Cosmo-26

Bounds on Goldstone Dispersion Relations

Not scheduled

20m

Gorlaeus gebouw (Leiden University)

Talk Dark Energy / Modified Gravity

Speaker

Warin Patrick McBlain (SISSA)

Description

Using the analyticity properties of retarded Green's functions, we show that the Goldstone dispersion relations can be written in terms of ‘typically-real functions’: a well-known class of functions in Geometric Function Theory. This identification yields optimal two-sided bounds on Wilson coefficients of higher-derivative operators as explicit functions of the sound speed $c_s$. We test these bounds against the $U(1)$ superfluid as a controlled UV completion, finding agreement across the physical range of $c_s$ and particularly in the relativistic limit $c_s\to 1$ regime. Our framework can be applied directly to the EFT of inflation and dark energy, constraining higher-derivative operators in terms of sound speed in both settings.