Speaker
Description
In this poster I would like to discuss our recent results on the pseudoscalar sterile neutrino self-interactions model.
In particular, we reassess the viability of a cosmological model including a fourth additional sterile neutrino species that self-interacts through a new pseudoscalar degree of freedom.
To that end, we perform a series of extensive analyses fitting various combinations of Cosmic Microwave Background data from Planck, the Atacama Cosmology Telescope and the South Pole Telescope, both alone and in combination with Baryon Acoustic Oscillation and Supernova Ia observations.
We show that the scenario under study, although capable to resolve the Hubble tension without worsening the $S_8$ tension, is severely constrained by high-multipole polarization data from both Planck and SPT.
Intriguingly, when trading Planck TE-EE data for those from ACT, we find a $> 3 \sigma$ preference for a non-zero sterile neutrino mass, $m_s=3.6^{+1.1}_{-0.6}$ eV (68 % C.L.), compatible with the range suggested by longstanding short-baseline (SBL) anomalies in neutrino oscillation experiments.
The preference is mostly driven by ACT favouring a higher value for the primordial spectral index $n_s$ with respect to Planck and SPT. The pseudoscalar model appears indeed to provide a better fit to ACT data with respect to $\Lambda$CDM ($\Delta\chi^2 \simeq -5$).
In particular, we show that the mild tension between Planck and ACT is due to the different pattern in the TE and EE power spectra on multipoles between $350 < \ell < 1000$.
