Munch

We explore the range of parameters for dark-matter sterile neutrinos in an extention of the Minimal Standard Model by three singlet fermions with masses below the electroweak scale (the $\nu$MSM). This simple model, which can explain a wide range of phenomena, including neutrino oscillations, baryogenesis, the pulsar velocities, and the early reionization, allows for the dark-matter sterile neutrinos to have masses as small as 0.5 keV. The presence of two heavier sterile neutrinos and the possibility of entropy production in their decays broadens the allowed range of parameters for the dark-matter sterile neutrinos (or other types of dark matter, for example, the gravitino). Of particular interest is the possibility of large mixing angles between active and sterile neutrinos, which may be accessible to laboratory experiments.

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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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Local Voids as the Origin of Large-angle Cosmic Microwave Background Anomalies

Authors: Kaiki Taro Inoue, Joseph Silk
Comments: 8 pages, 5 eps files

We explore the large angular scale temperature anisotropies in the cosmic microwave background due to expanding homogeneous local voids at redshift z~1. A compensated spherically symmetric homogeneous dust-filled void with radius \~3*10^2 h^{-1}Mpc, and density contrast ~-0.3 can be observed as a cold spot with a temperature anisotropy -1*10^{-5} surrounded by a slightly hotter ring. We find that a pair of these circular cold spots separated by ~50 degree can account both for the planarity of the octopole and the alignment between the quadrupole and the octopole in the cosmic microwave background (CMB) anisotropy. The cold spot in the Galactic southern hemisphere which is anomalous at the ~3sigma level can be explained by such a large void at z~1. The observed north-south asymmetry in the large-angle CMB power can be attributed to the asymmetric distribution of these local voids between the two hemispheres. The statistical significance of the low quadrupole is further reduced in this interpretation of the large angular scale CMB anomalies.

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High energy Gamma-Ray Bursts as a result of the collapse and total annihilation of neutralino clumps

Authors: R. S. Pasechnik, V. A. Beylin, V. I. Kuksa, G. M. Vereshkov
Comments: 9 pages, 4 figures

Rare astrophysical events - cosmological gamma-ray bursts with energies over GeV - are considered as an origin of information about some SUSY parameters. The model of generation of the powerful gamma-ray bursts is proposed. According to this model the gamma-ray burst represents as a result of the collapse and the total annihilation of the neutralino clump. About 80 % of the clump mass radiates during about 100 second at the final stage of annihilation. The annihilation spectrum and its characteristic energies are calculated in the framework of Split Higgsino model.

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What can we learn about dark energy evolution?

Authors: Marian Douspis (LATT, IAS), Yves Zolnierowski (LAPP), Alain Blanchard (LATT), Alain Riazuelo (IAP)
Comments: Submitted to Astronomy and Astrophysics

We examine some of the constraints that can be obtained on a two parameters model of dark energy in which the characteristic parameter of the equation of state $w (z) = P(z) / \rho (z)$ does not vary smoothly with time as usually assumed, but undergoes a transition between two values over a period that can be significantly shorter than the Hubble time. We find that the most recent SNIa survey allows a transition between $w \sim -0.2$ to $w \sim -1$ (the first value being somewhat arbitrary) at redshift as low as 0.1, despite the fact that data extend beyond $z \sim 1$. Surveys with precision anticipated for space experiments would allow to improve this constraint but not by much, as a transition occurring at redshift as low as $\sim 0.17$ could still remain undistinguishable from a standard cosmological constant. The addition of a prior on the matter density $\Omega\_\MAT = 0.27$ improves the constraints, although in a rather limited way. This suggests that Hubble diagram of distant SNIa might hardly reveal the actual nature of dark energy at redshift above 0.2. Even deep space experiments would fail to identify a rapid transition at redshift above 0.5. This suggests that only the local dynamics of the quintessence can be caught by SNIa Hubble diagram. The reason for this phenomenon is investigated. On the contrary without any prior, we found that existing constraints from combining CMB and SNIa already reject a transition at redshift below 1.5.

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Significant primordial star formation at redshifts z ~ 3-4

Authors: Raul Jimenez (UPenn), Zoltan Haiman (Columbia)
Comments: Nature in press, March 23rd issue. Under Nature embargo

Four recent observational results have challenged our understanding of high--redshift galaxies, as they require the presence of far more ultraviolet photons than should be emitted by normal stellar populations. First, there is significant ultraviolet emission from Lyman Break Galaxies (LBGs) at wavelenghts shorter than 912\AA. Second, there is strong Lyman alpha emission from extended ``blobs'' with little or no associated apparent ionizing continuum. Third, there is a population of galaxies with unusually strong Lyman-alpha emission lines. And fourth, there is a strong HeII (1640 \AA) emission line in a composite of LBGs. The proposed explanations for the first three observations are internally inconsistent, and the fourth puzzle has remained hitherto unexplained. Here we show that all four problems are resolved simultaneously if 10-30 percent of the stars in many galaxies at z ~ 3-4 are mainly primordial - unenriched by elements heavier than helium ('metals'). Most models of hierarchical galaxy formation assume efficient intra--galactic metal mixing, and therefore do not predict metal-free star formation at redshifts significantly below z ~5. Our results imply that micro-mixing of metals within galaxies is inefficient on a ~ Gyr time-scale, a conclusion that can be verified with higher resolution simulations, and future observations of the HeII emission line.

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Catalog Extraction in SZ Cluster Surveys: a matched filter approach

Authors: J.-B. Melin, J. G. Bartlett, J. Delabrouille
Comments: 14 pages, 11 figures, submitted to A&A

We present a method based on matched multifrequency filters for extracting cluster catalogs from Sunyaev-Zel'dovich (SZ) surveys. We evaluate its performance in terms of completeness, contamination rate and photometric recovery for three representative types of SZ survey: a high resolution single frequency radio survey (AMI), a high resolution ground-based multiband survey (SPT), and the Planck all-sky survey. These surveys are not purely flux limited, and they loose completeness significantly before their point-source detection thresholds. Contamination remains relatively low at <5% (less than 30%) for a detection threshold set at S/N=5 (S/N=3). We identify photometric recovery as an important source of catalog uncertainty: dispersion in recovered flux from multiband surveys is larger than the intrinsic scatter in the Y-M relation predicted from hydrodynamical simulations, while photometry in the single frequency survey is seriously compromised by confusion with primary cosmic microwave background anisotropy. The latter effect implies that follow-up in other wavebands (e.g., 90 GHz, X-ray) of single frequency surveys will be required. Cluster morphology can cause a bias in the recovered Y-M relation, but has little effect on the scatter; the bias would be removed during calibration of the relation. Point source confusion only slightly decreases multiband survey completeness; single frequency survey completeness could be significantly reduced by radio point source confusion, but this remains highly uncertain because we do not know the radio counts at the relevant flux levels.

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The QCD Axion and Moduli Stabilisation

Authors: Joseph P. Conlon (DAMTP, Cambridge)
Comments: 36 pages
Report-no: DAMTP-2006-17

We investigate the conditions for a QCD axion to coexist with stabilised moduli in string compactifications. We show how the simplest approaches to moduli stabilisation give unacceptably large masses to the axions. We observe that solving the F-term equations is insufficient for realistic moduli stabilisation and give a no-go theorem on supersymmetric moduli stabilisation with unfixed axions applicable to all string compactifications and relevant to much current work. We demonstrate how nonsupersymmetric moduli stabilisation with unfixed axions can be realised. We finally outline how to stabilise the moduli such that f_a is within the allowed window 10^9 GeV < f_a < 10^{12} GeV, with f_a ~ \sqrt{M_{SUSY} M_P}.

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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Minimal Supergravity, Inflation, and All That

Authors: M. Ibe, K.-I. Izawa, Y. Shinbara, T.T. Yanagida
Comments: 15pages, 4figures
Report-no: UT-06-01

We consider an inflationary model in the hidden-sector broken supergravity with an effectively large cutoff. The inflaton decay into right-handed neutrinos naturally causes the observed baryon asymmetry of the universe with a reheating temperature low enough to avoid the gravitino overproduction. We emphasize that all the phenomenological requirements from cosmology and particle physics are satisfied in the large-cutoff theory.

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