Munch: Monday, May 21, 2007

                               


 

 WHERE: 6TH FLOOR CONFERENCE ROOM
WHEN  : 12:30, MONDAY

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


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 arXiv:0705.2012 [ps, pdf, other] : Title: Implications for the Constrained MSSM from a new prediction for b to s gamma
Authors: Leszek Roszkowski (Univ. of Sheffield and CERN), Roberto Ruiz de Austri (Univ. Autonoma Madrid), Roberto Trotta (Univ. of Oxford)
Comments: 30 pages
We re-examine the properties of the Constrained MSSM in light of updated constraints, paying particular attention to the impact of the recent substantial shift in the Standard Model prediction for BR(B to X_s gamma). With the help of a Markov Chain Monte Carlo scanning technique, we vary all relevant parameters simultaneously and derive Bayesian posterior probability maps. We find that the case of \mu>0 remains favored, and that for \mu<0 it is considerably more difficult to find a good global fit to current constraints. In both cases we find a strong preference for a focus point region. This leads to improved prospects for detecting neutralino dark matter in direct searches, while superpartner searches at the LHC become more problematic, especially when \mu<0. In contrast, prospects for exploring the whole mass range of the lightest Higgs boson at the Tevatron and the LHC remain very good, which should, along with dark matter searches, allow one to gain access to the otherwise experimentally challenging focus point region. An alternative measure of the mean quality-of-fit which we also employ implies that present data are not yet constraining enough to draw more definite conclusions. We also comment on the dependence of our results on the choice of priors and on some other assumptions.

arXiv:0705.2171 [ps, pdf, other] : Title: Discovery of a Ringlike Dark Matter Structure in the Core of the Galaxy Cluster Cl 0024+17
Authors: M.J. Jee, H.C. Ford, G.D. Illingworth, R.L. White, T.J. Broadhurst, D.A. Coe, G.R. Meurer, A. Van Der Wel, N. Benitez, J.P. Blakeslee, R.J. Bouwens, L.D. Bradley, R. Demarco, N.L. Homeier, A.R. Martel, S. Mei
Comments: To appear in the June 1 issue of The Astrophysical Journal
We present a comprehensive mass reconstruction of the rich galaxy cluster Cl 0024+17 at z~0.4 from ACS data, unifying both strong- and weak-lensing constraints. The weak-lensing signal from a dense distribution of background galaxies (~120 per square arcmin) across the cluster enables the derivation of a high-resolution parameter-free mass map. The strongly-lensed objects tightly constrain the mass structure of the cluster inner region on an absolute scale, breaking the mass-sheet degeneracy. The mass reconstruction of Cl 0024+17 obtained in such a way is remarkable. It reveals a ringlike dark matter substructure at r~75" surrounding a soft, dense core at r~50". We interpret this peculiar sub-structure as the result of a high-speed line-of-sight collision of two massive clusters 1-2 Gyr ago. Such an event is also indicated by the cluster velocity distribution. Our numerical simulation with purely collisionless particles demonstrates that such density ripples can arise by radially expanding, decelerating particles that originally comprised the pre-collision cores. Cl 0024+17 can be likened to the bullet cluster 1E0657-56, but viewed $along$ the collision axis at a much later epoch. In addition, we show that the long-standing mass discrepancy for Cl 0024+17 between X-ray and lensing can be resolved by treating the cluster X-ray emission as coming from a superposition of two X-ray systems. The cluster's unusual X-ray surface brightness profile that requires a two isothermal sphere description supports this hypothesis.

arXiv:0705.2406 [ps, pdf, other] : Title: Decaying warm dark matter and neutrino masses
Authors: M. Lattanzi, J.W.F. Valle
Comments: 4 pages, 3 figures
Neutrino masses may arise from spontaneous breaking of ungauged lepton number. Due to quantum gravity effects the associated Goldstone boson - the majoron - will pick up a mass. We determine the lifetime and mass required by cosmic microwave background observations so that the massive majoron provides the observed dark matter of the Universe. The majoron DDM scenario fits nicely in models where neutrino masses arise a la seesaw, and may lead to other possible cosmological implications.

arXiv:0705.1615 [ps, pdf, other] : Title: Searching for non Gaussian signals in the BOOMERanG 2003 CMB maps
Authors: G. De Troia, P.A.R. Ade, J.J. Bock, J.R. Bond, J. Borrill, A. Boscaleri, P. Cabella, C.R. Contaldi, B.P. Crill, P. de Bernardis, G. De Gasperis, A. de Oliveira-Costa, G. Di Stefano, P. G. Ferreira, E. Hivon, A.H. Jaffe, T.S.Kisner, M. Kunz, W.C. Jones, A.E. Lange, M.Liguori, S. Masi, S. Matarrese, P.D. Mauskopf, C.J. MacTavish, A. Melchiorri, T.E. Montroy, P. Natoli, C.B. Netterfield, E. Pascale, F. Piacentini, D. Pogosyan, G.Polenta, S. Prunet, S. Ricciardi, G. Romeo, J.E. Ruhl, P. Santini, M. Tegmark, M. Veneziani, N. Vittorio
Comments: 5 pages, 4 figures
We analyze the BOOMERanG 2003 (B03) 145 GHz temperature map to constrain the amplitude of a non Gaussian, primordial contribution to CMB fluctuations. We perform a pixel space analysis restricted to a portion of the map chosen in view of high sensitivity, very low foreground contamination and tight control of systematic effects. We set up an estimator based on the three Minkowski functionals which relies on high quality simulated data, including non Gaussian CMB maps. We find good agreement with the Gaussian hypothesis and derive the first limits based on BOOMERanG data for the non linear coupling parameter f_NL as -350<f_NL<700 at 68% CL and -800<f_NL<1050 at 95% CL.

arXiv:0705.1955 [ps, pdf, other] : Title: Can we ever distinguish between quintessence and a cosmological constant?
Authors: Sirichai Chongchitnan, George Efstathiou
Comments: 10 pages, 6 figures. Submitted to Phys. Rev. D
Many ambitious experiments have been proposed to constrain dark energy and detect its evolution. At present, observational constraints are consistent with a cosmological constant and there is no firm evidence for any evolution in the dark energy equation of state w. In this paper, we pose the following question: suppose that future dark energy surveys constrain w at low redshift to be consistent with -1 to a percent level accuracy, what are the implications for models of dynamical dark energy? We investigate this problem in a model-independent way by following quintessence field trajectories in `energy' phase-space. Attractor dynamics in this phase-space leads to two classes of acceptable models: 1) models with flat potentials, i.e. an effective cosmological constant, and 2) models with potentials that suddenly flatten with a characteristic kink. The prospect of further constraining the second class of models from distance measurements and fluctuation growth rates at low redshift (z<3) seems poor. However, in some models of this second class, the dark energy makes a significant contribution to the total energy density at high redshift. Such models can be further constrained from observation of the cosmic microwave background anisotropies and from primordial nucleosynthesis. It is possible, therefore, to construct models in which the dark energy at high redshift causes observable effects, even if future dark energy surveys constrain w at low redshift to be consistent with -1 to high precision.

arXiv:0705.2269 [ps, pdf, other] : Title: Direct cosmological simulations of the growth of black holes and galaxies
Authors: Tiziana Di Matteo (CMU), Joerg Colberg (CMU), Volker Springel (MPA), Lars Hernquist (CfA), Debora Sijacki (MPA)
Comments: 22 pages, 17 figures, submitted to ApJ
We investigate the coupled formation and evolution of galaxies and their embedded supermassive black holes using state-of-the-art hydrodynamic simulations of cosmological structure formation. For the first time, we self-consistently follow the dark matter dynamics, radiative gas cooling, star formation, as well as black hole growth and associated feedback processes, starting directly from initial conditions appropriate for the LambdaCDM cosmology. Our modeling of the black hole physics is based on an approach we have developed in simulations of isolated galaxy mergers. Here we examine: (i) the predicted global history of black hole mass assembly (ii) the evolution of the local black hole-host mass correlations and (iii) the conditions that allow rapid growth of the first quasars, and the properties of their hosts and descendants today. We find a total black hole mass density in good agreement with observational estimates. The black hole accretion rate density peaks at lower redshift and evolves more strongly at high redshift than the star formation rate density, but the ratio of black hole to stellar mass densities shows only a moderate evolution at low redshifts. We find strong correlations between black hole masses and properties of the stellar systems, agreeing well with the measured local M_BH-sigma and M_BH -M_* relationships, but also suggesting (dependent on the mass range) a weak evolution with redshift in the normalization and the slope. Our simulations also produce massive black holes at high redshift, due to extended periods of exponential growth in regions that collapse early and exhibit strong gas inflows. These first supermassive BH systems however are not necessarily the most massive ones today, since they are often overtaken in growth by quasars that form later. (abridged)

arXiv:0705.2502 [ps, pdf, other] : Title: WIMP identification through a combined measurement of axial and scalar couplings
Authors: G. Bertone, D.G. Cerdeno, J.I. Collar, B. Odom
Comments: LaTeX, 4 pages 2 figures, uses revtex
We study the prospects for detecting Weakly Interacting Massive Particles (WIMPs), in a number of phenomenological scenarios, with a detector composed of a target simultaneously sensitive to both spin-dependent and spin-independent couplings, as is the case of COUPP (Chicagoland Observatory for Underground Particle Physics). First, we show that sensitivity to both couplings optimizes chances of initial WIMP detection. Second, we demonstrate that in case of detection, comparison of the signal on two complementary targets, such as in COUPP CF3I and C4F10 bubble chambers, allows a significantly more precise determination of the dark matter axial and scalar couplings. This strategy would provide crucial information on the nature of the WIMPs, and possibly allow discrimination between neutralino and Kaluza-Klein dark matter.

arXiv:0705.2588 [ps, pdf, other] : Title: Gamma-ray probe of cosmic-ray pressure in galaxy clusters and cosmological implications
Authors: Shin'ichiro Ando, Daisuke Nagai (Caltech)
Comments: 5 pages, 1 figure, submitted to MNRAS Letters
Cosmic rays produced in cluster accretion and merger shocks provide pressure to the intracluster medium (ICM) and affect the mass estimates of galaxy clusters. Although direct evidence for cosmic-ray ions in the ICM is still lacking, they produce gamma-ray emission through the decay of neutral pions produced in their collisions with ICM nucleons. We investigate the capability of the Gamma-ray Large Area Space Telescope (GLAST) and imaging atmospheric Cerenkov telescopes (IACTs) for constraining the cosmic-ray pressure contribution to the ICM. We show that GLAST can be used to place stringent upper limits, a few per cent for individual nearby rich clusters, on the ratio of energy densities of the cosmic rays and thermal gas. We further show that it is possible to place tight (< 30%) constraints for distant (z < 0.4) clusters, by stacking signals from samples of known clusters. The GLAST limits could be made more precise with the constraint on the cosmic-ray spectrum potentially provided by IACTs. Future gamma-ray observations of clusters can constrain the evolution of cosmic-ray energy density, which would have important implications for cosmological tests with upcoming X-ray and Sunyaev-Zel'dovich effect cluster surveys.

arXiv:0705.1158 [ps, pdf, other] : Title: Models of f(R) Cosmic Acceleration that Evade Solar-System Tests
Authors: Wayne Hu, Ignacy Sawicki (KICP, U. Chicago)
Comments: 13 pages, 10 figures. Submitted to Phys. Rev. D
We study a class of metric-variation f(R) models that accelerates the expansion without a cosmological constant and satisfies both cosmological and solar-system tests in the small-field limit of the parameter space. Solar-system tests alone place only weak bounds on these models, since the additional scalar degree of freedom is locked to the high-curvature general-relativistic prediction across more than 25 orders of magnitude in density, out through the solar corona. This agreement requires that the galactic halo be of sufficient extent to maintain the galaxy at high curvature in the presence of the low-curvature cosmological background. If the galactic halo and local environment in f(R) models do not have substantially deeper potentials than expected in LCDM, then cosmological field amplitudes |f_R| > 10^{-6} will cause the galactic interior to evolve to low curvature during the acceleration epoch. Viability of large-deviation models therefore rests on the structure and evolution of the galactic halo, requiring cosmological simulations of f(R) models, and not directly on solar-system tests. Even small deviations that conservatively satisfy both galactic and solar-system constraints can still be tested by future, percent-level measurements of the linear power spectrum, while they remain undetectable to cosmological-distance measures. Although we illustrate these effects in a specific class of models, the requirements on f(R) are phrased in a nearly model-independent manner.