Scalar Gravitational Waves in the Effective Theory of Gravity

TL;DR

This paper explores how quantum effects modify classical gravity, predicting scalar gravitational waves that could be emitted by neutron star mergers, expanding the understanding of gravitational wave phenomena.

Contribution

It introduces scalar gravitational wave solutions within the effective field theory of gravity, highlighting their properties and potential astrophysical sources.

Findings

Scalar waves coexist with tensor waves in the effective theory.

Scalar wave amplitudes and energy flux are positive and monopole in nature.

Neutron star mergers with gluonic condensates are promising sources.

Abstract

As a low energy effective field theory, classical General Relativity receives an infrared relevant modification from the conformal trace anomaly of the energy-momentum tensor of massless, or nearly massless, quantum fields. The local form of the effective action associated with the trace anomaly is expressed in terms of a dynamical scalar field that couples to the conformal factor of the spacetime metric, allowing it to propagate over macroscopic distances. Linearized around flat spacetime, this semi-classical EFT admits scalar gravitational wave solutions in addition to the transversely polarized tensor waves of the classical Einstein theory. The amplitude of the scalar wave modes, as well as their energy and energy flux which are positive and contain a monopole moment, are computed. Astrophysical sources for scalar gravitational waves are considered, with the excited gluonic condensates in the interiors of neutron stars in merger events with other compact objects likely to provide the strongest burst signals.