Higgs Physics at the Large Hadron Collider

In this talk I will begin by summarising the importance of the Higgs physics studies at the LHC. I will then give a short description of the pre-LHC constraints on the Higgs mass and the theoretical predictions for the LHC along with a discussion of the current experimental results, ending with prospects in the near future at the LHC. In addition to the material covered in the presented talk, I have included in the writeup, a critical appraisal of the theoretical uncertainties in the Higgs cross-sections at the Tevatron as well as a discussion of the recent experimental results from the LHC which have become available since the time of the workshop.Comment: LateX, 12 figures, 15 pages, Presented at the XIth Workshop on High Energy Physics Phenomenology, 2010, Ahmedabad, Indi

New one-loop techniques and first applications to LHC phenomenology

In this talk we describe our approach for the computation of multi-leg one-loop amplitudes and present some first results relevant for LHC phenomenology.Comment: 5 pages, to appear in the proceedings of the conference "Loops and Legs", Eisenach, 200

Next-to-leading order corrections to Wt production and decay

We present the results of a next-to-leading order calculation of Wt production, including the decays of both the top quark and the W boson. The effects of radiation in the decay of the top quark are also included. The separation of diagrams which appear in the real corrections, into singly- and doubly-resonant contributions, is performed using a b-jet veto which is motivated by the use of the bottom quark distribution function. We find that, for a choice of scale which is suitable for this approach, the QCD corrections are very mild and only change the cross section by up to 10% at the LHC, depending on the severity of the b-jet veto. When further cuts are applied, applicable for a Higgs boson search in the H->WW channel, we find that the radiative effects greatly decrease the number of background events expected from this process. In addition, the shapes of relevant distributions can be significantly changed at next-to-leading order.Comment: 31 pages, 12 figure

Higgs Boson Production and Decay in Little Higgs Models with T-parity

We study Higgs boson production and decay in a certain class of Little Higgs models with T-parity in which some T-parity partners of the Standard Model (SM) fermions gain their masses through Yukawa-type couplings. We find that the Higgs boson production cross section of a 120 GeV Higgs boson at the CERN LHC via gg fusion process at one-loop level could be reduced by about 45%, 35% and 20%, as compared to its SM prediction, for a relatively low new particle mass scale f = 600, 700 and 1000 GeV, respectively. On the other hand, the weak boson fusion cross section is close to the SM value. Furthermore, the Higgs boson decay branching ratio into di-photon mode can be enhanced by about 35% in small Higgs mass region in certain case, for the total decay width of Higgs boson in the Little Higgs model is always smaller than that in the SM.Comment: Replaced with version to appear in Phys. Lett. B, typos corrected and references adde

Soft gluons in Higgs plus two jet production

We investigate the effects of an all order QCD resummation of soft gluon emissions for Higgs boson production in association with two hard jets. We consider both the gluon-gluon fusion and weak boson fusion processes and show how to resum a large part of the leading logarithms in the jet veto scale. Our resummation improves on previous analyses which also aim to include the effects of multiple soft gluon radiation. In addition we calculate the interference between weak boson fusion and gluon-gluon fusion and find that it is small.Comment: 15 pages and 5 figure

Two-loop electroweak corrections to the Higgs-boson decay H -> gamma gamma

The complete set of two-loop electroweak corrections to the decay width of the Higgs boson into two photons is presented. Two-loop contributions involving weak bosons and the top quark are computed in terms of an expansion in the Higgs external momentum. Adding these results to the previously known light fermion contributions, we find that the total electroweak corrections for a Higgs boson with 100 GeV <m_H < 150 GeV are moderate and negative, between -4% < delta_EW < 0%. Combination with the QCD corrections, which are small and positive, gives a total correction to the one-loop results of | delta_{EW+QCD}|< 1.5 %.Comment: 15 page

On the top-antitop invariant mass spectrum at the LHC from a Higgs boson signal perspective

We investigate the effect of one-loop corrections of ${\cal O}(\alpha_S^2\alpha_W)$ on the $t\bar t$ invariant mass spectrum at the Large Hadron Collider (LHC) in presence of both resonant and non-resonant Higgs boson effects. We show that corrections of ${\cal O}(\alpha_S^2\alpha_W)$ involving a non-resonant Higgs boson are comparable to or even larger than those involving interference with the s-channel resonant Higgs boson amplitude and that both of these are subleading with respect to all other (non-Higgs) diagrams through that order. We also compute the contribution through ${\cal O}(\alpha_S^2\alpha_W^2)$ of resonant Higgs boson production (i.e. Higgs production via $gg$ fusion) as well as the pure QCD ones of ${\cal O}(\alpha_S^3)$. Altogether, we show that the well known peak-dip structure of the $M_{t\bar t}$ spectrum emerging from interference effects between the $t,u$-channel $gg$-induced Leading Order (LO) QCD diagrams and the one due to a Higgs boson in s-channel via $gg$-fusion is drastically swamped by the remainder of the terms of ${\cal O}(\alpha_S^2\alpha_W)$ discussed above.Comment: 6 pages, 8 figure

Soft-gluon effects in WW production at hadron colliders

We consider QCD radiative corrections to WW pair production in hadron collisions. We perform a calculation that consistently combines next-to-leading order predictions with soft-gluon resummation valid at small transverse momenta ptWW of the WW pair. We present results for the ptWW distribution at the LHC up to (almost) next-to-next-to-leading logarithmic accuracy, and study the effect of resummation on the charged-lepton distributions. Soft-gluon effects are typically mild, but they can be strongly enhanced when hard cuts are applied. The relevant distributions are generally well described by the MC@NLO event generator.Comment: 15 pages, 12 postscript figures. Error corrected in NLO plot for WW transverse-mass distribution. Results unchange

Higgs phenomenology of supersymmetric economical 3-3-1 model

We explore the Higgs sector in the supersymmetric economical 3-3-1 model and find new features in this sector. The charged Higgs sector is revised i.e., in difference of the previous work, the exact eigenvalues and states are obtained without any approximation. In this model, there are three Higgs bosons having masses equal to that of the gauge bosons--the W and extra X and Y. There is one scalar boson with mass of 91.4 GeV, which is closed to the $Z$ boson mass and in good agreement with present limit: 89.8 GeV at 95% CL. The condition of eliminating for charged scalar tachyon leads to splitting of VEV at the first symmetry breaking, namely, $w \simeq w^\prime$. The interactions among the standard model gauge bosons and scalar fields in the framework of the supersymmetric economical 3-3-1 model are presented. From these couplings, at some limit, almost scalar Higgs fields can be recognized in accordance with the standard model. The hadronic cross section for production of the bilepton charged Higgs boson at the CERN LHC in the effective vector boson approximation is calculated. Numerical evaluation shows that the cross section can exceed 35.8 fb.Comment: 33 pages, 1 figur

Next-to-leading order QCD corrections to W+W−W^+W^- production at the LHC in Randall Sundrum model

We present next-to-leading order QCD corrections to production of two $W$ bosons at the LHC in the Randall-Sundrum model. Various kinematical distributions are obtained to order $\alpha_s$ in QCD by taking into account all the parton level subprocesses. We estimate the impact of the QCD corrections on various observables and find that they are significant. We also show the reduction in factorization scale uncertainty when ${\cal O}(\alpha_s)$ effects are included.Comment: 16 pages, 5 figure