Toroidal tidal effects in microstate geometries

Abstract

Tidal effects in capped geometries computed in previous literature display no dynamics along internal (toroidal) directions. However, the dual CFT picture suggests otherwise. To resolve this tension, we consider a set of infalling null geodesics in a family of black hole microstate geometries with a smooth cap at the bottom of a long BTZ-like throat. Using the Penrose limit, we show that a string following one of these geodesics feels tidal stresses along all spatial directions, including internal toroidal directions. We find that the tidal effects along the internal directions are of the same order of magnitude as those along other, non-internal, directions. Furthermore, these tidal effects oscillate as a function of the distance from the cap — as a string falls down the throat it alternately experiences compression and stretching. We explain some physical properties of this oscillation and comment on the dual CFT interpretation.

Fuzzballs and Microstate Geometries: Black-Hole Structure in String Theory

“…While these calculations are done in microstate geometries of black holes that are far from real-world black holes, some of the physics they reveal could be universal, and characterize horizon-scale structure of generic black holes. Some of these calculations will be greatly modified by another remarkable feature of microstate-geometry physics: tidal scrambling [193,[204][205][206][207].…”

“…As a result of these tidal forces, the supergravity approximation can break down. In string theory, particle probes are actually strings whose oscillator modes are in their ground state; when the tidal forces exceed the string scale, these oscillator modes become excited [206,207]. Such excitations give the string a nonzero mass, and the energy comes from the kinetic energy of the probe.…”

“…Geodesic [193,204,205,205] and string-probe [206,207] analyses have revealed that tidal forces become large in microstate geometries and that this results in string excitations that causes tidal trapping of probes. This is an important first step in understanding the scrambling process in microstate geometries.…”

“…One would also like to understand the processes by which tidally trapped probes of microstate geometries [206,207] thermalize. There are two scales here: the curvature of the geometry controls the scattering and thermalization of vibrational modes on a given string, while the string coupling governs the rate at which excited strings split and join, as well as radiate supergravitons into the ambient geometry.…”

Real-time holography and hybrid WKB for BTZ wormholes

“…Echoes in supersymmetric microstate geometries have been analyzed in [43]; these results suggest that as the microstructure becomes more compact (making the microstate more typical), the echoes become more suppressed and washed out (as also argued in [44]). See also [45,46] for a discussion of how additional stringy tidal effects can excite heavy string modes to delay and smear echoes significantly, even in a coherent, atypical microstate.…”