Cosmological Topologically Massive Gravitons and Photons

TL;DR

This paper investigates topologically massive gravity in (2+1) dimensions with a negative cosmological constant, revealing a single bulk degree of freedom with chiral splitting and connections to Chern--Simons theories and boundary conformal field theories.

Contribution

It provides a detailed analysis of the mass spectrum, wave solutions, and the relationship between topologically massive gravity and electromagnetism at critical couplings.

Findings

Masses of excitations are split by chirality.

Existence of a single positive-energy bulk degree of freedom.

Equivalence to electromagnetism at critical couplings.

Abstract

We study topologically massive (2+1)-dimensional gravity with a negative cosmological constant. The masses of the linearized curvature excitations about AdS_3 backgrounds are not only shifted from their flat background values but, more surprisingly, split according to chirality. For all finite values of the topological mass, we find a single bulk degree of freedom with positive energy, and exhibit a complete set of normalizable, finite-energy wave packet solutions. This model can also be written as a sum of two higher-derivative SL(2,R) Chern--Simons theories, weighted by the central charges of the boundary conformal field theory. At two particular "critical" values of the couplings, one of these central charges vanishes, and linearized topologically massive gravity becomes equivalent to topologically massive electromagnetism; however, the physics of the bulk wave packets remains unaltered here.