Munch: Monday, June 18, 2007

                               


 

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

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


FAQ

What is Munch?
       Munch Archive

 arXiv:0706.1775 [ps, pdf, other] : Title: Galaxy-CMB Cross-Correlation as a Probe of Alternative Models of Gravity
Authors: Fabian Schmidt, Michele Liguori, Scott Dodelson
Comments: 10 pages, 6 figures, submitted to Phys. Rev. D
Bekenstein's alternative to general relativity, TeVeS, reduces to Modified Newtonian Dynamics (MOND) in the galactic limit. On cosmological scales, the (potential well <-> overdensity) relationship is quite different than in standard general relativity. Here we investigate the possibility of cross-correlating galaxies with the cosmic microwave background (CMB) to probe this relationship. At redshifts of order 2, the sign of the CMB-galaxy correlation differs in TeVeS from that in general relativity. We show that this effect is detectable and hence can serve as a powerful discriminator of these two models of gravity.

arXiv:0706.1264 (cross-list from hep-th) [ps, pdf, other] : Title: Interactions of Cosmic Superstrings
Authors: Mark G. Jackson
Comments: 22 pages, 6 figures
We develop methods by which cosmic superstring interactions can be studied in detail. These include the reconnection probability and emission of radiation such as gravitons or small string loops. Loop corrections to these are discussed, as well as relationships to $(p,q)$-strings. These tools should allow a phenomenological study of string models in anticipation of upcoming experiments sensitive to cosmic string radiation.

arXiv:0706.1340 [ps, pdf, other] : Title: Cluster abundances and S-Z power spectra: effects of non-Gaussianity and early dark energy
Authors: S. Sadeh, Y. Rephaeli, J. Silk
Comments: 12 pages, 5 figures, accepted for publication in MNRAS
In the standard Lambda CDM cosmological model with a Gaussian primordial density fluctuation field, the relatively low value of the mass variance parameter (sigma_8=0.74{+0.05}{-0.06}, obtained from the WMAP 3-year data) results in a reduced likelihood that the measured level of CMB anisotropy on the scales of clusters is due to the Sunyaev-Zeldovich (S-Z) effect. To assess the feasibility of producing higher levels of S-Z power, we explore two alternative models which predict higher cluster abundance. In the first model the primordial density field has a chi^2_1 distribution, whereas in the second an early dark energy component gives rise to the desired higher cluster abundance. We carry out the necessary detailed calculations of the levels of S-Z power spectra, cluster number counts, and angular 2-point correlation function of clusters, and compare (in a self-consistent way) their predicted redshift distributions. Our results provide a sufficient basis upon which the viability of the three models may be tested by future high quality measurements.

arXiv:0706.1462 (cross-list from hep-ph) [ps, pdf, other] : Title: MiniBooNE Results and Neutrino Schemes with 2 sterile Neutrinos: Possible Mass Orderings and Observables related to Neutrino Masses
Authors: Srubabati Goswami, Werner Rodejohann
Comments: 32 pages, 9 figures
The MiniBooNE and LSND experiments are compatible with each other when two sterile neutrinos are added to the three active ones. In this case there are eight possible mass orderings. In two of them both sterile neutrinos are heavier than the three active ones. In the next two scenarios both sterile neutrinos are lighter than the three active ones. The remaining four scenarios have one sterile neutrino heavier and another lighter than the three active ones. We analyze all scenarios with respect to their predictions for mass-related observables. These are the sum of neutrino masses as constrained by cosmological observations, the kinematic mass parameter as measurable in the KATRIN experiment, and the effective mass governing neutrinoless double beta decay. It is investigated how these non-oscillation probes can distinguish between the eight scenarios. We also remark on scenarios with three sterile neutrinos. In addition we make some comments on the possibility of using decays of high energy astrophysical neutrinos to discriminate between the mass orderings in presence of two sterile neutrinos.

arXiv:gr-qc/0703060 [ps, pdf, other] : Title: Stability of spherically symmetric solutions in modified theories of gravity
Authors: Michael D. Seifert
Comments: ReVTex; 19 pages, 3 figures. v2: references added, submitted to PRD
In recent years, a number of alternative theories of gravity have been proposed as possible resolutions of certain cosmological problems or as toy models for possible but heretofore unobserved effects. However, the implications of such theories for the stability structures such as stars have not been fully investigated. We use our "generalized variational principle", described in a previous work, to analyze the stability of static spherically symmetric solutions to spherically symmetric perturbations in three such alternative theories: Carroll et al.'s f(R) gravity, Jacobson & Mattingly's "Einstein-aether theory", and Bekenstein's TeVeS. We find that in the presence of matter, f(R) gravity is highly unstable; that the stability conditions for spherically symmetric curved vacuum Einstein-aether backgrounds are the same as those for linearized stability about flat spacetime, with one exceptional case; and that the ``kinetic terms'' of vacuum TeVeS are indefinite in a curved background, leading to an instability.

arXiv:0706.1577 (cross-list from hep-th) [ps, pdf, other] : Title: Cosmic string formation by flux trapping
Authors: Jose J. Blanco-Pillado, Ken D. Olum, Alexander Vilenkin
Comments: 15 pages and 9 figures
We study the formation of cosmic strings by confining a stochastic magnetic field into flux tubes in a numerical simulation. We use overdamped evolution in a potential that is minimized when the flux through each face in the simulation lattice is a multiple of the fundamental flux quantum. When the typical number of flux quanta through a correlation-length-sized region is initially about 1, we find a string network similar to that generated by the Kibble-Zurek mechanism. With larger initial flux, the loop distribution and the Brownian shape of the infinite strings remain unchanged, but the fraction of length in infinite strings is increased. A 2D slice of the network exhibits bundles of strings pointing in the same direction, as in earlier 2D simulations. We find, however, that strings belonging to the same bundle do not stay together in 3D for much longer than the correlation length. As the initial flux per correlation length is decreased, there is a point at which infinite strings disappear, as in the Hagedorn transition.

arXiv:0706.2101 [ps, pdf, other] : Title: Dark Matter Annihilation in Substructures Revised
Authors: L. Pieri, G. Bertone, E Branchini
Comments: 11 pages, 10 figures
Upcoming $\gamma$-ray satellites will search for Dark Matter annihilations in Milky Way substructures (or 'clumps'). The prospects for detecting these objects strongly depend on the assumptions made on the distribution of Dark Matter in substructures, and on the distribution of substructures in the Milky Way halo. By adopting extreme prescriptions for these quantities, we bracket the number of sources that can be detected with upcoming experiments such as GLAST. We find that scenarios leading to a high number of detectable sources, as well as scenarios where micro-clumps (i.e. clumps with mass as small as $10^{-6}M\odot$) can be detected, are severely constrained by the diffuse $\gamma$-ray background detected by EGRET. At most a handful of large mass substructures, and no micro-clumps, can be detected (at $3 \sigma$, with a 1-year exposure time, by a GLAST-like experiment) in the most optimistic scenarios.

arXiv:0706.2346 [ps, pdf, other] : Title: Non-Gaussianity analysis on local morphological measures of WMAP data
Authors: Y. Wiaux, P. Vielva, R. B. Barreiro, E. Martinez-Gonzalez
 The decomposition of a signal on the sphere with the steerable wavelet constructed from the second Gaussian derivative gives access to the orientation, signed-intensity, and elongation of the signal's local features. In the present work, the non-Gaussianity of the WMAP temperature data of the cosmic microwave background (CMB) is analyzed in terms of the first four moments of the statistically isotropic random fields associated with these local morphological measures, at wavelet scales corresponding to angular sizes between 27.5 arcminutes and 30 degrees on the celestial sphere. While no detection is made neither in the orientation analysis nor in the elongation analysis, a strong detection is made in the excess kurtosis of the signed-intensity of the WMAP data. The non-Gaussianity is observed with a significance level below 0.5% at a wavelet scale corresponding to an angular size around 10 degrees, and confirmed at neighbour scales. This supports a previous detection of an excess of kurtosis in the wavelet coefficient of the WMAP data with the axisymmetric Mexican hat wavelet (Vielva et al. 2004). Instrumental noise and foreground emissions are not likely to be at the origin of the excess of kurtosis. Large-scale modulations of the CMB related to some unknown systematics are rejected as possible origins of the detection. The observed non-Gaussianity may therefore probably be imputed to the CMB itself, thereby questioning the basic inflationary scenario upon which the present concordance cosmological model relies. Taking the CMB temperature angular power spectrum of the concordance cosmological model at face value, further analysis also suggests that this non-Gaussianity is not confined to the directions on the celestial sphere with an anomalous signed-intensity.


arXiv:0706.2151 [ps, pdf, other] : Title: Nonlocal Cosmology
Authors: S. Deser (Caltech and Brandeis), R. P. Woodard (U. of Florida)
Comments: 7 pages, no figures, uses LaTeX 2epsilon
We explore nonlocally modified models of gravity, inspired by quantum loop corrections, as a mechanism for explaining current cosmic acceleration. These theories enjoy two major advantages: they allow a delayed response to cosmic events, here the transition from radiation to matter dominance, and they avoid the usual fine tuning; instead, emulating Dirac's dictum, the required large numbers come from the large time scales involved.