Emerging links between gravity and condensed matter physics: a new kind of echo from quantum black holes

by Dr Sreenath K Manikandan (Nordita)

Thursday 31 Mar 2022, 13:00 → 15:00 Europe/Stockholm

AlbaNova C4:3059 - Café Planck (AlbaNova Main Building)

In this talk, we briefly review the framework of observing echoes from a black hole spacetime, in the ringdown phase of a binary black hole merger event. Subsequently, we discuss the possible emergence of a new kind of echo from black hole horizons, when the near-horizon gravitational scattering of test fields are accounted for. We argue that such considerations should modify the reflectivity of the near horizon region by acquiring an Andreev reflecting property, by making an analogy to the well known physics of superfluid (superconductor)/normal fluid (metal) junctions in condensed matter physics. The modified reflectivity leads to a new 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, the Andreev 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 hole horizons through gravitational wave observations. We conclude by briefly discussing the limitations of our proposal and the prospects of observing them in near-future gravitational wave observations. 

Reference: Manikandan, Sreenath K., and Karthik Rajeev. "New kind of echo from quantum black holes." Physical Review D 105.6 (2022): 064024.