model building of low-energy supersymmetry.

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Moduli-Induced Gravitino Problem

Authors: Motoi Endo, Koichi Hamaguchi, Fuminobu Takahashi
Comments: 5 pages, 1 figure
Report-no: DESY06-014

We investigate the cosmological moduli problem by studying a modulus decay in detail and find that the branching ratio of the gravitino production is generically of O(0.01-1), which causes another cosmological disaster. Consequently, the cosmological moduli problem cannot be solved simply by making the modulus mass heavier than 100 TeV. We also illustrate our results by explicitly calculating the branching ratio into the gravitinos in the mixed modulus--anomaly/KKLT- and racetrack-type models.

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Unified Model for Inflation and Dark Energy with Planck-Scale Pseudo-Goldstone Bosons

Authors: Eduard Masso, Gabriel Zsembinszki
Comments: 15 pages, 4 figures, RevTeX4
Report-no: UAB-FT-596

We present a model with a complex and a real scalar fields and a potential whose symmetry is explicitly broken by Planck-scale physics. For exponentially small breaking, the model accounts for the period of inflation in the early universe and for the period of acceleration of the late universe.

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Holographic dark energy with a constant vacuum energy density

Authors: B. Guberina, R. Horvat, H. Nikolic
Comments: 12 pages, 2 figures

We present a holographic dark-energy model in which the Newton constant $G_{N}$ scales in such a way as to render the vacuum energy density a true constant. Nevertheless, the model acts as a dynamical dark-energy model since the scaling of $G_{N}$ goes at the expense of deviation of concentration of dark-matter particles from its canonical form and/or of promotion of their mass to a time-dependent quantity, thereby making the effective equation of state (EOS) variable and different from -1 at the present epoch. Thus the model has a potential to naturally underpin Dirac's suggestion for explaining the large-number hypothesis, which demands a dynamical $G_{N}$ along with the creation of matter in the universe. We show that with the aid of observational bounds on the variation of the gravitational coupling, the effective-field theory IR cutoff can be strongly restricted, being always closer to the future event horizon than to the Hubble distance. As for the observational side, the effective EOS restricted by observation can be made arbitrary close to -1, and therefore the present model can be considered as a ``minimal'' dynamical dark-energy scenario. In addition, for nonzero but small curvature $(|\Omega_{k0}| \lsim 0.003)$, the model easily accommodates a transition across the phantom line for redshifts $z \lsim 0.2 $, as mildly favored by the data. A thermodynamic aspect of the scenario is also discussed.

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