The Lukewarm Frontier: Some Cosmological Consequences of 'Low Energy' Physics

Citation

Grin, Daniel (2010) The Lukewarm Frontier: Some Cosmological Consequences of 'Low Energy' Physics. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/EN34-1095. https://resolver.caltech.edu/CaltechTHESIS:05312010-162432249

Abstract

In this thesis, we present four projects featuring low characteristic energy scales relative to the scales relevant for supersymmetric dark matter production or inflation. We present a telescope search for decaying relic axions in the 3 − 8 eV mass range. We utilize larger telescope exposure and superior cluster mass modeling to improve sensitivity. Our results impose new stringent limits to the two-photon coupling or relic density of axions. We extend these results to non-standard sterile neutrinos.

We then reconsider cosmological constraints to axions. Our understanding of physics before big-bang nucleosynthesis is tenuous, and after arguing that a non-standard thermal history before nucleosynthesis is plausible and perhaps even natural, we calculate the abundance and typical momenta of thermal axions in such scenarios. We generalize existing cosmological constraints to axions, showing that the allowed axion mass range expands significantly in non-standard thermal histories. We then estimate the sensitivity of future experiments to axion masses and reheating temperatures.

We then study the ~ eV-scale physics of cosmological hydrogen ~ 10^4 states of hydrogen up to a maximum n ~ 250, and studying the associated convergence problem. We show that the recombination history is sufficiently converged for analysis of microwave anisotropy data from the Planck satellite if the maximum n ~ 128, and that previously ignored electric quadrupole transitions are indeed negligible to the precision necessary for Planck.

We conclude by presenting a new astrophysical limit to effective field theories of gravity in which the graviton propagator is damped at energies greater than a milli-eV.

Thesis Files