Munch

The dwarf spheroidal galaxy Draco has long been considered likely to be one of the brightest point sources of gamma-rays generated through dark matter annihilations. Recent studies of this object have found that it remains largely intact from tidal striping, and may be more massive than previously thought. In this article, we revisit Draco as a source of dark matter annihilation radiation, with these new observational constraints in mind. We discuss the prospects for the experiments MAGIC and GLAST to detect dark matter in Draco, as well as constraints from the observations of EGRET. We also discuss the possibility that the CACTUS experiment has already detected gamma-rays from Draco. We find that it is difficult to generate the flux reported by CACTUS without resorting to non-thermally produced WIMPs and/or a density spike in Draco's dark matter distribution due to the presence of an intermediate mass black hole. We also find that for most annihilation modes, a positive detection of Draco by CACTUS would be inconsistent with the lack of events seen by EGRET.

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D-term Inflation and Leptogenesis by Right-handed Sneutrino

Authors: Kenji Kadota, J. Yokoyama
Report-no: FERMILAB-PUB-05-544-A, RESCEU-41/05

We discuss a D-term inflation scenario where a right-handed sneutrino can be an inflaton field leading to a viable inflation and leptogenesis, with a minimal form of K\"ahler potential. The decay of an inflaton sneutrino can non-thermally create large enough lepton asymmetry. Its entropy production is also big enough to ameliorate the gravitino problem caused by too high a reheating temperature from the decay of a symmetry breaking field.

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What Do We Really Know About Cosmic Acceleration?

Authors: Charles Shapiro (1,2), Michael S. Turner (1,2) ((1) University of Chicago, (2) Kavli Institute for Cosmological Physics)
Comments: 9 pages, 8 figures

Essentially all of our knowledge of the acceleration history of the Universe - including the acceleration itself - is predicated upon the validity of general relativity. Without recourse to this assumption, we use SNeIa to analyze the expansion history and find (i) very strong (5 sigma) evidence for a period of acceleration, (ii) strong evidence that the acceleration has not been constant, (iii) evidence for an earlier period of deceleration and (iv) only weak evidence that the Universe has not been decelerating since z~0.3.

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Relic keV sterile neutrinos and reionization

Authors: Peter L. Biermann, Alexander Kusenko
Comments: 4 pages, 2 figures
Report-no: UCLA/05/TEP/35

A sterile neutrino with mass of several keV can account for cosmological dark matter, as well as explain the observed velocities of pulsars. We show that X-rays produced by the decays of these relic sterile neutrinos can boost the production of molecular hydrogen, which can speed up the cooling of gas and the early star formation, which can, in turn, lead to a reionization of the universe at a high enough redshift to be consistent with the WMAP results.

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The soft X-ray properties of quasars in the Sloan Digital Sky Survey

Authors: Shiyin Shen, Simon D.M. White, H.J. Mo, Wolfgang Voges, Guinevere Kauffmann, Christy Tremonti, Scott F. Anderson
Comments: 16 pages, 14 figures, 2 tables, MNRAS submitted

We use the ROSAT All Sky Survey (RASS) to study the soft X-ray properties of a homogeneous sample of 46,420 quasars selected from the third data release of the Sloan Digital Sky Survey (SDSS). Optical luminosities, both at rest-frame 2500\AA ($L_{2500}$) and in [OIII] ($L_{[\rm{OIII}]}$) span more than three orders of magnitude, while redshifts range over $0.1<z<5.4$. We detect 3366 quasars directly in the observed 0.1--2.4 keV band. Sub-samples of radio-loud and radio-quiet objects (RLQs and RQQs) are obtained by cross-matching with the FIRST catalogue. We study the distribution of X-ray luminosity as a function of optical luminosity, redshift and radio power using both individual detections and stacks of complete sets of similar quasars. At every optical luminosity and redshift $\log L_{2\kev}$ is, to a good approximation, normally distributed with dispersion $\sim 0.40$, at least brightwards of the median X-ray luminosity. This median X-ray luminosity of quasars is a power law of optical luminosity with index $\sim 0.53$ for $L_{2500}$ and $\sim 0.30$ for $L_{[\rm{OIII}]}$. RLQs are systematically brighter than RQQs by about a factor of 2 at given optical luminosity. The zero-points of these relations increase systematically with redshift, possibly in different ways for RLQs and RQQs. Evolution is particularly strong at low redshift and if the optical luminosity is characterised by $L_{[\rm{OIII}]}$. At low redshift and at given $L_{[\rm{OIII}]}$ the soft X-ray emission from type II AGN is more than 100 times weaker than that from type I AGN.

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The Epoch of Reionization

Authors: A. J. Benson (1), Naoshi Sugiyama (2), Adi Nusser (3), C. G. Lacey (4) ((1) University of Oxford, UK, (2) NAOJ, Tokyo, Japan, (3) Technion, Haifa, Israel, (4) University of Durham (UK))
Comments: 21 pages, submitted to MNRAS

We have modelled the process of reionization in the high redshift Universe to determine the epoch of reionization. Reionization is driven by star formation in high redshift galaxies. We employ a semi-analytic model of galaxy formation to track the formation of these galaxies, their influence on the intergalactic medium (IGM) and the back-reaction of the IGM on further galaxy formation. This represents a more complete and physical modelling of reionization than has been conducted in the past. In particular, compared to our previous work our new calculations contain significant improvements in the modelling of the effects of reionization on the galaxy population and in the cooling model used to compute the rate at which galaxies form (our new model includes photoheating from a self-consistently computed ionizing background and also includes cooling due to molecular hydrogen). We find that reionization can be achieved by z~14-15 in a cosmological model motivated by the results from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite, consistent with the optical depth to reionization measured by WMAP. However, a cosmological model with a running spectral index is able to achieve reionization before z~9 only with very extreme assumptions about the physics of feedback at high redshifts. These results assume that all ionizing photons in galaxies are able to escape and ionize the IGM. If this is not the case then the redshift of reionization could be substantially reduced. Under the assumption that early star formation leads to the formation of very massive stars we find that extended periods of partial reionization and double reionizations can occur. Such models do not fully reionize until z~6-7 but obtain an optical depth which is consistent with the results from the WMAP satellite. (abridged)

Cosmology with High-redshift Galaxy Survey: Neutrino Mass and Inflation

Authors: Masahiro Takada (1), Eiichiro Komatsu (2), Toshifumi Futamase (1) ((1)Tohoku Univ., Japan, (2)University of Texas at Austin)
Comments: 21 pages, 6 figures, submitted to PRD

(abridged) High-z galaxy redshift surveys open up exciting possibilities for precision determinations of neutrino masses and inflationary models. The high-z surveys are more useful for cosmology than low-z ones owing to much weaker non-linearities in matter clustering, redshift-space distortion and galaxy bias. We can then utilize the two-dimensional information of the linear power spectrum in angular and redshift space to measure the scale-dependent suppression of matter clustering due to neutrino free-streaming as well as the shape of the primordial power spectrum. To illustrate capabilities of high-z surveys for constraining neutrino masses and the primordial power spectrum, we compare three future redshift surveys covering 300 square degrees at 0.5<z<2, 2<z<4, and 3.5<z<6.5. We find that, combined with the CMB data expected from the Planck satellite, these surveys allow precision determination of the total neutrino mass with the projected errors of sigma(m_nu) =0.059, 0.043, and 0.025 eV, respectively, which are actually smaller than the lower limits to the neutrino masses implied from the neutrino oscillation experiments, by up to a factor of 4 for the highest redshift survey. The accuracies of constraining the tilt and running index of the primordial power spectrum, sigma(n_s)=(3.8, 3.7, 3.0)x10^-3, and sigma(alpha_s)=(5.9, 5.7, 2.4)x10^-3, respectively, are smaller than the current uncertainties by more than an order of magnitude, which will allow us to discriminate between candidate inflationary models. In particular, the error on alpha_s from the highest redshift survey is not very far away from the prediction of a class of simple inflationary models driven by a massive scalar field with self-coupling, alpha_s=-(0.8-1.2)x10^-3.

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Anisotropy of the cosmic gamma-ray background from dark matter annihilation

Authors: Shin'ichiro Ando, Eiichiro Komatsu
Comments: 15 pages, 12 figures

High-energy photons from dark matter annihilation contribute to the cosmic gamma-ray background (CGB). Since dark matter particles are weakly interacting, annihilation can happen only in high density regions such as dark matter halos. The precise shape of the energy spectrum of CGB depends on the nature of dark matter particles, as well as the cosmological evolution of dark matter halos. In order to discriminate between the signals from dark matter annihilation and other astrophysical sources, however, the information from the energy spectrum may not be sufficient. We show that dark matter annihilation also produces a characteristic anisotropy of the CGB, which provides a powerful tool for testing the origin. We develop the formalism based on a halo model approach to calculate the three-dimensional power spectrum of dark matter clumping, which determines the power spectrum of annihilation signals. We show that the sensitivity of future gamma-ray detectors such as GLAST should allow us to measure the angular power spectrum of CGB anisotropy, if dark matter particles are supersymmetric neutralinos and they account for most of the observed mean intensity of CGB in GeV region. On the other hand, if dark matter has a relatively small mass, and accounts for most of the CGB in MeV region, then the future Advanced Compton Telescope should be able to measure the anisotropy in MeV region. As the intensity of photons from annihilation is proportional to the density squared, we show that the predicted shape of the angular power spectrum of gamma rays from dark matter annihilation is different from that due to other astrophysical sources such as blazars. Therefore, the angular power spectrum of the CGB provides a smoking-gun signature of dark matter annihilation.

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