The implementation of the full next-to-leading order (NLO) QCD corrections to electroweak Higgs boson plus three jet production at hadron colliders such as the LHC within the Matchbox NLO framework of the Herwig++ event generator is discussed. We pre
sent numerical results for integrated cross sections and kinematic distributions.
Within the framework of the Lee Wick Standard Model (LWSM) we investigate Higgs pair production $gg to h_0 h_0$, $gg to h_0 tilde p_0$ and top pair production $gg to bar tt$ at the Large Hadron Collider (LHC), where the neutral particles from the Hig
gs sector ($h_0$, $tilde h_0$ and $tilde p_0$) appear as possible resonant intermediate states. We investigate the signal $gg to h_0 h_0 to bar b b gamma gamma$ and we find that the LW Higgs, depending on its mass-range, can be seen not long after the LHC upgrade in 2012. More precisely this happens when the new LW Higgs states are below the top pair threshold. In $gg to bar tt$ the LW states, due to the wrong-sign propagator and negative width, lead to a dip-peak structure instead of the usual peak-dip structure which gives a characteristic signal especially for low-lying LW Higgs states. We comment on the LWSM and the forward-backward asymmetry in view of the measurement at the TeVatron. Furthermore, we present a technique which reduces the hyperbolic diagonalization to standard diagonalization methods. We clarify issues of spurious phases in the Yukawa sector.
Weak boson fusion is expected to be an important Higgs production channel at the LHC. Complete one-loop results for weak boson fusion in the Standard Model have been obtained by calculating the full virtual electroweak corrections and photon radiatio
n and implementing these results into the public Monte Carlo program VBFNLO which includes the NLO QCD corrections. Furthermore the dominant supersymmetric one-loop corrections to neutral Higgs production, in the general case where the MSSM includes complex phases, have been calculated. These results have been combined with all one-loop corrections of Standard Model type and with the propagator-type corrections from the Higgs sector of the MSSM up to the two-loop level. Within the Standard Model the electroweak corrections are found to be as important as the QCD corrections after the application of appropriate cuts. The corrections yield a shift in the cross section of order 5% for a Higgs of mass 100-200 GeV, confirming the result obtained previously in the literature. For the production of a light Higgs boson in the MSSM the Standard Model result is recovered in the decoupling limit, while the loop contributions from superpartners to the production of neutral MSSM Higgs bosons can give rise to corrections in excess of 10% away from the decoupling region.
Higgs boson production in association with a hard central photon and two forward tagging jets is expected to provide valuable information on Higgs boson couplings in a range where it is difficult to disentangle weak-boson fusion processes from large
QCD backgrounds. We present next-to-leading order QCD corrections to Higgs production in association with a photon via weak-boson fusion at a hadron collider in the form of a flexible parton-level Monte Carlo program. The QCD corrections to integrated cross sections are found to be small for experimentally relevant selection cuts, while the shape of kinematic distributions can be distorted by up to 20% in some regions of phase space. Residual scale uncertainties at next-to-leading order are at the few-percent level.
Phenomenological implications of a minimal extension to the Standard Model are considered, in which a Nambu-Goldstone boson emerges from the spontaneous breaking of a global U(1) symmetry. This is felt only by a scalar field which is a singlet under
all Standard Model symmetries, and possibly by neutrinos. Mixing between the Standard Model Higgs boson field and the new singlet field may lead to predominantly invisible Higgs boson decays. The natural region in the Higgs boson mass spectrum is determined, where this minimally extended Standard Model is a valid theory up to a high scale related with the smallness of neutrino masses. Surprisingly, this region may coincide with low visibility of all Higgs bosons at the LHC. Monte-Carlo simulation studies of this nightmare situation are performed and strategies to search for such Higgs boson to invisible (Nambu-Goldstone boson) decays are discussed. It is possible to improve the signal-to-background ratio by looking at the distribution of either the total transverse momentum of the leptons and the missing transverse momentum, or by looking at the distribution of the azimuthal angle between the missing transverse momentum and the momentum of the lepton pair for the Z- and Higgs-boson associated production. We also study variations of the model with non-Abelian symmetries and present approximate formulae for Higgs boson decay rates. Searching for Higgs bosons in such a scenario at the LHC would most likely be solely based on Higgs to invisible decays.
We present the NLO QCD corrections for light Higgs pair production via vector boson fusion at the LHC within the CP conserving type II two higgs doublet model in the form of a fully flexible parton--level Monte Carlo program. Scale dependences on int
egrated cross sections and distributions are reduced with QCD K-factors of order unity.
We present the calculation of the dominant next to leading order QCD corrections to Higgs boson production in association with three jets via vector boson fusion in the form of a NLO parton-level Monte Carlo program. QCD corrections to integrated cro
ss sections are modest, while the shapes of some kinematical distributions change appreciably at NLO. Scale uncertainties are shown to be reduced at NLO for the total cross section and for distributions. We consider a central jet veto at the LHC and analyze the veto probability for typical vector boson fusion cuts. Scale uncertainties of the veto probability are sufficiently small at NLO for precise Higgs coupling measurements at the LHC.
