Scalar Bremsstrahlung in Gravity-Mediated Ultrarelativistic Collisions

Classical bremsstrahlung of a massless scalar field $\mathrm{\Phi }$ is 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 $\mathrm{\Phi }-$energy is found to be strongly enhanced by a $d-$dependent power of the Lorentz factor $\gamma$. 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 $\mathrm{\Phi }-\mathrm{\Phi }-graviton$ interaction in the frequency regime $\gamma \mathrm{/}b\lesssim \omega \lesssim {\gamma }^2\mathrm{/}b$ in all dimensions.