31 research outputs found
NA62 sensitivity to heavy neutral leptons in the low scale seesaw model
The sensitivity of beam dump experiments to heavy neutral leptons depends on
the relative strength of their couplings to individual lepton flavours in the
Standard Model. We study the impact of present neutrino oscillation data on
these couplings in the minimal type I seesaw model and find that it
significantly constrains the allowed heavy neutrino flavour mixing patterns. We
estimate the effect that the DUNE experiment will have on these predictions. We
then discuss implication that this has for the sensitivity of the NA62
experiment when operated in the beam dump mode and provide sensitivity
estimates for different benchmark scenarios. We find that the sensitivity can
vary by almost two orders of magnitude for general choices of the model
parameters, but depends only weakly on the flavour mixing pattern within the
parameter range that is preferred by neutrino oscillation data.Comment: 29 pages, 8 figures, 3 tables, version accepted by JHE
Non-perturbative production of fermionic dark matter from fast preheating
We investigate non-perturbative production of fermionic dark matter in the
early universe. We study analytically the gravitational production mechanism
accompanied by the coupling of fermions to the background inflaton field. The
latter leads to the variation of effective fermion mass during preheating and
makes the resulting spectrum and abundance sensitive to its parameters.
Assuming fast preheating that completes in less than the inflationary Hubble
time and no oscillations of the inflaton field after inflation, we find an
abundant production of particles with energies ranging from the inflationary
Hubble rate to the inverse duration of preheating. The produced fermions can
account for all observed dark matter in a broad range of parameters. As an
application of our analysis, we study non-perturbative production of heavy
Majorana neutrino in the model of Palatini Higgs inflation.Comment: 38 pages, 9 figures, v2 matches the published versio
Low-scale leptogenesis with three heavy neutrinos
Leptogenesis induced by the oscillations of GeV-scale neutrinos provides a
minimal and testable explanation of the baryon asymmetry of the Universe. In
this work we extend previous studies invoking only two heavy neutrinos to the
case of three heavy neutrinos. We find qualitatively new behaviour as a result
of lepton number violating oscillations and decays, strong flavour effects in
the washout and a resonant enhancement due to matter effects. An approximate
global symmetry (representing the difference of baryon and a
generalised lepton number) can protect the light neutrino masses from large
radiative corrections, while simultaneously providing the ingredients for the
resonant enhancement of the lepton asymmetry due to thermal contributions to
the heavy neutrino dispersion relations. This mechanism is particularly
efficient for large heavy neutrino mixing angles near the current experimental
limits, a regime in which leptogenesis is not feasible in the minimal scenario
with two heavy neutrinos. In this new parameter regime, low-scale leptogenesis
is testable by the LHC and other existing experiments.Comment: 39 pages plus appendices, 9 figures. v2: matches the version accepted
for publication on JHE
Perspectives to find heavy neutrinos with NA62
The sensitivity of beam dump experiments to heavy neutrinos depends on the
relative size of their mixings with the lepton flavours in the Standard Model.
We study the impact of present neutrino oscillation data on these mixing angles
in the minimal type I seesaw model. We find that current data significantly
constrains the allowed heavy neutrino flavour mixing patterns. Based on this,
we discuss the implications for the sensitivity of the NA62 experiment to heavy
neutrinos when operated in the beam dump mode. We find that NA62 is currently
the most sensitive experiment in the world for heavy neutrino masses between
that of the kaon and the -mesons. The sensitivity can vary by almost two
orders of magnitude if the heavy neutrinos exclusively couple to the tau
flavour, but depends only comparably weakly on the flavour mixing pattern
within the parameter range preferred by light neutrino oscillation data.Comment: Contribution to the proceedings of the 53rd Rencontres de Moriond on
Electroweak Interactions and Unified Theories (2018). 6 pages, 2 figure
Probing Leptogenesis at Future Colliders
We investigate the question whether leptogenesis, as a mechanism for
explaining the baryon asymmetry of the universe, can be tested at future
colliders. Focusing on the minimal scenario of two right-handed neutrinos, we
identify the allowed parameter space for successful leptogenesis in the heavy
neutrino mass range between and GeV. Our calculation includes the
lepton flavour violating contribution from heavy neutrino oscillations as well
as the lepton number violating contribution from Higgs decays to the baryon
asymmetry of the universe. We confront this parameter space region with the
discovery potential for heavy neutrinos at future lepton colliders, which can
be very sensitive in this mass range via displaced vertex searches. Beyond the
discovery of heavy neutrinos, we study the precision at which the
flavour-dependent active-sterile mixing angles can be measured. The measurement
of these mixing angles at future colliders can test whether a minimal type I
seesaw mechanism is the origin of the light neutrino masses, and it can be a
first step towards probing leptogenesis as the mechanism of baryogenesis. We
discuss how a stronger test could be achieved with an additional measurement of
the heavy neutrino mass difference.Comment: 30 pages plus appendix, 13 figures, references added, discussion
extended, two figures added, matches journal versio
An allowed window for heavy neutral leptons below the kaon mass
The extension of the Standard Model with two gauge-singlet Majorana fermions
can simultaneously explain two beyond-the-Standard-model phenomena: neutrino
masses and oscillations, as well as the origin of the matter-antimatter
asymmetry in the Universe. The parameters of such a model are constrained by
the neutrino oscillation data, direct accelerator searches, big bang
nucleosynthesis, and requirement of successful baryogenesis. We show that the
combination of all these constraints still leaves an allowed region in the
parameter space below the kaon mass. This region can be probed by the further
searches of NA62, DUNE, or SHiP experiments.Comment: 30 pages, 10 figure