Super-Hawking radiation

Abstract

We discuss modifications to the Hawking spectrum that arise when the asymptotic states are supertranslated or superrotated. For supertranslations we find nontrivial off-diagonal phases in the two-point correlator although the emission spectrum is eventually left unchanged, as previously pointed out in the literature. In contrast, superrotations give rise to modifications which manifest themselves in the emission spectrum and depend nontrivially on the associated conformal factor at future null infinity. We study Lorentz boosts and a class of superrotations whose conformal factors do not depend on the azimuthal angle on the celestial sphere and whose singularities at the north and south poles have been associated to the presence of a cosmic string. In spite of such singularities, superrotations still lead to finite spectral emission rates of particles and energy which display a distinctive power-law behavior at high frequencies for each angular momentum state. The integrated particle emission rate and emitted power, on the contrary, while finite for boosts, do exhibit ultraviolet divergences for superrotations, between logarithmic and quadratic. Such divergences can be ascribed to modes with support along the cosmic string. In the logarithimic case, corresponding to a superrotation which covers the sphere twice, the total power emitted still presents the Stefan-Boltzmann form but with an effective area which diverges logarithmically in the ultraviolet.

Quantum imprints of gravitational shockwaves

“…Hence the Unruh radiation spectrum is left invariant under these shockwaves -only excited states directly see the effect of the profile. Similar results were also obtained for Hawking radiation, see [35].…”

“…In this paper we show that, contrary to the conclusions of [33][34][35], a gravitational shockwave does leave a quantum imprint on the vacuum state of a test quantum scalar field, and, this imprint is accessible to local observers carrying UDW detectors in the shockwave spacetime. Namely, we show that the Wightman function contains an additional term that depends on the shockwave profile and that this term is nonzero between two spacetime events that are located on different sides of the shockwave null plane.…”

“…In summary, the studies [33][34][35] have reached the same conclusion: for asymptotic vacua both Unruh and Hawking spectra are unchanged by the presence of gravitational shockwaves, and, while gravitational shockwaves can leave imprints on test quantum fields, this will only happen for non-vacuum states. It is the purpose of the present paper to refute this last conclusion.…”

“…Similar questions have been investigated by a number of recent studies [32][33][34][35]. Our work is mainly motivated by [33,34] where the authors studied the impact of a 'matter induced' supertranslation on the Bogoliubov coefficients between the two asymptotic states.…”

“…However, since there is no localized number operator that agrees with the global number operator for the vacuum state, the Bogoliubov coefficients are arguably not a true local observable in this context, a result deeply connected to the Reeh-Schlieder theorem, see [36][37][38][39][40][41] for further discussions. Therefore, the results obtained in [32,33,35] are global results that no localized observers can easily access. The method employed in [34] is more suitable for local calculations, since it relies on a computation of the Wightman function of the quantum field on the shockwave background, which is known to be accessible to local observers, e.g.…”