Effect of the Trace Anomaly on the Cosmological Constant

TL;DR

This paper demonstrates through semiclassical analysis that the quantum trace anomaly does not influence the classical de Sitter attractor, thus not providing a solution to the cosmological constant problem.

Contribution

The study shows that the quantum trace anomaly does not affect the late-time de Sitter attractor, challenging previous ideas that it could solve the cosmological constant problem.

Findings

Trace anomaly does not alter the classical de Sitter attractor.

Quantum trace anomaly driven attractors are unstable when classical attractors are stable.

The analysis rules out the trace anomaly as a solution to the cosmological constant problem.

Abstract

It has been argued that the quantum (conformal) trace anomaly could potentially provide us with a dynamical explanation of the cosmological constant problem. In this paper, however, we show by means of a semiclassical analysis that the trace anomaly does not affect the cosmological constant. We construct the effective action of the conformal anomaly for flat FLRW spacetimes consisting of local quadratic geometric curvature invariants. Counterterms are thus expected to influence the numerical value of the coefficients in the trace anomaly and we must therefore allow these parameters to vary. We calculate the evolution of the Hubble parameter in quasi de Sitter spacetime, where we restrict our Hubble parameter to vary slowly in time, and in FLRW spacetimes. We show dynamically that a Universe consisting of matter with a constant equation of state, a cosmological constant and the quantum trace anomaly evolves either to the classical de Sitter attractor or to a quantum trace anomaly driven one. When considering the trace anomaly truncated to quasi de Sitter spacetime, we find a region in parameter space where the quantum attractor destabilises. When considering the exact expression of the trace anomaly, a stability analysis shows that whenever the trace anomaly driven attractor is stable, the classical de Sitter attractor is unstable, and vice versa. Semiclassically, the trace anomaly does not affect the classical late time de Sitter attractor and hence it does not solve the cosmological constant problem.