We study the production and decay of fourth generation leptons at the Large Hadron Collider (LHC).We find that for charged leptons with masses under a few hundred GeV, the dominant collider signal comes from the production through a W-boson of a char
ged and neutral fourth generation lepton. We present a sensitivity study for this process in events with two like-sign charged leptons and at least two associated jets. We show that with sqrts = 7 TeV and 1 inverse fb of data, the LHC can exclude fourth generation charged leptons with masses up to 250 GeV.
We revisit the current experimental bounds on fourth-generation Majorana neutrino masses, including the effects of right handed neutrinos. Current bounds from LEPII are significantly altered by a global analysis. We show that the current bounds on fo
urth generation neutrinos decaying to eW and mu W can be reduced to about 80 GeV (from the current bound of 90 GeV), while a neutrino decaying to tau W can be as light as 62.1 GeV. The weakened bound opens up a neutrino decay channel for intermediate mass Higgs, and interesting multi-particle final states for Higgs and fourth generation lepton decays.
In models of maximal flavor violation (MxFV) there is at least one new scalar $Phi_{FV}$ which couples to the quarks via $Phi_{FV} q_i q_j propto xi_{ij}$ where $xi_{i3},xi_{3i} sim V_{tb}$ for $i = 1,2$ and $xi_{33} sim V_{td}$ and $V$ is the CKM ma
trix. In this article, we explore the potential phenomenological implications of MxFV for collider experiments. We study MxFV signals of same-sign leptons from same-sign top-quark pair production at the Tevatron and at the LHC. We show that the current Tevatron dataset has strong sensitivity to this signature, for which there are no current limits. For example, if $m_{Phi_{FV}} sim 200$ GeV and the MxFV coupling $xi$ has a natural value of $sim 1$, we expect $sim 12$ MxFV events to survive a selection requiring a pair of same-sign leptons, a tagged $b$-jet and missing transverse energy, over a background of approximately 4-5 events.
