Coherent state path integral and super-symmetry for condensates composed of bosonic and fermionic atoms

TL;DR

This paper develops a super-symmetric path integral framework for bosonic and fermionic atoms, deriving effective equations for condensates and analyzing symmetries and Goldstone modes in a unified formalism.

Contribution

It introduces a super-symmetric coherent state path integral for mixed atom condensates and derives nonlinear sigma model equations with symmetry considerations.

Findings

Derived effective equations for molecular and BCS condensates.

Performed a coset decomposition simplifying the path integral measure.

Established a formalism unifying bosonic and fermionic condensate descriptions.

Abstract

A super-symmetric coherent state path integral on the Keldysh time contour is considered for bosonic and fermionic atoms which interact among each other with a common short-ranged two-body potential. We investigate the symmetries of Bose-Einstein condensation for the equivalent bosonic and fermionic constituents and specialize on the examination of super-symmetries for pair condensate terms. A Hubbard-Stratonovich transformation from 'Nambu'-doubled super-fields leads to a generating function with super-matrices for the self-energy whose manifold is given by the ortho-symplectic super-group Osp(S,S|2L). Effective equations are derived for anomalous terms which are related to the molecular- and BCS- condensate pairs. A change of integration measure for the coset decomposition Osp(S,S|2L)/U(L|S)xU(L|S) is performed, including a separation of density and anomalous parts of the self-energy with a gradient expansion for the Goldstone modes. The independent anomalous fields in the actions can be transformed by the inverse square root of the metric tensor of Osp(S,S|2L)/U(L|S) so that the coset integration measure with the super-Jacobi-determinant can be removed from the coherent state path integral and Gaussian-like integrations remain. The variations of the independent coset fields in the effective actions result in classical field equations for a nonlinear sigma model with the anomalous terms.