Multiphoton radiation in leptonic <Emphasis Type="Italic">W</Emphasis>-boson decays

We explore CP violation in decay processes in the presence of the anomalous right-handed and couplings. The complex anomalous top coupling can be a source of new CP violation and may lead to a deviation of the observed weak phase in decays, which accounts for the present disagreement of the observed between and decays. Direct CP violation is also predicted. Received: 27 November 2002, Revised: 28 March 2003, Published online: 2 June 2003     

Jet production in charged current deep inelastic <Emphasis Type="Italic">e</Emphasis><Superscript> + </Superscript><Emphasis Type="Italic">p</Emphasis> scatteringat HERA

The production rates and substructure of jets have been studied in charged current deep inelastic e ⁺ p scattering for Q ² > 200 GeV² with the ZEUS detector at HERA using an integrated luminosity of 110.5 pb^-1. Inclusive jet cross sections are presented for jets with transverse energies GeV and pseudorapidities in the range . Dijet cross sections are presented for events with a jet having GeV and a second jet having GeV. Measurements of the mean subjet multiplicity, , of the inclusive jet sample are presented. Predictions based on parton-shower Monte Carlo models and next-to-leading-order QCD calculations are compared to the measurements. The value of , determined from at for jets with GeV, is . The mean subjet multiplicity as a function of Q ² is found to be consistent with that measured in NC DIS.Received: 5 June 2003, Published online: 10 October 2003     

Probing the light neutral Higgs boson scenario of the <Emphasis Type="Italic">CP</Emphasis>-violating MSSM Higgs sector at the LHC

In the CP-violating minimal supersymmetric standard model (MSSM), for certain values of the CP-violating phases associated to the universal trilinear couplings (A_t, A_b) and the gluino mass , e.g., or , for GeV and -5, the lightest Higgs boson mass ( ) is GeV. This mass interval is still allowed by results of standard LEP Higgs searches because of a strongly suppressed H₁ZZ coupling. However, in the same region of parameter space in which these two conditions occur, the coupling is enhanced because the two mentioned sets of couplings satisfy a sum rule. In this paper we probe such a light Higgs scenario at the Large Hadron Collider (LHC) by studying associate production, leading to a signal. We show that the latter is readily accessible at the CERN hadron collider, upon the application of suitable selection cuts against the standard model (SM) backgrounds. Our parton level Monte Carlo (MC) analysis yields -45 signal events, completely free of SM background, for - 30 fb^-1 of accumulated luminosity, after taking into account the overall efficiency for tagging four b-jets.Received: 21 February 2005, Published online: 6 July 2005     

Lepton flavor violating <Emphasis Type="Italic">Z</Emphasis>-decays in supersymmetric seesaw model

In the supersymmetric seesaw model, large flavor mixings of sleptons induce the lepton flavor violating (LFV) interactions ( ), which give rise to various LFV processes. In this work we examine the LFV decays . Subject to the constraints from the existing neutrino oscillation data and the experimental bounds on the decays , these LFV Z-decays are found to be sizable, and among them the largest-rate channel can occur with a branching ratio of 10^-8 and may be accessible at the LHC or GigaZ experiment.Received: 1 September 2003, Published online: 20 November 2003     

Dilaton field induces a commutative D<Emphasis Type="Italic">p</Emphasis>-brane coordinate

It is well known that the space-time coordinates and the corresponding Dp-brane world-volume become non-commutative when the ends of the open string are attached to a Dp-brane with the Neveu-Schwarz background field . In this paper, we extend these considerations by including an additional dilaton field , linear in . In that case, the conformal part of the world-sheet metric becomes a new non-commutative variable, while the coordinate in the direction orthogonal to the hyper plane becomes commutative. Received: 15 November 2004, Revised: 11 May 2005, Published online: 6 October 2005 PACS: . Work supported in part by the Serbian Ministry of Science and Environmental Protection, under contract No. 1486.     

<Emphasis Type="Italic">CP</Emphasis> violation in the 3 jet and 4 jet decays of the <Emphasis Type="Italic">Z</Emphasis> boson at GigaZ

We review CP-violating effects in jet and 4 jet decays, assuming the presence of CP-violating effective and couplings. Longitudinal beam polarization is included in the studies. We propose a direct search for such CP-violating couplings by using various CP-odd observables. The data of a future linear collider running at the Z-resonance in the so-called GigaZ option should give significant information on the couplings. Finally we show that stringent bounds on the mass of excited b quarks can be derived if appropriate couplings are of a size characteristic of a strong interaction.Received: 21 August 2003, Published online: 20 November 2003     

<Emphasis Type="Italic">T</Emphasis>-odd correlations in the decay of scalar fermions

We define a CP-sensitive asymmetry in the sfermion decays , based on triple product correlations between the momenta of the outgoing fermions. We study this asymmetry in the MSSM with complex parameters. We show that the asymmetry is sensitive to the phases of the parameters and M₁. The leading contribution stems from the decay chain , for which we obtain analytic formulae for the amplitude squared. The asymmetry can go up to for , and up to for . We also estimate the rates necessary to measure the asymmetry.Received: 2 July 2003, Revised: 7 November 2003, Published online: 13 February 2004     

Jet production in <Emphasis Type="Italic">pA</Emphasis> and <Emphasis Type="Italic">AA</Emphasis> collisions in the perturbative QCD pomeron model

Inclusive cross-sections for gluon jet production are studied numerically in the perturbative QCD pomeron model for pA and central AA collisions at high energies. Two forms for the inclusive cross-sections, with and without emission from the triple pomeron vertex, are compared. The difference was found to reduce to a numerical factor for momenta below the saturation momentum Q _s. Above Q _s no difference was found at all. For pA collisions the gluon spectrum was found to be at momenta k below Q _s and above it. For central AA collisions it was found to be at momenta k below Q _s and above it. At large k the spectrum goes like , flattening with energy. The multiplicities turned out to be proportional to A ^0.7 for pA collisions and A for central AA collisions with a good precision. In the latter case they are becoming more peaked at the center with the growth of energy. Their absolute values are high and grow rapidly with energy in accordance with the high value of the BFKL intercept.Received: 12 October 2004, Revised: 22 November 2004, Published online: 21 January 2005     

Updated estimate of the muon magnetic momentusing revised results from <Emphasis Type="Italic">e</Emphasis><Superscript> + </Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>-</Superscript>annihilation

A new evaluation of the hadronic vacuum polarization contribution to the muon magnetic moment is presented. We take into account the reanalysis of the low-energy e ⁺ e ^-annihilation cross section into hadrons by the CMD-2 Collaboration. The agreement between e ⁺ e ^-and spectral functions in the channel is found to be much improved. Nevertheless, significant discrepancies remain in the center-of-mass energy range between 0.85 and , so that we refrain from averaging the two data sets. The values found for the lowest-order hadronic vacuum polarization contributions are where the errors have been separated according to their sources: experimental, missing radiative corrections in e ⁺ e ^-data, and isospin breaking. The corresponding Standard Model predictions for the muon magnetic anomaly read where the errors account for the hadronic, light-by-light (LBL) scattering and electroweak contributions. The deviations from the measurement at BNL are found to be (1.9 ) and (0.7 ) for the e ⁺ e ^-- and -based estimates, respectively, where the second error is from the LBL contribution and the third one from the BNL measurement.Received: 7 September 2003, Published online: 30 October 2003     

Inclusive photoproduction of <Emphasis Type="Italic">D</Emphasis><Superscript>*</Superscript> mesons with massive charm quarks

We have calculated the next-to-leading order cross sections for the inclusive production of D ^* mesons in collisions at HERA in two approaches using massive or massless charm quarks. The usual massive theory for the direct cross section with charm quarks only in the final state was transformed into a massive theory with subtraction by subtracting the mass divergent and additional finite terms calculated earlier in connection with the process . This theory approaches the massless theory with increasing transverse momentum. The difference between the massive and the massless approach with subtraction is studied in detail in those kinematic regions relevant for comparison with experimental data. With these results and including the resolved cross section which is dominated by the part originating from the charm in the photon, we compute the fully inclusive cross section and compare it with preliminary data from the ZEUS collaboration at HERA. We find on average good agreement.Received: 5 October 2004, Published online: 26 November 2004     

<Emphasis Type="Italic">T</Emphasis>-dependent Dyson-Schwinger equation in IR regime of QCD: the critical point

The quark mass function in QCD is revisited, using a gluon propagator in the form 1/(k ² + m _g ²) plus , where the second (IR) term gives linear confinement for m _g = 0 in the instantaneous limit, being another scale. To find we propose a new (differential) form of the Dyson-Schwinger equation (DSE) for , based on an infinitesimal subtractive renormalization via a differential operator which lowers the degree of divergence in integration on the RHS, by two units. This warrants in the integrand since its k-dependence is no longer sensitive to the principal term (p-k)² in the quark propagator. The simplified DSE (which incorporates the Ward-Takahashi (WT) identity in the Landau gauge) is satisfied for large p ² by = , except for Log factors. The limit p ² = 0 determines . A third limit, p ² = -m ₀ ², defines the dynamical mass m ₀ via . After two checks ( MeV and = ), for with MeV, the T-dependent DSE is used in the real time formalism to determine the critical index analytically, with the IR term partly serving as the H-field. We find MeV and check the vanishing of and at T _c.Received: 31 August 2004, Published online: 11 January 2005PACS: 24.85. + p, 12.38.Lg, 12.38.AwA.N. Mitra: Permanent address: 244 Tagore Park, Delhi-110009, India.     

Flavor changing neutral currents from lepton and <Emphasis Type="Italic">B</Emphasis> decays in the two Higgs doublet model

Constraints on the whole spectrum of lepton flavor violating vertices are shown in the context of the standard two Higgs doublet model. The vertex involving the e- mixing is much more constrained than the others, and the decays proportional to such a vertex are usually very suppressed. On the other hand, bounds on the quark sector are obtained from leptonic decays of the B_d,s⁰ mesons and from . We emphasize that although the B_d⁰- mixing restricts severely the d-b mixing vertex, the upper bound for this vertex could still give a sizable contribution to the decay with respect to the standard model contribution, from which we see that such a vertex could still play a role in the phenomenology.Received: 16 September 2004, Published online: 26 April 2005PACS: 12.60.Fr, 12.15.Mm, 12.15.Ff, 11.30.Hv     

Measurement of high-<Emphasis Type="Italic">Q</Emphasis><Superscript>2</Superscript> charged current cross sections in <Emphasis Type="Italic">e</Emphasis><Superscript> + </Superscript><Emphasis Type="Italic">p</Emphasis> deep inelastic scattering at HERA

Cross sections for e ⁺ p charged current deep inelastic scattering at a centre-of-mass energy of have been determined with an integrated luminosity of collected with the ZEUS detector at HERA. The differential cross sections , and for are presented. In addition, has been measured in the kinematic range and . The predictions of the Standard Model agree well with the measured cross sections. The mass of the W boson propagator is determined to be from a fit to . The chiral structure of the Standard Model is also investigated in terms of the (1-y)² dependence of the double-differential cross section. The structure-function has been extracted by combining the measurements presented here with previous ZEUS results from e ^- p scattering, extending the measurement obtained in a neutrino-nucleus scattering experiment to a significantly higher Q ² region.Received: 17 July 2003, Published online: 12 November 2003 ^a supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) ^b supported by the German Federal Ministry for Education and Research (BMBF), under contract numbers HZ1GUA 2, HZ1GUB 0, HZ1PDA 5, HZ1VFA 5 ^c supported by the MINERVA Gesellschaft für Forschung GmbH, the Israel Science Foundation, the U.S.-Israel Binational Science Foundation and the Benozyio Center for High Energy Physics ^d supported by the German-Israeli Foundation and the Israel Science Foundation ^e supported by the Italian National Institute for Nuclear Physics (INFN) ^f supported by the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) and its grants for Scientific Research ^g supported by the Korean Ministry of Education and Korea Science and Engineering Foundation ^h supported by the Netherlands Foundation for Research on Matter (FOM) ⁱ supported by the Polish State Committee for Scientific Research, grant no. 620/E-77/SPUB-M/DESY/P-03/DZ 247/2000-2002 ^j partially supported by the German Federal Ministry for Education and Research (BMBF) ^k supported by the Fund for Fundamental Research of Russian Ministry for Science and Education and by the German Federal Ministry for Education and Research (BMBF) ^l supported by the Spanish Ministry of Education and Science through funds provided by CICYT ^m supported by the Particle Physics and Astronomy Research Council, UK ⁿ supported by the US Department of Energy ^o supported by the US National Science Foundation ^p supported by the Polish State Committee for Scientific Research, grant no. 112/E-356/SPUB-M/DESY/P-03/DZ 301/2000-2002, 2 P03B 13922 ^q supported by the Polish State Committee for Scientific Research, grant no. 115/E-343/SPUB-M/DESY/P-03/DZ 121/2001-2002, 2 P03B 07022     

<Emphasis Type="Italic">B</Emphasis><Subscript><Emphasis Type="Italic">K</Emphasis></Subscript> from the lattice with Wilson quarks

We report our results for the bag parameter B _K obtained from the quenched simulations on the lattice with Wilson fermions for three values of the lattice spacing. We implemented the method by which no subtraction of the mixing with other four-fermion operators is needed. Our final result, in terms of the renormalization group invariant bag parameter, is .Received: 9 July 2004, Revised: 27 July 2004, Published online: 21 September 2004     

Twist-3 distribution amplitudes of the pion and kaon from the QCD sum rules

Twist-3 distribution amplitudes of the pion and kaon are studied in this paper. We calculate the first several moments for the twist-3 distribution amplitudes ( and ) of the pion and kaon by applying the QCD sum rules. Our results show that (i) the first three moments of and the first two moments of and of the pion and kaon can be obtained with 30 uncertainty; (ii) the fourth moment of the and the second moment of the can be obtained when the uncertainty are relaxed to 35 ; (iii) the fourth moment of the can be obtained only when the uncertainty are relaxed to 40 ; (iv) we have and after including the -corrections to the perturbative part. These moments will be helpful for constructing the twist-3 wave functions of the pion and kaon.Received: 6 January 2005, Revised: 29 March 2005, Published online: 22 June 2005PACS: 13.20.He, 11.55.Hx     

Complete one-loop calculation of the <Emphasis Type="Italic">T</Emphasis>-violating <Emphasis Type="Italic">D</Emphasis>-parameter in neutron decay in the MSSM

We investigate the violation of time reversal invariance in the decay of the free neutron in the framework of the minimal supersymmetric standard model (MSSM). The coefficient of the triple product of the neutron spin and the momenta of electron and neutrino, the so-called D parameter, is computed at one-loop order including all diagrams. We find that D is mainly sensitive to the trilinear A coupling in the squark sector and to the phase of the coefficient which mixes the two Higgs superfields. The maximal MSSM contribution using parameters still allowed by experiment is however at , while QED final state interactions give a value of . Explicit expressions for all relevant diagrams are given in an appendix.Received: 3 March 2003, Revised: 16 May 2003, Published online: 3 July 2003     

Hunting a light <Emphasis Type="Italic">CP</Emphasis>-violating Higgs boson via diffraction at the LHC

We study the central diffractive production of the (three neutral) Higgs bosons, with a rapidity gap on either side, in an MSSM scenario with CP-violation. We consider the and decay for the light H₁ boson and the four b-jet final state for the heavy H₂ and H₃ bosons, and discuss the corresponding backgrounds. A direct indication of the existence of CP-violation can come from the observation of either an azimuthal asymmetry in the angular distribution of the tagged forward protons (for the exclusive process) or of a contribution in the azimuthal correlation between the transverse energy flows in the proton fragmentation regions for the process with the diffractive dissociation of both incoming protons ( ). We emphasise the advantage of reactions with the rapidity gaps (that is, production by pomeron-pomeron fusion) to probe CP-parity and to determine the quantum numbers of the produced central object.Received: 16 January 2004, Published online: 31 March 2004     

Flavour-independent h<Superscript>0</Superscript>A<Superscript>0</Superscript> search and two Higgs doublet model interpretation of neutral Higgs boson searches at LEP

Upper limits on the cross-section of the pair-production process , assuming 100 branching fraction to hadrons, are derived from a new search for the hadrons final state, independently of the hadronic flavour of the decay products. This study, combined with previously published searches for the neutral Higgs bosons h⁰ and A⁰, is used to constrain the Type II Two Higgs Doublet Model (2HDM(II)) with no CP violation in the Higgs sector and no additional non-Standard Model particles besides the five Higgs bosons. The analysis combines LEP1 and LEP2 data collected with the OPAL detector up to the highest available centre-of-mass energies. The searches are sensitive to the and decay modes of the Higgs bosons. A benchmark scan of the 2HDM(II) parameter space is performed. Large regions of the 2HDM(II) parameter space explored are excluded at the 95% CL in the ( and planes, using both direct neutral Higgs boson searches and indirect limits derived from Standard Model high precision measurements. The region GeV and GeV is excluded at 95 % CL, independently of and for selected values of which are representative of a complete -scan.Received: 28 July 2004, Revised: 4 January 2005, Published online: 3 March 2005     

Exclusive radiative and electroweak b\to d and b\to s penguin decays at NLO

We provide standard model expectations for the rare radiative decays , and , and the electroweak penguin decays and at the next-to-leading order (NLO), extending our previous results to transitions. We consider branching fractions, isospin asymmetries and direct CP asymmetries. For the electroweak penguin decays, the lepton-invariant mass spectrum and forward-backward asymmetry is also included. Radiative and electroweak penguin transitions in are mainly interesting in the search for new flavor-changing neutral current interactions, but in addition the decays provide constraints on the CKM parameters . The potential impact of these constraints is discussed.Received: 16 January 2005, Published online: 16 March 2005 Corresponding author: Th. Feldmann     

Vector-meson electroproduction at small Bjorken-<Emphasis Type="Italic">x</Emphasis> and generalized parton distributions

We analyze electroproduction of light vector mesons ( ) at small Bjorken-x in an approach that includes the gluonic generalized parton distributions and a partonic subprocess, , . The subprocess is calculated to lowest order of perturbative QCD taking into account the transverse momenta of the quark and antiquark as well as Sudakov suppressions. Our approach allows us to investigate the transition amplitudes for all kinds of polarized virtual photons and polarized vector mesons. Modeling the generalized parton distributions through double distributions and using simple Gaussian wavefunctions for the vector mesons, we compute the longitudinal and transverse cross sections at large photon virtualities as well as the spin-density matrix elements for the vector mesons. Our results are in fair agreement with the findings of recent experiments performed at HERA.Received: 3 February 2005, Revised: 9 May 2005, Published online: 28 June 2005