S-parameter at Non-Zero Temperature and Chemical Potential

Understand

We compute the finite-temperature and matter density corrections to the S-parameter at the one loop level.

• At non-zero temperature T and matter density Lorentz symmetry breaks and therefore we suggest a suitable generalization of the S-parameter.
• By computing the plasma correction, we discover a reduction of the S-parameter in the physically relevant region of small external momenta for any non-zero chemical potential and T.
• In particular, the S-parameter vanishes at small m/T, where m is the mass of the fermions, due to the finite extent of the temporal direction.