Showing papers on "Pseudoscalar published in 2011"

Parity violation in the Cosmic Microwave Background from a pseudoscalar inflaton

Abstract: If the inflaton is a pseudoscalar, then it naturally interacts with gauge fields through the coupling ∝ Fμν μν. Through this coupling, the rolling inflaton produces quanta of the gauge field, that in their turn source the tensor components of the metric perturbations. Due to the parity-violating nature of the system, the right- and the left-handed tensor modes have different amplitudes. Such an asymmetry manifests itself in the form of non-vanishing TB and EB correlation functions in the Cosmic Microwave Background (CMB). We compute the amplitude of the parity-violating tensor modes and we discuss two scenarios, consistent with the current data, where parity-violating CMB correlation functions will be detectable in future experiments.

Parity violation in the Cosmic Microwave Background from a pseudoscalar inflaton

Abstract: If the inflaton is a pseudoscalar, then it naturally interacts with gauge fields via an axion-like coupling to $F_{\mu u} \tilde{F}^{\mu u}$. Through this coupling, the rolling inflaton produces quanta of the gauge field, that in their turn source the tensor components of the metric perturbations. Due to the parity-violating nature of the system, the right- and the left-handed tensor modes have different amplitudes. Such an asymmetry manifests itself in the form of non-vanishing TB and EB correlation functions in the Cosmic Microwave Background (CMB). We compute the amplitude of the parity-violating tensor modes and we discuss two scenarios, consistent with the current data, where parity-violating CMB correlation functions will be detectable in future experiments.

Isoscalar meson spectroscopy from lattice QCD

Abstract: We extract to high statistical precision an excited spectrum of single-particle isoscalar mesons using lattice QCD, including states of high spin and, for the first time, light exotic JPC isoscalars. The use of a novel quark field construction has enabled us to overcome the long-standing challenge of efficiently including quark-annihilation contributions. Hidden-flavor mixing angles are extracted and while most states are found to be close to ideally flavor mixed, there are examples of large mixing in the pseudoscalar and axial sectors in line with experiment. The exotic JPC isoscalar states appear at a mass scale comparable to the exotic isovector states.

π and ρ mesons, and their diquark partners, from a contact interaction

Abstract: We present a unified Dyson-Schwinger equation treatment of static and electromagnetic properties of pseudoscalar and vector mesons, and scalar and axial-vector diquark correlations, based upon a vector-vector contact interaction. A basic motivation for this paper is the need to document a comparison between the electromagnetic form factors of mesons and those diquarks that play a material role in nucleon structure. A notable result, therefore, is the large degree of similarity between related meson and diquark form factors. The simplicity of the interaction enables computation of the form factors at arbitrarily large spacelike Q(2), which enables us to expose a zero in the rho-meson electric form factor at z(Q)(rho) approximate to root 6m(rho). Notably, r(rho)z(Q)(rho) approximate to r(D)z(Q)(D), where r(rho) and r(D) are, respectively, the electric radii of the rho-meson and deuteron.

Proton size anomaly.

Abstract: A measurement of the Lamb shift in muonic hydrogen yields a charge radius of the proton that is smaller than the CODATA value by about 5 standard deviations. We explore the possibility that new scalar, pseudoscalar, vector, and tensor flavor-conserving nonuniversal interactions may be responsible for the discrepancy. We consider exotic particles that, among leptons, couple preferentially to muons and mediate an attractive nucleon-muon interaction. We find that the many constraints from low energy data disfavor new spin-0, spin-1, and spin-2 particles as an explanation.

Dark light-Higgs bosons.

Abstract: We study a limit of the nearly Peccei-Quinn-symmetric next-to-minimal supersymmetric standard model possessing novel Higgs and dark matter (DM) properties. In this scenario, there naturally coexist three light singletlike particles: a scalar, a pseudoscalar, and a singlinolike DM candidate, all with masses of order 0.1-10 GeV. The decay of a standard model-like Higgs boson to pairs of the light scalars or pseudoscalars is generically suppressed, avoiding constraints from collider searches for these channels. For a certain parameter window annihilation into the light pseudoscalar and exchange of the light scalar with nucleons allow the singlino to achieve the correct relic density and a large direct-detection cross section consistent with the DM direct-detection experiments, CoGeNT and DAMA/LIBRA, preferred region simultaneously. This parameter space is consistent with experimental constraints from LEP, the Tevatron, Υ, and flavor physics.

Pion and kaon valence-quark parton distribution functions

Abstract: A rainbow-ladder truncation of QCD's Dyson-Schwinger equations, constrained by existing applications to hadron physics, is employed to compute the valence-quark parton distribution functions of the pion and kaon. Comparison is made to pi-N Drell-Yan data for the pion's u-quark distribution and to Drell-Yan data for the ratio u(K)(x)/u(pi)(x): the environmental influence of this quantity is a parameter-free prediction, which agrees well with existing data. Our analysis unifies the computation of distribution functions with that of numerous other properties of pseudoscalar mesons.

Beyond Einstein-Cartan gravity: Quadratic torsion and curvature invariants with even and odd parity including all boundary terms

Abstract: Recently, gravitational gauge theories with torsion have been discussed by an increasing number of authors from a classical as well as from a quantum field theoretical point of view. The Einstein-Cartan(-Sciama-Kibble) Lagrangian has been enriched by the parity odd pseudoscalar curvature (Hojman, Mukku, and Sayed) and by torsion square and curvature square pieces, likewise of even and odd parity. (i) We show that the inverse of the so-called Barbero-Immirzi parameter multiplying the pseudoscalar curvature, because of the topological Nieh-Yan form, can only be appropriately discussed if torsion square pieces are included. (ii) The quadratic gauge Lagrangian with both parities, proposed by Obukhov et al. and Baekler et al., emerges also in the framework of Diakonov et al.(2011). We establish the exact relations between both approaches by applying the topological Euler and Pontryagin forms in a Riemann-Cartan space expressed for the first time in terms of irreducible pieces of the curvature tensor. (iii) Only in a Riemann-Cartan spacetime, that is, in a spacetime with torsion, parity violating terms can be brought into the gravitational Lagrangian in a straightforward and natural way. Accordingly, Riemann-Cartan spacetime is a natural habitat for chiral fermionic matter fields.

NLO QCD corrections to pseudoscalar Higgs production in the MSSM

Abstract: We present a calculation of the two-loop quark-squark-gluino contributions to pseudoscalar Higgs boson production via gluon fusion in the MSSM. We regularize the loop integrals using the Pauli-Villars method, and obtain explicit and compact analytic results based on an expansion in the heavy particle masses. Our results — valid when the pseudoscalar Higgs boson is lighter than squarks and gluinos — can be easily implemented in computer codes for an efficient and accurate determination of the pseudoscalar production cross section.

Predictive AdS/QCD Model for Mass Spectra of Mesons with Three Flavors

Abstract: The predictive soft-wall AdS/QCD model with a modified 5D metric at the infrared region is constructed to obtain a nontrivial dilaton solution for three flavor quarks u, d and s. Such a model is shown to incorporate both the chiral symmetry breaking and linear confinement. After considering some high-order terms including the U(1)(L) x U(1)(R) chiral symmetry breaking term, we find that the resulting predictions for the SU(3) octet and singlet resonance states of pseudoscalar, scalar, vector and axial-vector mesons agree well with the experimentally confirmed resonance states. Contributions from the instanton effects given by the determinant term are also discussed. It is observed that the chiral symmetry breaking phenomena of SU(3)(L) x SU(3)(R) and U(1)(L) x U(1)(R) can be well described in this model, while the SU(3) flavor symmetry breaking effect due to quark mass difference in the source term is not enough to explain all of the current experimental data.

The pseudoscalar hadronic channel contribution of the light-by-light process to the muon (g−2) μ within the nonlocal chiral quark model

Abstract: The light-by-light contribution to the anomalous magnetic moment of muon (g−2) μ from the hadronic exchanges in the neutral pseudoscalar meson channel is calculated in the nonlocal chiral quark model. The full kinematic dependence of the meson two-photon vertices from the virtualities of the mesons and photons is taken into account. It is demonstrated that the effect of the full kinematic dependence in the meson–photon vertices is to reduce the contribution of pseudoscalar exchanges comparing with the most of previous estimates and the result is $a_{\mu}^{\mathrm{PS,LbL}}=(5.85\pm0.87)\cdot10^{-10}$ . The status of various phenomenological and QCD short-distance constraints is discussed and the comparison with the predictions of other models is performed.

Decay constants of heavy pseudoscalar mesons from QCD sum rules

Abstract: We revisit the sum-rule extraction of the decay constants of the D, Ds, B and Bs mesons from the two-point correlator of heavy?light pseudoscalar currents. We use the operator product expansion of this correlator expressed in terms of the heavy-quark mass for which the perturbative expansion exhibits a reasonable convergence. Our main emphasis is laid on the control over the uncertainties in the decay constants, related both to the input quantum chromodynamics (QCD) parameters and to the limited intrinsic accuracy of the method of QCD sum rules. This becomes possible due to the application of our procedure of extracting hadron observables that involves as novel feature dual thresholds depending on the Borel parameter. For charmed mesons, we find the decay constants and . For beauty mesons, the decay constants turn out to be extremely sensitive to the precise value of . By requiring our sum-rule estimate to match the average of the lattice results for fB, a very accurate value is extracted, leading to fB = (193.4 ? 12.3(OPE) ? 4.3(syst))?MeV and .

The pseudoscalar hadronic channel contribution of the light-by-light process to the muon (g-2) within the nonlocal chiral quark model

Abstract: The light-by-light contribution to the anomalous magnetic moment of muon (g-2)_{\mu} from the hadronic exchanges in the neutral pseudoscalar meson channel is calculated in the nonlocal chiral quark model. The full kinematic dependence of the meson-two-photon vertices on the virtualities of the mesons and photons is taken into account. The status of various phenomenological and QCD short-distance constraints is discussed and the comparison with the predictions of other models is performed. It is demonstrated that the effect of the full kinematic dependence in the meson-photon vertices is to reduce the contribution of pseudoscalar exchages to a_\mu ^{PS,LbL} by approximately factor 1.5 in comparison with the most of previous estimates.

In-medium operator product expansion for heavy-light-quark pseudoscalar mesons

Abstract: The operator product expansion (OPE) for heavy-light-quark pseudoscalar mesons (D -mesons and B -mesons) in medium is determined, both for a moving meson with respect to the surrounding medium as well as for a meson at rest. First of all, the OPE is given in terms of normal-ordered operators up to mass dimension 5, and the mass of the heavy quark and the mass of the light quark are kept finite. The Wilson coefficients of such an expansion are infrared (IR) divergent in the limit of a vanishing light-quark mass. A consistent separation of scales necessitates an OPE in terms of non-normal-ordered operators, which implies operator mixing, where the IR-divergences are absorbed into the operators. It is shown that the Wilson coefficients of such an expansion are IR-stable, and the limit of a vanishing light-quark mass is perfomed. Details of the major steps for the calculation of the Wilson coefficients are presented. By a comparison with previous results obtained by other theoretical groups we have found serious disagreements.

Next-to-leading order thermal spectral functions in the perturbative domain

Abstract: Motivated by applications in thermal QCD and cosmology, we elaborate on a general method for computing next-to-leading order spectral functions for composite operators at vanishing spatial momentum, accounting for real, virtual as well as thermal corrections. As an example, we compute these functions (together with the corresponding imaginary-time correlators which can be compared with lattice simulations) for scalar and pseudoscalar densities in pure Yang-Mills theory. Our results may turn out to be helpful in non-perturbative estimates of the corresponding transport coefficients, which are the bulk viscosity in the scalar channel and the rate of anomalous chirality violation in the pseudoscalar channel. We also mention links to cosmology, although the most useful results in that context may come from a future generalization of our methods to other correlators.

Next-to-leading order thermal spectral functions in the perturbative domain

Abstract: Motivated by applications in thermal QCD and cosmology, we elaborate on a general method for computing next-to-leading order spectral functions for composite operators at vanishing spatial momentum, accounting for real, virtual as well as thermal corrections. As an example, we compute these functions (together with the corresponding imaginary-time correlators which can be compared with lattice simulations) for scalar and pseudoscalar densities in pure Yang-Mills theory. Our results may turn out to be helpful in non-perturbative estimates of the corresponding transport coefficients, which are the bulk viscosity in the scalar channel and the rate of anomalous chirality violation in the pseudoscalar channel. We also mention links to cosmology, although the most useful results in that context may come from a future generalization of our methods to other correlators.

Nonleptonic two-body decays of charmed mesons

Abstract: Nonleptonic decays of charmed mesons into two pseudoscalar mesons or one pseudoscalar meson and one vector meson are studied on the basis of a generalized factorization method considering the resonance effects in the pole model for the annihilation contributions. Large strong phases between different topological diagrams are considered in this work, simply taking the phase in the coefficients ${a}_{i}$. We find that the annihilation-type contributions calculated in the pole model are large in both of the $PP$ and $PV$ modes, which make our numerical results agree with the experimental data better than those previous calculations.

Heavy quarkonium spectra and its decays in a nonrelativistic model with Hulthen potential

Abstract: In this paper, we have made a comprehensive study of S wave quarkonium spectra in the general framework of a nonrelativistic potential model. The full potential used in our model consists of a Hulthen potential and a confining linear potential. The spin hyperfine interaction is introduced to obtain the masses of the pseudoscalar and vector mesons. The three-dimensional harmonic oscillator wavefunction is used as a trial wavefunction to obtain the mass spectra. The model parameters and the wavefunction that reproduce the mass spectra of and mesons are used to investigate the decay constants, leptonic decay widths, two-photon and two-gluon decay widths, and radiative decay widths of the S wave and mesons. The obtained values are compared with the experimental results and with the values obtained from other theoretical models. The predictions from our model are found to be in good agreement with the experimental results.

Spectroscopy and decay properties of the D{sub s} meson

Abstract: Using hydrogenic and Gaussian wave functions, mass spectra and decay properties of the D{sub s}(cs) meson are investigated in the framework of phenomenological quark-antiquark potential (Coulomb plus power) model consisting of a relativistic kinetic energy term. The spin-hyperfine, spin-orbit, and tensor interactions are employed to obtain the pseudoscalar and vector meson masses incorporating the effect of mixing. The decay constants (f{sub P/V}) are computed with QCD correction using the wave function at the origin. The leptonic branching fractions and electromagnetic transition rates are also calculated in this scheme. Our predictions at potential index {nu}=1 are in good agreement with experimental results as well as other theoretical models.

Properties of quarks and mesons in the Dyson-Schwinger/Bethe-Salpeter approach

Abstract: In this thesis, the Dyson-Schwinger - Bethe-Salpeter formalism is investigated and used to study the meson spectrum at zero temperature, as well as the chiral phase transition in finite-temperature QCD. First, the application of sophisticated matrix algorithms to the numerical solution of both the homogeneous Bethe-Salpeter equation (BSE) and the inhomogeneous vertex BSE is discussed, and the advantages of these methods are described in detail. Turning to the finite temperature formalism, the rainbow-truncated quark Dyson-Schwinger equation is used to investigate the impact of different forms of the effective interaction on the chiral transition temperature. A strong model dependence and no overall correlation of the value of the transition temperature to the strength of the interaction is found. Within one model, however, such a correlation exists and follows an expected pattern. In the context of the BSE at zero temperature, a representation of the inhomogeneous vertex BSE and the quark-antiquark propagator in terms of eigenvalues and eigenvectors of the homogeneous BSE is given. Using the rainbow-ladder truncation, this allows to establish a connection between the bound-state poles in the quark-antiquark propagator and the behavior of eigenvalues of the homogeneous BSE, leading to a new extrapolation technique for meson masses. This is used to study the ground- and excited-state meson spectrum for all quark masses from light to bottom, for pseudoscalar, scalar, vector, axialvector and tensor mesons. Good agreement with experiment is found, e.g., for all ground states in the bottomonium system. In addition, new applications of the inhomogeneous vertex BSE, such as the possibility to calculate on-shell quantities like decay constants, are investigated. Finally, we study the influence of the infrared behavior of the effective interaction on properties of pi and rho mesons.

GMOR-like relation in IR-conformal gauge theories

Abstract: A generalization of the Gell-Mann-Oaks-Renner relation to the case of infrared-conformal gauge theories is discussed. The starting point is the chiral Ward identity connecting the isovector pseudoscalar susceptibility to the chiral condensate, in a mass-deformed theory. A renormalization-group analysis shows that the pseudoscalar susceptibility is not saturated by the lightest state, but a contribution from the continuum part of the spectrum survives in the chiral limit. The computation also shows how infrared-conformal gauge theories behave differently, depending on whether the anomalous dimension of the chiral condensate be smaller or larger than 1. An application to lattice simulations is briefly discussed.

$O(\alpha_s v^2)$ correction to pseudoscalar quarkonium decay to two photons

Abstract: We investigate the $O(\alpha_s v^2)$ correction to the process of pseudoscalar quarkonium decay to two photons in nonrelativistic QCD (NRQCD) factorization framework. The short-distance coefficient associated with the relative-order $v^2$ NRQCD matrix element is determined to next-to-leading order in $\alpha_s$ through the perturbative matching procedure. Some technical subtleties encountered in calculating the ${O(\alpha_s)$ QCD amplitude are thoroughly addressed.

Heavy Pseudoscalar Mesons in a Schwinger-Dyson-Bethe-Salpeter Approach

Abstract: The mass spectrum of heavy pseudoscalar mesons, as quark–antiquark bound systems, is considered within the Bethe-Salpeter formalism with momentum-dependent masses of the constituents. This dependence is prior found by solving the Schwinger-Dyson equation for quark propagators in rainbow-ladder approximation. Such approximation is known to provide fast convergence of numerical methods and accurate results for lightest mesons. However, as the meson mass increases, the method becomes less stable and special attention must be devoted to details of means of solving the corresponding equations. We focus on the pseudoscalar sector and show that our numerical scheme describes fairly accurately the π, K, D, Ds and ηc ground states. The excited states are considered as well. Our calculations are directly related to future physics at FAIR.

STUDY OF CP VIOLATION IN $\Lambda_c^+$ DECAY

Abstract: In this paper, we study CP violation in and decays, where B, P and V denote a light spin-½ baryon, pseudoscalar and a vector meson respectively. In these processes the T odd CP violating triple-product (TP) correlations are examined. The genuine CP violating observables which are composed of the helicity amplitudes occurring in the angular distribution are constructed. Experimentally, by performing a full angular analysis it is shown how one may extract the helicity amplitudes and then obtain the TP asymmetries. We estimate the TP asymmetries in decays to be negligible in the Standard Model making these processes an excellent place to look for new physics. Taking a two-Higgs doublet model, as an example of new physics, we show that large TP asymmetries are possible in these decays. Finally, we discuss how BES-III and super τ-charm experiments will be sensitive to these CP violating signals in decays.

Results for light pseudoscalar mesons

Abstract: We present the current status of the MILC collaboration’s calculations of the properties of the light pseudoscalar meson sector. We use asqtad staggered ensembles with 2+1 dynamical flavors down to a≈ 0.045 fm and light quark mass down to 0.05ms. Here we describe fits to the data using chiral forms from SU(3) chiral perturbation theory, including all staggered taste violations at NLO and the continuum NNLO chiral logarithms. We emphasize issues of convergence of the chiral expansion.