Toward alleviating the H0 and S8 tensions with early dark energy-dark matter drag

Early dark energy, an additional component of dark energy active in the decade of redshift before recombination, has emerged as one of the most effective models at reducing the "H0 tension" between direct measurement of the Hubble parameter H0 in the late Universe and the ACDM prediction when calibrated on Planck. However, it requires a slight increase in the dark matter density omega cdm and primordial tilt ns that worsens the "S8 tension" between measurements of weak gravitational lensing at low redshifts and the Planck/ACDM prediction. Using a phenomenological fluid model, we investigate whether the inclusion of a drag term between dark matter and early dark energy can compensate for the effect of the increase in power at small-scales, such that both H0 and S8 tensions are simultaneously alleviated. We find that this works if the drag term is dynamically relevant in the post-recombination universe. However, a drag term active before or just around the time at which the early dark energy contribution to the energy density is maximum is significantly constrained due to its impact on the matter perturbations before recombination, and the subsequent modifications to the cosmic microwave background power spectra.