Precise prediction for the mass of the lightest Higgs boson in the MSSM

The leading diagrammatic two-loop corrections are incorporated into the prediction for the mass of the lightest Higgs boson, m_h, in the Minimal Supersymmetric Standard Model (MSSM). The results, containing the complete diagrammatic one-loop corrections, the new two-loop result and refinement terms incorporating leading electroweak two-loop and higher-order QCD contributions, are discussed and compared with results obtained by renormalization group calculations. Good agreement is found in the case of vanishing mixing in the scalar quark sector, while sizable deviations occur if squark mixing is taken into account.     

Decay widths of the neutral \mathcal{CP}-even MSSM Higgs bosons in the Feynman-diagrammatic approach

In the Minimal Supersymmetric Standard Model (MSSM) we incorporate the Higgs-boson propagator corrections, evaluated up to two-loop order, into the prediction of and for . The propagator corrections consist of the full one-loop contribution, including the effects of non-vanishing external momentum, and corrections of at the two-loop level. The results are supplemented with the dominant one-loop QED corrections and final state QCD corrections from both gluons and gluinos. The effects of the two-loop propagator corrections and of the one-loop gluino contributions are investigated in detail. Our results are compared with the result obtained within the renormalization group approach. Agreement within 10% is found for most parts of the MSSM parameter space. Received: 9 March 2000 / Published online: 14 April 2000     

Precise predictions for the Higgs-boson masses in the NMSSM

The particle discovered in the Higgs-boson searches at the LHC with a mass of about \(125 \, \mathrm{GeV}\) can be identified with one of the neutral Higgs bosons of the Next-to-Minimal Supersymmetric Standard Model (NMSSM). We calculate predictions for the Higgs-boson masses in the NMSSM using the Feynman-diagrammatic approach. The predictions are based on the full NMSSM one-loop corrections supplemented with the dominant and sub-dominant two-loop corrections within the Minimal Supersymmetric Standard Model (MSSM). These include contributions at \(\mathcal {O}{(\alpha _t \alpha _s, \alpha _b \alpha _s, \alpha _t^2,\alpha _t\alpha _b)}\), as well as a resummation of leading and subleading logarithms from the top/scalar top sector. Taking these corrections into account in the prediction for the mass of the Higgs boson in the NMSSM that is identified with the observed signal is crucial in order to reach a precision at a similar level as in the MSSM. The quality of the approximation made at the two-loop level is analysed on the basis of the full one-loop result, with a particular focus on the prediction for the Standard Model-like Higgs boson that is associated with the observed signal. The obtained results will be used as a basis for the extension of the code FeynHiggs to the NMSSM.     

Neutral MSSM Higgs-boson production at \mathrm{e^+e^-} colliders in the Feynman-diagrammatic approach

We calculate the cross sections for the neutral Higgs-boson production at colliders in the Minimal Supersymmetric Standard Model (MSSM) using the Feynman-diagrammatic approach and the on-shell renormalization scheme. We incorporate the Higgs-boson propagator corrections, evaluated up to two-loop order, into the prediction of the cross sections for the Higgs-boson production mechanism . The propagator corrections consist of the full one-loop contribution, including the effects of non-vanishing external momentum, and at the two-loop level of the dominant corrections of and further sub-dominant contributions. The results are supplemented with the complete set of one-loop vertex and box corrections. The effects of the two-loop propagator corrections are investigated in detail. We briefly discuss also the effect of the box contributions for high . We compare our results with the case where only the corrections to the effective mixing angle, evaluated within the renormalization-group-improved one-loop Effective Potential approach, are taken into account. We find agreement better than 10% for LEP2 energies and deviations larger than 20% for GeV. Received: 7 February 2001 / Published online: 23 March 2001     

On the NLO QCD corrections to Higgs production and decay in the MSSM

We present explicit analytic results for the two-loop top/stop/gluino contributions to the cross section for the production of CP-even Higgs bosons via gluon fusion in the MSSM, under the approximation of neglecting the Higgs boson mass with respect to the masses of the particles circulating in the loops. The results are obtained employing the low-energy theorem for Higgs interactions adapted to the case of particle mixing. We discuss the validity of the approximation used by computing the first-order correction in an expansion in powers of the Higgs boson mass. We find that, for the lightest CP-even Higgs boson, the gluino contribution is very well approximated by the result obtained in the limit of vanishing Higgs mass. As a byproduct of our calculation, we provide results for the two-loop QCD contributions to the photonic Higgs decay.     

On the radiative corrections to the neutral Higgs boson masses in the NMSSM

We provide a full one-loop calculation of the self energies and tadpoles of the neutral Higgs bosons of the NMSSM. In addition, we compute the two-loop corrections to the neutral Higgs boson masses in the effective potential approximation. With respect to earlier calculations, the newly-computed corrections can account for shifts of a few GeV in the light scalar and pseudoscalar masses, and they can also sizeably affect the mixing between singlet and MSSM-like Higgs scalars. Taking these corrections into account will be crucial for a meaningful comparison between the MSSM and NMSSM predictions for the Higgs sector.     

Higgs boson couplings to bottom quarks: two-loop supersymmetry-QCD corrections

We present two-loop supersymmetry (SUSY) QCD corrections to the effective bottom Yukawa couplings within the minimal supersymmetric extension of the standard model (MSSM). The effective Yukawa couplings include the resummation of the nondecoupling corrections Deltam_{b} for large values of tanbeta. We have derived the two-loop SUSY-QCD corrections to the leading SUSY-QCD and top-quark-induced SUSY-electroweak contributions to Deltam_{b}. The scale dependence of the resummed Yukawa couplings is reduced from O(10%) to the percent level. These results reduce the theoretical uncertainties of the MSSM Higgs branching ratios to the accuracy which can be achieved at a future linear e;{+}e;{-} collider.     

Higher-order corrected Higgs bosons in FeynHiggs2.4

Large higher-order corrections enter the Higgs boson sector of the MSSM via Higgs-boson self-energies. Their effects have to be taken into account for the correct treatment of loop-corrected Higgs-boson mass eigenstates as external (on-shell) or internal particles in Feynman diagrams. We review how the loop corrections, including momentum dependence and imaginary contributions, are correctly taken into account for external (on-shell) Higgs boson and how effective couplings can be derived. The procedures are implemented in the code FeynHiggs2.4.      

Top-quark pair production via polarized and unpolarized protons in the supersymmetric QCD

The QCD corrections to the top-quark pair production via both polarized and unpolarized gluon fusion in pp collisions are calculated in the minimal supersymmetric model (MSSM). We find that the MSSM QCD corrections can reach 4% and may be observable in future precise experiments. Furthermore, we studied CP violation in the MSSM. Our results show that the CP-violating parameter is sensitive to the masses of SUSY particles (it becomes zero when the c.m. energy is less than twice the masses of both the gluino and the stop quarks) and may reach . Received: 30 September 1998 / Revised version: 21 January 1999 / Published online: 28 May 1999     

Search for heavy neutral MSSM Higgs bosons with CMS: reach and Higgs mass precision

The search for MSSM Higgs bosons will be an important goal at the LHC. We analyze the search reach of the CMS experiment for the heavy neutral MSSM Higgs bosons with an integrated luminosity of 30 or 60 fb^-1. This is done by combining the latest results for the CMS experimental sensitivities based on full simulation studies with state-of-the-art theoretical predictions of the MSSM Higgs-boson properties. The results are interpreted in MSSM benchmark scenarios in terms of the parameters tan β and the Higgs-boson mass scale, M_A. We study the dependence of the 5σ discovery contours in the M_A–tan β plane on variations of the other supersymmetric parameters. The largest effects arise from a change in the higgsino mass parameter μ, which enters both via higher-order radiative corrections and via the kinematics of Higgs decays into supersymmetric particles. While the variation of μ can shift the prospective discovery reach (and correspondingly the ”LHC wedge” region) by about Δtan β=10, we find that the discovery reach is rather stable with respect to the impact of other supersymmetric parameters. Within the discovery region we analyze the accuracy with which the masses of the heavy neutral Higgs bosons can be determined. We find that an accuracy of 1–4% should be achievable, which could make it possible in favorable regions of the MSSM parameter space to experimentally resolve the signals of the two heavy MSSM Higgs bosons at the LHC.     

Approximating the radiatively corrected Higgs mass in the minimal supersymmetric model

To obtain the most accurate predictions for the Higgs masses in the minimal supersymmetric model (MSSM), one should compute the full set of one-loop radiative corrections, resum the large logarithms to all orders, and add the dominant two-loop effects. A complete computation following this procedure yields a complex set of formulae which must be analyzed numerically. We discuss a very simple approximation scheme which includes the most important terms from each of the three components mentioned above. We estimate that the Higgs masses computed using our scheme lie within 2 GeV of their theoretically predicted values over a very large fraction of MSSM parameter space.     

The Higgs mass in the CP violating MSSM,NMSSM and beyond

We discuss the automatised calculation of the Higgs mass in renormalisable supersymmetric models with complex parameters at the two-loop level. Our setup is based on the public codes SARAH and SPheno, which can now compute the two-loop corrections to masses of all neutral scalars in such theories. The generic ansatz for these calculations and the handling of the ‘Goldstone Boson catastrophe’ is described. It is shown that we find perfect agreement with other existing two-loop calculations performed in the \(\overline{\mathrm {DR}}\) scheme. We also use the functionality to derive results for the MSSM and NMSSM not available before: the Higgs mass in the constrained version of the complex MSSM and the impact of CP phases in the two-loop corrections beyond \(O(\alpha _s \alpha _t)\) for the scale-invariant NMSSM are briefly analysed.     

Predictions of SUSY masses in the minimal supersymmetric grand unified theory

The Minimal Supersymmetric Standard Model (MSSM) distinguishes itself from other GUT's by a successful prediction of many unrelated phenomena with a minimum number of parameters. Among them: a) Unification of the gauge couplings constants; b) Unification of the b-quark and τ-lepton masses; c) Proton stability; d) Electroweak symmetry breaking at a scale far below the unification scale and the corresponding relation between the gauge boson masses and the top quark mass. A combined fit of the free parameters in the MSSM to these low energy constraints shows that the MSSM model can satisfy these constraints simultaneously. From the fitted parameters the masses of the as yet unobserved superpartners of the SM particles are predicted, the top mass is constrained to a range between 140 and 200 GeV, and the second order QCD coupling constant is required to be between 0.108 and 0.132. The complete second order renormalization group equations for the gauge and Yukawa couplings are used and analytical solutions for the neutral gauge boson, the Higgs masses and the sparticle masses are derived, taking into account the one-loop corrections to the Higgs potential.     

Search for Higgs bosons in {\rm e^+e^-} collisions at 183 GeV

The data collected by the OPAL experiment at GeV were used to search for Higgs bosons which are predicted by the Standard Model and various extensions, such as general models with two Higgs field doublets and the Minimal Supersymmetric Standard Model (MSSM). The data correspond to an integrated luminosity of approximately 54 pb. None of the searches for neutral and charged Higgs bosons have revealed an excess of events beyond the expected background. This negative outcome, in combination with similar results from searches at lower energies, leads to new limits for the Higgs boson masses and other model parameters. In particular, the 95% confidence level lower limit for the mass of the Standard Model Higgs boson is 88.3 GeV. Charged Higgs bosons can be excluded for masses up to 59.5 GeV. In the MSSM, GeV and GeV are obtained for , no and maximal scalar top mixing and soft SUSY-breaking masses of 1 TeV. The range is excluded for minimal scalar top mixing and GeV. More general scans of the MSSM parameter space are also considered. Received: 27 October 1998 / Published online: 19 February 1999     

On the NLO QCD corrections to the production of the heaviest neutral Higgs scalar in the MSSM

We present a calculation of the two-loop top–stop–gluino contributions to Higgs production via gluon fusion in the MSSM. By means of an asymptotic expansion in the heavy particle masses, we obtain explicit and compact analytic formulas that are valid when the Higgs and the top quark are lighter than stops and gluino, without assuming a specific hierarchy between the Higgs mass and the top mass. Being applicable to the heaviest Higgs scalar in a significant region of the MSSM parameter space, our results complement earlier ones obtained with a Taylor expansion in the Higgs mass, and can be easily implemented in computer codes to provide an efficient and accurate determination of the Higgs production cross section.     

Electric dipole moments in the MSSM at large tanβ

Within the minimal supersymmetric standard model (MSSM), the large tanβ regime can lead to important modifications in the pattern of CP-violating sources contributing to low energy electric dipole moments (EDMs). In particular, four-fermion CP-violating interactions induced by Higgs exchange should be accounted for alongside the constituent EDMs of quarks and electrons. To this end, we present a comprehensive analysis of three low energy EDM observables—namely the EDMs of thallium, mercury and the neutron—at large tanβ, in terms of one- and two-loop contributions to the constituent EDMs and four-fermion interactions. We concentrate on the constrained MSSM as well as the MSSM with nonuniversal Higgs masses, and include the CP-violating phases of μ and A. Our results indicate that the atomic EDMs receive significant corrections from four-fermion operators, especially when Im(A) is the only CP-violating source, whereas the neutron EDM remains relatively insensitive to these effects. As a consequence, in a large portion of the parameter space, one cannot infer a separate bound on the electron EDM via the experimental constraint on the thallium EDM. Furthermore, we find that the electron EDM can be greatly reduced due to the destructive interference of one- and two-loop contributions with the latter being dominated by virtual staus.     

Leading Electroweak Corrections to the Neutral Higgs Boson Production at the Fermilab Tevatron

We calculate the leading electroweak corrections to the light neutral Higgs boson production via qq → WH at the Fermilab Tevatron in both the standard model and the minimal supersymmetric model, which arise from the top-quark and Higgs boson loop diagrams. We found that the leading electroweak corrections can exceed the QCD corrections for favorable values of the parameters in the MSSM, but such corrections are only about -2%~-4% in the SM, which are much smaller than the QCD corrections. For the mass region of 90 < mh, < 120 GeV, the leading electroweak corrections can reach -20% for large tan β, and these corrections may be observable at a high luminosity Tevatron; at the least, new constraints on the tan β can be established.     

Two-loop QCD amplitude for gg-->h, H in the minimal supersymmetric standard model

We present the two-loop QCD amplitude for the interaction of two gluons and a CP-even Higgs boson in the minimal supersymmetric standard model (MSSM). We apply a novel numerical method for the evaluation of Feynman diagrams with infrared, ultraviolet, and threshold singularities. We discuss subtleties in the ultraviolet renormalization of the amplitude with conventional dimensional regularization, dimensional reduction, and the four dimensional helicity scheme. Finally, we show numerical results for scenarios of supersymmetry breaking with a rather challenging phenomenology in which the Higgs signal in the MSSM is suppressed in comparison to the standard model.     

The Higgs boson sector of the complex MSSM in the Feynman-diagrammatic approach

In the Minimal Supersymmetric Standard Model with complex parameters (cMSSM) we calculate higher order corrections to the Higgs boson sector in the Feynman-diagrammatic approach using the on-shell renormalization scheme. The application of this approach to the cMSSM, being complementary to existing approaches, is analyzed in detail. Numerical examples for the leading fermionic corrections, including the leading two-loop effects, are presented. Numerical agreement within 10% with other approaches is found for small and moderate mixing in the scalar top sector. The leading fermionic corrections, supplemented by the full logarithmic one-loop and the leading two-loop contributions are implemented into the public Fortran code FeynHiggsFastC. Received: 6 August 2001 / Revised version: 8 October 2001 / Published online: 21 November 2001     

The low energy limit of the minimal nonlinear supersymmetric SU(5)-model; production and decay of Higgs particles

We consider the Higgssector in the low energy limit of the minimal nonlinear supersymmetric SU(5) model. We estimate radiative corrections to the Higgs masses using the effective potential. Furthermore Higgs boson decays are investigated and differences to the MSSM are discussed. Recieved: 28 October 1998 / Revised version: 17 December 1998 / Published online: 1 March 1999