Towards an Effective Field Theory Approach to Reheating
(50 pages)

Using Weinberg's background EFT method, the resonance and decay of the inflaton during reheating can be studied, however it is limited by an EFT cutoff much lower than the Planck scale. Focusing instead on the symmetry breaking due to fluctuations about the cosmological background, a hierarchy of scales is established and a new class of reheating EFTs proposed.

These new reheating models can, in principle, be used to predict gravitational wave signatures, and may prove useful for calculating future observables for gravitational wave astronomy. However, there are few observational constraints which can be used to fix the EFT coefficients, meaning that it is currently limited in its predictivity. The models also focus only on the first stages of preheating.

Minimal Quasidilaton
(19 pages)

A scalar field is introduced into minimal massive gravity, while respecting a global quasidilaton symmetry and allowing for stable selfaccelerating de Sitter bakcgrounds. The fiducial metric is taken as Minkowski space. The number of degrees of freedom is determined via Hamiltonian analysis. Although minimal massive gravity has three gravitational degrees of freedom, additional Hamiltonian constraints can be introduced along with the scalar field to ensure that the resulting theory still contains only three degrees of freedom. For a large choice of parameters, the selfaccelerating dS solutions are shown to be stable.

The resulting minimal quasidilaton theory of maassive gravity describes two gravitational degrees of freedom, and a single scalar degree of freedom. There is much interest in theories with such a dof count, as the gravitational degrees of freedom can be thought of as the two polarizations of observable gravitational waves, while the scalar field can then drive other processes such as the late time acceleration of the Universe.
