  An analytical study of the return time distribution of extreme events for
stochastic processes with power-law correlation has been carried on. The
calculation is based on an epsilon-expansion in the correlation exponent:
C(t)=|t|^{-1+epsilon}. The fixed point of the theory is associated with
stretched exponential scaling of the distribution; analytical expressions,
valid in the pre-asymptotic regime, have been provided. Also the permanence
time distribution appears to be characterized by stretched exponential scaling.
The conditions for application of the theory to non-Gaussian processes have
been analyzed and the relations with the issue of return times in the case of
multifractal measures have been discussed.
