A numerical polology sampler maps ghost- and tachyon-free regions of bosonic EFT coupling spaces and finds new particle branches, including a spin-one mode in general rank-2 tensor theories.
Transverse Fierz-Pauli symmetry
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abstract
We consider some flat space theories for spin 2 gravitons, with less invariance than full diffeomorphisms. For the massless case, classical stability and absence of ghosts require invariance under transverse diffeomorphisms (TDiff). Generic TDiff invariant theories contain a propagating scalar, which disappears if the symmetry is enhanced in one of two ways. One possibility is to consider full diffeomorphisms (Diff). The other (which we denote WTDiff) adds a Weyl symmetry, by which the Lagrangian becomes independent of the trace. The first possibility corresponds to General Relativity, whereas the second corresponds to "unimodular" gravity (in a certain gauge). Phenomenologically, both options are equally acceptable. For massive gravitons, the situation is more restrictive. Up to field redefinitions, classical stability and absence of ghosts lead directly to the standard Fierz-Pauli Lagrangian. In this sense, the WTDiff theory is more rigid against deformations than linearized GR, since a mass term cannot be added without provoking the appearance of ghosts.
representative citing papers
Breaking diffeomorphism invariance to transverse diffeomorphisms in the inflaton sector yields modified slow-roll parameters and power spectra with novel post-inflationary regimes for quadratic potentials.
citing papers explorer
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Numerical polology: towards next-generation model-building for cosmology
A numerical polology sampler maps ghost- and tachyon-free regions of bosonic EFT coupling spaces and finds new particle branches, including a spin-one mode in general rank-2 tensor theories.
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Inflation in theories with broken diffeomorphisms
Breaking diffeomorphism invariance to transverse diffeomorphisms in the inflaton sector yields modified slow-roll parameters and power spectra with novel post-inflationary regimes for quadratic potentials.