17 research outputs found
One-Loop Right-Handed Neutrino Threshold Corrections for Two-Loop Running in Supersymmetric Type I Seesaw Models
The renormalization group (RG) running of the neutrino mass operator is
required for comparing the predictions of neutrino models at high energy with
the experimental data at low energies. In the type I seesaw scenario with n_G
right-handed neutrinos, the RG running is also performed in the effective
theories above and between the thresholds given by the masses of the
right-handed neutrinos. At these thresholds, the effective theories are
matched. When calculating the two-loop RG running, the matching has to be
performed at the one-loop level. In this work, we calculate the one-loop
matching formulae in the MSSM extended by n_G right-handed neutrinos using
supergraph techniques. Moreover we present a general formula for one-loop
matching of superpotential operators which can readily be applied to any
supersymmetric theory where chiral superfields are integrated out.Comment: 15 pages, 4 figures; version to appear in JHE
Prospects for testing electroweak scale sterile neutrinos at future colliders
The extension of the Standard Model of particle physics by sterile neutrinos can naturally explain the smallness of neutrino masses as observed by neutrino oscillation and nuclear beta decay experiments. These hypothetical particles, also referred to as heavy neutrinos in the mass eigenbasis, can give rise to a testable phenomenology when they have masses around the electroweak scale. Hence they are actively searched for at, for instance, colliders such as the Large Hadron Collider. The proposed future colliders, which are currently in the design phase, will be more powerful than the operated colliders to date. The new possibilities which they provide to search for sterile neutrinos and to test the neutrino mass mechanism in the not too far future have therefore to be assessed.
In this thesis, various aspects of the sterile neutrino phenomenology as well as various searches for sterile neutrinos at colliders are investigated. In particular, we study the contributions from sterile neutrinos to the Higgs boson production mechanism at colliders, the implications of long-lived heavy neutrinos that lead to displaced vertex events, lepton-number violation as the manifestation of heavy neutrino-antineutrino oscillations, lepton-flavour violation as the consequence of leptonic mixing, the possibilities to resolve heavy neutrino-antineutrino oscillations, how to test the viable leptogenesis parameter space, and their implications to collider searches. These collider studies are investigated in the context of low scale seesaw scenarios featuring ns = 2 sterile neutrinos with masses in the range of O(1 GeV) and O(1 TeV), which constitutes the benchmark scenario. Within the benchmark scenario, analytical calculations, and analyses of Monte Carlo generated event samples are performed.
The investigated collider studies demonstrate promising avenues to test sterile neutrinos at future colliders. This contains novel possible search strategies by the search for Higgs bosons produced from heavy neutrinos and by probing the effects from heavy neutrino-antineutrino oscillations via the displaced vertex search. The assessed capabilities of the future colliders with respect to the sterile neutrino searches contribute to the physics case of the future colliders
Sterile neutrino searches via displaced vertices at LHCb
We explore the sensitivity of displaced vertex searches at LHCb for testing
sterile neutrino extensions of the Standard Model towards explaining the
observed neutrino masses. We derive estimates for the constraints on sterile
neutrino parameters from a recently published displaced vertex search at LHCb
based on run 1 data. They yield the currently most stringent limit on
active-sterile neutrino mixing in the sterile neutrino mass range between 4.5
GeV and 10 GeV. Furthermore, we present forecasts for the sensitivities that
could be obtained from the run 2 data and also for the high-luminosity phase of
the LHC.Comment: 5 pages, 6 Figures, 1 Table, version to appear in PL
Displaced vertex searches for sterile neutrinos at future lepton colliders
We investigate the sensitivity of future lepton colliders to displaced
vertices from the decays of long-lived heavy (almost sterile) neutrinos with
electroweak scale masses and detectable time of flight. As future lepton
colliders we consider the FCC-ee, the CEPC, and the ILC, searching at the
Z-pole and at the center-of-mass energies of 240, 350 and 500 GeV. For a
realistic discussion of the detector response to the displaced vertex signal
and the Standard Model background we consider the ILC's Silicon Detector (SiD)
as benchmark for the future lepton collider detectors. We find that displaced
vertices constitute a powerful search channel for sterile neutrinos, sensitive
to squared active-sterile mixing angles as small as .Comment: 13 pages plus references, 8 figures, 1 table, matches published
versio
Sterile neutrino searches at future , , and colliders
Sterile neutrinos are among the most attractive extensions of the SM to
generate the light neutrino masses observed in neutrino oscillation
experiments. When the sterile neutrinos are subject to a protective symmetry,
they can have masses around the electroweak scale and potentially large
neutrino Yukawa couplings, which makes them testable at planned future particle
colliders. We systematically discuss the production and decay channels at
electron-positron, proton-proton and electron-proton colliders and provide a
complete list of the leading order signatures for sterile neutrino searches.
Among other things, we discuss several novel search channels, and present a
first look at the possible sensitivities for the active-sterile mixings and the
heavy neutrino masses. We compare the performance of the different collider
types and discuss their complementarity.Comment: 20 pages + appendix + references, 21 figures, 10 Tables; added
references; extended discussion of displaced vertex searches at pp an ep
collider
Higgs production from sterile neutrinos at future lepton colliders
In scenarios with sterile (right-handed) neutrinos that are subject to an
approximate "lepton-number-like" symmetry, the heavy neutrinos (i.e. the mass
eigenstates) can have masses around the electroweak scale and couple to the
Higgs boson with, in principle, unsuppressed Yukawa couplings while accounting
for the smallness of the light neutrinos' masses. In these scenarios, the
on-shell production of heavy neutrinos and their subsequent decays into a light
neutrino and a Higgs boson constitutes a hitherto unstudied resonant
contribution to the Higgs production mechanism. We investigate the relevance of
this resonant mono-Higgs production mechanism in leptonic collisions, including
the present experimental constraints on the neutrino Yukawa couplings, and we
determine the sensitivity of future lepton colliders to the heavy neutrinos.
With Monte Carlo event sampling and a simulation of the detector response we
find that, at future lepton colliders, neutrino Yukawa couplings below the
percent level can lead to observable deviations from the SM and, furthermore,
the sensitivity improves with higher center-of-mass energies (for identical
integrated luminosities).Comment: 26 pages, 9 figures, 7 tables; v2: references adde
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
Lepton flavor violating dilepton dijet signatures from sterile neutrinos at proton colliders
In this article we investigate the prospects of searching for sterile neutrinos in lowscale seesaw scenarios via the lepton flavour violating (but lepton number conserving) dilepton dijet signature. In our study, we focus on the final state e±μ∓jj at the HL-LHC and the FCC-hh (or the SppC). We perform a multivariate analysis at the detector level including the dominant SM backgrounds from di-top, di-boson, and tri-boson. Under the assumption of the active-sterile neutrino mixings |VlN|2 = |θe|2 = |θμ|2 and |VτN|2 = |θτ|2 = 0, the sensitivities on the signal production cross section times branching ratio σ(pp → l±N) × BR(N → l∓jj) and on |VlN|2 for sterile neutrino mass MN between 200 and 1000 GeV are derived. For the benchmark MN = 500 GeV, when ignoring systematic uncertainties at the HL-LHC (FCC-hh/SppC) with 3 (20) ab−1 luminosity, the resulting 2-σ limits on |VlN|2 are 4.9 × 10−3 (7.0 × 10−5), while the 2-σ limit on σ × BR are 4.4 × 10−2 (1.6 × 10−2) fb, respectively. The effect of the systematic uncertainty is also studied and found to be important for sterile neutrinos with smaller masses. We also comment on searches with τ±μ∓jj and τ±e∓jj final states