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W. Hollik

Publications and source records attributed to W. Hollik.

At least 91 records · Page 5Linked to original sources
arXiv2002

FeynHiggs1.2: Hybrid MSbar/on-shell Renormalization for the CP-even Higgs Boson Sector in the MSSM

An updated version is presented of the Fortran code FeynHiggs for the evaluation of the neutral CP-even Higgs sector masses and mixing angles. It differs from the previous version by a modification of the renormalization scheme concerning the treatment of subleading terms at the one-loop level; the two-loop corrections, for which the leading contributions of O(alpha_t alphas) and O(alpha_t^2) are implemented, are not affected by the modified renormalization prescription. Besides stabilizing the Higgs mass calculations and avoiding unphysically large threshold effects, the mass of the lightest MSSM Higgs boson, m_h, is increased by 1-2 GeV for most parts of the MSSM parameter space.

hep-ph↗
arXiv2001

Top Dipole Form Factors and Loop-induced CP-violation in Supersymmetry

The one-loop Minimal Supersymmetric Standard Model (MSSM) contributions to the weak and electromagnetic dipole form factors of the top quark are presented. Far from the Z peak, they are not sufficient to account for all the new physics effects. In the context of the calculation of the process e^+e^- -> t tbar to one loop in the MSSM, we compare the impact on the phenomenology of the CP-violating dipole form factors of the top quark with the contribution from CP-violating box graphs. Some exemplificative observables are analyzed and the relevance of both the contributions is pointed out. The one-loop expressions for the electromagnetic and weak dipole form factors in a general renormalizable theory and the SM and MSSM couplings and conventions are also given.

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arXiv2001

Dipole Form Factors and Loop-induced CP-violation in Supersymmetry

The one-loop Minimal Supersymmetric Standard Model (MSSM) contributions to the weak and electromagnetic dipole form factors of heavy fermions are reviewed. For the $Z$ boson on shell, the weak-magnetic and weak-electric dipole moments of the $τ$ lepton and the $b$ quark can be defined and directly connected to observables. But far from the $Z$ peak, the weak and electromagnetic dipole form factors are not enough to account for all the new physics effects. In the context of the calculation of the process $e^+e^-\to t\bar{t}$ to one loop in the MSSM, we compare the impact on the phenomenology of the CP-violating dipole form factors of the top quark with the contribution from CP-violating box graphs. Some exemplificative observables are analyzed and the relevance of both the contributions is pointed out. The set of tensor integrals employed, the one-loop expressions for the electromagnetic and weak dipole form factors in a general renormalizable theory and the SM and MSSM couplings and conventions are also given.

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arXiv2001

Electroweak Radiative Corrections to Neutral-Current Drell-Yan Processes at Hadron Colliders

We calculate the complete electroweak O(alpha) corrections to pp, pbar p -> l+l- X (l=e, mu) in the Standard Model of electroweak interactions. They comprise weak and photonic virtual one-loop corrections as well as real photon radiation to the parton-level processes q bar q -> gamma,Z -> l+l-. We study in detail the effect of the radiative corrections on the l+l- invariant mass distribution, the cross section in the Z boson resonance region, and on the forward-backward asymmetry, A_FB, at the Fermilab Tevatron and the CERN Large Hadron Collider. The weak corrections are found to increase the Z boson cross section by about 1%, but have little effect on the forward-backward asymmetry in the Z peak region. Threshold effects of the W box diagrams lead to pronounced effects in A_FB at m(l+l-) approx 160 GeV which, however, will be difficult to observe experimentally. At high di-lepton invariant masses, the non-factorizable weak corrections are found to become large.

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arXiv2001

Regularization and supersymmetry-restoring counterterms in supersymmetric QCD

We calculate symmetry-restoring counterterms in supersymmetric QCD at the one-loop level. First we determine loop corrections to the supersymmetry and gauge transformations and find counterterms in such a way that the symmetry algebra holds at the one-loop level. Then these results are used to derive the symmetry-restoring counterterms to all trilinear interactions. In order to obtain unique results it is crucial to use the Slavnov-Taylor identity, which does not only contain supersymmetric and gauge Ward identities but also describes the symmetry algebra. In dimensional regularization this procedure yields unique non-zero values for the counterterms. In contrast, in dimensional reduction we find that no non-symmetric counterterms are needed, neither for the symmetry transformations nor for the physical interactions. For the considered cases this result constitutes a definite test of the supersymmetry and gauge invariance of the scheme.

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arXiv2001

Neutral MSSM Higgs-boson production at e+e- colliders in the Feynman-diagrammatic approach

We calculate the cross sections for the neutral Higgs-boson production at e+e- 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 e+e- -> hZ, hA. 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 O(alpha alpha_s) 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 $\sqrt{s}$. 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 $\sqrt{s}$ = 500 GeV.

hep-ph↗
arXiv2001

Two-loop electroweak contributions to $Δr$

A review is given on the quantum correction $Δr$ in the $W$--$Z$ mass correlation at the electroweak two-loop level, as derived from the calculation of the muon lifetime in the Standard Model. Exact results for $Δr$ and the $W$-mass prediction including ${\mathcal{O}}(α^2)$ corrections with fermion loops are presented and compared with previous results of a next-to-leading order expansion in the top-quark mass.

hep-ph↗
arXiv2000

Radiative Corrections to Chargino Production in Electron-Positron Collisions

The results of a complete one-loop calculation for the production of chargino pairs in electron-positron collisions, including the option of polarized beams, are presented. The calculation has been performed in the on-shell renormalization scheme. Applications to the integrated cross section, to the forward-backward asymmetry for unpolarized beams, and to the left-right asymmetry show that the higher-order effects have a sizeable influence on the theoretical predictions and therefore should be properly taken into account for detailed studies in the MSSM.

hep-ph↗
arXiv2000

Calculation of fermionic two-loop contributions to muon decay

The computation of the correction Δr in the W-Z mass correlation, derived from muon decay, is described at the two-loop level in the Standard Model. Technical aspects which become relevant at this level are studied, e.g. gauge-parameter independent mass renormalization, ghost-sector renormalization and the treatment of γ_5. Exact results for Δr and the W mass prediction including O(α^2) corrections with fermion loops are presented and compared with previous results of a next-to-leading order expansion in the top-quark mass.

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arXiv2000

Reconciling the Two-Loop Diagrammatic and Effective Field Theory Computations of the Mass of the Lightest CP-even Higgs Boson in the MSSM

The mass of the lightest CP-even Higgs boson of the minimal supersymmetric extension of the Standard Model (MSSM) has previously been computed including O(alpha alpha_s) two-loop contributions by an on-shell diagrammatic method, while approximate analytic results have also been obtained via renormalization-group-improved effective potential and effective field theory techniques. Initial comparisons of the corresponding two-loop results revealed an apparent discrepancy between terms that depend logarithmically on the supersymmetry-breaking scale, and different dependences of the non-logarithmic terms on the squark mixing parameter, X_t. In this paper, we determine the origin of these differences as a consequence of different renormalization schemes in which both calculations are performed. By re-expressing the on-shell result in terms of MS-bar parameters, the logarithmic two-loop contributions obtained by the different approaches are shown to coincide. The remaining difference, arising from genuine non-logarithmic two-loop contributions, is identified, and its effect on the maximal value of the lightest CP-even Higgs boson mass is discussed. Finally, we show that in a simple analytic approximation to the Higgs mass, the leading two-loop radiative corrections can be absorbed to a large extent into an effective one-loop expression by evaluating the running top quark mass at appropriately chosen energy scales.

hep-ph↗
arXiv2000

Physics Impact of GigaZ

By running the prospective high-energy e^+ e^- collider TESLA in the GigaZ mode on the Z resonance, experiments can be performed on the basis of more than 10^9 Z events. They will allow the measurement of the effective electroweak mixing angle to an accuracy of approximately +- 10^-5. Likewise the W boson mass is expected to be measurable with an error of about 6 MeV near the W^+ W^- threshold. In this note, we study the accuracy with which the Higgs boson mass can be determined from loop corrections to these observables in the Standard Model. The comparison with a directly observed Higgs boson may be used to constrain new physics scales affecting the virtual loops. We also study constraints on the heavy Higgs particles predicted in the Minimal Supersymmetric Standard Model, which are very difficult to observe directly for large masses. Similarly, it is possible to constrain the mass of the heavy scalar top particle.

hep-ph↗
arXiv2000

Constraints on tan beta in the MSSM from the Upper Bound on the Mass of the Lightest Higgs boson

We investigate the possibilities for constraining tan beta within the MSSM by combining the theoretical result for the upper bound on the lightest Higgs-boson mass as a function of tan beta with the informations from the direct experimental search for this particle. We discuss the commonly used ``benchmark'' scenario, in which the parameter values m_top = 175 GeV and M_susy = 1 TeV are chosen, and analyze in detail the effects of varying the other SUSY parameters. We furthermore study the impact of the new diagrammatic two-loop result for mh, which leads to an increase of the upper bound on mh by several GeV, on present and future constraints on tan beta. We suggest a slight generalization of the ``benchmark'' scenario, such that the scenario contains the maximal possible values for mh(tan beta) within the MSSM for fixed m_top and M_susy. The implications of allowing values for m_top, M_susy beyond the ``benchmark'' scenario are also discussed.

hep-ph↗
arXiv2000

Pair production of charged MSSM Higgs bosons by gluon fusion

The production of pairs of charged Higgs bosons as predicted by the minimal supersymmetric standard model (MSSM) via the gluon fusion mechanism is investigated. The amplitudes at the leading one-loop order for the parton process gg -> H+ H- are calculated with the complete set of MSSM particles. Numerical results are presented for the cross section of the inclusive hadron process p p -> gg -> H+ H- + X at the LHC.

hep-ph↗
arXiv2000

Top-Quark Production and Decay in the MSSM

We review the features of top-quark decays and loop-induced effects in the production cross section and CP-violating observables of e+e- -> t t-bar which are specific to the R-parity conserving Minimal Supersymmetric Standard Model (MSSM).

hep-ph↗
arXiv2000

Decay widths of the neutral 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 $Γ$(h -> ff) and BR(h -> ff) for f = b, c, $τ$. The propagator corrections consist of the full one-loop contribution, including the effects of non-vanishing external momentum, and corrections of O(alpha alpha_s) 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.

hep-ph↗
arXiv2000

FeynHiggsFast: a program for a fast calculation of masses and mixing angles in the Higgs Sector of the MSSM

FeynHiggsFast is a Fortran code for the calculation of the masses and the mixing angle of the neutral CP-even Higgs bosons in the MSSM up to two-loop order. It is based on a compact analytical approximation formula of the complete diagrammatic one-loop and the dominant two-loop contributions. At the one-loop level a leading logarithmic result is used, taking into account all sectors of the MSSM. At the two-loop level at O(alpha alpha_s) the leading logarithmic and non-logarithmic contributions are taken into account. The approximation formula is valid for arbitrary choices of the parameters in the Higgs sector of the model. Comparing its quality to the full diagrammatic result, we find agreement better than 2 GeV for most parts of the MSSM parameter space.

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