1,721,006 research outputs found
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
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
Three Extra Mirror or Sequential Families: Case for a Heavy Higgs Boson and Inert Doublet
No full textWe study the possibility of the existence of extra fermion families and an extra Higgs doublet. We find that requiring the extra Higgs doublet to be inert leaves space for three extra families, allowing for mirror fermion families and a dark matter candidate at the same time. The emerging scenario is very predictive: It consists of a standard model Higgs boson, with a mass above 400 GeV, heavy new quarks between 340 and 500 GeV, light extra neutral leptons, and an inert scalar with a mass below MZ.We study the possibility of the existence of extra fermion families and an extra Higgs doublet. We find that requiring the extra Higgs doublet to be inert leaves space for three extra families, allowing for mirror fermion families and a dark matter candidate at the same time. The emerging scenario is very predictive: It consists of a standard model Higgs boson, with a mass above 400 GeV, heavy new quarks between 340 and 500 GeV, light extra neutral leptons, and an inert scalar with a mass below M(Z)
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
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