Ultracompact Minihalos as Probes of Inflationary Cosmology.

Cosmological inflation generates primordial density perturbations on all scales, including those far too small to contribute to the cosmic microwave background. At these scales, isolated ultracompact minihalos of dark matter can form well before standard structure formation, if the perturbations have sufficient amplitude. Minihalos affect pulsar timing data and are potentially bright sources of gamma rays.

Gravitational wave consistency relations for multifield inflation.

We study the tensor spectral index n(t) and the tensor-to-scalar ratio r in the simplest multifield extension to single-field, slow-roll inflation models. We show that multifield models with potentials V∼[under ∑]iλ_{i}|ϕ_{i}|^{p} have different predictions for n(t)/r than single-field models, even when all the couplings are equal λ_{i}=λ_{j}, due to the probabilistic nature of the fields' initial values. We analyze well-motivated prior probabilities for the λ_{i} and initial conditions to make detailed predictions for the marginalized probability distribution of n(t)/r.

Simple predictions from multifield inflationary models.

We explore whether multifield inflationary models make unambiguous predictions for fundamental cosmological observables. Focusing on N-quadratic inflation, we numerically evaluate the full perturbation equations for models with 2, 3, and O(100) fields, using several distinct methods for specifying the initial values of the background fields. All scenarios are highly predictive, with the probability distribution functions of the cosmological observables becoming more sharply peaked as N increases.