Special Seminar: The Fading Dark Sector In Light of DESI

Speaker: David Wu, Graduate Student, Harvard University

Title: The Fading Dark Sector In Light of DESI

Abstract: In this talk, I will present a string-inspired cosmological model with a coupled dark sector that evolves with a scalar field, which we refer to as the fading dark sector (FDS). The model provides an excellent fit to DESI DR2 baryon acoustic oscillation measurements and cosmic microwave background observations from Planck and ACT, while remaining remarkably consistent across different supernova datasets. Across these dataset combinations, the FDS is statistically comparable to the CPL parameterization in outperforming LCDM, while providing a physical explanation for the apparent phantom behavior without violating the null energy condition. I will then discuss recent progress on the full-shape analysis of the FDS using the DESI DR1 galaxy power spectrum in combination with techniques from the effective field theory of large-scale structure. This provides a complementary probe of dark sector interactions and an opportunity to further distinguish the FDS from phenomenological models of evolving dark energy.