Fast Radio Bursts (FRBs) are bright, transient pulses of light in the radio frequency range. More than 600 unique FRB sources have been identified since their first discovery in 2007, and the number only continues to grow. A characteristic property of them is the Dispersion Measure (DM), defined as the integrated electron density along the line of sight. Today we know that the majority of FRBs are of extragalactic origin and, thus, can be used to trace the large-scale structure of the Universe. Dark energy leaves a significant imprint on such scales. Over the recent years, scalar-tensor modified gravity theories have been proposed as a possible driving mechanism of dark energy. In this talk, I will discuss whether FRBs can be used in the future to test such theories. To do so, I combine an artificial FRB survey feasible within the next ten years with weak lensing data from surveys like KiDS1000 or Euclid. During the presentation, I will introduce the weak lensing and DM statistic, that are subsequently used to calculate covariances between cosmological parameters with Fisher forecast and Monte-Carlo-Markov-Chains. Cross-correlating FRBs with weak-lensing data leads to significantly tighter constraints on modified gravity than weak-lensing alone. Arguably, this originates from the DM sensitivity on baryonic cosmological parameters, making FRBs a valuable probe for future cosmological analyses.
