Cosmology with varying fundamental constants from hyperlight, coupled scalars

Understand

The fundamental constants at recombination can differ from their present-day values due to degeneracies in cosmological parameters, raising the possibility of yet-undiscovered physics coupled directly to the Standard Model.

• We study the cosmology of theories in which a new, hyperlight scalar field modulates the electron mass and fine-structure constant at early times.
• We find new degeneracies in cosmologies that pair early recombination with a new contribution to the matter density arising at late times, whose predictions can be simultaneously consistent with CMB and low-redshift distance measurements.
• Such "late dark matter" already exists in the Standard Model in the form of massive neutrinos but is necessarily realized by the scalar responsible for shifting the early-time fundamental constants.