Gravitational bremsstrahlung in ultra-planckian collisions

TL;DR

This paper presents a classical calculation of gravitational bremsstrahlung in ultra-planckian particle collisions across multiple dimensions, analyzing energy emission, angular distribution, and the impact of extra dimensions on radiation efficiency.

Contribution

It generalizes the post-linear formalism of General Relativity to higher dimensions and provides detailed predictions for gravitational radiation in ultra-planckian collisions.

Findings

Radiation efficiency depends on impact parameter, Lorentz factor, and number of extra dimensions.

Low frequency gravitons contribute negligibly to total energy.

Ultra-planckian collisions may be strongly damped by radiation, affecting theoretical models.

Abstract

A classical computation of gravitational bremsstrahlung in ultra-planckian collisions of massive point particles is presented in an arbitrary number d of toroidal or non-compact extra dimensions. Our method generalizes the post-linear formalism of General Relativity to the multidimensional case. The total emitted energy, as well as its angular and frequency distribution are discussed in detail. In terms of the gravitational radius r_S of the collision energy, the impact parameter b and the Lorentz factor in the CM frame, the leading order radiation efficiency in the Lab frame is shown to be of order (r_S/b)^{3(d+1)} gamma_{cm} for d=0, 1 and of order (r_S/b)^{3(d+1)} gamma_{cm}^{2d-3} for d>1, up to a known d-dependent coefficient and a ln gamma_{cm} factor for d=2, while the characteristic frequency of the radiation is gamma/b. The contribution of the low frequency part of the radiation (soft gravitons) to the total radiated energy is shown to be negligible for all values of d. The domain of validity of the classical result is discussed. Finally, it is shown that within the region of validity of our approach the efficiency can obtain unnatural values greater than one, which is interpreted to mean that the peripheral ultra-planckian collisions should be strongly radiation damped.