Speaker
Description
The past decade has seen the rise of high-precision cosmological observations accompanied by emerging tensions among various datasets when interpreted within the standard cosmological model (ΛCDM). Recently, baryonic acoustic oscillation (BAO) measurements from the Dark Energy Spectroscopic Instrument (DESI) have shown a mild discrepancy with current cosmic microwave background (CMB) data. While a time-dependent dark energy component offers a better fit to the combined BAO+CMB dataset, it comes at the high cost of introducing two new phenomenological parameters and has the undesirable feature of exacerbating the Hubble tension. I'll briefly summarize alternative new-physics proposals and primarily focus on a (speculative, but minimal) scenario in which the optical depth to reionization is underestimated. I'll discuss the plausibility of this scenario in light of several recent rebuttals, the current status of an ongoing reanalysis of Planck large-scale polarization, and will conclude with open questions and time for discussion.