Positivity bounds on effective field theories with spontaneously broken Lorentz invariance

Understand

We derive positivity bounds on EFT coefficients in theories where boosts are spontaneously broken.

• We employ the analytic properties of the retarded Green's function of conserved currents (or of the stress-energy tensor) and assume the theory becomes conformal in the UV.
• The method is general and applicable to both cosmology and condensed matter systems.
• As a concrete example, we look at the EFT of conformal superfluids which describes the universal low-energy dynamics of CFT's at large chemical potential and we derive inequalities on the coefficients of the operators, in three dimensions, at NLO and NNLO.