Comparing models for a unitary black hole S-matrix

TL;DR

This paper compares different models of the black hole S-matrix, focusing on recent nonisometric models and nonviolent unitarization, analyzing their features, challenges, and implications for black hole evolution.

Contribution

It provides a comparative analysis of nonisometric and nonviolent unitarization models using qubit representations, highlighting their differences and unresolved issues.

Findings

Nonisometric models pose puzzles for internal excitation evolution.

Qubit models effectively illustrate nonviolent unitarization features.

Remaining questions involve extending models for comprehensive evolution understanding.

Abstract

This paper compares features, challenges, and puzzles of different models for a unitary black hole S-matrix, focussing on both recent nonisometric models, as well as "nonviolent unitarization," which is based on new quantum interactions of a black hole. As a foundation for comparison, the description of real-time Hawking evolution is first overviewed, including leading effects of gravitational dressing and backreaction. Connection is then made to qubit models for evolution, and some technology is outlined to facilitate their description. Important features of both nonisometric models and nonviolent unitarization are investigated in qubit models, which illustrate essential differences between the respective approaches. The nonisometric models present puzzles for understanding evolution of internal outgoing excitations, which can be excited by interactions such as particle decay. Qubit models for nonviolent unitarization are further developed, and nicely illustrate aspects of that approach. Some remaining questions in generalizing to more complete models for evolution are discussed.