The geometry of null-like disformal transformations

TL;DR

This paper explores how null-like disformal transformations affect geometric objects and symmetries in spacetime, revealing non-diagonalizable operators and implications for metric compatibility.

Contribution

It provides a detailed analysis of null-like disformal transformations, including their impact on geometric structures, symmetries, and the disformal operator's properties.

Findings

Disformal transformations alter geometric objects in null-like directions.

The disformal operator is not diagonalizable in the null-like case.

Introduction of disformal Killing vector fields and analysis of symmetry properties.

Abstract

Motivated by the hindrance of defining metric tensors compatible with the underlying spinor structure, other than the ones obtained via a conformal transformation, we study how some geometric objects are affected by the action of a disformal transformation in the closest scenario possible: the disformal transformation in the direction of a null-like vector field. Subsequently, we analyze symmetry properties such as mutual geodesics and mutual Killing vectors, generalized Weyl transformations that leave the disformal relation invariant, and introduce the concept of disformal Killing vector fields. In most cases, we use the Schwarzschild metric, in the Kerr-Schild formulation, to verify our calculations and results. We also revisit the disformal operator using a Newman-Penrose basis to show that, in the null-like case, this operator is not diagonalizable.