Early modified gravity in light of the H0 tension and LSS data

We present a model of early modified gravity (EMG) consisting in a scalar field a with a nonminimal coupling to the Ricci curvature of the type M-pl(2) + xi sigma(2) plus a cosmological constant and a small effective mass and demonstrate its ability to alleviate the H-0 tension while providing a good fit to cosmic microwave background (CMB) anisotropies and baryon acoustic oscillations (BAO) data. In this model the scalar field, frozen deep in the radiation era, grows around the redshift of matter-radiation equality because of the coupling to nonrelativistic matter. The small effective mass, which we consider here as induced by a quartic potential, then damps the scalar field into coherent oscillations around its minimum at sigma = 0, leading to a weaker gravitational strength at early times and naturally recovering the consistency with laboratory and Solar System tests of gravity. We analyze the capability of EMG with positive xi to fit current cosmological observations and compare our results to the case without an effective mass and to the popular early dark energy models with xi = 0. We show that EMG with a quartic coupling of the order of lambda similar to O(eV(4)/M-pl(4)) can substantially alleviate the H-0 tension also when the full shape of the matter power spectrum is included in the fit in addition to CMB and Supernovae (SN) data.

Automated summary

The early modified gravity model proposed involves a scalar field with nonminimal coupling to the Ricci curvature, showing potential in alleviating the H-0 tension while fitting well with CMB anisotropies and BAO data. The scalar field in the model remains frozen in the radiation era, growing near matter-radiation equality and dampening into coherent oscillations due to a small effective mass induced by a quartic potential, ultimately leading to weaker gravitational strength at early times. Comparative analysis with other models suggests that this EMG model can significantly alleviate the H-0 tension when considering the full shape of the matter power spectrum in addition to CMB and SN data.