# Quasilocal mass and multipole expansion in scalar-tensor gravity

## TL;DR

This paper extends the concept of quasilocal mass to scalar-tensor gravity and compares it with multipole expansions, confirming that the quasilocal mass at infinity aligns with the monopole term, supporting its validity.

## Contribution

It generalizes the Hawking-Hayward quasilocal mass to scalar-tensor gravity and demonstrates its consistency with multipole expansion at spatial infinity.

## Key findings

- Quasilocal mass at infinity matches the monopole term.
- The generalized quasilocal mass aligns with multipole expansion.
- Supports the validity of the quasilocal mass in scalar-tensor gravity.

## Abstract

A generalization of the Hawking-Hayward quasilocal mass to scalar-tensor gravity is compared, in vacuo and for asymptotically flat stationary geometries, with a recent multipole expansion of the gravitational field. The quasilocal mass seen at spatial infinity coincides with the monopole term, lending credibility to this construct.