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W. Hollik

Publications and source records attributed to W. Hollik.

At least 73 records · Page 4Linked to original sources
arXiv2004

The Higgs Working Group: Summary Report 2003

Theoretical progress in Higgs boson production and background processes is discussed with particular emphasis on QCD corrections at and beyond next-to-leading order as well as next-to-leading order electroweak corrections. The residual theoretical uncertainties of the investigated processes are estimated in detail. Moreover, recent investigations of the MSSM Higgs sector and other extensions of the SM Higgs sector are presented. The potential of the LHC and a high-energy linear e+e- collider for the measurement of Higgs couplings is analyzed.

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arXiv2004

Electroweak corrections to $γZ$ production at hadron colliders

In this paper we present the results from a calculation of the full electroweak one-loop corrections for $γZ$ vector-boson pair production at hadron colliders. The cases of proton--antiproton as well as proton--proton collisions, at the Tevatron and the LHC, respectively, are considered. Results are presented for the distribution of the $γZ$ invariant mass and for the transverse momentum of the final-state photon. The higher-order electroweak effects are numerically significant, in particular for probing possible anomalous gauge-boson couplings.

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arXiv2004

SUSY-electroweak one-loop contributions to Flavour-Changing Higgs-Boson Decays

The SUSY-EW one-loop quantum contributions to flavour-changing MSSM Higgs-boson decays into $b \bar s$ and $s \bar b$ are computed and discussed. We use the full diagrammatic approach that is valid for all $\tan β$ values and do not rely on the mass-insertion approximation for the characteristic flavour-changing parameter. We analyze in full detail the dependence of these flavour-changing partial widths on all the relevant MSSM parameters and also study the non-decoupling behaviour of these widths with the SUSY mass parameters. We find that these contributions are sizable as compared to the SM ones, and together with the SUSY-QCD contributions they can be very efficient as an indirect method in the future search for Supersymmetry.

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arXiv2003

The sfermion mass spectrum of the MSSM at the one-loop level

The sfermion-mass spectrum of the minimal supersymmetric standard model is investigated at the one-loop level. An on-shell scheme has been specified for renormalization of the basic breaking parameters of the sfermionic sector. Owing to SU(2)-invariance, the soft-breaking mass parameters of the left-chiral scalar fermions of each isospin doublet are identical. Thus, one of the sfermion-masses of each doublet can be expressed in terms of the other masses and receives a mass shift at the one-loop level with respect to the lowest-order value, which can be of $O(10$ GeV). Both strong and electroweak contributions have been calculated for scalar quarks and leptons.

hep-ph↗
arXiv2003

Electroweak radiative corrections to deep-inelastic neutrino scattering - implications for NuTeV ?

We calculate the O(alpha) electroweak corrections to charged- and neutral-current deep-inelastic neutrino scattering off an isoscalar target. The full one-loop-corrected cross sections, including hard photonic corrections, are evaluated and compared to an earlier result which was used in the NuTeV analysis. In particular, we compare results that differ in input-parameter scheme, treatment of real photon radiation and factorization scheme. The associated shifts in the theoretical prediction for the ratio of neutral- and charged-current cross sections can be larger than the experimental accuracy of the NuTeV result.

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arXiv2003

Higgs decays in the Two Higgs Doublet Model: Large quantum effects in the decoupling regime

We study the Higgs-boson decays h0 -> b \bar{b}, h0 -> γγand h0 -> γZ within the framework of the Two Higgs Doublet Model (THDM) in the context of the decoupling regime, together with tree level unitarity constraints. We show that when the light CP-even Higgs boson of the THDM mimics the Standard-Model Higgs boson, not only the one-loop effects to h0 -> {γγ,γZ} but also the one-loop contribution to h0 -> b \bar{b} can be used to distinguish between THDM and SM. The size of the quantum effects in h0 -> b \bar{b} are of the same order as in h0 -> {γγ,γZ} and can reach 25% in both cases.

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arXiv2003

Restoration of supersymmetric Slavnov-Taylor and Ward identities in presence of soft and spontaneous symmetry breaking

Supersymmetric Slavnov-Taylor and Ward identities are investigated in presence of soft and spontaneous symmetry breaking. We consider an abelian model where soft supersymmetry breaking yields a mass splitting between electron and selectron and triggers spontaneous symmetry breaking, and we derive corresponding identities that relate the electron and selectron masses with the Yukawa coupling. We demonstrate that the identities are valid in dimensional reduction and invalid in dimensional regularization and compute the necessary symmetry-restoring counterterms.

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arXiv2003

Complete fermionic two-loop results for the M_W-M_Z interdependence

The complete fermionic two-loop contributions to the prediction for the W-boson mass from muon decay in the electroweak Standard Model are evaluated exactly, i.e. no expansion in the top-quark and the Higgs-boson mass is made. The result for the W-boson mass is compared with the previous result of an expansion up to next-to-leading order in the top-quark mass. The predictions are found to agree with each other within about 5 MeV. A simple parameterization of the new result is presented, approximating the full result better than 0.4 MeV for M_H < 1 TeV.

hep-ph↗
arXiv2003

Electroweak two-loop corrections to the MW-MZ mass correlation in the Standard Model

Recently exact results for the complete fermionic two-loop contributions to the prediction for the W-boson mass from muon decay in the electroweak Standard Model have been published [hep-ph/0007091]. This paper illustrates the techniques that have been applied for this calculation, in particular the renormalisation procedure and the treatment of IR-divergent QED contributions. Numerical results are presented in terms of simple parametrisation formulae and compared in detail with a previous result of an expansion up to next-to-leading order in the top-quark mass. An estimate of the remaining theoretical uncertainties of the MW-prediction from unknown higher-order corrections is given. For the bosonic two-loop corrections a partial result is presented, yielding the Higgs-mass dependence of these contributions.

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arXiv2003

Towards High-Precision Predictions for the MSSM Higgs Sector

The status of the evaluation of the MSSM Higgs sector is reviewed. The phenomenological impact of recently obtained corrections is discussed. In particular it is shown that the upper bound on m_h within the MSSM is shifted upwards. Consequently, lower limits on tan beta obtained by confronting the upper bound as function of tan beta with the lower bound on m_h from Higgs searches are significantly weakened. Furthermore, the region in the M_A-tan beta-plane where the coupling of the lightest Higgs boson to down-type fermions is suppressed is modified. The presently not calculated higher-order corrections to the Higgs-boson mass matrix are estimated to shift the mass of the lightest Higgs boson by up to 3 GeV.

hep-ph↗
arXiv2003

Quantum effects to the Higgs boson self-couplings in the SM and in the MSSM

We show that the effects of heavy Higgs particles and heavy top-squarks in the one-loop self-couplings of the lightest CP-even MSSM Higgs boson decouple from the low energy theory when the self-couplings are expressed in terms of the Higgs boson mass M_h0. Our conclusion is that the h^0 self-interactions become very close to those of the SM Higgs boson and, therefore, MSSM quantum effects could only be revealed by very high precision experiments.

hep-ph↗
arXiv2002

The Higgs Boson Masses of the Complex MSSM: A Complete One-Loop Calculation

In the Minimal Supersymmetric Standard Model with complex parameters (cMSSM) we perform a complete one-loop calculation for the Higgs boson masses (including the momentum dependence) and the mixing angles. These corrections are obtained in the Feynman-diagrammatic approach using the on-shell renormalization scheme. The impact of the newly evaluated corrections is analyzed numerically. The full one-loop result, supplemented by the leading two-loop contributions taken over from the real MSSM are implemented into the public Fortran code FeynHiggs2.0.

hep-ph↗
arXiv2002

Sfermion Precision Measurements at a Linear Collider

At future e+- e- linear colliders, the event rates and clean signals of scalar fermion production - in particular for the scalar leptons - allow very precise measurements of their masses and couplings and the determination of their quantum numbers. Various methods are proposed for extracting these parameters from the data at the sfermion thresholds and in the continuum. At the same time, NLO radiative corrections and non-zero width effects have been calculated in order to match the experimental accuracy. The substantial mixing expected for the third generation sfermions opens up additional opportunities. Techniques are presented for determining potential CP-violating phases and for extracting tan(beta) from the stau sector, in particular at high values. The consequences of possible large mass differences in the stop and sbottom system are explored in dedicated analyses.

hep-ph↗
arXiv2002

Complete electroweak one-loop radiative corrections to top-pair production at TESLA -- a comparison

Electroweak one-loop radiative corrections to the process e^+ e^- -> t tbar are revisited. Two groups from Karlsruhe and Bielefeld/Zeuthen performed independent calculations of both (virtual and soft) QED contributions and weak virtual corrections. For the angular distribution an agreement of at least eight digits for the weak corrections and of at least seven digits for additional photonic corrections is established.

hep-ph↗
arXiv2002

Renormalization of supersymmetric Yang-Mills theories with soft supersymmetry breaking

The renormalization of supersymmetric Yang-Mills theories with soft supersymmetry breaking is presented using spurion fields for introducing the breaking terms. It is proven that renormalization of the fields and parameters in the classical action yields precisely the correct counterterms to cancel all divergences. In the course of the construction of higher orders additional independent parameters appear, but they can be shown to be irrelevant in physics respects. Thus, the only parameters with influence on physical amplitudes are the supersymmetric and the well-known soft breaking parameters.

hep-ph↗
arXiv2002

Complete one-loop corrections to the mass spectrum of charginos and neutralinos in the MSSM

The mass spectrum of the chargino--neutralino sector in the minimal supersymmetric standard model (MSSM) is calculated at the one-loop level, based on the complete set of one-loop diagrams. On-shell renormalization conditions are applied to determine the counterterms for the gaugino-mass-parameters $M_1, M_2$ and the Higgsino-mass parameter $μ$. The input is fixed in terms of three pole masses (two charginos and one neutralino); the other pole masses receive a shift with respect to the tree-level masses, which can amount to several GeV. The detailed evaluation shows that both the fermionic/sfermionic loop contributions and the non-(s)fermionic loop contributions are of the same order of magnitude and are thus relevant for precision studies at future colliders.

hep-ph↗
arXiv2002

The Higgs Working Group: Summary Report (2001)

Report of the Higgs working group for the Workshop `Physics at TeV Colliders', Les Houches, France, 21 May - 1 June 2001. It contains 7 separate sections: A. Theoretical Developments B. Higgs Searches at the Tevatron C. Experimental Observation of an invisible Higgs Boson at LHC D. Search for the Standard Model Higgs Boson using Vector Boson Fusion at the LHC E. Study of the MSSM channel $A/H \to ττ$ at the LHC F. Searching for Higgs Bosons in $t\bar t H$ Production G. Studies of Charged Higgs Boson Signals for the Tevatron and the LHC

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