63 research outputs found
Probing seesaw at LHC
We have recently proposed a simple SU(5) theory with an adjoint fermionic
multiplet on top of the usual minimal spectrum. This leads to the hybrid
scenario of both type I and type III seesaw and it predicts the existence of
the fermionic SU(2) triplet between 100 GeV and 1 TeV for a conventional GUT
scale of about 10^{16} GeV, with main decays into W (Z) and leptons, correlated
through Dirac Yukawa couplings, and lifetimes shorter than about 10^{-12} sec.
These decays are lepton number violating and they offer an exciting signature
of Delta L=2 dilepton events together with 4 jets at future pp (p\bar p)
colliders. Increasing the triplet mass endangers the proton stability and so
the seesaw mechanism could be directly testable at LHC.Comment: 19 pages, discussion on leptogenesis added, new references, main
conclusions unchange
First Limits on Left-Right Symmetry Scale from LHC Data
We use the early Large Hadron Collider data to set the lower limit on the
scale of Left-Right symmetry, by searching for the right-handed charged gauge
boson via the final state with two leptons and two jets, for 33/pb
integrated luminosity and 7 TeV center-of-mass energy. In the absence of a
signal beyond the Standard Model background, we set the bound M_WR > 1.4 TeV at
95% C.L.. This result is obtained for a range of right-handed neutrino masses
of the order of few 100 GeV, assuming no accidental cancelation in right-handed
lepton mixings.Comment: 4 pages, added reference
Type II Seesaw at LHC: the Roadmap
In this Letter we revisit the type-II seesaw mechanism based on the addition
of a weak triplet scalar to the standard model. We perform a comprehensive
study of its phenomenology at the LHC energies, complete with the electroweak
precision constraints. We pay special attention to the doubly-charged
component, object of collider searches for a long time, and show how the
experimental bound on its mass depends crucially on the particle spectrum of
the theory. Our study can be used as a roadmap for future complete LHC studies.Comment: 5 pages, 4 figures; added discussion on collider signatures including
the impact on SM Higgs searches and accommodating Higgs to two photon rate,
and references; latest version agrees with the published on
Left-right symmetry at LHC and precise 1-loop low energy data
Despite many tests, even the Minimal Manifest Left-Right Symmetric Model
(MLRSM) has never been ultimately confirmed or falsified. LHC gives a new
possibility to test directly the most conservative version of left-right
symmetric models at so far not reachable energy scales. If we take into account
precise limits on the model which come from low energy processes, like the muon
decay, possible LHC signals are strongly limited through the correlations of
parameters among heavy neutrinos, heavy gauge bosons and heavy Higgs particles.
To illustrate the situation in the context of LHC, we consider the "golden"
process . For instance, in a case of degenerate heavy neutrinos
and heavy Higgs masses at 15 TeV (in agreement with FCNC bounds) we get
fb at TeV which is consistent with muon
decay data for a very limited masses in the range (3008 GeV, 3040 GeV).
Without restrictions coming from the muon data, masses would be in the
range (1.0 TeV, 3.5 TeV). Influence of heavy Higgs particles themselves on the
considered LHC process is negligible (the same is true for the light, SM
neutral Higgs scalar analog). In the paper decay modes of the right-handed
heavy gauge bosons and heavy neutrinos are also discussed. Both scenarios with
typical see-saw light-heavy neutrino mixings and the mixings which are
independent of heavy neutrino masses are considered. In the second case heavy
neutrino decays to the heavy charged gauge bosons not necessarily dominate over
decay modes which include only light, SM-like particles.Comment: 16 pages, 10 figs, KL-KS and new ATLAS limits taken into accoun
Implications of Flavor Dynamics for Fermion Triplet Leptogenesis
We analyze the importance of flavor effects in models in which leptogenesis
proceeds via the decay of Majorana electroweak triplets. We find that depending
on the relative strengths of gauge and Yukawa reactions the asymmetry can
be sizably enhanced, exceeding in some cases an order of magnitude level. We
also discuss the impact that such effects can have for TeV-scale triplets
showing that as long as the asymmetry is produced by the dynamics of the
lightest such triplet they are negligible, but open the possibility for
scenarios in which the asymmetry is generated above the TeV scale by heavier
states, possibly surviving the TeV triplet related washouts. We investigate
these cases and show how they can be disentangled at the LHC by using Majorana
triplet collider observables and, in the case of minimal type III see-saw
models even through lepton flavor violation observables.Comment: 22 pages, 9 figures, extended discussion on collider phenomenology,
references added. Version matches publication in JHE
The present and future status of heavy neutral leptons
The existence of nonzero neutrino masses points to the likely existence of multiple Standard Model neutral fermions. When such states are heavy enough that they cannot be produced in oscillations, they are referred to as heavy neutral leptons (HNLs). In this white paper, we discuss the present experimental status of HNLs including colliders, beta decay, accelerators, as well as astrophysical and cosmological impacts. We discuss the importance of continuing to search for HNLs, and its potential impact on our understanding of key fundamental questions, and additionally we outline the future prospects for next-generation future experiments or upcoming accelerator run scenarios
Combined explanations of B-physics anomalies: the sterile neutrino solution
In this paper we provide a combined explanation of charged- and neutral-current B-physics anomalies assuming the presence of a light sterile neutrino NR which contributes to the B \u2192 D(*)\u3c4\u3bd processes. We focus in particular on two simplified models, where the mediator of the flavour anomalies is either a vector leptoquark U1\u3bc 3c (3, 1, 2/3) or a scalar leptoquark S1 3c (3\uaf , 1, 1/3). We find that U1\u3bc can successfully reproduce the required deviations from the Standard Model while being at the same time compatible with all other flavour and precision observables. The scalar leptoquark instead induces a tension between Bs mixing and the neutral-current anomalies. For both states we present the limits and future projections from direct searches at the LHC finding that, while at present both models are perfectly allowed, all the parameter space will be tested with more luminosity. Finally, we study in detail the cosmological constraints on the sterile neutrino NR and the conditions under which it can be a candidate for dark matter
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