Speaker
Description
We generalize the semiclassical treatment of graviton radiation to
gravitational scattering at very large energies $\sqrt{s}\gg m_P$ and finite
scattering angles $\Theta_s$, so as to approach the collapse regime of impact
parameters $b \simeq b_c \sim R\equiv 2G\sqrt{s}$. Our basic tool is the
extension of the recently proposed, unified form of radiation to the string-based ACV
reduced-action model and to its resummed-eikonal exchange. By superimposing
that radiation all-over eikonal scattering, we are able to derive the
corresponding (unitary) coherent-state operator. The resulting graviton
spectrum, tuned on the gravitational radius $R$, fully agrees with previous
calculations for small angles $\Theta_s\ll 1$ but, for sizeable angles
$\Theta_s(b)\leq \Theta_c = O(1)$ acquires an exponential cutoff of the
large $\omega R$ region, due to energy conservation, so as to emit a finite
fraction of the total energy. In the approach-to-collapse regime of
$b\to b_c^+$ we find a radiation enhancement due to large tidal forces, so
that the whole energy is radiated off, with a large multiplicity
$\langle N \rangle \sim Gs \gg 1$ and a well-defined frequency cutoff of order $R^{-1}$.
The latter corresponds to the Hawking temperature for a black hole of mass
notably smaller than $\sqrt{s}$.
I shall also show preliminary results for collisions below the critical impact parameter ($b < b_c$) where a classical collapse is expected, but a quantum-mechanical mechanism can avoid or reduce information loss.
