Effective theory of excitations in a Feshbach resonant superfluid

TL;DR

This paper develops an effective field theory for Feshbach resonant superfluids, capturing fermionic quasiparticles and phonons, and explains experimental heat capacity data through a non-perturbative approach.

Contribution

It introduces a convergent, order-by-order effective field theory for resonant superfluids that includes both quasiparticles and phonons with non-perturbative interactions.

Findings

Calculated specific heat using the effective theory.

Proposed a mechanism for the empirical power law of energy versus temperature.

The theory converges and improves systematically via low energy expansion.

Abstract

A strongly interacting Fermi gas, such as that of cold atoms operative near a Feshbach resonance, is difficult to study by perturbative many-body theory to go beyond mean field approximation. Here I develop an effective field theory for the resonant superfluid based on broken symmetry. The theory retains both fermionic quasiparticles and superfluid phonons, the interaction between them being derived non-perturbatively. The theory converges and can be improved order by order, in a manner governed by a low energy expansion rather than by coupling constant. I apply the effective theory to calculate the specific heat and propose a mechanism of understanding the empirical power law of energy versus temperature recently measured in a heat capacity experiment.