Radovan Dermisek

Limits on Vectorlike Leptons from Searches for Anomalous Production of Multi-Lepton Events

A bstractWe consider extensions of the Standard Model by vectorlike leptons and set limits on a new charged lepton, e4±, using the ATLAS search for anomalous production of multi-lepton events. It is assumed that only one Standard Model lepton, namely the muon, dominantly mixes with vectorlike leptons resulting in possible decays e4± → W±νμ, e4± → Zμ±, and e4± → hμ±. We derive generally applicable limits on the new lepton treating the branching ratios for these processes as free variables. We further interpret the general limits in two scenarios with e4± originating predominantly from either the SU(2) doublet or the SU(2) singlet. The doublet case is more constrained as a result of larger production cross-section and extra production processes e4±ν4 and ν4ν4 in addition to e4±e4−, where ν4 is a new neutral state accompanying e4. We find that some combinations of branching ratios are poorly constrained, whereas some are constrained up to masses of more than 500 GeV. In the doublet case, assuming BR(ν4 → Wμ) = 1, all masses below about 300 GeV are ruled out. Even if this condition is relaxed and additional decay modes, ν4 → Zνμ and ν4 → hνμ, are allowed, below the Higgs threshold still almost all of the parameter space (of independent branching ratios) is ruled out. Nevertheless, even assuming the maximal production cross-section, which coincides with the doublet case, the new charged lepton can still be as light as the LEP-II limit allows. We discuss several possible improvements of current experimental analyses that would dramatically reduce the allowed parameter space, even with current data.

Direct production of a light CP-odd Higgs boson at the Tevatron and LHC

We show that the existing CDF L=630 pb{sup -1} Tevatron data on pp{yields}{mu}{sup +{mu}-}X places substantial limits on a light CP-odd Higgs boson a with m{sub a} 2m{sub {tau}}for which BR(a{yields}{mu}{sup +{mu}-}) is relatively small. Extrapolation of this existing CDF analysis to L=10 fb{sup -1} suggests that Tevatron limits on the abb coupling strength in the region m{sub a}>8 GeV could be comparable to or better than limits from Upsilon decays in the m{sub a}<7 GeV region. We also give rough estimates of future prospects at the LHC, demonstrating that early running will substantially improve limits on a light a (or perhaps discover a signal). In particular, outside the Upsilon peak region, integrated luminosity of only 5 fb{sup -1}-20 fb{sup -1} (depending on m{sub a} and {radical}(s)) could reveal a peak in M{sub {mu}}{sup +}{sub {mu}}{sup -} and will certainly place important new limits on a light a. The importance of such limits in the context of next-to-minimal supersymmetric model Higgs discovery and (g-2){sub {mu}}are outlined.

A new avenue to charged Higgs discovery in multi-Higgs models

A bstractCurrent searches for the charged Higgs at the LHC focus only on the τν, cs, and tb final states. Instead, we consider the process pp → Φ → W±H∓ → W+W−A where Φ is a heavy neutral Higgs boson, H± is a charged Higgs boson, and A is a light Higgs boson, with mass either below or above the

Two Higgs doublet model with vectorlike leptons and contributions to pp → W W and H → W W

b\overline{b}

Contributions of flavor violating couplings of a Higgs boson to pp → W W

threshold. The cross-section for this process is typically large when kinematically open since H± → W±A can be the dominant decay mode of the charged Higgs. The final state we consider has two leptons and missing energy from the doubly leptonic decay of the W+W− and possibly additional jets; it is therefore constrained by existing SM Higgs searches in the W+W− channel. We extract these constraints on the cross-section for this process as a function of the masses of the particles involved. We also apply our results specifically to a type-II two Higgs doublet model with an extra Standard-Model-singlet and obtain new and powerful constraints on mH ± and tan β. We point out that a slightly modified version of this search, with more dedicated cuts, could be used to possibly discover the charged Higgs, either with existing data or in the future.

YUKAWA COUPLING UNIFICATION IN SO(10) SUPERSYMMETRIC GRAND UNIFIED THEORIES

A bstractWe study a two Higgs doublet model extended by vectorlike leptons mixing with one family of standard model leptons. Generated flavor violating couplings between heavy and light leptons can dramatically alter the decay patterns of heavier Higgs bosons. We focus on pp → H → ν4νμ → W μνμ, where ν4 is a new neutral lepton, and study possible effects of this process on the measurements of pp → W W and H → W W since it leads to the same final states. We discuss predictions for contributions to pp → W W and H →WW and their correlations from the region of the parameter space that satisfies all available constraints including precision electroweak observables and from pair production of vectorlike leptons. Large contributions, close to current limits, favor small tan β region of the parameter space. We find that, as a result of adopted cuts in experimental analyses, the contribution to pp → W W can be an order of magnitude larger than the contribution to H → W W . Thus, future precise measurements of pp → W W will further constrain the parameters of the model. In addition, we also consider possible contributions to pp → W W from the heavy Higgs decays into a new charged lepton e4 (H → e4μ → W μνμ), exotic SM Higgs decays, and pair production of vectorlike leptons.

Trilepton Signatures of Light Charged and CP-odd Higgs Bosons in Top Quark Decays

A bstractWe study contributions to pp→W+W−→ℓνℓℓ′νℓ′

New decay modes of heavy Higgs bosons in a two Higgs doublet model with vectorlike leptons

pp\to {W}^{+}{W}^{-}\to \ell {\nu}_{\ell }{\ell}^{\prime }{\nu}_{\ell^{\prime }}