Speaker
Description
The three-flavour framework of neutrino oscillations successfully
explains most experimental results; however, persistent anomalies at both short-
and long-baseline experiments hint at the existence of additional light sterile states.
In particular, eV-scale sterile neutrinos are motivated by LSND and MiniBooNE
results, while sub-eV sterile states have been proposed to address the T2K–NOνA
tension and the absence of the expected solar upturn, respectively. Such sterile
states are singlets under the Standard Model gauge group and mix only through
their admixture with active neutrinos. In this work, we investigate the
phenomenology of the 3 + 2 scenario, incorporating one eV-scale sterile neutrino
together with a sub-eV state, and analyse their impact on absolute-mass related
observables: the sum of neutrino masses constrained by cosmology, the effective
electron neutrino mass from beta decay, and the effective Majorana mass probed
in neutrinoless double beta decay. We demonstrate that the presence of two sterile
states can significantly modify the allowed parameter space compared to the
three-flavour and 3+1 frameworks, with some mass-ordering schemes already
disfavored by current cosmological and laboratory limits. Finally, we assess the
implications of upcoming sensitivities from KATRIN, Project 8, and nEXO,
highlighting the complementary role of sub-eV sterile neutrinos in probing physics
beyond the minimal three-flavor paradigm.
