*Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow,119992 , Russia*\

Introduction
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Brane-world scenarios with a 3-brane identified with the observable Universe which is embedded in a higher-dimensional space-time provide an alternative to the standard 4D cosmology [@BDL1; @BDL2; @kraus; @col; @maeda], reviews [@rubrev; @maart; @durrer]. A necessary requirement on these models is that they should reproduce the main observational cosmological data, the age of the Universe, abundances of elements produced in primordial nucleosynthesis, etc. A general property of the models with extra dimensions is that gravity propagates in the extra dimensions independent of whether the ordinary matter is confined to the brane or not. This entails a peculiar property of the models with extra dimensions which is absent in the standard cosmology: gravitons which are produced in reactions of particles of matter on the brane can escape from the brane and propagate in the bulk [@tan; @heb; @lan1; @lan2; @rusdur; @kir]. As a consequence the Einstein equations contain terms accounting for the graviton emission. Cosmological evolution of matter on the brane is also affected by this process.

Roughly the energy loss on the brane due to the process $a+b\rightarrow G +X$ can be estimated as $$\f{d\h{\r}}{dt}=-<n_a n_b \s_{a+b\rightarrow 