  In this paper we will study quantum field theory of fluctuation modes around
the rolling tachyon solution on non-BPS D-brane effective action. The goal of
this paper is to study particle production during the decay of non-BPS D-brane
and explore possible relation with minisuperspace calculation. We find that the
number of particles produced on half S-brane exponentially grows for large time
which suggests that linearised approximation breaks down and also that
backreaction of fluctuation field on classical solution should be taken into
account.
