Speaker
Description
The cosmic microwave background (CMB) provides a powerful probe of neutrinos and other relativistic species in the early universe. In this talk, I will present a robust, model-agnostic framework for detecting the unique phase shift imprinted in the CMB acoustic peaks by free-streaming particles. I will introduce two complementary methods, one leveraging the shifts in the observed power spectra and another extracting the phase shift directly from the underlying perturbations in the photon-baryon fluid. Applying these techniques to current CMB data from Planck, ACT, and SPT, we achieve a high-significance detection of the phase shift and confirm consistency with the Standard Model expectation of three free-streaming neutrinos. I will also discuss forecasts for upcoming experiments, namely for the Simons Observatory and CMB-S4, which will enhance the precision of this measurement, opening new avenues for testing beyond-the-Standard-Model scenarios. Finally, I will highlight ongoing work investigating how delayed neutrino decoupling -- arising from dark matter–neutrino interactions or other exotic physics -- could modify the phase shift and its potential imprint on future 21cm-line observations.
