A New Mechanism for Bubble Nucleation: Classical Transitions (2009)
Easther, Richard, Giblin Jr, John T., Hui, Lam, Lim, Eugene A.
Given a scalar field with metastable minima, bubbles nucleate quantum mechanically. When bubbles collide, energy stored in the bubble walls is converted into kinetic energy of the field. This kinetic...
Generating Gravitational Waves After Inflation (2009)
I review two mechanisms by which gravitational waves can be generated at the end of inflation: preheating, and gravitons Hawking radiated during the decay of very small primordial black holes. These...
The "in-in" Formalism and Cosmological Perturbations (2009)
Adshead, Peter, Easther, Richard, Lim, Eugene A.
We describe an efficient scheme for evaluating higher order contributions to primordial cosmological perturbations using the "in-in" formalism, which is the basis of modern calculations of...
GUT-Scale Primordial Black Holes: Consequences and Constraints (2008)
Anantua, Richard, Easther, Richard, Giblin Jr, John T.
We consider signatures of very light primordial black holes which evaporate before primordial nucleosynthesis begins. This population is unconstrained unless one assumes that the decaying black holes...
CMBPol Mission Concept Study: Probing Inflation with CMB Polarization (2008)
Baumann, Daniel, Jackson, Mark G, Adshead, Peter, Amblard, Alexandre, Ashoorioon, Amjad, Bartolo, Nicola, ...
We 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...
CMBPol Mission Concept Study: Probing Inflation with CMB Polarization (2008)
Baumann, Daniel, Jackson, Mark G., Adshead, Peter, Amblard, Alexandre, Ashoorioon, Amjad, Bartolo, Nicola, ...
We 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...
Neutrinos and Future Concordance Cosmologies (2008)
Adshead, Peter, Easther, Richard
We review the free parameters in the concordance cosmology, and those which might be added to this set as the quality of astrophysical data improves. Most concordance parameters encode information...
Cosmology With Many Light Scalar Fields: Stochastic Inflation and Loop Corrections (2008)
Adshead, Peter, Easther, Richard, Lim, Eugene A.
We explore the consequences of the existence of a very large number of light scalar degrees of freedom in the early universe. We distinguish between participator and spectator fields. The former have...
Fine-tuning criteria for inflation and the search for primordial gravitational waves (2008)
Bird, Simeon, Peiris, Hiranya V., Easther, Richard
We revisit arguments that simple models of inflation with a small red tilt in the scalar power spectrum generically yield an observable tensor spectrum. We show that criteria for fine-tuning based...
Primordial Black Holes, Eternal Inflation, and the Inflationary Parameter Space after WMAP5 (2008)
Peiris, Hiranya V., Easther, Richard
We consider constraints on inflation driven by a single, minimally coupled scalar field in the light of the WMAP5 dataset, as well as ACBAR and the SuperNova Legacy Survey. We use the Slow Roll...
Adshead, Peter, Easther, Richard
Slow roll reconstruction is derived from the Hamilton-Jacobi formulation of inflationary dynamics. It automatically includes information from sub-leading terms in slow roll, and facilitatesthe...
Thermal Inflation and the Gravitational Wave Background (2008)
Easther, Richard, Giblin Jr, John T., Lim, Eugene A., Park, Wan-Il, Stewart, Ewan D.
We consider the impact of thermal inflation -- a short, secondary period of inflation that can arise in supersymmetric scenarios -- on the stochastic gravitational wave background. We show that while...
Generation and Characterization of Large Non-Gaussianities in Single Field Inflation (2008)
Chen, Xingang, Easther, Richard, Lim, Eugene A.
Inflation driven by a single, minimally coupled, slowly rolling field generically yields a negligible primordial non-Gaussianity. We discuss two distinct mechanisms by which a non-trivial potential...
Gravitational Waves From the End of Inflation: Computational Strategies (2007)
Easther, Richard, Giblin Jr, John T., Lim, Eugene A.
Parametric resonance or preheating is a plausible mechanism for bringing about the transition between the inflationary phase and a hot, radiation dominated universe. This epoch results in the rapid...
The Eternal Sunshine of the Spotless Mind (2007)
Easther, Richard, Lim, Eugene A.
We extend the worldline measure for pocket formation in eternal inflation to allow for time-ordered bubble formation. Such a time-ordering is equivalent to imposing a preferred time-slicing on the...
Gravitational Wave Production At The End Of Inflation (2006)
Easther, Richard, Giblin Jr, John T., Lim, Eugene A.
We consider gravitational wave production due to parametric resonance at the end of inflation, or ``preheating''. This leads to large inhomogeneities which source a stochastic background of...
Large Non-Gaussianities in Single Field Inflation (2006)
Chen, Xingang, Easther, Richard, Lim, Eugene A.
We compute the 3-point correlation function for a general model of inflation driven by a single, minimally coupled scalar field. Our approach is based on the numerical evaluation of both the...
Non-Gaussianities in Multi-field Inflation (2006)
Battefeld, Thorsten, Easther, Richard
We compute the amplitude of the non-Gaussianities in inflationary models with multiple, uncoupled scalar fields. This calculation thus applies to all models of assisted inflation, including...
Slow Roll Reconstruction: Constraints on Inflation from the 3 Year WMAP Dataset (2006)
Peiris, Hiranya, Easther, Richard
We study the constraints on the inflationary parameter space derived from the 3 year WMAP dataset using ``slow roll reconstruction'', using the SDSS galaxy power spectrum to gain further leverage...
Implications of a Running Spectral Index for Slow Roll Inflation (2006)
Easther, Richard, Peiris, Hiranya
We analyze the weak (2 sigma) evidence for a running spectral index seen in the three-year WMAP dataset and its implications for single field, slow roll inflation. We assume that the running is...
Peiris, Hiranya, Easther, Richard
We introduce a new method for applying an inflationary prior to a cosmological dataset that includes relations between observables at arbitrary order in the slow roll expansion. The process is based...
Stochastic Gravitational Wave Production After Inflation (2006)
Easther, Richard, Lim, Eugene A.
In many models of inflation, the period of accelerated expansion ends with preheating, a highly non-thermal phase of evolution during which the inflaton pumps energy into a specific set of momentum...
The Lyth Bound and the End of Inflation (2006)
Easther, Richard, Kinney, William H., Powell, Brian A.
We derive an extended version of the well-known Lyth Bound on the total variation of the inflaton field, incorporating higher order corrections in slow roll. We connect the field variation...
Journal of Cosmology and Astroparticle Physics (2006)
An Iop, Sissa Journal, Hiranya V Peiris, Richard Easther
Recovering the inflationary potential and primordial power spectrum with a slow roll prior: methodology and application to WMAP three year data
Random Matrices and the Spectrum of N-flation (2005)
Easther, Richard, McAllister, Liam
N-flation is a promising embedding of inflation in string theory in which many string axions combine to drive inflation. We characterize the dynamics of a general N-flation model with non-degenerate...
Cosmology From Random Multifield Potentials (2005)
Aazami, Amir, Easther, Richard
We consider the statistical properties of vacua and inflationary trajectories associated with a random multifield potential. Our underlying motivation is the string landscape, but our calculations...
Counting Pockets with World Lines in Eternal Inflation (2005)
Easther, Richard, Lim, Eugene A., Martin, Matthew R.
We consider the long standing puzzle of how to obtain meaningful probabilities in eternal inflation. We demonstrate a new algorithm to compute the probability distribution of pocket universe types,...
Boundary Effective Field Theory and Trans-Planckian Perturbations: Astrophysical Implications (2005)
Easther, Richard, Kinney, William H., Peiris, Hiranya
We contrast two approaches to calculating trans-Planckian corrections to the inflationary perturbation spectrum: the New Physics Hypersurface [NPH] model, in which modes are normalized when their...
The Hubble Slow Roll Expansion for Multi Field Inflation (2005)
Easther, Richard, Giblin Jr, John T
We examine the dynamics of inflation driven by multiple, interacting scalar fields and derive a multi field version of the Hubble slow roll expansion. We show that the properties of this expansion...
Multiple Inflation, Cosmic String Networks and the String Landscape (2005)
Burgess, C. P., Easther, Richard, Mazumdar, Anupam, Mota, David F., Multamaki, Tuomas
Motivated by the string landscape we examine scenarios for which inflation is a two-step process, with a comparatively short inflationary epoch near the string scale and a longer period at a much...
Observing Trans-Planckian Signatures in the Cosmic Microwave Background (2004)
Easther, Richard, Kinney, William H, Peiris, Hiranya
We examine the constraints cosmological observations can place on any trans-Planckian corrections to the primordial spectrum of perturbations underlying the anisotropies in the Cosmic Microwave...
String windings in the early universe (2004)
Easther, Richard, Greene, Brian R., Jackson, Mark G., Kabat, Daniel
We study string dynamics in the early universe. Our motivation is the proposal of Brandenberger and Vafa, that string winding modes may play a key role in decompactifying three spatial dimensions. We...
Folded Inflation, Primordial Tensors, and the Running of the Scalar Spectral Index (2004)
I discuss folded inflation, an inflationary model embedded in a multi-dimensional scalar potential, such as the stringy landscape. During folded inflation, the field point evolves along a path that...
Tuning Locked Inflation: Supergravity versus Phenomenology (2004)
Easther, Richard, Khoury, Justin, Schalm, Koenraad
We analyze the cosmological consequences of locked inflation, a model recently proposed by Dvali and Kachru that can produce significant amounts of inflation without requiring slow-roll. We pay...
Evolution of gravitational waves in Randall-Sundrum cosmology (2003)
Easther, Richard, Langlois, David, Maartens, Roy, Wands, David
We investigate the evolution of gravitational wave perturbations about a brane cosmology embedded in a five-dimensional anti-de Sitter bulk. During slow-roll inflation in a Randall-Sundrum...
Do We Live in a Vanilla Universe? Theoretical Perspectives on WMAP (2003)
I discuss the theoretical implications of the WMAP results, stressing WMAP's detection of a correlation between the E-mode polarization and temperature anisotropies, which provides strong support for...
Brane gases in the early universe: thermodynamics and cosmology (2003)
Easther, Richard, Greene, Brian R., Jackson, Mark G., Kabat, Daniel
We consider the thermodynamic and cosmological properties of brane gases in the early universe. Working in the low energy limit of M-theory we assume the universe is a homogeneous but anisotropic...
Brane gas cosmology in M-theory: late time behavior (2002)
Easther, Richard, Greene, Brian R., Jackson, Mark G., Kabat, Daniel
We investigate the late-time behavior of a universe containing a supergravity gas and wrapped 2-branes in the context of M-theory compactified on T^10. The supergravity gas tends to drive uniform...
Monte Carlo reconstruction of the inflationary potential (2002)
Easther, Richard, Kinney, William H.
We present Monte Carlo reconstruction, a new method for ``inverting'' observational data to constrain the form of the scalar field potential responsible for inflation. This stochastic technique is...
Easther, Richard, Greene, Brian R., Kinney, William H., Shiu, Gary
We derive a general expression for the power spectra of scalar and tensor fluctuations generated during inflation given an arbitrary choice of boundary condition for the mode function at a short...
Cosmological String Gas on Orbifolds (2002)
Easther, Richard, Greene, Brian R., Jackson, Mark G.
It has long been known that strings wound around incontractible cycles can play a vital role in cosmology. In particular, in a spacetime with toroidal spatial hypersurfaces, the dynamics of the...
Imprints of Short Distance Physics On Inflationary Cosmology (2001)
Easther, Richard, Greene, Brian R., Kinney, William H., Shiu, Gary
We analyze the impact of certain modifications to short distance physics on the inflationary perturbation spectrum. For the specific case of power-law inflation, we find distinctive -- and possibly...
Inhomogeneity and Nonlinear Preheating (2001)
Parry, Matthew, Easther, Richard
We investigated the possibility that nonlinear gravitational effects influence the preheating era after inflation, using numerical solutions of the inhomogeneous Einstein field equations. We compared...
Inflation as a Probe of Short Distance Physics (2001)
Easther, Richard, Greene, Brian R., Kinney, William H., Shiu, Gary
We show that a string-inspired Planck scale modification of general relativity can have observable cosmological effects. Specifically, we present a complete analysis of the inflationary perturbation...
Inflationary perturbations from a potential with a step (2001)
Adams, Jennifer, Cresswell, Bevan, Easther, Richard
We use a numerical code to compute the density perturbations generated during an inflationary epoch which includes a spontaneous symmetry breaking phase transition. A sharp step in the inflaton...
Fermions, Gauge Theories, and the Sinc Function Representation for Feynman Diagrams (2000)
Petrov, Dmitri, Easther, Richard, Guralnik, Gerald, Hahn, Stephen, Wang, Wei-Mun
We extend our new approach for numeric evaluation of Feynman diagrams to integrals that include fermionic and vector propagators. In this initial discussion we begin by deriving the Sinc function...
Attractive Forces Between Global Monopoles and Domain Walls (2000)
Alexander, Stephon, Brandenberger, Robert, Easther, Richard
We study the interaction between stable monopoles and domain walls in a $SO(3) \times Z(2)$ scalar field theory. Numerical simulations reveal that there is an attractive force between the monopole...
The Sinc Function Representation and Three-Loop Master Diagrams (1999)
Easther, Richard, Guralnik, Gerald, Hahn, Stephen
We test the Sinc function representation, a novel method for numerically evaluating Feynman diagrams, by using it to evaluate the three-loop master diagrams. Analytical results have been obtained for...
Gravity, Parametric Resonance and Chaotic Inflation (1999)
Easther, Richard, Parry, Matthew
We investigate the possibility that nonlinear gravitational effects influence the preheating era after inflation. Our work is based on numerical solutions of the inhomogeneous Einstein field...
Preheating, Parametric Resonance and the Einstein Field Equations (1999)
Parry, Matthew, Easther, Richard
We consider the interaction between perturbations in the inflaton and in the metric during the preheating phase in simple inflationary models. By numerically integrating the Einstein field equations...
On the Interaction of Monopoles and Domain Walls (1999)
Alexander, Stephon, Brandenberger, Robert, Easther, Richard, Sornborger, Andrew
We study the interaction between monopoles and embedded domain walls in a O(3) linear sigma model. We discover that there is an attractive force between the monopole and the wall. We provide evidence...
Fast Evaluation of Feynman Diagrams (1999)
Easther, Richard, Guralnik, Gerald, Hahn, Stephen
We develop a new representation for the integrals associated with Feynman diagrams. This leads directly to a novel method for the numerical evaluation of these integrals, which avoids the use of...
Holography, Cosmology and the Second Law of Thermodynamics (1999)
Easther, Richard, Lowe, David A.
We propose that in time dependent backgrounds the holographic principle should be replaced by the generalized second law of thermodynamics. For isotropic open and flat universes with a fixed equation...
Inhomogeneity and the Post-Inflationary Universe (1999)
Easther, Richard, Parry, Matthew
We discuss the interaction between perturbations in the inflaton and the background during the preheating phase in simple inflationary models. By numerically solving the Einstein field equations we...
Preheating and the Einstein Field Equations (1998)
Parry, Matthew, Easther, Richard
We inaugurate a framework for studying preheating and parametric resonance after inflation without resorting to any approximations, either in gravitational perturbation theory or in the evolution of...
Chaos after Two-Field Inflation (1998)
We show that two-field inflation can be followed by an era in which the field dynamics become chaotic, and discuss the possible consequences of this for two-field inflationary models. [PASCOS...
Nonsingular Dilaton Cosmology (1998)
Brandenberger, R., Easther, Richard, Maia, J.
We study spatially homogeneous and isotropic solutions to the equations of motion derived from dilaton gravity, in the presence of a special combination of higher derivative terms in the...
Chaotic Dynamics and Two-Field Inflation (1997)
Easther, Richard, Maeda, Kei-ichi
We demonstrate the existence of chaos in realistic models of two-field inflation. The chaotic motion takes place after the end of inflation, when the fields are free to oscillate and their motion is...
Vacuum fluctuations in axion-dilaton cosmologies (1997)
Copeland, E. J., Easther, Richard, Wands, David
We study axion-dilaton cosmologies derived from the low-energy string effective action. We present the classical homogeneous Friedmann-Robertson-Walker solutions and derive the semi-classical...
One-Loop Superstring Cosmology and the Non-Singular Universe (1996)
Easther, Richard, Maeda, Kei-ichi
We study the cosmological implications of the one-loop terms in the string expansion. In particular, we find non-singular solutions which interpolate between a contracting universe and an expanding...
An Inflationary Model with an Exact Perturbation Spectrum (1995)
We present a new, exact scalar field cosmology for which the spectrum of scalar (density) perturbations can be calculated exactly. We use this exact result to the probe the accuracy of approximate...
Tree-level String Cosmology (1995)
Easther, Richard, Maeda, Kei-ichi, Wands, David
In this paper we examine the classical evolution of a cosmological model derived from the low-energy tree-level limit of a generic string theory. The action contains the metric, dilaton, central...
Inflationary Perturbations and Exponential Potentials (1994)
We consider the spectrum of primordial fluctuations produced by inflationary models where the inflaton potential is the sum of two exponential terms. A wide range of spectra result, with the only...
Exact Superstring Motivated Cosmological Models (1993)
We present a number of new, exact scalar field cosmologies where the potential consists of two or more exponential terms. Such potentials are motivated by supergravity or superstring models...
Calculating the Critical Temperature for Coleman-Weinberg GUTs (1992)
Easther, Richard, Moreau, William
We study the finite temperature effective potential of the Higgs scalar in GUTs with Coleman-Weinberg symmetry breaking. The critical temperature is derived without employing a high temperature...
Matchmaker, Matchmaker, Make Me a Match
Neal Bouffard, Richard Easther, Tom Johnson, Richard J. Morrison, Jan Vink
Effective marriage matching, i.e. forming specific couples from pools of potential marriage partners, is vital for the success of dynamic longitudinal microsimulation models. This paper identifies...
In this paper we examine the classical evolution of a cosmological model derived from the low-energy tree-level limit of a generic string theory. The action contains the metric, dilaton, central...