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B. Grzadkowski

Publications and source records attributed to B. Grzadkowski.

At least 37 records · Page 2Linked to original sources
arXiv2001

CP Violation in Higgs-Boson Interactions

We consider a general two-Higgs-doublet model with CP violation in the scalar sector, that leads, at the one-loop level of the perturbation expansion, to CP-violation in the process $e^+e^- \to t\bar{t} \to l^\pm ...$ and $e^+e^- \to t\bar{t} \to b/\bar{b} ...$. The goal of this study is to include {\it consistently} CP-violating effects in distributions of top-quark decay products ($l^\pm$ or $b/\bar{b}$) that emerge {\it both} from $t\bar{t}$ production {\it and} from $t$ or $\bar{t}$ decay processes.

hep-ph↗
arXiv2000

Do precision electroweak constraints guarantee $e^+e^-$ collider discovery of at least one Higgs boson of a two-Higgs-doublet model?

We consider a CP-conserving two-Higgs-doublet type II model with a light scalar or pseudoscalar neutral Higgs boson ($\h=\hl$ or $\h=\ha$) that has no $ZZ/WW$ coupling and, thus, cannot be detected in $\epem\to Z\h$ (Higgs-strahlung) or $ν\antiν\h$ (via $WW$ fusion). Despite sum rules which ensure that the light $\h$ must have significant $t\anti t$ or $b\anti b$ coupling, for a wedge of moderate $\tanb$, that becomes increasingly large as $\mh$ increases, the $\h$ can also escape discovery in both $b\anti b \h$ and $t\anti t \h$ production at a $\rts=500-800\gev$ $\epem$ collider (for expected luminosities). If the other Higgs bosons happen to be too heavy to be produced, then no Higgs boson would be detected. We demonstrate that, despite such high masses for the other Higgs bosons, only the low-$\tanb$ portion of the no-discovery wedges in $[\mh,\tanb]$ parameter space can be excluded due to failure to fit precision electroweak observables. In the $\tanb\gsim 1$ regions of the no-discovery wedges, we find that the 2HDM fit to precision electroweak observables has small $Δχ^2$ relative to the best minimal one-doublet SM fit.

hep-ph↗
arXiv2000

Search Strategies for Non-Standard Higgs Bosons at Future e^+e^- Colliders

Already in the simplest two-Higgs-doublet model with CP violation in the Higgs sector, the $3\times3$ mixing matrix for the neutral Higgs bosons can substantially modify their couplings, thereby endangering the ``classical'' Higgs search strategies. However, there are sum rules relating Yukawa and Higgs-Z couplings which ensure that the ZZ, $b\anti b$ and $t\anti t$ couplings of a given neutral 2HDM Higgs boson cannot all be simultaneously suppressed. This result implies that any single Higgs boson will be detectable at an e^+e^- collider if the Z+Higgs, $b\anti b+$Higgs {\it and} $t\anti t+$Higgs production channels are all kinematically accessible {\it and} if the integrated luminosity is sufficient. We explore, as a function of Higgs mass, the luminosity required to guarantee Higgs boson detection, and find that for moderate $\tanβ$ values the needed luminosity is unlikely to be available for all possible mixing scenarios. The additional difficulties for the case when the two-doublet Higgs sector is extended by adding one more singlet are summarized. Implications of the sum rules for Higgs discovery at the Tevatron and LHC are briefly discussed.

hep-ph↗
arXiv2000

Signals of CP Violation in Distributions of Top-Quark Decay Products at Linear Colliders

Angular and energy distributions for leptons and bottom quarks in the process e+e- --> t tbar --> l/b ... have been calculated assuming the most general top-quark couplings. The double distributions depend both on modification of the top-quark production and tbW decay vertices. However, the leptonic angular distribution turned out to be insensitive to non-standard parts of tbW vertex. The method of optimal observables have been used to estimate sensitivity of future measurements at linear e+e- colliders

hep-ph↗
arXiv2000

How Valuable is Polarization at a Muon Collider? A Test Case: Determining the CP Nature of a Higgs Boson

We study the use of polarization asymmetries at a muon collider to determine the CP-even and CP-odd couplings of a Higgs boson to $μ^+mu^-$. We determine achievable accuracy as a function of beam polarization and luminosity. The appropriate techniques for dealing with the polarization precession are outlined. Strategies especially appropriate for a two-Higgs-doublet model (including the MSSM) are given. Our general conclusion is that polarization will be very useful, especially if the proton source is such that full luminosity in the storage ring can be retained even after imposing cuts on the originally accepted muons necessary for $P\gsim 0.4$ for each beam.

hep-ph↗
arXiv1999

Probing Top-Quark Couplings at Polarized NLC

The energy spectrum of the lepton(s) in e^+e^- --> tt-bar --> l^{+-} ...../l^+l^-..... at next linear colliders (NLC) is studied for arbitrary longitudinal beam polarizations as a possible test of new physics in top-quark couplings. The most general non-standard couplings for gamma-tt-bar, Ztt-bar and Wtb vertices are considered. Expected precision of the non-standard-parameter determination is estimated applying the optimal-observable procedure.

hep-ph↗
arXiv1999

Finding the CP-Violating Higgs Bosons at e^+e^- Colliders

We discuss a general two-Higgs-doublet model with CP violation in the Higgs sector. In general, the three neutral Higgs fields of the model all mix and the resulting physical Higgs bosons have no definite CP properties. We derive a new sum rule relating Yukawa and Higgs-Z couplings which implies that a neutral Higgs boson cannot escape detection at an e^+e^- collider if it is kinematically accessible in Z+Higgs, $b\anti b+$Higgs and $t\anti t+$Higgs production, irrespective of the mixing angles and the masses of the other neutral Higgs bosons. We also discuss modifications of the sum rules and their phenomenological consequences in the case when the two-doublet Higgs sector is extended by adding one or more singlets.

hep-ph↗
arXiv1998

Effects of Non-Standard Interactions for the Energy Spectrum of Secondary Leptons in e^+e^- --> t t-bar

The process of top-quark pair production followed by semileptonic decays at future high-energy e^+e^- linear colliders is investigated as a possible test of physics beyond the Standard Model. Assuming the most general non-standard forms for gamma t t-bar, Z t t-bar and Wtb couplings, the energy spectrum of the single lepton l^{+-} and the energy correlation of l^+ and l^- emerging from the process e^+e^- --> t t-bar --> l^{+-} ... /l^+l^- ... are calculated. Expected precision of the non-standard-parameter determination is estimated adopting the recently-proposed optimal method.

hep-ph↗
arXiv1998

Four-Fermi Effective Operators in Top-Quark Production and Decay

Effects of four-Fermi-type new interactions are studied in top-quark pair production and their subsequent decays at future e^+e^- colliders. Secondary-lepton-energy distributions are calculated for arbitrary longitudinal beam polarizations. An optimal-observables procedure is applied for the determination of new parameters.

hep-ph↗
arXiv1997

CP Violation, Top Quarks and the Tevatron Upgrade

In order to observe a signal of possible CP violation in top-quark couplings, we study top-quark production and decay under the conditions of the Tevatron upgrade. Transverse energy asymmetries sensitive to CP violation are defined. Applying the recently proposed optimal method, we calculate the statistical significance for the direct observation of CP violation in the production and subsequent decay of top quarks.

hep-ph↗
arXiv1997

LEP Limits on CP-Violating Non-Minimal Higgs Sectors

We derive a sum rule which shows how to extend LEP limits on the masses of the lightest CP-even and CP-odd Higgs bosons of a CP-conserving two-Higgs-doublet model to any two Higgs bosons of a general CP-violating two-Higgs-doublet model. We generalize the analysis to a Higgs sector consisting of an arbitrary number of Higgs doublets and singlets, giving explicit limits for the CP-conserving and CP-violating two-doublet plus one-singlet Higgs sectors.

hep-ph↗
arXiv1996

Probing CP Violation via Top Polarization at NLC

Possible $CP$-violation in top-quark couplings is discussed. It is shown that the lepton-energy distributions in $e^+ e^- \to t\bar{t} \to \ell^+\ell^-X / \ell^\pm X$ at next linear colliders (NLC) could give us useful information for this study. The statistical significance of $CP$-violating-parameter determination is estimated.

hep-ph↗
arXiv1996

Determining the top-antitop and $ZZ$ Couplings of a Neutral Higgs Boson of Arbitrary CP Nature at the NLC

The optimal procedure for extracting the coefficients of different components of a cross section which takes the form of unknown coefficients times functions of known kinematical form is developed. When applied to $\epem\to t\anti t+$Higgs production at $\rts=1\tev$ and integrated luminosity of $200\fbi$, we find that the $t\anti t\to$Higgs CP-even and CP-odd couplings and, to a lesser extent, the $ZZ\to$Higgs (CP-even) coupling can be extracted with reasonable errors, assuming the Higgs sector parameter choices yield a significant production rate. Indeed, the composition of a mixed-CP Higgs eigenstate can be determined with sufficient accuracy that a SM-like CP-even Higgs boson can be distinguished from a purely CP-odd Higgs boson at a high level of statistical significance, and vice versa.

hep-ph↗
arXiv1995

CP VIOLATION IN FERMIONIC DECAYS OF HIGGS BOSONS

We demonstrate that decay angle correlations in $\taum\taup$ and $t\anti t$ decay modes could allow a determination of whether or not a neutral Higgs boson is a CP eigenstate. Sensitivity of the correlations is illustrated in the case of the $\epem\rta Z \hn$ and $\mupmum\rta \hn$ production processes for a two-doublet Higgs model with CP-violating neutral sector. A very useful technique for minimizing `depolarization' factor suppressions of the correlations is introduced.

hep-ph↗
arXiv1995

Using Decay Angle Correlations to Detect CP Violation in the Neutral Higgs Sector

We demonstrate that decay angle correlations in $\taum\taup$ and $t\anti t$ decay modes could allow a determination of whether or not a neutral Higgs boson is a CP eigenstate. Sensitivity of the correlations is illustrated in the case of the $\epem\rta Z \hn$ and $\mupmum\rta \hn$ production processes for a two-doublet Higgs model with CP-violating neutral sector. A very useful technique for minimizing `depolarization-factor' suppressions of the correlations in the $t\anti t$ mode is introduced.

hep-ph↗