| Details: |
The Standard Model of Cosmology, while remarkably successful, is currently facing a period of intense scrutiny due to persistent tensions in measurements of the Hubble constant ($H_0$) and the growth of structure ($\sigma_8$). These discrepancies signal that we may be at the frontier of new physics beyond the $\Lambda$CDM paradigm.
In the first part of this talk, we present a framework for an Interacting Dark Sector (IDS) derived from fundamental field-theoretic actions. Utilizing field-fluid mapping and disformal transformations, we demonstrate how interactions between dark energy and dark matter can naturally drive an Early Dark Energy (EDE) phase. Unlike traditional EDE models that rely on highly fine-tuned potentials, our model generates the required energy injection and rapid dilution through the dynamics of the interaction itself, providing a robust and theoretically motivated resolution to the Hubble tension.
However, the proliferation of dark sector models requires definitive observational tests. In the second part, we propose Integrated Cosmological Memory (ICM) as a powerful tool to probe the background evolution of the Universe. We show that the cumulative memory signal encodes the integrated expansion history, effectively mimicking the electromagnetic Integrated Sachs-Wolfe effect in the gravitational sector. Finally, we demonstrate that the ratio of this memory component to the primary oscillatory signal breaks the degeneracy between luminosity distance and cosmology. This establishes a novel class of self-calibrating "dark sirens" capable of constraining the late-time dark energy equation of state with sub-percent precision using next-generation detectors like Cosmic Explorer and Einstein Telescope. |