"Munch", May 8th, 2006

FAQ What is Munch? Munch Archive --------- 1 May 2006 24 Apr 2006 17 Apr 2006 10 Apr 2006 03 Apr 2006 27 Mar 2006 13 Mar 2006 6 Mar 2006

AMANDA Observations Constrain the Ultra-High Energy Neutrino Flux Authors: Francis Halzen, Dan Hooper Comments: 4 pages, 3 figures Report-no: MADPH-06-1465; FERMILAB-PUB-06-097-A A number of experimental techniques are currently being deployed in an effort to make the first detection of ultra-high energy cosmic neutrinos. To accomplish this goal, techniques using radio and acoustic detectors are being developed, which are optimally designed for studying neutrinos with energies in the PeV-EeV range and above. Data from the AMANDA experiment, in contrast, has been used to place limits on the cosmic neutrino flux at less extreme energies (up to ~10 PeV). In this letter, we show that by adopting a different analysis strategy, optimized for much higher energy neutrinos, the same AMANDA data can be used to place a limit competitive with radio techniques at EeV energies. We also discuss the sensitivity of the IceCube experiment, in various stages of deployment, to ultra-high energy neutrinos. Full-text: PostScript, PDF, or Other formats Lyman Limit Systems in Cosmological Simulations Authors: Katharina Kohler, Nickolay Y. Gnedin Comments: 9 pages, 8 figures submitted to ApJ We used cosmological simulation with self-consistent radiative transfer to investigate the physical nature of Lyman Limit systems at z=4. In agreement with previous studies, we find that most of Lyman Limit systems are ionized by the cosmological background, while higher column density systems seem to be illuminated by the local sources of radiation. In addition, we find that most of Lyman limit systems in our simulations are located within the virial radii of galaxies with a wide range of masses, and are physically associated with them (``bits and pieces'' of galaxy formation). While the finite resolution of our simulations cannot exclude an existence of a second population of self-shielded, neutral gas clouds located in low mass dark matter halos (``minihalos''), our simulations are not consistent with ``minihalos'' dominating the total abundance of Lyman limit systems. Full-text: PostScript, PDF, or Other formats Observational Signatures and Non-Gaussianities of General Single Field Inflation Authors: Xingang Chen, Min-xin Huang, Shamit Kachru, Gary Shiu Comments: 50 pages, 5 figures Report-no: MAD-TH-06-3; UFIFT-HEP-06-9; SU-ITP-06/12; SLAC-PUB-11840; CU-TP-1147 We perform a general study of primordial scalar non-Gaussianities in single field inflationary models. We consider models where the inflaton Lagrangian is an arbitrary function of the scalar field and its first derivative, and the sound speed is arbitrary. We find that under reasonable assumptions, the non-Gaussianity is completely determined by 5 parameters. In special limits of the parameter space, one finds distinctive ``shapes'' of the non-Gaussianity. In models with a small sound speed, several of these shapes would become potentially observable in the near future. Different limits of our formulae recover various previously known results. Full-text: PostScript, PDF, or Other formats Model selection forecasts for the spectral index from the Planck satellite Authors: Cédric Pahud, Andrew R Liddle, Pia Mukherjee, David Parkinson Comments: 4 pages RevTeX with one figure included The recent WMAP3 results have placed measurements of the spectral index n_S in an interesting position. While parameter estimation techniques indicate that the Harrison-Zel'dovich spectrum n_S=1 is strongly excluded (in the absence of tensor perturbations), Bayesian model selection techniques reveal that the case against n_S=1 is not yet conclusive. In this paper, we forecast the ability of the Planck satellite mission to use Bayesian model selection to convincingly exclude (or favour) the Harrison-Zel'dovich model. Full-text: PostScript, PDF, or Other formats Improved Calculation of the Primordial Gravitational Wave Spectrum in the Standard Model Authors: Yuki Watanabe, Eiichiro Komatsu (Univ. of Texas at Austin) Comments: 25 papes, 11 figures, submitted to PRD We show that the energy density spectrum of the primordial gravitational waves has characteristic features due to the successive changes in the relativistic degrees of freedom during the radiation era. These changes make the evolution of radiation energy density deviate from the conventional adiabatic evolution, \rho_r~ a^{-4}, and thus cause the expansion rate of the universe to change suddenly at each transition which, in turn, modifies the spectrum of primordial gravitational waves. We take into account all the particles in the Standard Model of elementary particles. In addition, free-streaming of neutrinos damps the amplitude of gravitational waves, leaving characteristic features in the energy density spectrum. Our calculations are solely based on the standard model of cosmology and particle physics, and therefore these features must exist. Our calculations significantly improve the previous ones which ignored these effects and predicted a smooth, featureless spectrum. Full-text: PostScript, PDF, or Other formats Galaxy orbits and the intracluster gas temperature in clusters Authors: Latchezar Benatov (1), Ken Rines (1), Priyamvada Natarajan (1,2), Andrey Kravtsov (3,4), Daisuke Nagai (5) ((1) Department of Physics, Yale; (2) Department of Astronomy, Yale; (3) Department of Astronomy and Astrophysics, University of Chicago; (4) Kavli Institute for Cosmological Physics, University of Chicago; (5) Theoretical Astrophysics, California Institute of Technology) Comments: 9 pages, 6 figures, accepted for publication in MNRAS In this paper we examine how well galaxies and intra-cluster gas trace the gravitational potential of clusters. Utilizing mass profiles derived from gravitational lensing and X-ray observations, coupled with measured galaxy velocities, we solve for the velocity anisotropy parameter using the anisotropic Jeans equation. This is done for five clusters, three at low redshift: A2199, A496 and A576 and two at high redshifts: A2390 and MS1358. With X-ray temperature profiles obtained from Chandra and ASCA/ROSAT data, we estimate the ratio of energy in the galaxies compared to the X-ray gas. We find that none of these clusters is strictly in hydro-static equilibrium. We compare the properties of our sample with clusters that form in high-resolution cosmological N-body simulations that include baryonic physics. Simulations and data show considerable scatter both these profiles. We demonstrate the future feasibility and potential for directly comparing the orbital structure of clusters inferred from multi-wavelength observations with high resolution simulated clusters. Full-text: PostScript, PDF, or Other formats The Discovery of Three New z>5 Quasars in the AGN and Galaxy Evolution Survey Authors: Richard J. Cool (Arizona), Christopher S. Kochanek, Daniel J. Eisenstein, Daniel Stern, Kate Brand, Michael J. I. Brown, Arjun Dey, Peter R. Eisenhardt, Xiaohui Fan, Anthony H. Gonzalez, Richard F. Green, Buell T. Jannuzi, Eric H. McKenzie, George H. Rieke, Marcia Rieke, Baruch T. Soifer, Hyron Spinrad, Richard J. Elston Comments: 9 page, 7 figures. Accepted for publication in AJ We present the discovery of three z>5 quasars in the AGN and Galaxy Evolution Survey (AGES) spectroscopic observations of the NOAO Deep Wide-Field Survey (NDWFS) Bootes Field. These quasars were selected as part of a larger Spitzer mid-infrared quasar sample with no selection based on optical colors. The highest redshift object, NDWFS J142516.3+325409, z=5.85, is the lowest-luminosity z>5.8 quasar currently known. We compare mid-infrared techniques for identifying z>5 quasars to more traditional optical techniques and show that mid-infrared colors allow for selection of high-redshift quasars even at redshifts where quasars lie near the optical stellar locus and at z>7 where optical selection is impossible. Using the superb multi-wavelength coverage available in the NDWFS Bootes field, we construct the spectral energy distributions (SEDs) of high-redshift quasars from observed Bw-band to 24 microns (rest-frame 600 Angstroms - 3.7 microns). We show that the three high-redshift quasars have quite similar SEDs, and the rest-frame composite SED of low-redshift quasars from the literature shows little evolution compared to our high-redshift objects. We compare the number of z>5 quasars we have discovered to the expected number from published quasar luminosity functions. While analyses of the quasar luminosity function are tenuous based on only three objects, we find that a relatively steep luminosity function with Psi L^(-3.2) provides the best agreement with the number of high-redshift quasars discovered in our survey. Full-text: PostScript, PDF, or Other formats The Spin-Resolved Atomic Velocity Distribution and 21-cm Line Profile of Dark-Age Gas Authors: Christopher M. Hirata, Kris Sigurdson (IAS) Comments: 25 pages, 6 figures, submitted to Mon. Not. Roy. Astron. Soc The 21-cm hyperfine line of atomic hydrogen (HI) is a promising probe of the cosmic dark ages. In past treatments of 21-cm radiation it was assumed the hyperfine level populations of HI could be characterized by a velocity-independent ``spin temperature'' T_s determined by a competition between 21-cm radiative transitions, spin-changing collisions, and (at lower redshifts) Lyman-alpha scattering. However we show here that, if the collisional time is comparable to the radiative time, the spin temperature will depend on atomic velocity, T_s=T_s(v), and one must replace the usual hyperfine level rate equations with a Boltzmann equation describing the spin and velocity dependence of the HI distribution function. We construct here the Boltzmann equation relevant to the cosmic dark ages and solve it using a basis-function method. Accounting for the actual spin-resolved atomic velocity distribution results in up to a 2 per cent suppression of the 21-cm emissivity, and a redshift and angular-projection dependent suppression or enhancement of the linear power spectrum of 21-cm fluctuations of up to 5 per cent. The effect on the 21-cm line profile is more dramatic --- its full-width at half maximum (FWHM) can be enhanced by up to 60 per cent relative to the velocity-independent calculation. We discuss the implications for 21-cm tomography of the dark ages. Full-text: PostScript, PDF, or Other formats Gauge invariant MSSM inflaton Authors: Rouzbeh Allahverdi, Juan Garcia-Bellido, Kari Enqvist, Anupam Mazumdar Comments: 4 revtex pages Report-no: NORDITA-2006-13, IFT-UAM/CSIC-06-18, HIP-2006-22/TH We argue that all the necessary ingredients for a successful inflation are present in the flat directions of the Minimally Supersymmetric Standard Model. We show that out of many gauge invariant combinations of squarks, sleptons and Higgses, there are two directions, ${\bf LLe}$, and ${\bf udd}$, which are promising candidates for the inflaton. The model predicts more than $10^6$ e-foldings with an inflationary scale of $H_{\rm inf}\sim {\cal O}(1-10)$ GeV, provides a tilted spectrum with an amplitude of $\delta_H\sim 10^{-5}$ and a negligible tensor perturbation. The temperature of the thermalized plasma could be as low as $T_{rh}\sim {\cal O}(1-10)$ TeV. Parts of the inflaton potential can be determined independently of cosmology by future particle physics experiments. Full-text: PostScript, PDF, or Other formats Enlarging the parameter space of standard hybrid inflation Authors: Rachel Jeannerot (Leiden U.), Marieke Postma (NIKHEF, Amsterdam) Comments: 32 pages, 10 figures We show that the parameter space for F-term inflation which predict the formation of cosmic strings is larger than previously estimated. Firstly, because realistic embeddings in GUT theories alter the standard scenerio, making the inflationary potential less steep. Secondly, the strings which form at the end of inflation are not necessarily topologically stable down to low scales. In shifted and smooth inflation strings do not form at all. We also discuss D-term inflation; here the possibilities are much more limited to enlargen paramer space. Full-text: PostScript, PDF, or Other formats