Stability of multi-field cosmological solutions in the presence of a fluid

TL;DR

This paper investigates the stability of multi-field cosmological solutions with a perfect fluid, finding that the stability criterion remains unchanged from the fluid-free case and no new fluid-related instabilities occur in relevant scenarios.

Contribution

It demonstrates that the stability condition for multiple scalar fields in identical potentials remains the same with or without a perfect fluid, and rules out new fluid-induced instabilities in cosmological models.

Findings

Stability condition is d^2V_i/dφ_i^2 > 0, same as without fluid.

No new instabilities associated with the fluid are found.

Results are relevant for assisted quintessence cosmological models.

Abstract

We explore the stability properties of multi-field solutions in the presence of a perfect fluid, as appropriate to assisted quintessence scenarios. We show that the stability condition for multiple fields $\phi_i$ in identical potentials $V_i$ is simply $d^2V_i/d \phi_i^2 > 0$, exactly as in the absence of a fluid. A possible new instability associated with the fluid is shown not to arise in situations of cosmological interest.