Abstract
Gravitational shockwaves are simple exact solutions of Einstein equations representing the fields of ultrarelativistic sources and idealized gravitational waves (shocks). Historically, much work has focused on shockwaves in the context of possible black hole formation in high energy particle collisions, yet they remain at the forefront of research even today. Representing hard modes in the bulk, shocks give rise to the gravitational memory effect at the classical level and implant supertranslation (BMS) hair onto a classical spacetime at the quantum level. The aim of this paper is to further our understanding of the ‘information content’ of such supertranslations. Namely, we show that, contrary to the several claims in the literature, a gravitational shockwave does leave a quantum imprint on the vacuum state of a test quantum field and that this imprint is accessible to local observers carrying Unruh-DeWitt (UDW) detectors in this spacetime.
Highlights
Theorems [6,7,8], and supertranslation asymptotic symmetries [9,10,11,12,13,14,15,16,17]: the so-called IR triangle
Much work has focused on shockwaves in the context of possible black hole formation in high energy particle collisions, yet they remain at the forefront of research even today
Therein, the Bogoliubov coefficients were shown to have physical manifestation only for non-vacuum states of the field; in particular, it was shown that the vacuum expectation values of the number operators associated to both Minkowski and Rindler observers are not altered by the shockwave
Summary
Theorems [6,7,8], and supertranslation asymptotic symmetries [9,10,11,12,13,14,15,16,17]: the so-called IR triangle. 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. New effects such as the anti-Unruh and anti-Hawking effects, only accessible to local and finite time interaction observers, have been observed within this framework [55,56,57,58]
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