The Trace Anomaly and Dynamical Vacuum Energy in Cosmology

TL;DR

This paper explores how the trace anomaly introduces massless scalar fields affecting gravity at large scales, leading to a dynamical vacuum energy that depends on boundary conditions rather than ultraviolet physics.

Contribution

It demonstrates that the trace anomaly induces scalar degrees of freedom that modify Einstein's equations, resulting in a dynamical vacuum energy in cosmology.

Findings

Trace anomaly leads to long-range scalar effects in gravity.

Vacuum energy becomes boundary-condition dependent.

Quantum effects influence cosmological constant dynamics.

Abstract

The trace anomaly of conformal matter implies the existence of massless scalar poles in physical amplitudes involving the stress-energy tensor. These poles may be described by a local effective action with massless scalar fields, which couple to classical sources, contribute to gravitational scattering processes, and can have long range gravitational effects at macroscopic scales. In an effective field theory approach, the effective action of the anomaly is an infrared relevant term that should be added to the Einstein-Hilbert action of classical General Relativity to take account of macroscopic quantum effects. The additional scalar degrees of freedom contained in this effective action may be understood as responsible for both the Casimir effect in flat spacetime and large quantum backreaction effects at the horizon scale of cosmological spacetimes. These effects of the trace anomaly imply that the cosmological vacuum energy is dynamical, and its value depends on macroscopic boundary conditions at the cosmological horizon scale, rather than sensitivity to the extreme ultraviolet Planck scale.