  Recent scenarios of the TeV-scale brane cosmology suggest a possibility of
existence in the early universe of two-dimensional topological defects:
relativistic membranes. Like cosmic strings, oscillating membranes could emit
gravitational radiation contributing to a stochastic background of
gravitational waves. We calculate dilaton and gravitational radiation from a
closed toroidal membrane excited along one homology cycle. The spectral-angular
distributions of dilaton and gravitational radiation are obtained in a closed
form in terms of Bessel's functions. The angular distributions are affected by
oscillating factors due to an interference of radiation from different segments
of the membrane. The dilaton radiation power is dominated by a few lower
harmonics of the basic frequency, while the spectrum of the gravitational
radiation contains also a substantial contribution from higher harmonics. The
radiative lifetime of the membrane is determined by its tension and depends
weakly on the ratio of two radii of the torus. Qualitatively it is equal to the
ratio of the membrane area at the maximal extension to the gravitational radius
of the membrane as a whole.
