Richard Easther

CMBPol Mission Concept Study Probing Ination with CMB Polarization

We summarize the utility of precise cosmic microwave background (CMB) polarization measurements as probes of the physics of ination. We focus on the prospects for using CMB measurementsWe summarize the utility of precise cosmic microwave background (CMB) polarization measurements as probes of the physics of inflation. We focus on the prospects for using CMB measurements to differentiate various inflationary mechanisms. In particular, a detection of primordial B‐mode polarization would demonstrate that inflation occurred at a very high energy scale, and that the inflaton traversed a super‐Planckian distance in field space. We explain how such a detection or constraint would illuminate aspects of physics at the Planck scale. Moreover, CMB measurements can constrain the scale‐dependence and non‐Gaussianity of the primordial fluctuations and limit the possibility of a significant isocurvature contribution. Each such limit provides crucial information on the underlying inflationary dynamics. Finally, we quantify these considerations by presenting forecasts for the sensitivities of a future satellite experiment to the inflationary parameters.

Oscillons after Inflation

Oscillons are massive, long-lived, localized excitations of a scalar field. We show that in a class of well-motivated single-field models, inflation is followed by self resonance, leading to copious oscillon generation and a lengthy period of oscillon domination. These models are characterized by an inflaton potential which has a quadratic minimum and is shallower than quadratic away from the minimum. This set includes both string monodromy models and a class of supergravity inspired scenarios and is in good agreement with the current central values of the concordance cosmology parameters. We assume that the inflaton is weakly coupled to other fields so as not to quickly drain energy from the oscillons or prevent them from forming. An oscillon-dominated universe has a greatly enhanced primordial power spectrum on very small scales relative to that seen with a quadratic potential, possibly leading to novel gravitational effects in the early Universe.

Bayesian analysis of inflation. II. Model selection and constraints on reheating

We discuss the model selection problem for inflationary cosmology. We couple ModeCode, a publicly-available numerical solver for the primordial perturbation spectra, to the nested sampler MultiNest, in order to efficiently compute Bayesian evidence. Particular attention is paid to the specification of physically realistic priors, including the parametrization of the post-inflationary expansion and associated thermalization scale. It is confirmed that while present-day data tightly constrains the properties of the power spectrum, it cannot usefully distinguish between the members of a large class of simple inflationary models. We also compute evidence using a simulated Planck likelihood, showing that while Planck will have more power than WMAP to discriminate between inflationary models, it will not definitively address the inflationary model selection problem on its own. However, Planck will place very tight constraints on any model with more than one observationally-distinct inflationary regime -- e.g. the large- and small-field limits of the hilltop inflation model -- and put useful limits on different reheating scenarios for a given model.

Constraining monodromy inflation

We use cosmic microwave background (CMB) data from the 9-year WMAP release to derive constraints on monodromy inflation, which is characterized by a linear inflaton potential with a periodic modulation. We identify two possible periodic modulations that significantly improve the fit, lowering χ{sup 2} by approximately 10 and 20. However, standard Bayesian model selection criteria assign roughly equal odds to the modulated potential and the unmodulated case. A modulated inflationary potential can generate substantial primordial non-Gaussianity with a specific and characteristic form. For the best-fit parameters to the WMAP angular power spectrum, the corresponding non-Gaussianity might be detectable in upcoming CMB data, allowing nontrivial consistency checks on the predictions of a modulated inflationary potential.

MULTIMODECODE : an efficient numerical solver for multifield inflation

We present MultiModeCode, a Fortran 95/2000 package for the numerical exploration of multifield inflation models. This program facilitates efficient Monte Carlo sampling of prior probabilities for inflationary model parameters and initial conditions and is the first publicly available code that can efficiently generate large sample-sets for inflation models with

Gravitational waves from oscillon preheating

\mathcal O(100)

Gravitational waves from the end of inflation: Computational strategies

fields. The code numerically solves the equations of motion for the background and first-order perturbations of multi-field inflation models with canonical kinetic terms and arbitrary potentials, providing the adiabatic, isocurvature, and tensor power spectra at the end of inflation. For models with sum-separable potentials MultiModeCode also computes the slow-roll prediction via the

Supersymmetry, nonthermal dark matter, and precision cosmology

\delta N

The Knotted Sky I: Planck constraints on the primordial power spectrum

formalism for easy model exploration and validation. We pay particular attention to the isocurvature perturbations as the system approaches the adiabatic limit, showing how to avoid numerical instabilities that affect some other approaches to this problem. We demonstrate the use of MultiModeCode by exploring a few toy models. Finally, we give a concise review of multifield perturbation theory and a users manual for the program.

Ultracompact Minihalos as Probes of Inflationary Cosmology

A bstractOscillons are long-lived, localized excitations of nonlinear scalar fields which may be copiously produced during preheating after inflation, leading to a possible oscillon dominated phase in the early Universe. For example, this can happen after axion monodromy inflation, on which we run our simulations. We investigate the stochastic gravitational wave background associated with an oscillon-dominated phase. An isolated oscillon is spherically symmetric and does not radiate gravitational waves, and we show that the flux of gravitational radiation generated between oscillons is also small. However, a significant stochastic gravitational wave background may be generated during preheating itself (i.e, when oscillons are forming), and in this case the characteristic size of the oscillons is imprinted on the gravitational wave power spectrum, which has multiple, distinct peaks.