Showing papers on "Pseudoscalar published in 1995"

Screening of the topological charge in a correlated instanton vacuum

Abstract: Screening of the topological charge due to fermion-induced interactions is an important phenomenon, closely related with the resolution of the strong {ital CP} and U(1) problems. We study the mechanism of such screening in a ``correlated instanton vacuum,`` as opposed to the ``random`` one. Both scalar and pseudoscalar gluonic correlators are analyzed by means of an observable that minimizes finite size effects. Screening of the topological charge is established. This allows us to calculate the {eta}{prime} mass without having to invert the Dirac operator. We suggest that this method might be used in lattice QCD calculations as well. Our results for the screening of the topological charge are in agreement with the chiral Ward identities, and the scalar gluonic correlator satisfies a low energy theorem first derived by Novikov {ital et} {ital al}. We also propose a modified Witten-Veneziano formula, in which the topological susceptibility is not defined for an {ital infinite} box in a world {ital without} fermions, but for a {ital small} box in the real world.

HIGLU: A Program for the Calculation of the Total Higgs Production Cross Section at Hadron Colliders via Gluon Fusion including QCD Corrections

Abstract: A program for the calculation of the total Higgs production cross section viagluon fusion at hadron colliders including next–to–leading order QCD corrections ispresented. It is suitable especially for Standard Model Higgs bosons and the neutralHiggs particles of the minimal supersymmetric extension. The program provides amodel–independent calculation for scalar [CP–even] as well as pseudoscalar [CP–odd] Higgs bosons including the contributions of virtual top and bottom quarksinside the loop coupled to the Higgs particles. The relevant input parameters canbe chosen from an input file. As a special case the minimal supersymmetric exten-sion of the Standard Model can be investigated. The corresponding couplings areimplemented including the leading higher order corrections. 1 e–mail address: spira@desy.de 2 Supported by Bundesministerium fu¨r Bildung und Forschung (BMBF), Bonn, Germany, under Con-tract 05 6 HH 93P (5) and by EU Program Human Capital and Mobility through Network Physics atHigh Energy Colliders under Contract CHRX–CT93–0357 (DG12 COMA).

Numerical evidence for the observation of a scalar glueball

Abstract: We compute from lattice QCD in the valence (quenched) approximation the partial decay widths of the lightest scalar glueball to pairs of pseudoscalar quark-antiquark states. These predictions and values obtained earlier for the scalar glueball's mass are in good agreement with the observed properties of ${f}_{J}(1710)$ and inconsistent with all other observed meson resonances.

Low-energy theorems in Higgs physics

Abstract: We present low-energy theorems for the calculation of loop amplitudes with external scalar or pseudoscalar Higgs bosons which are light compared to the loop particles. Starting from existing lowest-order versions of these theorems, we show how their applicability may be extended to the two-loop level. To illustrate the usefulness of these theorems, we discuss a number of applications to Higgs production and decay at and beyond the one-loop order.

Light spinless particle coupled to photons.

Abstract: A pseudoscalar or scalar particle $\phi$ that couples to two photons but not to leptons, quarks and nucleons would have effects in most of the experiments searching for axions, since these are based on the $a \gamma \gamma $ coupling. We examine the laboratory, astrophysical and cosmological constraints on $\phi$ and study whether it may constitute a substantial part of the dark matter. We also generalize the $\phi$ interactions to possess $SU(2) \times U(1)$ gauge invariance, and analyze the phenomenological implications.

Low-Energy Theorems in Higgs Physics

Abstract: We present low-energy theorems for the calculation of loop amplitudes with external scalar or pseudoscalar Higgs bosons which are light compared to the loop particles. Starting from existing lowest-order versions of these theorems, we show how their applicability may be extended to the two--loop level. To illustrate the usefulness of these theorems, we discuss a number of applications to Higgs production and decay at and beyond the one--loop order.

Physics of B c -mesons

Abstract: The mass spectrum for the system (c) is considered in the framework of potential models for the heavy quarkonium. Spin-dependent splittings, with account taken of the change of a constant representing the effective Coulomb interaction between the quarks, and widths of radiative transitions between the (c) levels are calculated. In the framework of QCD sum rules, the masses of the lightest vector Bc* and pseudoscalar Bc states are estimated, the scaling relation for leptonic constants of heavy quarkonia is derived, and the leptonic constant fBc is evaluated. The Bc decays are considered in the framework both of the potential models and of the QCD sum rules. The relations, following from the approximate spin symmetry for the heavy quarks in the heavy quarkonium, are analysed for the form factors of the semileptonic weak exclusive decays of Bc. The Bc lifetime is evaluated with account taken of the corrections to the spectator mechanism of the decay, because of the quark binding into the meson. The total and differential cross sections of the Bc production in different interactions are calculated. The analytic expressions for the fragmentational production cross sections of Bc are derived. The possibility of the practical search for Bc in current and planned experiments at electron–positron and hadron colliders is analysed.

Fermionic decays of neutral MSSM Higgs bosons at the one-loop level

Abstract: The results of a complete one-loop calculation for the fermionic decay width h^0, H^0, A^0 -> f bar(f) of the neutral MSSM Higgs bosons are presented and the dominant light Higgs decay channel h^0 -> b bar(b) is discussed in detail. The enhancement of the partial decay width h^0 -> b bar(b) compared to the standard Higgs decay is shown for pseudoscalar masses M_A < 300 GeV. Simpler approximation formulae for the Higgs decays are given and their quality is discussed by introducing an effective neutral scalar mixing angle sin(alpha)_eff. Finally the Higgs branching ratios in b bar(b), c bar(c), tau^+ tau^- are calculated.

Radiative weak decays of charm mesons

Abstract: We address standard model predictions for flavor-changing radiative transitions of the pseudoscalar charm mesons. Short-distance contributions in D radiative transitions are contrasted with those in B decays. A full analysis is presented of the c\ensuremath{\rightarrow}u+\ensuremath{\gamma} electromagnetic penguin amplitude with QCD radiative corrections included. Given the importance of long-range effects for the charm sector, special attention is paid to such contributions as the vector dominance and pole amplitudes. A number of two-body final states in exclusive charm radiative decays is considered and the corresponding branching ratio predictions are given.

Isospin breaking in chiral perturbation theory and the decaysη →πℓν andτ →ηπν

Abstract: Violation of isospin due tomu≠md and electromagnetism is investigated within the framework of the standard model. We discuss the electromagnetic contributions to the masses of the pseudoscalar mesons and theKl3 amplitudes. The decay η→πlν is calculated at the one-loop level in chiral perturbation theory including an estimate of the electromagnetic contributions. Adding all four decay channels, we obtain 2.0·10−13 as a rather accurate upper bound for the branching ratio. We determine the leading meson resonance contributions to τ→ηπν predicting a branching ratio of 1.2·10−5.

Worldline Path Integrals for Fermions with General Couplings

Abstract: We derive a worldline path integral representation for the effective action of a multiplet of Dirac fermions coupled to the most general set of matrix-valued scalar, pseudoscalar, vector, axial vector and antisymmetric tensor background fields. By representing internal degrees of freedom in terms of worldline fermions as well, we obtain a formulation which manifestly exhibits chiral gauge invariance.

Worldline Path Integrals for Fermions with Scalar, Pseudoscalar and Vector Couplings

Abstract: A systematic derivation is given of the worldline path integrals for the effective action of a multiplet of Dirac fermions interacting with general matrix-valued classical background scalar, pseudoscalar, and vector gauge fields. The first path integral involves worldline fermions with antiperiodic boundary conditions on the worldline loop and generates the real part of the one loop (Euclidean) effective action. The second path integral involves worldline fermions with periodic boundary conditions and generates the imaginary part of the (Euclidean) effective action, i.e. the phase of the fermion functional determinant. Here we also introduce a new regularization for the phase of functional determinants resembling a heat-kernel regularization. Compared to the known special cases, our worldline Lagrangians have a number of new interaction terms; the validity of some of these terms is checked in perturbation theory. In particular, we obtain the leading order contribution (in the heavy mass expansion) to the Wess-Zumino-Witten term, which generates the chiral anomaly.

New planforms in systems of partial differential equations with Euclidean symmetry

Abstract: Dionne & Golubitsky [10] consider the classification of planforms bifurcating (simultaneously) in scalar partial differential equations that are equivariant with respect to the Euclidean group in the plane. In particular, those planforms corresponding to isotropy subgroups with one-dimensional fixed-point space are classified. Many important Euclidean-equivariant systems of partial differential equations essentially reduce to a scalar partial differential equation, but this is not always true for general systems. We extend the classification of [10] obtaining precisely three planforms that can arise for general systems and do not exist for scalar partial differential equations. In particular, there is a class of one-dimensional ‘pseudoscalar’ partial differential equations for which the new planforms bifurcate in place of three of the standard planforms from scalar partial differential equations. For example, the usual rolls solutions are replaced by a nonstandard planform called anti-rolls. Scalar and pseudoscalar partial differential equations are distinguished by the representation of the Euclidean group.

Static and dynamic properties of pseudoscalar mesons

Abstract: We report the results of form factors, charge radii and decay constants of both light and heavy flavoured pseudoscalar mesons in a QCD inspired quark model. We use the quantum mechanical perturbation theory and discuss its limitations in the present problem. Several predictions are also made for bottom and top flavours.

Currents and their couplings in the weak sector of the standard model

Abstract: Beta-decay and muon-capture experiments in nuclei are reviewed. The conserved vector current hypothesis is confirmed through the observed constancy of the vector coupling constant determined from the superallowed Fermi transitions and from the measurement of the weak-magnetism term in mirror Gamow-Teller transitions. The axial-vector and pseudoscalar coupling constants in the nucleon are determined from neutron decay and muon capture on the proton respectively. In finite nuclei, evidence for these coupling constants being reduced relative to their free-nucleon values is discussed. Meson-exchange currents are shown to be an important correction to the time-like part of the axial current as evident in first-forbidden beta decays. Tests of the Standard Model are discussed, as well as extensions beyond it involving right-hand currents and scalar interactions.

Is the quenched spectrum in agreement with experiment

Abstract: We analyze the meson spectrum in quenched QCD using lattice gauge theory. By studying hadron propagation with a variety of operators (both smeared and local), we are able to extract the ground state and first excited state masses with confidence. We pay attention to the correlations among the data used in the fits to extract these masses and couplings. We compare the resulting hadron spectrum with experiment and find evidence for a significant departure in the pseudoscalar and vector meson masses.

Currents and their couplings in the weak sector of the standard model

Abstract: Beta-decay and muon-capture experiments in nuclei are reviewed. The conserved vector current hypothesis is confirmed through the observed constancy of the vector coupling constant determined from the superallowed Fermi transitions and from the measurement of the weak-magnetism term in mirror Gamow-Teller transitions. The axial-vector and pseudoscalar coupling constants in the nucleon are determined from neutron decay and muon capture on the proton respectively. In finite nuclei, evidence for these coupling constants being reduced relative to their free-nucleon values is discussed. Meson-exchange currents are shown to be an important correction to the time-like part of the axial current as evident in first-forbidden beta decays. Tests of the Standard Model are discussed, as well as extensions beyond it involving right-hand currents and scalar interactions.

The Spectrum of the Nucleons and the Strange Hyperons and Chiral Dynamics

Abstract: The spectra of the nucleons, $\Delta$ resonances and the strange hyperons are well described by the constituent quark model if in addition to the harmonic confinement potential the quarks are assumed to interact by exchange of the $SU(3)_F$ octet of pseudoscalar mesons, which are the Goldstone bosons associated with the hidden approximate chiral symmetry of QCD. In its $SU(3)_F$ invariant approximation the pseudoscalar exchange interaction splits the multiplets of $SU(6)_{FS}\times U(6)_{conf}$ in the spectrum to multiplets of $SU(3)_F\times SU(2)_S\times U(6)_{conf}$. The position of these multiplets differ in the baryon sectors with different strangeness because of the mass splitting of the pseudoscalar octet and the different constituent masses of the u,d and s quarks that breaks $SU(3)_F$ flavor symmetry. A description of the whole spectrum, to an accuracy of $\simeq$ 4\% or better, is achieved if one matrix element of the boson interaction for each oscillator shell is extracted from the empirical mass splittings. The ordering of the positive and negative parity states moreover agrees with the empirical one in all sectors of the spectrum. A discussion of the conceptual basis of the model and its various phenomenological ramifications is presented.

Chiral and gluon condensates at finite temperature

Abstract: We investigate the thermal behaviour of gluon and chiral condensates within an effective Lagrangian of pseudoscalar mesons coupled to a scalar glueball. This Lagrangian mimics the scale and chiral symmetries of QCD.

Inclusive production of neutral vector mesons in hadronic Z decays

Abstract: Data on the inclusive production of the neutral vector mesonsρ 0(770),ω(782), K*0(892), andφ(1020) in hadronic Z decays recorded with the ALEPH detector at LEP are presented and compared to Monte Carlo model predictions. Bose-Einstein effects are found to be important in extracting a reliable value for theρ 0 production rate. An averageρ 0 multiplicity of 1.45±0.21 per event is obtained. Theω is detected via its three pion decay modeω→π + π − π 0 and has a total rate of 1.07±0.14 per event. The multiplicity of the K*0 is 0.83±0.09, whilst that of theφ is 0.122±0.009, both measured using their charged decay modes. The measurements provide information on the relative production rates of vector and pseudoscalar mesons, as well as on the relative probabilities for the production of hadrons containing u, d, and s quarks.