Isocurvature Perturbations in Quintessence Cosmologies

TL;DR

This paper systematically analyzes the initial conditions and evolution of cosmological perturbations in universes with quintessence, identifying the dominant modes and concluding that quintessence does not introduce new independent perturbation modes.

Contribution

It provides a matrix-based formulation of perturbation evolution and clarifies the role of quintessence in cosmological initial conditions.

Findings

Identifies four dominant early-time modes: adiabatic, CDM isocurvature, baryon isocurvature, neutrino isocurvature.

Shows quintessence does not add new independent perturbation modes.

Uses eigenvalue analysis to characterize perturbation evolution.

Abstract

We present a systematic treatment of the initial conditions and evolution of cosmological perturbations in a universe containing photons, baryons, neutrinos, cold dark matter, and a scalar quintessence field. By formulating the evolution in terms of a differential equation involving a matrix acting on a vector comprised of the perturbation variables, we can use the familiar language of eigenvalues and eigenvectors. As the largest eigenvalue of the evolution matrix is fourfold degenerate, it follows that there are four dominant modes with non-diverging gravitational potential at early times, corresponding to adiabatic, cold dark matter isocurvature, baryon isocurvature and neutrino isocurvature perturbations. We conclude that quintessence does not lead to an additional independent mode.