# Neutron star mergers as a probe of modifications of general relativity with finite-range scalar forces

**Authors:** Laura Sagunski, Jun Zhang, Matthew C. Johnson, Luis Lehner, Mairi Sakellariadou, Steven L. Liebling, Carlos Palenzuela, David Neilsen  
**arXiv:** [1709.06634](https://arxiv.org/abs/1709.06634)  
**Date:** 2017-09-19  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/1709.06634v1/

## Key points

- Gravitational radiation from binary neutron star mergers can provide constraints on finite-range forces from a universally coupled massive scalar field
- Scalar degrees of freedom are often found in extensions of General Relativity
- Metric $f(R)$ gravity is equivalent to General Relativity and includes a universally coupled scalar field with a non-linear potential determined by the choice of $f(R)$
- Neutron stars or other compact objects with significant scalar charge experience an attractive finite-range scalar force that affects both the inspiral and merger phases of binary systems
- The authors analyze the inspiral dynamics in the Newtonian limit and forecast constraints on the mass of the scalar and charge of compact objects using data from Advanced LIGO
- Comparative studies between binary neutron star mergers in General Relativity and those in a one-parameter model of $f(R)$ gravity are conducted using fully relativistic hydrodynamical simulations
- The simulations provide insights into how the scalar field influences the merger and post-merger dynamics
- Analyzing the full waveform (including inspiral, merger, and post-merger) can explore different regions of parameter space for both this specific $f(R)$ gravity model and finite-range scalar forces in general
- Observations of gravitational radiation from binary neutron star mergers can be used to constrain finite-range forces arising from a universally coupled massive scalar field
- The research sheds light on how such forces affect various phases of binary systems and their implications for testing General Relativity in strong-field dynamical regimes.

## Summary

This paper explores the potential of future observations of gravitational radiation from binary neutron star mergers to provide constraints on finite-range forces from a universally coupled massive scalar field. Such scalar degrees of freedom are often found in extensions of General Relativity. The study focuses specifically on metric $f(R)$ gravity, which is equivalent to General Relativity and includes a universally coupled scalar field with a non-linear potential determined by the choice of $f(R)$. The presence of a significant scalar charge in neutron stars or other compact objects leads to an attractive finite-range scalar force that affects both the inspiral and merger phases of binary systems. To investigate this, the authors first analyze the inspiral dynamics in the Newtonian limit and forecast constraints on the mass of the scalar and charge of compact objects using data from the Advanced LIGO gravitational wave observatory. Next, they conduct comparative studies between binary neutron star mergers in General Relativity and those in a one-parameter model of $f(R)$ gravity using fully relativistic hydrodynamical simulations. These simulations provide insights into how the scalar field influences the merger and post-merger dynamics. The authors also discuss how analyzing the full waveform (including inspiral, merger, and post-merger) can be used to explore different regions of parameter space for both this specific $f(R)$ gravity model as well as more generally for finite-range scalar forces. In summary, this paper investigates how observations of gravitational radiation from binary neutron star mergers can be used to constrain finite-range forces arising from a universally coupled massive scalar field. The findings shed light on how such forces affect various phases of binary systems and highlight their implications for testing General Relativity in strong-field dynamical regimes.