Testing f(R) gravity models with quasar X-ray and UV fluxes

Understand

Recently, Active Galactic Nuclei (AGNs) have been proposed as standardizable candles, thanks to an observed non-linear relation between their X-ray and optical-ultraviolet (UV) luminosities, which provides an independent measurement of their distances.

• In this paper, we use these observables for the first time to estimate the parameters of f(R) gravity models (specifically the Hu-Sawicki and the exponential models) together with the cosmological parameters.
• The importance of this type of modified gravity theories lies in the fact that they can explain the late time accelerated expansion of the universe without the inclusion of a dark energy component.
• We have also included other observable data to the analyses such as estimates of the Hubble parameter H(z) from Cosmic Chronometers, the Pantheon Type Ia supernovae compilation, and Baryon Acoustic Oscillations measurements.