Probing dark particles and primordial perturbations

Abstract

Quantized fields have been proposed as the source of both the nearly scale-invariant spectrum of Gaussian perturbations in the cosmic microwave background and the extra dark matter evident in the rotation curves of galaxies. In this thesis, we address the former by expanding the primordial scalar curvature perturbation to third polynomial order in scalar elds, and calculating non-Gaussianities which could be observed in future studies of the cosmic microwave background and large scale structure of galactic distribution. In the second part, we develop constraints on the mass and coupling of a generic species of bosonic dark matter with observations of old neutron stars, which would be extinguished over the lifetime of the universe by dark matter collecting into black holes at the core of the neutron stars for certain masses and couplings of bosonic dark matter. The local expansion of the scalar curvature perturbation is a phenomenological ansatz which encompasses many inflationary theories. We calculate the primordial non-Gaussianity of the bispectrum and trispectrum arising from up to cubic terms in the local expansion of the scalar curvature perturbation. We compute to three-loop order and for general momenta. A procedure for evaluating the leading behavior of the resulting loop-integrals is developed and discussed. Finally, we survey unique non-linear signals which could arise from the cubic term in the squeezed limit. In particular, it is shown that loop corrections can cause fsq: NL to change sign as the momentum scale is varied. There also exists a momentum limit where NL < 0 can be realized, which demonstrates that the SY Inequality depends on the external momenta used to calculate the trispectrum. Baryon interactions with bosonic dark matter are constrained by the potential for dark matter-rich neutron stars to collapse into black holes. We consider the effect of dark matter self-interactions and dark matter annihilation on these bounds, and treat the evolution of the black hole after formation. We show that, for nonannihilating dark matter, these bounds extend up to mX 10^5-7 GeV, depending on the strength of self-interactions. However, these bounds are completely unconstraining for annihilating bosonic dark matter with an annihilation cross-section of h avi & 10^-38 cm3=s. Dark matter decay does not significantly affect these bounds. We thus show that bosonic dark matter accessible to near-future direct detection experiments must participate in an annihilation or self-interaction process to avoid black hole collapse constraints from very old neutron stars.