  In many situations a BCS-type superconductor will develop an imbalance
between the populations of the holelike and electronlike spectral branches.
This imbalance suppresses the gap. It has been noted by Gal'perin et al. [Sov.
Phys. JETP 54, 1126 (1981)] that at large imbalance, when the gap is
substantially suppressed, an instability develops. The analytic treatment of
the system beyond the instability point is complicated by the fact that the
Boltzmann approach breaks down. We study the short-time behavior following the
instability, in the collisionless regime, using methods developed by Yuzbashyan
et al. [J. Phys. A 38, 7831 (2005); Phys. Rev. B 72, 220503(R) (2005)].
