Speaker
Description
Early Dark Energy (EDE) is a well-studied extension of ΛCDM
proposed to address the Hubble tension. In these models, a new dark
energy component, typically described by an axion-like scalar field,
becomes dynamically relevant at early times and then rapidly dilutes
around matter-radiation equality, leaving a negligible contribution to
the late-time energy budget. Throughout this active phase, EDE can raise
the CMB-inferred value of the present expansion rate by reducing the
sound horizon before recombination. However, in its simplest form, EDE
typically requires a larger physical dark matter density and therefore
worsens the S8 tension with weak-lensing measurements. In this talk, I
will present a model in which cold dark matter is coupled to an
axion-like EDE field through a pure momentum-transfer interaction. This
class of coupling is known to preserve the background conservation of
the dark matter energy density, while modifying the dark matter Euler
equation and the EDE perturbations. Using recent cosmological data I
will discuss the implications of momentum-transfer interactions for a
single EDE field to simultaneously resolve both the H0 and S8 tensions.