The third way to 3D gravity
Routh, Alasdair J
International Journal of Modern Physics D
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Bergshoef, E., Merbis, W., Routh, A. J., & Townsend, P. (2015). The third way to 3D gravity. International Journal of Modern Physics D, 24 (1544015)https://doi.org/10.1142/S0218271815440150
Consistency of Einstein’s gravitational field equation Gµν ∝ Tµν imposes a “conservation condition” on the T-tensor that is satisfied by (i) matter stress tensors, as a consequence of the matter equations of motion, and (ii) identically by certain other tensors, such as the metric tensor. However, there is a third way, overlooked until now because it implies a “nongeometrical” action: one not constructed from the metric and its derivatives alone. The new possibility is exemplified by the 3D “minimal massive gravity” model, which resolves the “bulk vs boundary” unitarity problem of topologically massive gravity with anti-de Sitter asymptotics. Although all known examples of the third way are in three spacetime dimensions, the idea is general and could, in principle, apply to higher-dimensional theories.
AJR is supported by a grant from the London Mathematical Society, and he would also like to thank the University of Groningen for hospitality during the writing of this essay.
External DOI: https://doi.org/10.1142/S0218271815440150
This record's URL: https://www.repository.cam.ac.uk/handle/1810/250511