Doppler shifted Hawking radiation from acoustic black holes in ultra-relativistic heavy-ion collisions

Abstract

In a hydrodynamic flow, with flow becoming supersonic at some point, the subsonic-supersonic boundary behaves as the horizon of a black hole. Possibility of detecting Hawking radiation from such acoustic black holes has been investigated in a variety of laboratory systems, ranging from cold atom systems, to condensed matter systems with hydrodynamic flow of electrons, to relativistic heavy-ion collisions (at relatively lower collision energies). Ultra-relativistic heavy-ion collisions, with boost-invariant longitudinal flow of the quark-gluon plasma (QGP) in a wide rapidity window has eluded this remarkable possibility because in this case the black hole horizon is dynamical, moving away from center with sound velocity, leading to infinite red shift of Hawking radiation. We show here that such a conclusion is premature. The QGP flow at very large rapidities, necessarily deviates from Bjroken boost invariant flow. Due to this, an observer close to that region sees black hole horizon with a finite redshift. It leads to non-trivial prediction of Hawking radiation affecting particle momentum distributions for a window of rapidities, leaving near central rapidity regions unaffected.