Unitarity problems in 3D gravity theories

Gokhan Alkac, Luca Basanisi, Ercan Kilicarslan, and Bayram Tekin
Phys. Rev. D 96, 024010 – Published 11 July 2017

Abstract

We revisit the problem of the bulk-boundary unitarity clash in 2+1–dimensional gravity theories, which has been an obstacle in providing a viable dual two-dimensional conformal field theory for bulk gravity in anti–de Sitter (AdS) spacetime. Chiral gravity, which is a particular limit of cosmological topologically massive gravity (TMG), suffers from perturbative log-modes with negative energies inducing a nonunitary logarithmic boundary field theory. We show here that any f(R) extension of TMG does not improve the situation. We also study the perturbative modes in the metric formulation of minimal massive gravity—originally constructed in a first-order formulation—and find that the massive mode has again negative energy except in the chiral limit. We comment on this issue and also discuss a possible solution to the problem of negative-energy modes. In any of these theories, the infinitesimal dangerous deformations might not be integrable to full solutions; this suggests a linearization instability of AdS spacetime in the direction of the perturbative log-modes.

  • Received 28 March 2017

DOI:https://doi.org/10.1103/PhysRevD.96.024010

© 2017 American Physical Society

Physics Subject Headings (PhySH)

Gravitation, Cosmology & Astrophysics

Authors & Affiliations

Gokhan Alkac1, Luca Basanisi1, Ercan Kilicarslan2, and Bayram Tekin2

  • 1Van Swinderen Institute for Particle Physics and Gravity, University of Groningen, Nijenborgh 4, 9747 AG Groningen, Netherlands
  • 2Department of Physics, Middle East Technical University, 06800 Ankara, Turkey

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Issue

Vol. 96, Iss. 2 — 15 July 2017

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