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Adam Christopherson (University of Nottingham)
Title: Effects of Non-Adiabatic Cosmological Perturbations
Abstract: Non-adiabatic pressure, or entropy, perturbations naturally arise in any system containing more than one fluid, or scalar field. In this talk I will review standard cosmological perturbation theory and introduce the notion of non-adiabatic pressure perturbations. I will then discuss two scenarios in which they occur: firstly as a relative entropy perturbation between relativistic and non-relativistic matter species in the standard concordance cosmology, and then as isocurvature perturbations in models of inflation consisting of more than one scalar field.
Finally, I will discuss an important effect of non-adiabatic pressure perturbations in higher order perturbation theory. I will show that vorticity is generated at second order in perturbation theory from a coupling between linear density and entropy perturbations. This could prove important for observations in the form of B mode polarisation of the CMB, and also for magnetic field generation in the early universe.
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