Effect of the trace anomaly on the cosmological constant

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.PACS numbers: 98.80.-k, 04.62.+v, 95.36.+x

Late-time quantum backreaction from inflationary fluctuations of a nonminimally coupled massless scalar

“…Indeed, at the classical level, photons couple conformally to gravity and hence their quantum backreaction can be treated as that of any conformally coupled field. The quantum backreaction of conformal fields can be represented by local higher-derivative curvature terms, and a general study [40] shows that their late-time backreaction is completely negligible. However, when one includes couplings of gauge fields to other fields such as (light) massless scalars, a significant photon production during inflation is in fact possible [41,42], making a detailed study of the late-time backreaction from gauge fields worthwhile.…”

Dynamics driven by the Trace Anomaly in FLRW Universes

“…The two asymptotes divide this graph into three distinct regions that are not connected for finite time evolution. The region bounded by the two asymptotes contains initial conditions for H(t) such that H(t) grows for late times towards H A 0 and initial conditions such that H(t) asymptotes to the de Sitter attractor H C 0 , separated by a branching point [1]:…”

“…This paper aims at summarising the main results of [1], as presented at the "Invisible Universe Conference" in Paris (2009). We show that the cosmological constant problem is not solved by the trace anomaly.…”

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