New fermions at the LHC and mass of the Higgs boson

Unification at MGUT∼3×¹⁰¹⁶ GeV$M_{\mathrm{GUT}}\sim 3\times {10}^{16}\text{GeV}$ of the three Standard Model (SM) gauge couplings can be achieved by postulating the existence of a pair of vectorlike fermions carrying SM charges and masses of order 300 GeV–1 TeV. The presence of these fermions significantly modifies the vacuum stability and perturbativity bounds on the mass of the SM Higgs boson. The new vacuum stability bound in this extended SM is estimated to be 117 GeV, to be compared with the SM prediction of about 128 GeV. An upper bound of 190 GeV is obtained based on perturbativity arguments. The impact on these predictions of type I seesaw physics is also discussed. The discovery of a relatively ‘light’ Higgs boson with mass ∼117 GeV$\sim 117\text{GeV}$ could signal the presence of new vectorlike fermions within reach of the LHC.     

Distinguishing a SM-like MSSM Higgs boson from SM Higgs boson at muon collider

We explore the possibility of distinguishing the SM-like MSSM Higgs boson from the SM Higgs boson via Higgs boson pair production at future muon collider. We study the behavior of the production cross-section in SM and MSSM with Higgs boson mass for various MSSM parameters tan β and m _A . We observe that at fixed CM energy, in the SM, the total cross-section increases with the increase in Higgs boson mass whereas this trend is reversed for the MSSM. The changes that occur for the MSSM in comparison to the SM predictions are quantified in terms of the relative percentage deviation in cross-section. The observed deviations in cross-section for different choices of Higgs boson masses suggest that the measurements of the cross-section could possibly distinguish the SM-like MSSM Higgs boson from the SM Higgs boson.      

Background and signal estimation for a low mass Higgs boson at the LHC

The discovery of the Higgs boson(s) is the major goal of the LHC which will start taking data in 2008. In this work a data driven extraction of the background and statistical signal significance in the H→ZZ→4ℓ decay channel is presented. The background for Higgs masses as low as 130 GeV can be extracted with an error of 20%, using a sideband measurement from a single 30 fb^-1 experiment. The predicted background distribution is best described by a double asymmetric Gaussian. An analytic formula is introduced which provides an accurate p-value that a Higgs discovery claim is consistent with a background fluctuation. The formula can be used in a single real measurement at LHC using as input the measured background and the profile likelihood asymmetric errors of this measurement. The method presented here can be applied to the general case of extrapolating from a signal-free data region to a candidate signal region. This is the case of supersymmetry searches at the LHC. PACS  14.80.Bn; 06.20.Dk     

Inflation,LHC and the Higgs boson

After the Higgs boson has been discovered, the Standard Model of particle physics became a confirmed theory, potentially valid up to the Planck scale and allowing one to trace the evolution of the Universe from the inflationary stage till the present days. We discuss the relation between the results from the LHC and the inflationary cosmology. We overview the Higgs inflation, and its relation to the possible metastability of the electroweak vacuum. A short overview of the bounds on the metastability of the electroweak vacuum in the models with inflation not related to the Higgs boson is presented.     

Mass and width of a composite Higgs boson

The scalar Higgs boson mass in a Technicolor model was obtained by Elias and Scadron with the analysis of an homogeneous Bethe–Salpeter equation (BSE), however it was performed before the most recent developments of walking gauge theories. It was not observed in their work that dynamically generated technifermion mass may vary according to the theory dynamics that forms the scalar bound state. This will be done in this work and we also call attention that their calculation must change to take into account the normalization condition of the BSE. We compute the width of the composite boson and show how the gauge group and fermion content of a technicolor theory can be inferred from the measurement of the mass and width of the scalar boson.     

Four weak gauge boson production at photon linear collider and heavy Higgs signal

We study the signals and backgrounds for a heavy Higgs boson in the processes γγ → WWWW, γ → WWZZ at the proton linear collider. The results are based on the complete tree-level SM calculation for these reactions. We show that the invariant mass spectrum of central WW, ZZ pairs is sensitive to the signal from Higgs boson with a mass up to 1 TeV linear collider for integrated luminosity of 300 fb⁻¹. At 1.5 TeV PLC Higgs boson with a mass up to 700 GeV can be studied. The nonresonant longitudinal gauge boson scattering (m_H = ∞) can be detected in photon-photon collisions at e⁺e⁻ center-of-mass energy of 3 TeV.     

Ways to detect a light Higgs boson at the LHC

We summarize the possible processes which may be used to search for a Higgs boson, of mass in the range 114-130 GeV, at the LHC. We discuss, in detail, two processes with rapidity gaps: exclusive Higgs production with tagged outgoing protons and production by Weak Boson Fusion, in each case taking as the signal. We make an extensive study of all possible backgrounds, and discuss the relevant experimental issues. We emphasize the special features of these signals, and of their background processes, and show that they could play an important role in identifying a light Higgs boson at the LHC. Received: 5 July 2002 / Published online: 30 August 2002     

Associated production of Higgs boson and tt at LHC

One of the future goals of the LHC is to precisely measure the properties of the Higgs boson. The associated production of a Higgs boson and top quark pair is a promising process to investigate the related Yukawa interaction and the properties of the Higgs. Compared with the pure scalar sector in the Standard Model, the Higgs sector contains both scalars and pseudoscalars in many new physics models, which makes the ttH interaction more complex and provides a variety of phenomena. To investigate the ttH interaction and the properties of the Higgs, we study the top quark spin correlation observables at the LHC.     

LHT model and Higgs boson production in association with a weak gauge boson at the LHC

Considering the process pp → VH+X(V = W or Z) is a significant channel for searching for a light Higgs boson,we calculate the contributions of the littlest Higgs model with T-parity(called LHT model) to its production cross section.We find that,in most of the parameter space,the value of the relative correction parameter R is very small.However,with reasonable values of the free parameters,its value can be significantly larger.     

具有T宇称的最小Higgs模型与LHC上Higgs波色子与弱规范波色子的联合产生

Considering the process pp→VH ＋X（V = W or Z） is a significant channel for searching for a light Higgs boson, we calculate the contributions of the littlest Higgs model with T-parity （called LHT model） to its production cross section. We find that, in most of the parameter space, the value of the relative correction parameter R is very small. However, with reasonable values of the free parameters, its value can be significantly larger.