Signatures of a new force in the dark matter sector

Details Signatures of a new force in the dark matter sector Signatures of a new force in the dark matter sector

Nov 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010phdt........88s&link_type=abstract

ProQuest Dissertations And Theses; Thesis (Ph.D.)--Harvard University, 2010.; Publication Number: AAT3415369; ISBN: 978112409249

Computer Science

Scientific paper

Recent anomalies in direct and indirect detection experiments motivate dark matter (DM) models containing an expanded "dark sector", where the DM interacts via some new force. In this dissertation, we argue that a new gauge interaction at the GeV scale, coupled to thermal relic O (TeV) DM, provides a natural explanation of signals observed by WMAP, PAMELA, Fermi, INTEGRAL/SPI and DAMA/LIBRA. In such models, the large positron excess observed by PAMELA is generated by a velocity-dependent "Sommerfeld enhancement" to annihilation. We discuss the Sommerfeld enhancement for a general N-state system, and study in detail a scenario where the DM has a single nearly-degenerate excited state, including developing an accurate semi-analytic approximation for the enhancement. Models with Sommerfeld-enhanced DM annihilation are strongly constrained by the cosmic microwave background. We numerically model the cooling of DM annihilation products in the recombination epoch, and find that the annihilation cross sections required to produce the observed cosmic-ray excesses are already close to the 95% confidence limits from WMAP5; large regions of the parameter space for Sommerfeld enhancement can be ruled out. We study the effect of Sommerfeld enhancement on the freezeout of DM annihilation, and show that in a simple model with a single nearly-degenerate excited state, there remain regions of parameter space that give the correct thermal relic density, are consistent with the CMB constraints, and have present-day annihilation cross sections of the correct size to produce the cosmic-ray excesses. This work concludes with several loosely related projects. We consider the direct detection of a model where the force carrier is a GeV-scale scalar that mixes with the Standard Model Higgs, and find that such models can be naturally hidden from direct detection. We describe a novel statistic for determining the fraction of emission originating from unresolved point sources in a dataset, with significant advantages over the two-point function. Finally, we present an analysis of the first-year photon data from Fermi. We identify a spectrally hard, spatially extended gamma-ray excess in the inner Galaxy, characterize its morphology and spectrum, and argue that it constitutes the inverse Compton scattering counterpart of the WMAP Haze.

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