# Strong lensing constraints on modified gravity models

## TL;DR

This paper uses strong gravitational lensing observations to test and constrain a broad class of modified gravity theories that affect photon trajectories, finding results consistent with general relativity.

## Contribution

It provides the first strong-lensing constraints on a wide class of modified gravity models where extra fields influence lensing effects.

## Key findings

- Lensing parameter $\Gamma$ measured as 1.24±0.65, consistent with GR.
- Constraints narrow the parameter space of certain modified gravity models.
- Supports the viability of GR over some alternative theories.

## Abstract

We impose the first strong-lensing constraints on a wide class of modified gravity models where an extra field that modifies gravity also couples to photons (either directly or indirectly through a coupling with baryons) and thus modifies lensing. We use the nonsingular isothermal ellipsoid (NIE) profile as an effective potential, which produces flat galactic rotation curves. If a concrete modified gravity model gives a flat rotation curve, then the parameter $\Gamma$ that characterizes the lensing effect must take some definite value. We find that $\Gamma = 1.24\pm0.65$ at $1\sigma$, consistent with general relativity ($\Gamma = 1$). This constrains the parameter space in some recently proposed models.