3 research outputs found
Very Light Sterile Neutrinos at NOvA and T2K
Over the last several years, our understanding of neutrino oscillations has
developed significantly due to the long-baseline measurements of muon-neutrino
disappearance and muon-to-electron-neutrino appearance at the T2K and NOvA
experiments. However, when interpreted under the
standard-three-massive-neutrinos paradigm, a tension has emerged between the
two experiments' data. Here, we examine whether this tension can be alleviated
when a fourth, very light neutrino is added to the picture. Specifically, we
focus on the scenario in which this new neutrino has a mass similar to, or even
lighter than, the three mostly-active neutrinos that have been identified to
date. We find that, for some regions of parameter space, the four-neutrino
framework is favored over the three-neutrino one with moderate (a little under
two sigma) significance. Interpreting these results, we provide future outlook
for near-term and long-term experiments if this four-neutrino framework is
indeed true.Comment: 18 pages, 13 figures, 6 table
Majorana versus Dirac Constraints on the Neutrino Dipole Moments
Massive neutrinos are guaranteed to have nonzero electromagnetic moments and,
since there are at least three neutrino species, these dipole moments define a
matrix. Here, we estimate the current upper bounds on all independent neutrino
electromagnetic moments, concentrating on Earth-bound experiments and
measurements with solar neutrinos, including the very recent results reported
by XENONnT. We make no simplifying assumptions and compare the hypotheses that
neutrinos are Majorana fermions or Dirac fermions. In particular, we fully
explore constraints in the Dirac-neutrino parameter space. Majorana and Dirac
neutrinos are different; for example, the upper bounds on the magnitudes of the
elements of the dipole moment matrix are weaker for Dirac neutrinos, relative
to Majorana neutrinos. The potential physics reach of next-generation
experiments also depends on the nature of the neutrino. We find that a
next-generation experiment two orders of magnitude more sensitive to the
neutrino electromagnetic moments via elastic scattering may
discover that the neutrino electromagnetic moments are nonzero if the neutrinos
are Dirac fermions. Instead, if the neutrinos are Majorana fermions, such a
discovery is ruled out by existing solar neutrino data, unless there are more
than three light neutrinos.Comment: 20 pages, 3 figures, 2 table