Invertible disformal transformations with arbitrary higher-order derivatives

TL;DR

This paper introduces a generalized class of invertible disformal transformations involving higher-order derivatives, enabling the construction of more comprehensive ghost-free scalar-tensor theories that maintain consistent matter coupling.

Contribution

It develops a novel, more general form of invertible disformal transformations with higher derivatives, expanding the landscape of ghost-free scalar-tensor theories.

Findings

New class of ghost-free scalar-tensor theories derived

Matter fields can be coupled without extra degrees of freedom

Enhanced theoretical framework for scalar-tensor modifications

Abstract

Invertible disformal transformations serve as a useful tool to explore ghost-free scalar-tensor theories. In this paper, we construct a generalization of invertible disformal transformations that involves arbitrary higher-order covariant derivatives of the scalar field. As a result, we obtain a more general class of ghost-free scalar-tensor theories than ever. Notably, our generalization is such that matter fields can be consistently coupled to these theories without introducing an unwanted extra degree of freedom in the unitary gauge.