Munch: Monday, June 4, 2007

                               


 

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

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


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       Munch Archive

 arXiv:0705.3655 [ps, pdf, other] : Title: Evidence Of Dark Matter Annihilations In The WMAP Haze
Authors: Dan Hooper, Douglas P. Finkbeiner, Gregory Dobler
Comments: 4 pages, 3 figures
The WMAP experiment has revealed an excess of microwave emission from the region around the center of our Galaxy. It has been suggested that this signal, known as the ``WMAP Haze'', could be synchrotron emission from relativistic electrons and positrons generated in dark matter annihilations. In this letter, we revisit this possibility. We find that the angular distribution of the WMAP Haze matches the prediction for dark matter annihilations with a cusped density profile, $\rho(r) \propto r^{-1.2}$ in the inner kiloparsecs. Comparing the intensity in different WMAP frequency bands, we find that a wide range of possible WIMP annihilation modes are consistent with the spectrum of the haze for a WIMP with a mass in the 100 GeV to multi-TeV range. Most interestingly, we find that to generate the observed intensity of the haze, the dark matter annihilation cross section is required to be approximately equal to the value needed for a thermal relic, $\sigma v \sim 3 \times 10^{-26}$ cm$^3$/s. No boost factors are required. If dark matter annihilations are in fact responsible for the WMAP Haze, and the slope of the halo profile continues into the inner Galaxy, GLAST is expected to detect gamma rays from the dark matter annihilations in the Galactic Center if the WIMP mass is less than several hundred GeV.

arXiv:0705.3980 [ps, pdf, other] : Title: Detection of Gravitational Lensing in the Cosmic Microwave Background
Authors: Kendrick M. Smith, Oliver Zahn, Olivier Dore
Comments: 27 pages, 20 figures
Gravitational lensing of the cosmic microwave background (CMB), a long-standing prediction of the standard cosmolgical model, is ultimately expected to be an important source of cosmological information, but first detection has not been achieved to date. We report a 3.4 sigma detection, by applying quadratic estimator techniques to all sky maps from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite, and correlating the result with radio galaxy counts from the NRAO VLA Sky Survey (NVSS). We present our methodology including a detailed discussion of potential contaminants. Our error estimates include systematic uncertainties from density gradients in NVSS, beam effects in WMAP, Galactic microwave foregrounds, resolved and unresolved CMB point sources, and the thermal Sunyaev-Zeldovich effect.

arXiv:0705.3100 [ps, pdf, other] : Title: Prospects for Constraining Neutrino Mass Using Planck and Lyman-Alpha Forest Data
Authors: Steven Gratton, Antony Lewis, George Efstathiou
Comments: 6 pages, 4 figures
In this paper we investigate how well Planck and Lyman-Alpha forest data will be able to constrain the sum of the neutrino masses, and thus, in conjunction with flavour oscillation experiments, be able to determine the absolute masses of the neutrinos. It seems possible that Planck, together with a Lyman-Alpha survey, will be able to put pressure on an inverted hierarchial model for the neutrino masses. However, even for optimistic assumptions of the precision of future Lyman-Alpha datasets, it will not be possible to confirm a minimal-mass normal hierarchy.

arXiv:0705.4298 [ps, pdf, other] : Title: Towards Closing the Window on Strongly Interacting Dark Matter: Far-Reaching Constraints from Earth's Heat Flow
Authors: Gregory D. Mack (Ohio State), John F. Beacom (Ohio State), Gianfranco Bertone (IAP)
Comments: 12 pages, 2 figures
We point out a new and largely model-independent constraint on the dark matter scattering cross section with nucleons, applying when this quantity is larger than for typical weakly interacting dark matter candidates. When the dark matter capture rate in Earth is efficient, the rate of energy deposition by dark matter self-annihilation products would grossly exceed the measured heat flow of Earth. This improves the spin-independent cross section constraints by many orders of magnitude, and closes the window between astrophysical constraints (at very large cross sections) and underground detector constraints (at small cross sections). In the applicable mass range, from about 1 to about 10^{10} GeV, the scattering cross section of dark matter with nucleons is then bounded from above by the latter constraints, and hence must be truly weak, as usually assumed.

arXiv:0705.4311 [ps, pdf, other] : Title: The Likely Cause of the EGRET GeV Anomaly and its Implications
Authors: F. W. Stecker, S. D. Hunter, D. A. Kniffen (NASA/GSFC)  (suggested by Jeter)
Comments: 4 pg, 2 figs
Analysis of data from the EGRET gamma-ray detector on the Compton Gamma Ray Observatory indicated an anomaly in the form of an excess diffuse galactic flux at GeV energies over that which was theoretically predicted. Various explanations for this anomaly have been put forth, including the invocation of supersymmetric dark matter annihilation. We reexamine these explanations here, including a new discussion of the possible systematic errors in the sensitivity determination of the EGRET detector. We conclude that the most likely explanation of the EGRET ``GeV anomaly'' was an error in the estimation of the of the EGRET sensitivity at energies above ~1 GeV. We give reasons why such a situation could have occurred. We find evidence from our new all-sky analysis which is inconsistent with the assumption that the anomaly can be a signal of supersymmetric dark matter annihilation. We also reconfirm the original results of the EGRET team on the extragalactic gamma-ray background spectrum. There are important implications of our analysis for the upcoming Gamma Ray Large Area Telescope (GLAST) mission.

arXiv:0705.3854 [ps, pdf, other] : Title: Hadronic Gamma Rays from Supernova Remnants  (suggested by Jeter)
Authors: I. V. Moskalenko (Stanford), T. A. Porter (UCSC), M. A. Malkov, P. H. Diamond (UCSD)
Comments: 4 pages, 3 figures. Contribution to the 30th ICRC, Merida, Mexico, 2007
A gas cloud near a supernova remnant (SNR) provides a target for pp-collisions leading to subsequent gamma-ray emission through neutral pion decay. The assumption of a power-law ambient spectrum of accelerated particles with index near -2 is usually built into models predicting the spectra of very-high energy (VHE) gamma-ray emission from SNRs. However, if the gas cloud is located at some distance from the SNR shock, this assumption is not necessarily correct. In this case, the particles which interact with the cloud are those leaking from the shock and their spectrum is approximately monoenergetic with the injection energy gradually decreasing as the SNR ages. The gamma-ray spectrum resulting from particle interactions with the gas cloud will be flatter than expected, with the cutoff defined by the pion momentum distribution in the laboratory frame. We evaluate the flux of particles escaping from a SNR shock and apply the results to the VHE diffuse emission detected by the HESS at the Galactic centre.

arXiv:0705.3042 [ps, pdf, other] : Title: How robust are the constraints on cosmology and galaxy evolution from the lens-redshift test?
Authors: Pedro R. Capelo (Yale), Priyamvada Natarajan (Yale)
Comments: 16 pages, 10 figures, 2 tables. Invited contribution submitted to the "Gravitational Lensing" Focus Issue of the New Journal of Physics
The redshift distribution of galaxy lenses in known gravitational lens systems provides a powerful test that can potentially discriminate amongst cosmological models. However, applications of this elegant test have been curtailed by two factors: our ignorance of how galaxies evolve with redshift, and the absence of methods to deal with the effect of incomplete information in lensing systems. In this paper, we investigate both issues in detail. To tackle the first, we explore how to turn the problem around and extract the properties of evolving galaxies, assuming that the cosmology is well determined by other techniques. To deal with the second, we propose a new nested Monte-Carlo method to quantify the effects of incomplete data. We apply the lens-redshift test to an improved sample of seventy verified lens systems derived from recent observations, primarily from the SDSS, SLACS and the CLASS surveys. We find that the limiting factor in applying the lens-redshift test derives from poor statistics and biased sampling. Many lenses that uniformly sample the underlying true image separation distribution will be needed to use this test as a complementary method to measure the value of the cosmological constant or the properties of evolving galaxies. Planned future surveys by missions like the SNAP satellite or LSST are likely to usher in a new era for strong lensing studies that utilize this test. With expected catalogues of thousands of new strong lenses, the lens-redshift could offer a powerful tool to probe cosmology as well as galaxy evolution.

arXiv:0705.3323 [ps, pdf, other] : Title: Measuring the Baryon Acoustic Oscillation scale using the SDSS and 2dFGRS
Authors: Will J. Percival, Shaun Cole, Daniel J. Eisenstein, Robert C. Nichol, John A. Peacock, Adrian C. Pope, Alexander S. Szalay
Comments: 14 pages, 13 figures, submitted to MNRAS
We introduce a method to constrain general cosmological models using Baryon Acoustic Oscillation (BAO) distance measurements from galaxy samples covering different redshift ranges, and apply this method to analyse samples drawn from the SDSS and 2dFGRS. BAO are detected in the clustering of the combined 2dFGRS and SDSS main galaxy samples, and measure the distance--redshift relation at z=0.2. BAO in the clustering of the SDSS luminous red galaxies measure the distance--redshift relation at z=0.35. The observed scale of the BAO calculated from these samples and from the combined sample are jointly analysed using estimates of the correlated errors, to constrain the form of the distance measure D_V(z)=[(1+z)^2D_A^2cz/H(z)]^(1/3). Here D_A is the angular diameter distance, and H(z) is the Hubble parameter. This gives r_s/D_V(0.2)=0.1980+/-0.0058 and r_s/D_V(0.35)=0.1094+/-0.0033 (1sigma errors), with correlation coefficient of 0.39, where r_s is the comoving sound horizon scale at recombination. Matching the BAO to have the same measured scale at all redshifts then gives D_V(0.35)/D_V(0.2)=1.812+/-0.060. The recovered ratio is roughly consistent with that predicted by the higher redshift SNLS supernovae data for Lambda cosmologies, but does require slightly stronger cosmological acceleration at low redshift. If we force the cosmological model to be flat with constant w, then we find Om_m=0.249+/-0.018 and w=-1.004+/-0.089 after combining with the SNLS data, and including the WMAP measurement of the apparent acoustic horizon angle in the CMB.

arXiv:0705.3345 [pdf] : Title: Direct Dark Matter Searches
Authors: N. J. Spooner
Comments: Submitted to JPSJ, 20 pages, 5 figures
For many working in particle physics and cosmology successful discovery and characterisation of the new particles that most likely explain the non-baryonic cold dark matter, known to comprise the majority of matter in the Universe, would be the most significant advance in physics for a century. Reviewed here is the current status of direct searches for such particles, in particular the so-called Weakly Interacting Massive Particles (WIMPs), together with a brief overview of the possible future direction of the field extrapolated from recent advances. Current best limits are at or below 10-7 pb for spin-independent neutralino coupling, sufficient that experiments are already probing SUSY models. However, new detectors with tonne-scale mass and/or capability to correlate signal events to our motion through the Galaxy will likely be needed to determine finally whether WIMPs exist. 

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:0705.1158 [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.