  We study the nucleation of a single pore in a fluctuating lipid membrane,
specifically taking into account the membrane fluctuations, as well as the
shape fluctuations of the pore. For large enough pores, the nucleation free
energy is well-described by shifts in the effective membrane surface tension
and the pore line tension. Using our framework, we derive the stability
criteria for the various pore formation regimes. In addition to the well-known
large-tension regime from the classical nucleation theory of pores, we also
find a low-tension regime in which the effective line and surface tensions can
change sign from their bare values. The latter scenario takes place at
sufficiently high temperatures, where the opening of a stable pore of finite
size is entropically favorable.
