The contribution of off-shell gluons to the structure functions F 2 and F_{\mathrm {L}}^c and the unintegrated gluon distributions

We calculate the perturbative parts of the structure functions F ₂ ^c and for a gluon target having non-zero transverse momentum squared at order . The results of the double convolution (with respect to the Bjorken variable and the transverse momentum) of the perturbative part and the unintegrated gluon densities are compared with the HERA experimental data for F ₂ ^c . The contribution from the structure function ranges in 10-30% of that of F ₂ ^c at the kinematical range of the HERA experiments. Received: 18 April 2002 / Revised version: 24 July 2002 / Published online: 7 October 2002 RID="a" ID="a" e-mail: kotikov@sunse.jinr.ru RID="b" ID="b" e-mail: gonzalo@fpaxp1.usc.es     

Fourth generation effects in processes induced by the $b \rightarrow s$ transition

We study the effects of sequential fourth quark generation in rare decays induced by the transition and in B _s ⁰- mixing. Using the experimental values on the branching ratios of the and decays, the allowed regions for and are determined as a function of the t ^' quark mass. Received: 3 April 2003 / Published online: 2 June 2003 RID="a" ID="a" e-mail: taliev@metu.edu.tr RID="b" ID="b" e-mail: ozpineci@ictp.trieste.it RID="c" ID="c" e-mail: savci@metu.edu.tr     

Spin structure function g 1 (x, Q) and the DHGHY integral I(Q) at low Q: predictions from the GVMD model

Theoretical predictions for the polarized nucleon structure function g ₁ (x, Q ² ) at low Q² are obtained in the framework of the generalized vector meson dominance model. Contributions from both light and heavy vector mesons are evaluated. In the photoproduction limit the first moment of g₁ is related to the static properties of the nucleon via the Drell-Hearn-Gerasimov-Hosoda-Yamamoto sum rule. This property is employed to fix the magnitude of the light vector meson contribution to g₁, using the recent measurements in the region of baryonic resonances. The results are compared to the data on g ₁ (x, Q ² ). Finally, the DHGHY moment function I(Q ² ) is calculated, and our theoretical predictions are confronted with the recent preliminary data obtained at the Jefferson Laboratory. Received: 9 July 2002 / Published online: 7 October 2002 RID="a" ID="a" e-mail: badelek@fuw.edu.pl RID="b" ID="b" e-mail: jan.kwiecinski@ifj.edu.pl RID="c" ID="c" e-mail: ziaja@tsl.uu.se     

Extraction of the neutron charge form factor G<Superscript>n</Superscript><Subscript>E</Subscript>(Q<Superscript>2</Superscript>) from the charge form factor of deuteron G<Superscript>d</Superscript><Subscript>C</Subscript>(Q<Superscript>2</Superscript>)

We extract the neutron charge form factor G ⁿ _E(Q ²) from the charge form factor of deuteron G ^d _C(Q ²) obtained from T ₂₀(Q ²) data at 0≤Q ²≤ 1.717 (GeV/c)². The extraction is based on the relativistic impulse approximation in the instant form of the relativistic Hamiltonian dynamics. Our results (12 new points) are compatible with existing values of the neutron charge form factor of other authors. We propose a fit for the whole set (36 points) taking into account the data for the slope of the form factor at Q ² = 0. Received: 26 July 2002 / Accepted: 18 September 2002 / Published online: 4 February 2003 RID="a" ID="a"e-mail: krutov@ssu.samara.ru RID="b" ID="b"e-mail: troitsky@theory.sinp.msu.ru Communicated by V.V. Anisovich     

Nucleon form factors from a covariant quark core: Limits in their description

In treating the relativistic 3-quark problem, a dressed-quark propagator parameterization is used which is compatible with recent lattice data and pion observables. Furthermore 2-quark correlations are modeled as a series of quark loops in the scalar and axialvector channel. The resulting reduced Faddeev equations are solved for nucleon and delta. Nucleon electromagnetic form factors are calculated in a fully covariant and gauge-invariant scheme. Whereas the proton electric form factor G _E and the nucleon magnetic moments are described correctly, the neutron electric form factor and the ratio G _E/G _M for the proton appear to be quenched. The influence of vector mesons on the form factors is investigated which amounts to a 25% modification of the electromagnetic proton radii within this framework. Received: 16 April 2002 / Accepted: 29 August 2002 / Published online: 17 January 2003 RID="a" ID="a"Supported by a Feodor-Lynen fellowship of the Alexander-von-Humboldt foundation and the Australian Research Council. RID="b" ID="b"Address after April 30: MPI für Metallforschung, Heisenbergstr. 1, 70569 Stuttgart, Germany. RID="c" ID="c"e-mail: Reinhard.Alkofer@uni-tuebingen.de Communicated by A. Sch?fer     

Chiral order and fluctuations in multi-flavour QCD

Multi-flavour chiral perturbation theory (PT) may exhibit instabilities due to vacuum fluctuations of sea pairs. Keeping the fluctuations small would require a very precise fine tuning of the low-energy constants and to , . A small deviation from these critical values - like the one suggested by the phenomenology of OZI-rule violation in the scalar channel - is amplified by huge numerical factors inducing large effects of vacuum fluctuations. This would lead in particular to a strong N_f dependence of chiral symmetry breaking (SB) and a suppression of the multi-flavour chiral order parameters. A simple resummation is shown to cure the instability of PT, but it modifies the standard expressions of some O(p ² ) and O(p ⁴ ) low-energy parameters in terms of observables. On the other hand, for r= m _s /m &gt; 15, the two-flavour condensate is not suppressed, due to the contribution induced by massive vacuum pairs. Thanks to the latter, the standard two-flavour PT is protected from multi-flavour instabilities and could provide a well-defined expansion scheme in powers of non-strange quark masses. Received: 31 July 2002 / Revised version: 6 November 2002 / Published online: 15 January 2003 RID="a" ID="a" e-mail: sdg@hep.phys.soton.ac.uk RID="b" ID="b" e-mail: luca.girlanda@pd.infn.it ^* Present address: ECT^*, Villa Tambosi, Strada delle Tabarelle 286, 38050 Trento, Italy RID="c" ID="c" e-mail: stern@ipno.in2p3.fr     

<Emphasis Type="Italic">B</Emphasis> to light meson transition form factors calculated in perturbative QCD approach

We calculate the , (P is the light pseudoscalar meson, V the light vector meson) form factors in the large-recoil limit in the perturbative QCD approach, including both the vector (axial vector) and tensor operators. In general there are two leading components and for the B meson wave functions. We consider both contributions of them. Sudakov effects ( and threshold resummation) are included to regulate the soft end-point singularity. By choosing the hard scale as the maximum virtualities of the internal particles in the hard b quark decay amplitudes, Sudakov factors can effectively suppress the long-distance soft contribution. The hard contribution can be dominant in these approaches. Received: 27 December 2002 / Published online: 5 May 2003 RID="a" ID="a" e-mail: lucd@mail.ihep.ac.cn RID="b" ID="b" e-mail: yangmz@mail.ihep.ac.cn     

Sensitivity of the pQCD deuteron structure to the nucleon form factors

We discuss the applicability of pQCD to the elastic scattering of electrons on protons and deuterons. We analyze the Q²-dependence of the reduced deuteron form factor, taking into account the recent data on the electric proton form factor and we find that the value of the QCD-scale parameter Λ differs essentially from the value Λ = 0.1 GeV, previously found using the dipole parametrization of the electromagnetic nucleon form factors G_E and G_M. Moreover, the predicted scaling behavior of the reduced deuteron form factor cannot be recovered in the Dirac and Pauli representations for the nucleon electromagnetic form factors. Received: 14 October 2002 / Accepted: 12 November 2002 / Published online: 11 March 2003 RID="a" ID="a"Permanent address: National Science Center KFTI, 310108 Kharkov, Ukraine. RID="b" ID="b"e-mail: etomasi@cea.fr Communicated by V.V. Anisovich     

Two-photon annihilation into baryon-antibaryon pairs

We study the handbag contribution to two-photon annihilation into baryon-antibaryon pairs at large energy and momentum transfer. We derive factorization of the process amplitude into a hard subprocess and form factors describing the soft transition, assuming that the process is dominated by configurations where the (anti)quark approximately carries the full momentum of the (anti)baryon. The form factors represent moments of time-like generalized parton distributions, so-called distribution amplitudes. A characteristic feature of the handbag mechanism is the absence of isospin-two components in the final state, which in combination with flavor symmetry provides relations among the form factors for the members of the lowest-lying baryon octet. Assuming dominance of the handbag contribution, we can describe current experimental data with form factors of plausible size, and predict the cross sections of presently unmeasured channels. Received: 3 July 2002 / Revised version: 7 October 2002 / Published online: 20 November 2002 RID="a" ID="a" e-mail: mdiehl@physik.rwth-aachen.de RID="b" ID="b" e-mail: kroll@physik.uni-wuppertal.de RID="c" ID="c" e-mail: cvogt@nordita.dk     

Confronting spectral functions from ee annihilation and $\tau$ decays: consequences for the muon magnetic moment

Vacuum polarization integrals involve the vector spectral functions which can be experimentally determined from two sources: (i) e ⁺ e ^- annihilation cross sections and (ii) hadronic decays. Recently results with comparable precision have become available from CMD-2 on one side, and ALEPH, CLEO and OPAL on the other. The comparison of the respective spectral functions involves a correction from isospin-breaking effects, which is evaluated. After the correction it is found that the dominant spectral functions do not agree within experimental and theoretical uncertainties. Some disagreement is also found for the spectral functions. The consequences of these discrepancies for vacuum polarization calculations are presented, with the emphasis on the muon anomalous magnetic moment. The work includes a complete re-evaluation of all exclusive cross sections, taking into account the most recent data that became available in particular from the Novosibirsk experiments and applying corrections for the missing radiative corrections. 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 Standard Model predictions for the muon magnetic anomaly read where the errors account for the hadronic, light-by-light scattering and electroweak contributions. We observe deviations with the recent BNL measurement at the 3.0 (e ⁺ e ^- ) and 0.9 () level, when adding experimental and theoretical errors in quadrature. Received: 27 August 2002 / Revised version: 10 January 2003 / Published online: 26 February 2003 RID="a" ID="a" e-mail: davier@lal.in2p3.fr RID="b" ID="b" e-mail: simon.eidelman@cern.ch RID="c" ID="c" e-mail: hoecker@lal.in2p3.fr RID="d" ID="d" e-mail: zhangzq@lal.in2p3.fr     

How well can we reconstruct the $t\bar{t}$ system near its threshold at future ee linear colliders?

We developed a new method for the full kinematical reconstruction of the system near its threshold at future linear e ⁺ e ^- colliders. In the core of the method lies likelihood fitting which is designed to improve measurement accuracies of the kinematical variables that specify the final states resulting from decays. The improvement is demonstrated by applying this method to a Monte Carlo sample generated with various experimental effects including beamstrahlung, finite acceptance and resolution of the detector system, etc. In most cases the fit takes a broad non-Gaussian distribution of a given kinematical variable to a nearly Gaussian shape, thereby justifying phenomenological analyses based on simple Gaussian smearing of the parton-level momenta. The standard deviations of the resultant distributions of various kinematical variables are given in order to facilitate such phenomenological analyses. A possible application of the kinematical fitting method and its expected impact are also discussed. Received: 4 March 2003 / Published online: 23 May 2003 RID="a" ID="a" e-mail: ikematsu@post.kek.jp RID="b" ID="b" e-mail: fujiik@jlcuxf.kek.jp RID="c" ID="c" e-mail: hioki@ias.tokushima-u.ac.jp RID="d" ID="d" e-mail: sumino@tuhep.phys.tohoku.ac.jp RID="e" ID="e" e-mail: tohrut@hiroshima-u.ac.jp     

Chiral magnetism of the nucleona

We study the quark mass expansion of the magnetic moments of the nucleon in a chiral effective field theory including nucleons, pions and delta-resonances as explicit degrees of freedom. We point out that the usual power counting applied so far to this problem misses important quark mass structures generated via an intermediate isovector M1 nucleon-delta transition. We propose a modified power counting and compare the resulting chiral extrapolation function to available (quenched) lattice data. The extrapolation is found to work surprisingly well, given that the lattice data result from rather large quark masses. Our calculation raises the hope that extrapolations of lattice data utilizing chiral effective field theory might be applicable over a wider range in quark masses than previously thought, and we discuss some open questions in this context. Furthermore, we observe that within the current lattice data uncertainties the extrapolations presented here are consistent with the Padé fit ansatz introduced by the Adelaide group a few years ago. Received: 23 April 2002 / Accepted: 18 July 2002 / Published online: 17 December 2002 RID="c" ID="c"e-mail: themmert@physik.tu-muenchen.de RID="d" ID="d"e-mail: weise@ect.it Communicated by A. Sch?fer     

Circumstantial evidence for rotating mass matrix from fermion mass and mixing data

It is shown that existing data on the mixing between up and down fermion states and on the hierarchical mass ratios between fermion generations, as far as can be so analyzed at present, are all consistent with the two phenomena being both consequences of a mass matrix rotating in generation space with changing energy scale. As a result, the rotating mass matrix can be traced over some 14 orders of magnitude in energy from the mass scale of the t quark at 175 GeV to below that of the atmospheric neutrino at 0.05 eV. Received: 27 August 2002 / Published online: 24 January 2003 RID="a" ID="a" e-mail: jose.m.bordes@uv.es RID="b" ID="b" e-mail: h.m.chan@rl.ac.uk RID="c" ID="c" e-mail: tsou@maths.ox.ac.uk     

Deconstruction of gauge symmetry breaking by discrete symmetry and G unification

We deconstruct the non-supersymmetric SU(5) breaking by discrete symmetry on the space-time and in the Higgs mechanism deconstruction scenario. Also we explain the subtle point of how to exactly match the continuum results with the latticized results on the quotient space S ¹ /Z ₂ and . We also propose an effective deconstruction scenario and discuss the gauge symmetry breaking by the discrete symmetry on the theory space in this approach. As an application, we suggest the G^N unification where G^N is broken down to by the bifundamental link fields and the doublet-triplet splitting can be achieved. Received: 10 October 2002 / Revised version: 23 March 2003 / Published online: 13 May 2003 RID="a" ID="a" Current address: School of Natural Sciences, Institute for Advanced Study, Einstein Drive, Princeton, NJ 08540, USA e-mail: tli@sns.ias.edu RID="b" ID="b" e-mail: liutao@sas.upenn.edu     

Fluctuations of the quark densities in nuclei

We study the static scalar susceptibility of the nuclear medium, i.e., the change of the quark condensate for a small modification of the quark mass. In the linear sigma model it is linked to the in-medium sigma propagator and its magnitude increases due to the mixing with the softer modes of the nucleon-hole excitations. We show that the pseudoscalar susceptibility, which is large in the vacuum, owing to the smallness of the pion mass, follows the density evolution of the quark condensate and thus decreases. At normal nuclear matter density the two susceptibilities become much closer, a partial chiral symmetry restoration effect as they become equal when the full restoration is achieved. Received: 20 July 2002 / Accepted: 14 September 2002 / Published online: 21 January 2003 RID="a" ID="a"e-mail: chanfray@ipnl.in2p3.fr Communicated by A. Molinari     

A flexible parameterization of the CKM matrix via the singular-value-decomposition method

We investigate a flexible method by which we can test the unitarity of the quark flavor-mixing matrix step by step. Singular-value-decomposition (SVD) techniques are used in analyzing the mixing matrix over a broader parameter region than the unitarity region. Unitary constraints let us extract CP-violating properties without any specific parameterization when the magnitudes of at least three mixing-matrix elements in three-generation quark mixing are given. This method can al so be applied to the analysis of lepton flavor mixing, in which only a few moduli are presently measured. Received: 27 November 2002 / Published online: 7 March 2003 RID="a" ID="a" e-mail: cskim@yonsei.ac.kr RID="b" ID="b" e-mail: jdkim@cskim.yonsei.ac.kr     

The ratios among condensates from e+e− (I=1) data

We calculate the ratios among condensates from the ρ channel (I=1) e⁺e⁻ data in a systematic way. We use quotients of SVZ sum rules for different moments of the correlation functions. The results turn out to be very accurate. A factor of 1.6 for the ratio of the four quark condensate over the gluon condensate compared with the standard value is predicted.     

Explicit model realizing parton-hadron duality

An explicit model realizing parton-hadron duality and fitting the data is suggested. Complex nonlinear Regge trajectories are important ingredients of the model. The inclusion of Δ and N^* trajectories should account for all resonances in the direct channel. The exotic trajectory is responsible for the smooth background. Received: 7 June 2002 / Accepted: 3 July 2002 / Published online: 10 December 2002 RID="a" ID="a"e-mail: fiore@cs.infn.it RID="b" ID="b"e-mail: flachi@ifae.es RID="c" ID="c"e-mail: jenk@gluk.org RID="d" ID="d"e-mail: sasha@len.uzhgorod.ua RID="e" ID="e"e-mail: vladimir@cfif.ist.utl.pt Communicated by V.V. Anisovich     

Confinement and mass gap in abelian gauge

First, we present a simple confining abelian pure gauge theory. Classically, its kinetic term is not positive definite, and it contains a simple UV regularized F⁴ interaction. This provokes the formation of a condensate such that, at the saddle point of the effective potential, the wave function normalization constant of the abelian gauge fields vanishes exactly. Then we study SU(2) pure Yang-Mills theory in an abelian gauge and introduce an auxiliary field for a BRST invariant condensate of dimension 2, which renders the charged sector massive. Under simple assumptions its effective low energy theory reduces to the confining abelian model discussed before, and the VEV of is seen to scale correctly with the renormalization point. Under these assumptions, the confinement condition Z _eff = 0 also holds for the massive charged sector, which suppresses the couplings of the charged fields to the abelian gauge bosons in the infrared regime. Received: 27 November 2002 / Published online: 14 April 2003 RID="a" ID="a" e-mail: Ulrich.Ellwanger@th.u-psud.fr RID="b" ID="b" e-mail: Nicolas.Wschebor@th.u-psud.fr ^* Unité Mixte de Recherche - CNRS - UMR 8627