Munch

Authors: Gabriela Barenboim, Olga Mena Requejo, Chris Quigg
Categories: astro-ph
Comments: 19 pages, 12 figures in 19 files, uses iopart.cls, iopart10.clo
Report-no: FERMILAB-PUB-05/379-T

In an undulant universe, cosmic expansion is characterized by alternating periods of acceleration and deceleration. We examine cosmologies in which the dark-energy equation of state varies periodically with the number of e-foldings of the scale factor of the universe, and use observations to constrain the frequency of oscillation. We find a tension between a forceful response to the cosmic coincidence problem and the standard treatment of structure formation.

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Insights into Dark Energy: Interplay Between Theory and Observation

Authors: Rachel Bean, Sean Carroll, Mark Trodden
Categories: astro-ph
Comments: White paper submitted to the Dark Energy Task Force, 5 pages + 2 pages references, 2 figures

The nature of Dark Energy is still very much a mystery, and the combination of a variety of experimental tests, sensitive to different potential Dark Energy properties, will help elucidate its origins. This white paper briefly surveys the array of theoretical approaches to the Dark Energy problem and their relation to experimental questions.

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Dark energy - dark matter - and black holes: The music of the universe

Authors: Peter L. Biermann (Max Planck Institute for Radioastronomy, Bonn, Germany)
Categories: astro-ph
Comments: 8 pages, Invited review lecture at Carpathian Summer School in Physics 2005 (CSSP2005)

Here we review the recent evidence for dark energy, dark matter and black holes as components of an expanding universe, for the vantage point of a non-expert; we speculate on a specific DM particle.

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Did WMAP see Moving Local Structures?

Authors: Asantha Cooray, Naoki Seto
Categories: astro-ph
Comments: 10 pages, 6 figures, use PDF file to print out

The divergence of the momentum density field of the large scale structure generates a secondary anisotropy contribution to the Cosmic Microwave Background (CMB). While the effect is best described as a non-linear extension to the well-known integrated Sachs-Wolfe effect, due to mathematical coincidences, the anisotropy contribution is also described as the lensing of the dipole seen in the rest-frame of a moving mass. Given the closeness, there is a remote possibility that local concentrations of mass in the form of the Great Attractor and the Shapley concentration generate large angular scale fluctuations in CMB and could potentially be responsible, at least partly, for some of the low-multipole anomalies in WMAP data. While the local anisotropy contribution peaks at low multipoles, for reasonable models of the mass and velocity distributions associated with local super structures we find that the amplitude of temperature anisotropies is at most at a level of 10$^{-2}$ $\mu$K and is substantially smaller than primordial fluctuations. It is extremely unlikely that the momentum density of local mass concentrations is responsible for any of the large angular scale anomalies in WMAP data.

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Dark matter search by exclusive studies of X-rays following WIMPs nuclear interactions

Authors: H. Ejiri, Ch.C. Moustakidis, J.D. Vergados
Categories: hep-ph hep-ex nucl-th
Comments: 10 pages, 2 tables

It is shown that weakly interacting massive particles (WIMPs), which are possible cold dark matter candidates, can be studied by exclusive measurements of X-rays following WIMPs nuclear interactions. Inner-shell atomic electrons are ionized through WIMPs nuclear interaction, and then mono-energetic X-rays are emitted when they are filled by outer-shell electrons. The number of inner-shell holes amounts to as large as one per five nuclear recoils for K-shell and several per recoil for L-shell in the case of medium heavy target nuclei interacting with 100 GeV WIMPs, and then the K and L X-ray peaks show up in the 5-50 keV region. Consequently exclusive studies of the X-rays in coincidence with the nuclear recoils and the ionization electrons are found to provide excellent opportunities to detect WIMPs such as the Lightest Super Symmetric Particles (LSP).

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Supernova Cosmology and the ESSENCE project

Authors: Jesper Sollerman, Claudio Aguilera, Andy Becker, Stephane Blondin, Pete Challis, Alejandro Clocchiatti, Alex Filippenko, Ryan Foley, Peter M. Garnavich, Malcolm Hicken, Saurabh Jha, Robert Kirshner, Kevin Krisciunas, Bruno Leibundgut, Weidong Li, Thomas Matheson, Gajus Miknaitis, Armin Rest, Adam G. Riess, Maria Elena Salvo, Brian P. Schmidt, Chris Smith, Jason Spyromilio, Chris Stubbs, Nicholas B. Suntzeff, John L. Tonry, Michael Wood-Vasey, Brian Barris, Tamara Davis, Edvard Mortsell
Categories: astro-ph
Comments: Submitted to EPS13

The proper usage of Type Ia supernovae (SNe Ia) as distance indicators has revolutionized cosmology, and added a new dominant component to the energy density of the Universe, dark energy. Following the discovery and confirmation era, the currently ongoing SNe Ia surveys aim to determine the properties of the dark energy. ESSENCE is a five year ground-based supernova survey aimed at finding and characterizing 200 SNe Ia in the redshift domain z=[0.2-0.8]. The goal of the project is to put constraints on the equation of state parameter, w, of the dark energy with an accuracy of <10%. This paper presents these ongoing efforts in the context of the current developments in observational cosmology.

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Devaluation: a dynamical mechanism for a naturally small cosmological constant

Authors: Katherine Freese, James T. Liu, Douglas Spolyar
Categories: hep-ph
Comments: 6 pages and prepared in ReV-TeX
Report-no: MCTP-05-94

We propose a natural solution to the cosmological constant problem consistent with the standard cosmology and successful over a broad range of energies. This solution is based on the existence of a new field, the devaluton, with its potential modeled on a tilted cosine. After inflation, the universe reheats and populates the devaluton's many minima. As the universe cools, domain walls form between different regions. The domain wall network then evolves and sweeps away regions of higher vacuum energy in favor of lower energy ones. Gravitation itself provides a cutoff at a minimum vacuum energy, thus leaving the universe with a small cosmological constant comparable in magnitude to the present day dark energy density.

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Virial masses and the baryon fraction in galaxies

Authors: H. Hoekstra, B.C. Hsieh, H.K.C. Yee, H. Lin, M.D. Gladders
Categories: astro-ph
Comments: 13 pages, accepted for publication in the ApJ

We have measured the weak lensing signal as a function of restframe luminosity for a sample of `isolated' galaxies. These results are based on four-band photometry from the Red-Sequence Cluster Survey, enabling us to determine photometric redshifts for a large number of galaxies. We select a secure sample of lenses with photometric redshifts 0.2<z<0.4 and study the relation between the virial mass and baryonic contents. In addition, we discuss the implications of the derived photometric redshift distribution for published cosmic shear studies. The virial masses are derived from a fit to the observed lensing signal. For a galaxy with a fiducial luminosity of 10^10 h^-2 L_Bsun we obtain a mass M_vir=9.9^{+1.5}_{-1.3}\times 10^11 h^-1 M_sun. The virial mass as a function of luminosity is consistent with a power-law ~L^1.5, with similar slopes for the three filters considered here. These findings are in excellent agreement with results from the Sloan Digital Sky Survey and semi-analytic models of galaxy formation. We measure the fraction of mass in stars and the baryon fraction in galaxies by comparing the virial mass-to-light ratio to predicted stellar mass-to-light ratios. We find that star formation is inefficient in converting baryons into stars, with late-type galaxies converting ~33% and early-type galaxies converting only ~14% of baryons into stars. Our results imply that the progenitors of early-type galaxies must have low stellar mass fractions, suggestive of a high formation redshift.

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Why is the Zel'dovich Approximation so Accurate?

Authors: A. Yoshisato, M. Morikawa, N. Gouda, H. Mouri
Categories: astro-ph
Comments: 16 pages, to appear in The Astrophysical Journal

Why does the Zel'dovich approximation (ZA) work well for a gravitational collapse in the universe? This problem is examined by focussing the dependence on the dimensionality of the collapse. The ZA is known to be exact for a one-dimensional collapse. We show that the ZA is more accurate in the order of three-, two-, and one-dimensional collapses. Furthermore, using models for spheroidal collapse, we show that the ZA remains accurate in any collapse, which becomes progressively lower-dimensional with the passage of time. That is, the ZA is accurate because the essence of the gravitational collapse is incorporated in the ZA.

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Inflation in AdS/CFT

Authors: Ben Freivogel, Veronika E. Hubeny, Alexander Maloney, Rob Myers, Mukund Rangamani, Stephen Shenker
Categories: hep-th
Comments: 34 pages + appendices, 18 figures

We study the realization of inflation within the AdS/CFT correspondence. We assume the existence of a string landscape containing at least one stable AdS vacuum and a (nearby) metastable de Sitter state. Standard arguments imply that the bulk physics in the vicinity of the AdS minimum is described by a boundary CFT. We argue that large enough bubbles of the dS phase, including those able to inflate, are described by mixed states in the CFT. Inflating degrees of freedom are traced over and do not appear explicitly in the boundary description. They nevertheless leave a distinct imprint on the mixed state. Analytic continuation allows us, in principle, to recover a large amount of nonperturbatively defined information about the inflating regime. Our work also shows that no scattering process can create an inflating region, even by quantum tunneling, since a pure state can never evolve into a mixed state under unitary evolution.

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Preheating in a Minimal Supersymmetric SO(10) Model

Authors: Takeshi Fukuyama, Tatsuru Kikuchi, Wade Naylor
Categories: hep-ph astro-ph
Comments: 3 pages
Report-no: RITS-PP-005

We discuss instant preheating in a supersymmetric model. In this scenario, at the last stage of inflation, the inflaton field first decays into another scalar field with an enormous number density, via the instant preheating mechanism. Subsequently, the produced scalar field decays into normal matter accompanied by the usual reheating mechanism. As an inflationary model, we identify the inflaton as a field which gives rise to a mass for the right-handed neutrino. To make a definite prediction, especially for the right-handed neutrino, we consider a minimal supersymmetric ${\rm SO}(10)$ model. One of the interesting consequences of the instant preheating mechanism is the fact that the reheating temperature is proportional to the mass of the decayed particle, {\it the right-handed sneutrino}, $T_R \propto M_R$. This is very different from the ordinary perturbative reheating scenario in which the reheating temperature is proportional to the mass of the inflaton.

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