1,720,964 research outputs found
Majorana Higgses at colliders
Full text linkCollider signals of heavy Majorana neutrino mass origin are studied in the minimal Left-Right symmetric model, where their mass is generated spontaneously together with the breaking of lepton number. The right-handed triplet Higgs boson ∆, responsible for such breaking, can be copiously produced at the LHC through the Higgs portal in the gluon fusion and less so in gauge mediated channels. At ∆ masses below the opening of the V V decay channel, the two observable modes are pair-production of heavy neutrinos via the triplet gluon fusion gg → ∆ → NN and pair production of triplets from the Higgs h → ∆∆ → 4N decay. The latter features tri- and quad same-sign lepton final states that break lepton number by four units and have no significant background. In both cases up to four displaced vertices may be present and their displacement may serve as a discriminating variable. The backgrounds at the LHC, including the jet fake rate, are estimated and the resulting sensitivity to the Left-Right breaking scale extends well beyond 10 TeV. In addition, sub-dominant radiative modes are surveyed: the γγ, Zγ and lepton flavour violating ones. Finally, prospects for ∆ signals at future e+e− colliders are presented
Keung-Senjanović process at the LHC: From lepton number violation to displaced vertices to invisible decays
Full text linkIn the context of left-right symmetry, we revisit the Keung-Senjanovic production of right-handed W-R bosons and heavy neutrinos N at high energy colliders. We develop a multibinned sensitivity measure and use it to estimate the sensitivity for the entire range of N masses, spanning the standard and merged prompt signals, displaced vertices and the invisible N region. The estimated sensitivity of the LHC with 300/fb integrated luminosity ranges from 5 to beyond 7 TeV, while the future 33(100) TeV collider's reach with 3/ab extends to 12(26) TeV
Left-Right Symmetry: From the LHC to Neutrinoless Double Beta Decay
No full textThe Large Hadron Collider has the potential to probe the scale of left-right symmetry restoration and the associated lepton number violation. Moreover, it offers the hope of measuring the right-handed leptonic mixing matrix. We show how this, together with constraints from lepton flavor violating processes, can be used to make predictions for neutrinoless double beta decay. We illustrate this connection in the case of the type-II seesaw.The Large Hadron Collider has the potential to probe the scale of left-right symmetry restoration and the associated lepton number violation. Moreover, it offers the hope of measuring the right-handed leptonic mixing matrix. We show how this, together with constraints from lepton flavor violating processes, can be used to make predictions for neutrinoless double beta decay. We illustrate this connection in the case of the type-II seesaw
Type II neutrino seesaw mechanism at the LHC: The roadmap
No full textIn this article, 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
Left-right symmetry at LHC
No full textWe revisit the issue of the limit on the scale of left-right symmetry breaking. We focus on the minimal SUð2ÞL SUð2ÞR Uð1ÞBL gauge theory with the seesaw mechanism and discuss the two possibilities of defining left-right symmetry as parity or charge conjugation. In the commonly adopted case of parity, we perform a complete numerical study of the quark mass matrices and the associated left and right mixing matrices without any assumptions usually made in the literature about the ratio of vacuum expectation values. We find that the usual lower limit on the mass of the right-handed gauge boson from the K mass difference, MWR > 2:5 TeV, is subject to a possible small reduction due to the difference between right and left Cabibbo angles. In the case of charge conjugation the limit on MWR is somewhat more robust. However, the more severe bounds from CP-violating observables are absent in this case. In fact, the free phases can also resolve the present mild discrepancy between the standard model and CP violation in the B sector. Thus, even in the minimal case, both charged and neutral gauge bosons may be accessible at the Large Hadron Collider with spectacular signatures of lepton number violation.We revisit the issue of the limit on the scale of left-right symmetry breaking. We focus on the minimal SU(2)(L) x SU(2)(R) x U(1)(B-L) gauge theory with the seesaw mechanism and discuss the two possibilities of defining left-right symmetry as parity or charge conjugation. In the commonly adopted case of parity, we perform a complete numerical study of the quark mass matrices and the associated left and right mixing matrices without any assumptions usually made in the literature about the ratio of vacuum expectation values. We find that the usual lower limit on the mass of the right-handed gauge boson from the K mass difference, M(WR) > 2.5 TeV, is subject to a possible small reduction due to the difference between right and left Cabibbo angles. In the case of charge conjugation the limit on M(WR) is somewhat more robust. However, the more severe bounds from CP-violating observables are absent in this case. In fact, the free phases can also resolve the present mild discrepancy between the standard model and CP violation in the B sector. Thus, even in the minimal case, both charged and neutral gauge bosons may be accessible at the Large Hadron Collider with spectacular signatures of lepton number violation
Neutrinoless Double Beta Decay: Low Left-Right Symmetry Scale?
No full textExperiments in progress may confirm a nonzero neutrinoless double beta decay rate in conflict with the cosmological upper limit on neutrino masses and thus require new physics beyond the Standard Model. A natural candidate is the Left-Right symmetric theory, which led originally to neutrino mass and the seesaw mechanism. In the absence of cancelations of large Dirac Yukawa couplings, we show how such a scenario would require a low scale of Left-Right symmetry breaking roughly below 10 TeV, tantalizingly close to the LHC reach
Limits on the left-right symmetry scale and heavy neutrinos from early LHC data
No full textWe 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 WR via the final state with two leptons and two jets, for 33 pb1 integrated luminosity and 7 TeV center-of-mass energy. This signal is kinematically observable for right-handed neutrino lighter than WR. In the absence of a signal beyond the standard model background, we set the bound MWR * 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 cancellation in right-handed lepton mixings.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 W(R) via the final state with two leptons and two jets, for 33 pb(-1) integrated luminosity and 7 TeV center-of-mass energy. This signal is kinematically observable for right-handed neutrino lighter than WR. In the absence of a signal beyond the standard model background, we set the bound M(WR) greater than or similar to 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 cancellation in right-handed lepton mixings
Inert doublet dark matter and mirror/extra families after Xenon100
No full textIt was shown recently that mirror fermions, naturally present in a number of directions for new physics, seem to require an inert scalar doublet in order to pass the electroweak precision tests. This provides a further motivation for considering the inert doublet as a dark matter candidate. Moreover, the presence of extra families enhances the standard model Higgs-nucleon coupling, which has crucial impact on the Higgs and dark matter searches. We study the limits on the inert dark matter mass in view of recent Xenon100 data. We find that the mass of the inert dark matter must lie in a very narrow window 75 ` 1 GeV while the Higgs boson must weigh more than 400 GeV. For the sake of completeness we discuss the cases with fewer extra families, where the possibility of a light Higgs boson opens up, enlarging the dark matter mass window to 12 mh-76 GeV. We find that Xenon100 constrains the DM-Higgs interaction, which in turn implies a lower bound on the monochromatic gamma ray flux from DM annihilation in the galactic halo. For the mirror case, the predicted annihilation cross section lies a factor of 4–5 below the current limit set by Fermi LAT, thus providing a promising indirect detection signal.It was shown recently that mirror fermions, naturally present in a number of directions for new physics, seem to require an inert scalar doublet in order to pass the electroweak precision tests. This provides a further motivation for considering the inert doublet as a dark matter candidate. Moreover, the presence of extra families enhances the standard model Higgs-nucleon coupling, which has crucial impact on the Higgs and dark matter searches. We study the limits on the inert dark matter mass in view of recent Xenon100 data. We find that the mass of the inert dark matter must lie in a very narrow window 75 +/- 1 GeV while the Higgs boson must weigh more than 400 GeV. For the sake of completeness we discuss the cases with fewer extra families, where the possibility of a light Higgs boson opens up, enlarging the dark matter mass window to 1 2 m(h)-76 GeV. We find that Xenon100 constrains the DM-Higgs interaction, which in turn implies a lower bound on the monochromatic gamma ray flux from DM annihilation in the galactic halo. For the mirror case, the predicted annihilation cross section lies a factor of 4-5 below the current limit set by Fermi LAT, thus providing a promising indirect detection signal
Lepton Number Violation in Higgs Decay at LHC
No full textWe show that within the left-right symmetric model, lepton number violating decays of the Higgs boson can be discovered at the LHC. The process is due to the mixing of the Higgs boson with the triplet that breaks parity. As a result, the Higgs boson can act as a gateway to the origin of the heavy Majorana neutrino mass. To assess the LHC reach, a detailed collider study of the same-sign dileptons plus jets channel is provided. This process is complementary to the existing nuclear and collider searches for lepton number violation and can probe the scale of parity restoration even beyond other direct searches
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