Cosmology seminar: Adam Christopherson

Adam Christopherson is a Postdoctoral Research Associate in the Particle Theory group at the University of Florida, USA.

Scalar fields in cosmology: from inflation to axion dark matter

Scalar fields are commonplace in cosmology, often being invoked to explain the accelerated expansion in the early universe (inflation) and at late times (dark energy). This reliance on scalar fields has become somewhat more justified recently with the detection of the first scalar field in nature - the Higgs boson at the LHC. In this talk I will focus on two pieces of recent work involving scalar fields. First, I will consider a particular model of inflation embedded in a scalar-tensor theory. This model contains two fields, one that drives inflation, and a second that stabilizes the Planck mass (or the gravitational constant) in the early universe. In this model, the stabilization occurs a few efolds after inflation. We show, by performing a numerical calculation, that the non-minimal coupling of the second field to the Ricci scalar can boost the amplitude of the curvature perturbation, even if the Planck mass varies only a small amount.

Secondly, I will discuss some recent work on the axion as a dark matter candidate. Structure formation with dark matter is commonly modeled using Newtonian physics, where we are able to understand much in the linear regime. While this is reliable for WIMPs, for a candidate like the axion - which is really a quantum field - this description as a classical, pressureless fluid, is perhaps incomplete. I will show that the wavefunction approach reproduces the usual evolution equation for the density perturbation, albeit with an additional ‘quantum pressure’ term, at linear order in perturbation theory. I will then discuss the various relationships between the descriptions of cold dark matter in terms of a pressureless fluid, in terms of a wavefunction of a classical scalar field, and a quantum scalar field, identifying regimes in which the various descriptions coincide and where they differ. This is the first step towards the goal of describing structure formation with axions, and I will close with some future prospects.

Organizer

Phil Bull
Published Apr. 15, 2015 12:17 PM - Last modified Apr. 15, 2015 12:17 PM