Abstract
We propose that a quantum black hole can produce a new kind of late-time gravitational echoes, facilitated by a near-horizon process analogous to Andreev reflection in condensed matter systems. In comparison to the traditional echo scenarios where the near-horizon region is treated as an ordinary reflector, we argue that, consequent to near-horizon gravitational scattering, this region is better described by an Andreev reflector. Such interactions lead to a novel contribution to gravitational echoes with a characteristic phase difference, an effect which is analogous to how Andreev reflections lead to propagating particle-like and hole-like components with a relative phase in certain condensed matter scenarios. Moreover, this novel contribution to the echo signal encodes information about the `near-horizon quantum state', hence offering a possible new window to probe the quantum nature of black holes.
Highlights
We propose that a quantum black hole can produce a new kind of late-time gravitational echoes, facilitated by a near-horizon process analogous to Andreev reflection in condensed matter systems
Such interactions lead to a novel contribution to gravitational echoes with a characteristic phase difference, an effect which is analogous to how Andreev reflections lead to propagating particlelike and holelike components with a relative phase in certain condensed matter scenarios
The idea that the quantum state of a black hole may be effectively characterized by a simple many-body quantum wave function, such as the condensate ground state of a quantum superfluid, is in harmony with the well-known fact that black holes are characterized by very few parameters in their classical rendition
Summary
For several reasons, are one of the most peculiar objects in nature. On the one hand, as mathematical constructions in general relativity (GR), they are remarkably simple in their rendition [1], while on the other, they seem to possess thermodynamic properties [2–4] which are usually ascribed to objects that have a microscopic structure. We analyze the consequence of applying a different kind of boundary condition at the event horizon where the near-horizon region is treated as an Andreev reflector [17–19,24,39] While this consideration is primarily motivated by proposals that treat an evaporating black hole as a leaking superfluid quantum condensate, such modifications may be understood as emerging from the gravitational self-interaction of test fields in the background of an evaporating black hole. When the test field is a tensor mode of perturbation, our analysis suggests a fundamentally new kind of gravitational wave echo that can be detected Such modified boundary conditions may be of relevance to exotic compact objects other than black holes such as neutron stars [40–42]. VI, we conclude by discussing the implications of our prediction for near-future gravitational observations
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