Demagnifying Gravitational Lenses as Probes of Dark Matter Structures and Nonminimal Couplings to Gravity

Abstract Magnification of total image fluxes is typically considered a defining feature of gravitational microlensing. In contrast, I will show that nonminimal couplings to gravity can generate regions of negative gravitational potential curvature, giving rise to the distinctive possibility of demagnification. Such events, appearing as flux troughs in microlensing light curves, provide a direct probe of dark matter structures and, crucially, offer a means to disentangle nonminimal couplings to gravity from other astrophysical and cosmological models.