5 research outputs found
HNL mass degeneracy: implications for low-scale seesaws, LNV at colliders and leptogenesis
Low-scale seesaw variants protected by lepton number symmetry provide a
natural explanation of the smallness of neutrino masses but, unlike their
higher-scale counterparts, with potentially testable phenomenology. The
approximate lepton number symmetry arranges the heavy neutrinos in pseudo-Dirac
pairs, which might be accessible at collider or even beam dump experiments if
their mass is low enough and their mixing with the active neutrinos
sufficiently large. Despite their pseudo-Dirac nature, their small mass
splittings may lead to oscillations that prevent the cancellation of their
potential lepton-number-violating signals. Interestingly, these small
splittings may also resonantly enhance the production of a lepton number
asymmetry for low-scale leptogenesis scenarios or, for extremely degenerate
states, lead to an asymmetry large enough to resonantly produce a keV sterile
neutrino dark matter candidate with the correct relic abundance via the
Shi-Fuller mechanism. In this work we explore the parameter space of the
different low-scale seesaw mechanisms and study the size of these splittings,
given their important and interesting phenomenological consequences. While all
low-scale seesaw variants share the same dimension 5 and 6 operators when
integrating out the heavy states, we point out that the mass splitting of the
pseudo-Dirac pairs are very different in different realizations such as the
inverse or linear seesaw. This different phenomenology could offer a way to
discriminate between low-scale seesaw realizations.Comment: 27 pages, 6 figures. Matches published version in JHE
Bounds on lepton non-unitarity and heavy neutrino mixing
We present an updated and improved global fit analysis of current flavor and
electroweak precision observables to derive bounds on unitarity deviations of
the leptonic mixing matrix and on the mixing of heavy neutrinos with the active
flavours. This new analysis is motivated by new and updated experimental
results on key observables such as , the invisible decay width of the
boson and the boson mass. It also improves upon previous studies by
considering the full correlations among the different observables and
explicitly calibrating the test statistic, which may present significant
deviations from a distribution. The results are provided for three
different Type-I seesaw scenarios: the minimal scenario with only two
additional right-handed neutrinos, the next to minimal one with three extra
neutrinos, and the most general one with an arbitrary number of heavy neutrinos
that we parametrize via a generic deviation from a unitary leptonic mixing
matrix. Additionally, we also analyze the case of generic deviations from
unitarity of the leptonic mixing matrix, not necessarily induced by the
presence of additional neutrinos. This last case relaxes some correlations
among the parameters and is able to provide a better fit to the data.
Nevertheless, inducing only leptonic unitarity deviations avoiding both the
correlations implied by the right-handed neutrino extension as well as more
strongly constrained operators is challenging and would imply significantly
more complex UV completions.Comment: 27 pages + appendices, 7 figures, 7 table
Bounds on lepton non-unitarity and heavy neutrino mixing
Abstract We present an updated and improved global fit analysis of current flavour and electroweak precision observables to derive bounds on unitarity deviations of the leptonic mixing matrix and on the mixing of heavy neutrinos with the active flavours. This new analysis is motivated by new and updated experimental results on key observables such as V ud , the invisible decay width of the Z boson and the W boson mass. It also improves upon previous studies by considering the full correlations among the different observables and explicitly calibrating the test statistic, which may present significant deviations from a χ 2 distribution. The results are provided for three different Type-I seesaw scenarios: the minimal scenario with only two additional right-handed neutrinos, the next to minimal one with three extra neutrinos, and the most general one with an arbitrary number of heavy neutrinos that we parametrise via a generic deviation from a unitary leptonic mixing matrix. Additionally, we also analyze the case of generic deviations from unitarity of the leptonic mixing matrix, not necessarily induced by the presence of additional neutrinos. This last case relaxes some correlations among the parameters and is able to provide a better fit to the data. Nevertheless, inducing only leptonic unitarity deviations avoiding both the correlations implied by the right-handed neutrino extension as well as more strongly constrained operators is challenging and would imply significantly more complex UV completions
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Transcutaneous ultrasound-facilitated coronary thrombolysis during acute myocardial infarction
In preclinical experiments, the combination of transcutaneous, low-frequency ultrasound and thrombolytic therapy has shown improved patency rates over thrombolytics alone. A total of 25 patients with myocardial infarction were treated with a thrombolytic agent and adjunctive transcutaneous ultrasound. No unanticipated major adverse events were observed