Lightest Neutral Higgs Boson Research Articles

Determining the CP nature of a neutral Higgs boson at the CERN large hadron collider.

We demonstrate that certain weighted moments of $t\anti t \h$ production can provide a determination of the CP nature of a light neutral Higgs boson produced and detected in this mode at the CERN LHC.

Decisive test of superstring-inspired E(6) models.

We point out that in a large class of superstring--inspired $E(6)$ models, either an e+e- collider operating at a center--of--mass energy $\rs= 1.5$ TeV or higher must detect the pair production of charged or neutral exotic leptons, or an e+e- collider with $\rs \geq 300$ GeV must discover at least one light neutral Higgs boson with invisible branching ratio exceeding 50\%. If neither of these two signals is seen, the lightest neutral exotic lepton would overclose the universe, and the model could be completely excluded, independent of the values of the numerous free parameters. Future Higgs searches might lower the energy of the e+e- collider needed to test these models decisively. The only assumptions we have to make are that $R-$parity is exact, so that the lightest exotic lepton is stable if it is lighter than the lightest neutralino, and that no $SO(10)$ singlet scalar gets a vacuum expectation of order $10^{10}$ GeV or higher. If the second condition is violated, the model effectively reduces to an $SO(10)$ model as far as collider experiments are concerned.

Radiative corrections to the masses of supersymmetric Higgs bosons

Abstract The lightest neutral Higgs boson in the minimal supersymmetric extension of the standard model has a tree-level mass less than that of the Z 0 . We calculate radiative corrections to its mass and to that of the heavier CP -even neutral Higgs boson. We find large corrections that increase with the top quark and squark masses, and vary with the ratio of vacuum expectation values ν 2 / ν 1 . These radiative corrections can be as large as O(100) GeV, and have the effect of (i) invalidating lower bounds on ν 2 / ν 1 inferred from unsuccessful Higgs searches at LEP I, (ii) in many cases, increasing the mass of the lighter CP -even Higgs boson beyond m z , (iii) often, increasing the mass of the heavier CP -even Higgs boson beyond the LEP reach, into a range more accessible to the LHC or SSC.

Search for the neutral Higgs bosons of the minimal supersymmetric standard model from Z 0 decays

We present the results from a search for the light neutral scalar Higgs boson h° and the pseudoscalar Higgs boson A° of the minimal super-symmetric standard model. The analysis is based on a data sample corresponding to 71 000 hadronic Z° decays recorded with the L3 detector at LEP. No evidence for the existence of the neutral Higgs bosons h° and A° has been found. The region of h° and A° masses up to 41.5 GeV is excluded at 95% confidence level.

The effect of a light neutral Higgs boson to the Z-lineshape

The cross sections and branching ratios for e +e −→Hqq̄ and e +e −→H ff in the vicinity of the Z boson peak are calculated with the parameters reported by the ALEPH Collaboration at LEP. We find that the light neutral Higgs boson in the mass range below 2 GeV can be determined clearly by the Z-lineshape provided that the event number of Z→hadrons or charged leptons is enhanced to 10 6 or more. To fit the present ALEPH data, the current mass of the top quark in the standard model should be above 1 2 m z .

Two-photon decay width of the Higgs boson in left-right-symmetric theories.

We calculate the ${W}_{R}$ contribution to the two-photon decay width of the light neutral Higgs boson ${H}_{1}^{0}$ in left-right-symmetric models. We find that this contribution is suppressed relative to the standard-model (SM) ${W}_{L}$ contribution by a factor ${(\frac{{M}_{L}}{{M}_{R}})}^{4}$. This result arises because the ${W}_{R}$ coupling to ${H}_{1}^{0}$ is not proportional to its own mass ${M}_{R}$, as a SM-like coupling would suggest, but rather to the lighter mass ${M}_{L}$. As a consequence, $\ensuremath{\Gamma}({H}_{1}^{0}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma})$ in left-right-symmetric theories has essentially the same value as in the standard model.

Lower limit of the Higgs mass from a neutrino experiment

Theoretical predictions of Higgs production from the decay π→evh and of the branching ratio h→e +e − are used to estimate the number of Higgs that would have been detected in the neutrino experiment RSC (BNL) for different Higgs masses. A lower limit for a light neutral Higgs boson is deduced.

Higgs bosons in a nonminimal supersymmetric model.

The minimal supersymmetric standard model contains two Higgs doublets which must mix via a mass parameter whose magnitude remains to be explained. We explore an extension of the minimal model to include a singlet Higgs field whose vacuum expectation value determines the mixing. We study the spectrum and couplings of Higgs bosons in this extended model and compare them with those in the minimal model. We examine a number of limiting cases analytically and also make numerical studies of the extended model both with and without constraints from the renormalization-group analysis of a parent superstring-inspired grand-unified-theory model. We establish the conditions for there to be a charged Higgs boson lighter than the ${W}^{\ifmmode\pm\else\textpm\fi{}}$ and the circumstances under which there is no light neutral Higgs boson. With a particularly simple set of boundary conditions at the unification scale, the renormalization-group equations imply that one or more Higgs bosons are light enough to be found at the CERN LEP or SLAC Linear Collider and that many supersymmetric particles should be accessible to these accelerators and the Fermilab Tevatron; relatively few would require the Superconducting Super Collider, Large Hadron Collider, or a TeV-scale ${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$ collider for discovery. Finally, we analyze the possible production mechanisms and phenomenological signatures of the different Higgs bosons at these machines.

Implications of a light charged Higgs boson

In the standard model with two Higgs doublets, there exists one neutral scalar of mass m 0⩽√2 m + where m + is the mass of the charged Higgs boson. We discuss the implications of such a light neutral Higgs boson in the light of the proposal that the recently observed B 0−B 0 mixing could be due to the contribution of the charged Higgs boson in the box diagram.

Production rates for the light neutral Higgs boson in N = 1 supergravity theories

An evaluation of the expected production rates for the light neutral Higgs boson in canonical N =1 supergravity theories with a minimal low energy particle content is presented for a top quark mass in the range 30 GeV ⩽ m t ⩽ 50 GeV. It is shown that these production rates are suppressed with respect to the corresponding production rates of the conventional Higgs boson by at most a factor of two as long as m t ⩽ 50 GeV.

General upper bounds on the light-neutral-Higgs-boson mass in minimal low-energy supergravity.

Using the most general analytic solutions of the relevant renormalization-group equations for the minimal supersymmetric extension of the standard model, it is explicitly shown through the numerical optimization of the ratio of the two Higgs-field vacuum expectation values that the absolute upper bound for the mass of the light neutral Higgs boson significantly exceeds previous estimates. For a top-quark mass in the range 30< or approx. =m/sub t/< or approx. =50 GeV, this bound is still restrictive enough to have important phenomenological consequences.

Low-energy constraints on supergravity parameters

Abstract We make a careful analysis of the constraints on supergravity parameters from the requirement of SU(2)×U(1) symmetry breaking. Since we obtain fully analytic solutions to the relevant renormalization group equations, we are able to explore the whole range of parameters. Breaking electroweak symmetry with a light top quark leads to a strong correlation between the dimensionless parameters and the mass ratios in the supergravity lagrangian. However, the overall mass scale, e.g. m 3 2 , is not fixed by this requirements. The bound on the lightest neutral Higgs boson is reexamined. The lightest squark is usually an s-top, but we easily find cases where it is a s-bottom. Unfortunately the low-energy constraints provide no useful guidelines for experimentalists.

Single-Majoron emission in micro decay.

The \ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\theta} and \ensuremath{\mu}\ensuremath{\rightarrow}e${\ensuremath{\rho}}_{L}$ decays, where \ensuremath{\theta} is a Nambu-Goldstone boson associated with the B-L breakdown and ${\ensuremath{\rho}}_{L}$ is a very light neutral Higgs boson, are evaluated in the framework of the triplet model of Gelmini and Roncadelli. It is shown that the widths of these decay modes may be comparable to the \ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma} one.

Upper mass bounds for the light neutral higgs boson in N=1 supergravity theories

A new evaluation of absolute upper mass bounds for the light neutral Higgs boson in N=1 supergravity theories with a minimal low energy particle content is presented for a top quark mass in the range 30 GeV⩽ m t ⩽50 GeV. The bounds are found to significantly exceed previous estimated values. The effects due to some noncanonical versions of the model are shown to be rather unimportant. A finite gaugino mass, however, lowers the bounds significantly.