Astrophysics

At the end of inflation, dynamical instability can rapidly deposit the energy of homogeneous cold inflation into excitations of other fields. This process (known as preheating) essentially starts the hot big bang as we know it. I will present simulations of several preheating models using a new numerical solver DEFROST I developed. The results trace the evolution of the fields, which quickly become very inhomogeneous as the instability kicks in. Surprisingly, there appears to be a certain universality across preheating models with different decay channels. After initial transient, the field density distributions quickly become stationary and lognormal to high precision. I will discuss possible connection of this observation to scalar field turbulence.

New low frequency radio telescopes currently being built open up the possibility of observing the 21 cm radiation before the Epoch of Reionization in the future, in particular at redshifts 200 ≥ z ≥ 30, also known as the dark ages. At these high redshifts, Cosmic Microwave Back-ground (CMB) radiation is absorbed by neutral hydrogen at its 21 cm hyperfine transition. This redshifted 21 cm signal thus carries information about the state of the early Universe and can be used to test fundamental physics. We study the constraints these observations can put on the variation of fundamental constants and on fundamental mass scales. We show that the 21 cm radiation is very sensitive to the variations in the fine structure constant and can in principle place constraints comparable to or better than the other astrophysical experiments. Cosmic strings, if they exist, contribute to the anisotropies in the primordial gas leaving an imprint on the 21 cm radiation. They can tell us about the fundamental mass scales involved in the theories beyond the standard model. We show that the 21 cm radiation can potentially probe cosmic strings of tension ~10−12 asumming intercommutation probability of 1. Making such observations will require radio telescopes of collecting area 10 − 106 km2 compared to ~ 1 km2 of current telescopes.