Speaker
Description
The electron neutrino degeneracy parameter, $\xi_{\nu_\mathrm{e}} = \mu_{\nu_\mathrm{e}} / T$, is tightly constrained by Big Bang Nucleosynthesis (BBN), while the degeneracy parameters of the other neutrino species, $\xi_{\nu_\mathrm{x}}$, remain weakly constrained by cosmological observations alone. In this talk, we present constraints on $\xi_{\nu_\mathrm{e}}$ and $\xi_{\nu_\mathrm{x}}$ using two complementary approaches: a constant free-parameter treatment to obtain physical bounds, and a model-independent reconstruction based on the Piecewise Cubic Hermite Interpolating Polynomial (PCHIP) formalism, allowing $\xi_{\nu}$ to vary with redshift and probing the origin of these bounds. We also consider two scenarios for neutrinos, specifically three degenerate neutrinos ($\xi_{\nu_\mathrm{e}}$ = $\xi_{\nu_\mathrm{x}}$) and the case in which we actually differentiate between $\xi_{\nu_\mathrm{e}}$ and $\xi_{\nu_\mathrm{x}}$. We perform a cosmological analysis combining CMB data from Planck, SPT, and ACT with BAO measurements from DESI, and reassess the results after including BBN observables from either EMPRESS, which allows for a non-zero chemical potential, or LBT, which is compatible with the standard $\xi_\nu$ = 0 prediction.