Search results for "Lepton"
showing 10 items of 1512 documents
Invisible Higgs boson decays in spontaneously broken R parity
2004
The Higgs boson may decay mainly to an invisible mode characterized by missing energy, instead of the Standard Model channels. This is a generic feature of many models where neutrino masses arise from the spontaneous breaking of ungauged lepton number at relatively low scales, such as spontaneously broken R-parity models. Taking these models as framework, we reanalyze this striking suggestion in view of the recent data on neutrino oscillations that indicate non-zero neutrino masses. We show that, despite the smallness of neutrino masses, the Higgs boson can decay mainly to the invisible Goldstone boson associated to the spontaneous breaking of lepton number. This requires a gauge singlet su…
Photo-transmutation of leptons
2001
By photo-transmutation of leptons we mean photon-lepton reactions of the following type: $\gamma l_\alpha \longrightarrow \gamma l_\beta$ with $l_\alpha \neq l_\beta$, occurring as a consequence of the lepton mass matrix changing its orientation (rotating) under changing scales. In this paper, we first discuss these reactions in general terms, then proceed to the calculation of their cross sections in two specific schemes, one within the framework of the conventional Standard Model, the other being the so-called Dualized Standard Model we ourselves advocate. Although the cross section obtained is generally small the calculation reveals certain special circumstances where these reactions may…
The solar LMA neutrino oscillation solution in the Zee model
2001
We examine the neutrino mass matrix in the version of Zee model where both Higgs doublets couple to the leptons. We show that in this case one can accommodate the large mixing angle (LMA) MSW solution of the solar neutrino problem, while avoiding maximal solar mixing and conflicts with constraints on lepton family number-violating interactions. In the simplified scenario we consider, we have the neutrino mass spectrum characterized by $m_1 \simeq m_2 \simeq \sqrt{\Delta m^2_\mathrm{atm}}/\sin 2\theta$ and $m_3/m_1 \simeq \cos 2\theta$, where $\theta$ is the solar mixing angle.
Possible lepton universality breaking in Upsilon decays: a light CP-odd Higgs interpretation and consequences
2011
A light CP-odd Higgs boson mixing with η b hadronic resonances can show up by inducing a slight but observable lepton universality breaking in Upsilon decays. Besides, hyperfine splittings m ϒ ( n S ) − m η b ( n S ) might also be sensitive to the mixing providing another hint of the existence of such a light pseudoscalar Higgs. On the other hand, recent findings from astroparticle and cosmology favouring a light dark matter constituent (with mass about 10 GeV or less) cast a new interest into the search for invisible decays of ϒ resonances performed at B factories.
Phenomenology of supersymmetry with broken R-parity
1985
Abstract In some phenomenological supersymmetric models R -parity (+1 for particles, −1 for sparticles) is spontaneously broken along with tau-lepton number L τ by a vacuum expectation value υ τ of the tau sneutrino ν τ . To avoid excess stellar energy loss through majorons, there should also be explicit L τ violation through right-handed neutrinos. To have a sufficiently light ν τ , either υ τ is very small which is unnatural and boring, and/or the Higgs mixing parameter ϵ is very small. We find that in the limit ϵ → 0: -both the forward-backward asymmetry in e + e − → τ + τ − and the τ lifetime are unchanged, -Z 0 → ggν⊥ decays are possible where ν τ is an extra neutrino, -squarks and glu…
Tau lepton mixing with charginos and its effects on chargino searches at e+e− colliders
1998
In bilinear R-Parity violating models where a term \epsilon_3L_3H_2 is introduced in the superpotential, the tau lepton can mix with charginos. We show that this mixing is fully compatible with LEP1 precision measurements of the Z\tau\tau and W\tau\nu_\tau couplings even for large values of \epsilon_3 and of the induced vacuum expectation value v_3 of the tau-sneutrino. The single production of charginos at e+e- colliders is possible in this case and we present numerical values of the cross-section at LEP1, LEP2 and an NLC. We find maximum values of 10 pb at LEP1 and 1 fb at NLC, while the corresponding values at LEP2 are too small to observe.
Lepton physics versus neutrino mass
1990
Abstract The relationship between the strength of lepton flavour violating processes and the magnitude of the neutrino mass is rather model dependent. I review this question within different neutrino mixing models including superstring inspired models. Processes such as μ → e + γ , μ → 3 e , μ - e conversion in nuclei, etc. as well as lepton flavour violating Z ° decays can occur even if the physical neutrinos are strictly massless. As a result, the corresponding rates are unconstrained by bounds on the neutrino mass that follow from laboratory, astrophysics and cosmology and can therefore be large. Leptonic CP violation may also occur even when the physical neutrinos are strictly massless.
Is charged lepton flavor violation a high energy phenomenon?
2013
Searches for rare processes such as mu --> e gamma put stringent limits on lepton flavour violation expected in many Beyond the Standard Model physics scenarios. This usually precludes the observation of flavour violation at high energy colliders such as the LHC. We here discuss a scenario where right-handed neutrinos are produced via a Z' portal but which can only decay via small flavour violating couplings. Consequently, the process rate is unsuppressed by the small couplings and can be visible despite unobservably small mu --> e gamma rates.
Weakly interacting dark matter particle of a minimal technicolor theory
2007
We consider the possibility that a massive fourth family neutrino, predicted by a recently proposed minimal technicolor theory, could be the source of the dark matter in the Universe. The model has two techniflavors in the adjoint representation of a SU(2) techicolor gauge group and its consistency requires the existence of a fourth family of leptons. By a suitable hypercharge assignment the techniquarks together with the new leptons look like a conventional fourth standard model family. We show that the new (Majorana) neutrino N can be the dark matter particle if m{sub N}{approx}100-500 GeV and the expansion rate of the Universe at early times is dominated by an energy component scaling as…
Measurement of the top pair production cross section in 8 TeV proton-proton collisions using kinematic information in thelepton+jetsfinal state with …
2015
A measurement is presented of the (tt) over bar inclusive production cross section in pp collisions at a center-ofmass energy of pffisffiffi root s = 8 TeV using data collected by the ATLAS detector at the CERN Large Hadron Collider. The measurement was performed in the lepton + jets final state using a data set corresponding to an integrated luminosity of 20.3 fb(-1). The cross section was obtained using a likelihood discriminant fit and b-jet identification was used to improve the signal-to-background ratio. The inclusive (tt) over bar production cross section was measured to be 260 +/- 1(stat)(-23)(+22)(stat) +/- 8(lumi) +/- 4(beam) pb assuming a top-quark mass of 172.5 GeV, in good agre…