Strong lensing constraints on modified gravity models

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 profile as an effective potential which produces flat galactic rotational curves. If a concrete modified gravity model gives a flat rotational curve, then the parameter Γ that characterizes the lensing effect must take some definite value. We find that Γ=1.24±0.65 at 1σ, consistent with general relativity (Γ=1). This constrains the parameter space in some recently proposed models.