Global Dynamics of Cosmological Expansion with Minimally Coupled Scalar Field

TL;DR

This paper analyzes the long-term behavior of a cosmological model with matter and a scalar field, identifying conditions for acceleration and classifying possible expansion regimes.

Contribution

It provides a complete classification of the asymptotic behaviors of the universe with a minimally coupled scalar field, including conditions for acceleration.

Findings

Two main types of expansion: exponential and subexponential.

Acceleration occurs when scalar field energy dominates or matter violates strong energy condition.

Constraints on matter's equation of state from Big Bang and eternal expansion.

Abstract

We give a complete description of the asymptotic behavior of a Friedmann-Robertson-Walker Universe with ``normal'' matter and a minimally coupled scalar field. We classify the conditions under which the Universe is or is not accelerating. In particular, we show that only two types of large time behavior exist: an exponential regime, and a subexponential expansion with the logarithmic derivative of the scale factor tending to zero. In the case of the subexponetial expansion the Universe accelerates when the scalar field energy density is dominant and the potential behaves in a specified manner, or if matter violates the strong energy conditon $\rho + 3p >0$. When the expansion is exponential the Universe accelerates, and the scalar field energy density is dominant. We also find that the existence of the Big Bang and a never ending expansion of the Universe constrain the equation of state of matter at large and small densities, respectively.