Inflation from Magnetic Drift



In a series of collaborative papers [1,2, 3], I introduced a new, general mechanism for realizing a phase of inflation, using an analog of magnetic drift, rather than a flat potential, to slow down the inflaton's roll. The original Chromo-Natural model produces chiral gravitational waves, but appears in conflict with Planck data in its basic form. We are identifying extensions that evade these dangers now.

Neutrinos: reconciling Planck with the Local Universe



In the simplest six parameter model of Lambda-CDM, the data from the Planck satellite and local measures of the Hubble expansion rate and the abundance of galaxy clusters disagree sharply. New neutrino physics could be the answer! When we perform a joint analysis of Planck, H0 data, Baryon Acoustic Oscillation galaxy data, and X-ray cluster abundances we find >3 sigma evidence for neutrino physics beyond the standard model -- a fractionally populated new species and a summed neutrino mass of around 0.4eV.

Massive Gravity and its cosmology



I was the first to point out that the galilean-invariant scalar field that emerges in massive gravity can enhance gravitational lensing; other popular scalar-tensor gravity theories have no new lensing effects. I am now studying how to detect or constrain this novel effect. I have also discovered the most general exact self-accelerating solution to the the theory of massive gravity yet found.

The Gelaton Scenario



The distinctive features of single field inflationary models with non-minimal kinetic terms, like Dirac-Born-Infeld and k-inflation, can be captured by more familiar multiple field inflationary systems. At least one heavy field, which we call the gelaton, has an effective potential which depends on the kinetic energy of the inflaton. Integrating out the gelaton gives rise to an effectively single field system for which the speed of sound for the adiabatic fluctuations is reduced, generating potentially observable equilateral non-Gaussianity, while causing negligible isocurvature fluctuations.

Structure formation in galileon gravity



I am using N-body, particle-mesh codes to study cosmological growth history in models with a galilean invariant scalar field. I have used galaxy survey data, redshift space distortions and galaxy infall kinematics to place limits on the model parameters. Current observations of bulk flows may hint at the kind of new physics found in these models.

Stochastic Inflation Revisited



Stochastic inflation is the study of the global inflationary space, where quantum perturbations grow to horizon size and affect the overall progress of inflation. It is the best way to study eternal inflation and to understand the global structure of inflationary models. I have generalized this formalism to theories of inflation with non-standard kinetic energy terms, like DBI inflation.

Cosmic superstrings



I am continuing to study the distinctive phenomenology of cosmic superstrings. Their contributions to the small angular scale power and B-mode polarization of the CMB could be seen within the next couple of years. In the meantime, I have worked out one of their effects on the 21 cm radiation that will eventually be the richest resource for observational data.