The ultrarelativistic limit of Kerr

Tim Adamo, Andrea Cristofoli*, Piotr Tourkine

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

The massless (or ultrarelativistic) limit of a Schwarzschild black hole with fixed energy was determined long ago in the form of the Aichelburg-Sexl shockwave, but the status of the same limit for a Kerr black hole is less clear. In this paper, we explore the ultrarelativistic limit of Kerr in the class of Kerr-Schild impulsive pp-waves by exploiting a relation between the metric profile and the eikonal phase associated with scattering between a scalar and the source of the metric. This gives a map between candidate metrics and tree-level, 4-point scattering amplitudes. At large distances from the source, we find that all candidates for the massless limit of Kerr in this class do not have spin effects. This includes the metric corresponding to the massless limit of the amplitude for gravitational scattering between a scalar and a massive particle of infinite spin. One metric, discovered by Balasin and Nachbagauer, does have spin and finite size effects at short distances, leading to a remarkably compact scattering amplitude with many interesting properties. We also discuss the classical single copy of the ultrarelativistic limit of Kerr in electromagnetism.

Original languageEnglish
Article number107
Journal Journal of High Energy Physics
Issue number2
Publication statusPublished - 10 Feb 2023

Keywords / Materials (for Non-textual outputs)

  • Classical Theories of Gravity
  • Scattering Amplitudes


Dive into the research topics of 'The ultrarelativistic limit of Kerr'. Together they form a unique fingerprint.

Cite this