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Bayesian Limits on Primordial Isotropy Breaking
C. Armendariz-Picon, Larne Pekowsky
It is often assumed that primordial perturbations are statistically isotropic, which implies, among other properties, that their power spectrum is invariant under rotations. In thi…
Creating Statistically Anisotropic and Inhomogeneous Perturbations
C. Armendariz-Picon
In almost all structure formation models, primordial perturbations are created within a homogeneous and isotropic universe, like the one we observe. Because their ensemble averages…
Why should primordial perturbations be in a vacuum state?
C. Armendariz-Picon
In order to calculate the power spectrum generated during a stage of inflation, we have to specify the quantum state of the inflaton perturbations, which is conventionally assumed…
Near Scale Invariance with Modified Dispersion Relations
C. Armendariz-Picon
We describe a novel mechanism to seed a nearly scale invariant spectrum of adiabatic perturbations during a non-inflationary stage. It relies on a modified dispersion relation that…
Footprints of Statistical Anisotropies
C. Armendariz-Picon
We propose and develop a formalism to describe and constrain statistically anisotropic primordial perturbations. Starting from a decomposition of the primordial power spectrum in s…
Haloes of k-Essence
C. Armendariz-Picon, Eugene A. Lim
We study gravitationally bound static and spherically symmetric configurations of k-essence fields. In particular, we investigate whether these configurations can reproduce the pro…
Non-Adiabatic Perturbations from Single-Field Inflation
C. Armendariz-Picon
If the inflaton decays into several components during reheating, and if the corresponding decay rates are functions of spacetime-dependent quantities, it is possible to generate en…
Liberating the Inflaton from Primordial Spectrum Constraints
C. Armendariz-Picon
I discuss a mechanism that renders the spectral index of the primordial spectrum and the inflationary stage independent of each other. If a scalar field acquires an appropriate tim…
Scale Invariance without Inflation?
C. Armendariz-Picon, Eugene A. Lim
We propose a new alternative mechanism to seed a scale invariant spectrum of primordial density perturbations that does not rely on inflation. In our scenario, a perfect fluid domi…
Predictions and Observations in Theories with Varying Couplings
C. Armendariz-Picon
We consider a toy universe containing conventional matter and an additional real scalar field, and discuss how the requirements of gauge and diffeomorphism invariance essentially s…
Measuring the Speed of Sound of Quintessence
Joel K. Erickson, R. R. Caldwell, Paul J. Steinhardt +2
Quintessence, a time-varying energy component that may account for the accelerated expansion of the universe, can be characterized by its equation of state and sound speed. In this…
Essentials of k-essence
C. Armendariz-Picon, V. Mukhanov, Paul J. Steinhardt
We recently introduced the concept of "k-essence" as a dynamical solution for explaining naturally why the universe has entered an epoch of accelerated expansion at a late stage of…
A Dynamical Solution to the Problem of a Small Cosmological Constant and Late-time Cosmic Acceleration
C. Armendariz-Picon, V. Mukhanov, Paul J. Steinhardt
Increasing evidence suggests that most of the energy density of the universe consists of a dark energy component with negative pressure, a ``cosmological constant" that causes the…