Scalar bremsstrahlung in gravity-mediated ultrarelativistic collisions

Classical bremsstrahlung of a massless scalar fieldis studied in gravity mediated ultra-relativistic collisions with impact parameter b of two massive point particles in the presence of d non-compact or toroidal extra dimensions. The spectral and angular distribution of the scalar radiation are analyzed, while the total emitted �−energy is found to be strongly enhanced by a d−dependent power of the Lorentz factor γ. The direct radiation amplitude from the accelerated particles is shown to interfere destructively (in the first two leading ultra-relativistic orders) with the one due to the � − � − graviton interaction in the frequency regime γ/b . ω . γ 2 /b in all dimensions.