paper

Mapping relativistic to ultra/non-relativistic conformal symmetries in 2D and finite deformations

arXiv:2106.09750 · doi:10.1007/JHEP11(2021)133

Abstract

The conformal symmetry algebra in 2D (Diff()Diff()) is shown to be related to its ultra/non-relativistic version (BMSGCA) through a nonlinear map of the generators, without any sort of limiting process. For a generic classical CFT, the BMS generators then emerge as composites built out from the chiral (holomorphic) components of the stress-energy tensor, and , closing in the Poisson brackets at equal time slices. Nevertheless, supertranslation generators do not span Noetherian symmetries. BMS becomes a bona fide symmetry once the CFT is marginally deformed by the addition of a term to the Hamiltonian. The generic deformed theory is manifestly invariant under diffeomorphisms and local scalings, but it is no longer a CFT because its energy and momentum densities fulfill the BMS algebra. The deformation can also be described through the original CFT on a curved metric whose Beltrami differentials are determined by the variation of the deformed Hamiltonian with respect to and . BMS symmetries then arise from deformed conformal Killing equations, corresponding to diffeomorphisms that preserve the deformed metric and stress-energy tensor up to local scalings. As an example, we briefly address the deformation of free bosons, which coincides with ultra-relativistic limits only for . Furthermore, Cardy formula and the S-modular transformation of the torus become mapped to their corresponding BMS (or flat) versions.

18 pages. Minor changes, typos corrected and references added

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