Generalized Ward identity and gauge invariance of the   color-superconducting gap
  We derive a generalized Ward identity for color-superconducting quark matter via the functional integral approach. The identity implies the gauge independence of the color-superconducting gap parameter on the quasi-particle mass shell to subleading order in covariant gauge. 
Defu Hou (Frankfurt U. & Huazhong Normal U.), Qun Wang (Frankfurt U. &   Shangdong U.) and Dirk H. Rischke (Frankfurt U.)