Showing papers on "Pseudoscalar published in 2001"
TL;DR: In this paper, a lattice hadron spectrum calculation using three flavors of dynamical quarks (two light and one strange) and quenched simulations for comparison is presented.
Abstract: We present results from a lattice hadron spectrum calculation using three flavors of dynamical quarks --- two light and one strange---and quenched simulations for comparison. These simulations were done using a one-loop Symanzik improved gauge action and an improved Kogut-Susskind quark action. The lattice spacings, and hence also the physical volumes, were tuned to be the same in all the runs to better expose differences due to flavor number. Lattice spacings were tuned using the static quark potential, so as a by-product we obtain updated results for the effect of sea quarks on the static quark potential. We find indications that the full QCD meson spectrum is in better agreement with experiment than the quenched spectrum. For the ${0}^{++}$ ${(a}_{0})$ meson we see a coupling to two pseudoscalar mesons, or a meson decay on the lattice.
248 citations
TL;DR: In this article, the procedure to calculate masses and matrix elements in the presence of mixing of the basis states is explained in detail and applied to the two-loop calculation in Chiral Perturbation Theory of pseudoscalar masses and decay constants including quark mass isospin breaking.
185 citations
TL;DR: In this paper, the invariant mass distributions of the ππ and KK systems for invariant masses up to 1.2 GeV from the J/Ψ→φππ(KK) decays are studied.
121 citations
TL;DR: In this article, a correlation between glueball mass, mixing, and flavour symmetry breaking was identified, and it was concluded that the glueball may be rather lighter than some quenched lattice QCD computations have suggested.
Abstract: Lattice QCD predictions have motivated several recent studies of the mixing between the predicted JPC = 0++ glueball and a qqbar nonet in the 1.3 to 1.7 GeV region. We show that results from apparently different approaches have some common features, explain why this is so and abstract general conclusions. We place particular emphasis on the flavour dependent constraints imposed by decays of the f0(1370), f0(1500) and f0(1700) to all pairs of pseudoscalar mesons. From these results we identify a systematic correlation between glueball mass, mixing, and flavour symmetry breaking and conclude that the glueball may be rather lighter than some quenched lattice QCD computations have suggested. We identify experimental tests that can determine the dynamics of a glueball in this mass region and discuss quantitatively the feasibility of decoding glueball-qqbar mixing.
119 citations
TL;DR: In this article, the dominant contributions to the muon g-2 at the two-loop level due to a light pseudoscalar boson that may exist in any exotic Higgs sector in most extensions of the standard model were calculated.
Abstract: We calculate the dominant contributions to the muon g - 2 at the two-loop level due to a pseudoscalar boson that may exist in any exotic Higgs sector in most extensions of the standard model. The leading effect comes from diagrams of the Barr-Zee type. A sufficiently light pseudoscalar Higgs boson can give rise to contribution as large as the electroweak contribution which is measurable in the next round of g - 2 experiment. The coming improved data on muon g - 2 can put the best limit on the possible existence of a light pseudoscalar boson in physics beyond the standard model.
115 citations
TL;DR: In this paper, the form factors for B → π and D → K ( π ) semileptonic decays on the lattice were computed by using full nonperturbative O(a) improvement, in the quenched approximation.
96 citations
TL;DR: In this article, the authors derived power counting rules for the calculation of in-medium pion properties and established the different scales for the range of applicability of this perturbative expansion.
Abstract: An explicit expression of the generating functional of two-flavor low-energy QCD with external sources in the presence of non-vanishing nucleon densities has been derived recently [1]. Within this approach we derive power counting rules for the calculation of in-medium pion properties. We develop the so-called standard rules for residual nucleon energies of the order of the pion mass and a modified scheme (non-standard counting) for vanishing residual nucleon energies. We also establish the different scales for the range of applicability of this perturbative expansion, which are \sqrt{6}\pi f_\pi\simeq 0.7 GeV for the standard and 6\pi^2 f_\pi^2/2m_N\simeq 0.27 GeV for non-standard counting, respectively. We have performed a systematic analysis of n-point in-medium Green functions up to and including next-to-leading order when the standard rules apply. These include the in-medium contributions to quark condensates, pion propagators, pion masses and couplings of the axial-vector, vector and pseudoscalar currents to pions. In particular, we find a mass shift for negatively charged pions in heavy nuclei that agrees with recent determinations from deeply bound pionic Pb-207. We have also established the absence of in-medium renormalization in the \pi^0 \to \gamma\gamma decay amplitude up to the same order. The study of \pi\pi scattering requires the use of the non-standard counting and the calculation is done at leading order. Even at that order we establish new contributions not considered so far. We also point towards further possible improvements of this scheme and touch upon its relation to more conventional many-body approaches.
85 citations
TL;DR: In this paper, the authors present a derivation of the transformation between the Q and U Stokes parameters and the E and B scalar and pseudoscalar fields, and emphasize the geometrical properties that such transformation must satisfy.
Abstract: We present a derivation of the transformation between the Q and U Stokes parameters and the E and B scalar and pseudoscalar fields. We emphasize the geometrical properties that such transformation must satisfy. We present the E and B decompositions of some simple maps and of a model for a supernova remnant. We discuss the relative amplitudes of the E and B components, and argue that for generic random maps E and B should have roughly the same amplitudes.
80 citations
Posted Content•
TL;DR: In this article, the sign of the pseudoscalar pole contribution to the muon g 2 was corrected, which was due to the fact that the algebraic manipulation program FORM treats -tensor so as to satisfy 1 2 3 4 1.3 4 11 22 33 44 = 24, as opposed to the expected value 24 when Minkowski space-time metric is specied.
Abstract: We correct the error in the sign of the pseudoscalar pole contribution to the muon g 2, which dominates the O( 3 ) hadronic light-by-light scattering eect. The error originates from the fact that the algebraic manipulation program FORM treats -tensor so as to satisfy 1 2 3 4 1 2 3 4 11 22 33 44 = 24, as opposed to the expected value 24 when Minkowski space-time metric is specied (at least in the version available before 1995). Replacing the part 1 2 3 4 1 2 3 4 by 1 1 2 2 3 3 4 4 in the FORM-formatted programs, we obtained a positive value for the pseudoscalar pole contribution, which agrees with the recent result obtained by Knecht et al.
80 citations
TL;DR: Considering nonforward scattering amplitude off the heavy quark in the Small Velocity limit, this article derived exact superconvergent sum rules for spin of the light cloud and led to the lower bound ϱ2>3/4 for the slope of the Isgur-Wise function.
59 citations
Posted Content•
TL;DR: In this paper, the results for the proton and neutron electric and magnetic form factors as well as the nucleon axial and induced pseudoscalar form factors are presented for the chiral constituent quark model based on Goldstone-boson-exchange dynamics.
Abstract: Results for the proton and neutron electric and magnetic form factors as well asthe nucleon axial and induced pseudoscalar form factors are presented for the chiral constituent quark model based on Goldstone-boson-exchange dynamics. The calculations are performed in a covariant framework using the point-form approach to relativistic quantum mechanics. The direct predictions of the model yield a remarkably consistent picture of the electroweak nucleon structure.
TL;DR: In this paper, the authors apply the maximum entropy method to extract the spectral functions for pseudoscalar and vector mesons from hadron correlators previously calculated at four different lattice spacings in quenched QCD with the Wilson quark action.
Abstract: We apply the maximum entropy method to extract the spectral functions for pseudoscalar and vector mesons from hadron correlators previously calculated at four different lattice spacings in quenched QCD with the Wilson quark action. We determine masses and decay constants for the ground and excited states of the pseudoscalar and vector channels from the position and area of peaks in the spectral functions. We obtain the results mp 1 5660(590) MeV and mr 1 51540(570) MeV for the first excited state masses, in the continuum limit of quenched QCD. We also find unphysical states that have an infinite mass in the continuum limit, and argue that they are bound states of two doublers of the Wilson quark action. If the interpretation is correct, this is the first time that the state of doublers has been identified in lattice QCD numerical simulations.
TL;DR: In this paper, the renormalization constant of the scalar density for Ginsparg-Wilson fermions is computed non-perturbatively, based on a matching of renormalisation group invariant masses at fixed pseudoscalar meson mass.
Abstract: We present a method to compute non-perturbatively the renormalization constant of the scalar density for Ginsparg-Wilson fermions. It relies on chiral symmetry and is based on a matching of renormalization group invariant masses at fixed pseudoscalar meson mass, making use of results previously obtained by the ALPHA Collaboration for O(a)-improved Wilson fermions. Our approach is quite general and enables the renormalization of scalar and pseudoscalar densities in lattice regularizations that preserve chiral symmetry and of fermion masses in any regularization. As an application we compute the non-perturbative factor which relates the renormalization group invariant quark condensate to its bare counterpart, obtained with overlap fermions at β = 5.85 in the quenched approximation.
TL;DR: In this article, the DDρ form factor is evaluated in a QCD sum rule calculation for both D and ρ off-shell mesons, and it is shown that the momentum dependence of the form factors is very different if the D or the ρ meson is offshell, but they lead to the same coupling constant in the vertex.
TL;DR: Bressloff et al. as discussed by the authors showed that pseudoscalar bifurcations are possible from trivial states when Euclidean equivariant systems are restricted to a planar lattice.
Abstract: Bosch Vivancos, Chossat and Melbourne showed that two types of steadystate bifurcations are possible from trivial states when Euclidean equivariant systems are restricted to a planar lattice—scalar and pseudoscalar—and began the study of pseudoscalar bifurcations. The scalar bifurcations have been well studied since they appear in planar reaction–diffusion systems and in plane layer convection problems. Bressloff, Cowan, Golubitsky, Thomas and Wiener showed that bifurcations in models of the visual cortex naturally contain both scalar and pseudoscalar bifurcations, due to a different action of the Euclidean group in that application. In this paper, we review the symmetry discussion in Bressloff et al and we continue the study of pseudoscalar bifurcations. Our analysis furthers the study of pseudoscalar bifurcations in three ways. (a) We complete the classification of axial subgroups on the hexagonal lattice in the shortest wavevector case proving the existence of one new planform—a solution with triangular D3 symmetry. (b) We derive bifurcation diagrams for generic bifurcations giving, in particular, the stability of solutions to perturbations in the hexagonal lattice. For the simplest (codimension zero) bifurcations, these bifurcation diagrams are identical to those derived by Golubitsky, Swift and Knobloch � = � � � � .
TL;DR: In this paper, the baryon-baryon octet interaction was investigated in a unified framework of the resonating-group method which employs the spin-flavor wave functions with explicit color degrees of freedom.
Abstract: The baryon-baryon interaction for the complete baryon octet is investigated in a unified framework of the resonating-group method which employs the spin-flavor ${\mathrm{SU}}_{6}$ wave functions with explicit color degrees of freedom. The interaction Hamiltonian is composed of the phenomenological confinement potential, the color Fermi-Breit interaction with explicit flavor symmetry breaking, and the effective meson-exchange potentials of scalar, pseudoscalar, and vector-meson types, acting between quarks. For the scalar- and vector-meson exchanges, the momentum-dependent higher-order terms are incorporated to reduce the attractive effect of the central interaction at higher energies. The single-particle potentials of the octet baryons, predicted by the G-matrix calculation, now have proper repulsive behavior in the momentum region ${q}_{1}=5--20 {\mathrm{fm}}^{\ensuremath{-}1}.$ A moderate contribution of the spin-orbit interaction from the scalar-meson exchange is also included. As to the vector mesons, a dominant contribution is the quadratic spin-orbit force generated from the $\ensuremath{\rho}$-meson exchange. This paper discusses the nucleon-nucleon interaction up to ${T}_{\mathrm{lab}}=800 \mathrm{MeV}.$ The nucleon-nucleon phase shifts at the nonrelativistic energies up to ${T}_{\mathrm{lab}}=350 \mathrm{MeV}$ are greatly improved, and now have attained the accuracy almost comparable to that of one-boson-exchange potentials. The deuteron properties and the low-energy observables of the nucleon-nucleon interaction are examined in the particle basis by incorporating the isospin symmetry breaking through the mass difference of the neutral and charged pions and the Coulomb effect as well. The nuclear saturation properties and the single-particle potential of the nucleon in symmetric nuclear matter are examined through the G-matrix calculation which uses the quark-exchange kernel directly.
TL;DR: In this article, a renormalization-group-improved rainbow-ladder truncation is used to solve the Bethe-Salpeter equations. But the bound state amplitudes are identical, as are the positions and residues of the pseudoscalar and scalar poles in the vertices.
Abstract: Inhomogeneous pseudoscalar and scalar Bethe-Salpeter equations solved using a renormalization-group-improved rainbow-ladder truncation exhibit bound state poles below and above T{sub c}, the critical temperature for chiral symmetry restoration. Above T{sub c} the bound state amplitudes are identical, as are the positions and residues of the pseudoscalar and scalar poles in the vertices. In the chiral limit the {pi}{sup 0}{yields}{gamma}{gamma} coupling vanishes at T{sub c}, as do f{sub {pi}}, m{sub {sigma}}, and g{sub {sigma}{pi}{pi}}. For light current-quark masses the 2{pi} decay channel of the isoscalar-scalar bound state remains open until very near T{sub c}, and the widths of the dominant pion decay modes remain significant in the vicinity of the crossover.
TL;DR: In this article, the double Borel sum rule for the three point function of two pseudoscalar and one vector meson currents is evaluated in a QCD sum rule calculation for both D and rho off-shell mesons.
Abstract: The DDrho form factor is evaluated in a QCD sum rule calculation for both D and rho off-shell mesons. We study the double Borel sum rule for the three point function of two pseudoscalar and one vector meson currents. We find that the momentum dependence of the form factors is very different if the D or the rho meson is off-shell, but they lead to the same coupling constant in the DDrho vertex. We discuss two different approaches to extract the DDrho coupling constant.
TL;DR: In this article, the energy loss rates of degenerate neutron-star matter due to thermal bremsstrahlung of pseudoscalar particles and axions via neutron-proton collisions together with the mean-free path and the energy spectrum from neutron-neutron, neutronproton, and neutron processes are calculated.
Abstract: The energy-loss rates of degenerate neutron-star matter due to thermal bremsstrahlung of pseudoscalar particles and axions via neutron-proton collisions together with the mean-free path and the energy spectrum from neutron-neutron, neutron-proton, and neutron-neutron processes are calculated. Analytic expressions for these quantities are obtained in the general case where the pseudoscalar particle couples to the proton and neutron with different strengths and the protons and the neutrons have different Fermi momenta. These rates are compared with those of other authors.
TL;DR: In this article, the renormalization constant of the scalar density for Ginsparg-Wilson fermions is computed non-perturbatively, based on a matching of renormalisation group invariant masses at fixed pseudoscalar meson mass.
Abstract: We present a method to compute non-perturbatively the renormalization constant of the scalar density for Ginsparg-Wilson fermions. It relies on chiral symmetry and is based on a matching of renormalization group invariant masses at fixed pseudoscalar meson mass, making use of results previously obtained by the ALPHA Collaboration for O(a)-improved Wilson fermions. Our approach is quite general and enables the renormalization of scalar and pseudoscalar densities in lattice regularizations that preserve chiral symmetry and of fermion masses in any regularization. As an application we compute the non-perturbative factor which relates the renormalization group invariant quark condensate to its bare counterpart, obtained with overlap fermions at beta=5.85 in the quenched approximation.
TL;DR: In this article, an effective field theory of pions, nucleons and delta isobars was proposed for the capture of the proton from the TRIUMF experiment, and it was shown that the discrepancy between theory and experiment might be due to Δ (1232) related effects, which are only included via higher-order contact interactions in the standard chiral approach.
TL;DR: In this article, the authors considered the L = 1 q\bar{q} scalar mesons in pseudoscalar nonet in SU(3) chiral symmetry.
Abstract: Following the re-establishment of the \sigma(600) and the \kappa(900), the light scalar mesons a_0(980) and f_0(980) together with the \sigma(600) and the \kappa(900) are considered as the chiral scalar partner of pseudoscalar nonet in SU(3) chiral symmetry, and the high mass scalar mesons a_0(1450), K^*_0(1430), f_0(1370) and f_0(1710) turned out to be considered as the L=1 q\bar{q} scalar mesons. We assume that the high mass of the L=1 q\bar{q} scalar mesons is caused by the mixing with the light scalar mesons. For the structure of the light scalar mesons, we adopted the qq\bar{q}\bar{q} model in order to explain the "scalar meson puzzle". The inter-mixing between the light scalar nonet and the high mass L=1 q\bar{q} nonet and the intra-mixing among each nonet are analyzed by including the glueball into the high mass scalar nonet.
TL;DR: The conclusion is that this is not the case, for the efficiency loophole cannot be eliminated, and experimental tests of Bell inequalities performed with pseudoscalar mesons cannot be definitive.
TL;DR: In this paper, lower and upper bounds for the flavor changing Yukawa couplings in the leptonic sector were derived in the framework of the general two Higgs doublet model.
Abstract: Current experimental data from the $g\ensuremath{-}2$ muon factor seem to show the necessity of physics beyond the standard model (SM), since the difference between SM and experimental predictions is approximately $2.6\ensuremath{\sigma}.$ In the framework of the general two Higgs doublet model, we calculate the muon anomalous magnetic moment to get lower and upper bounds for the flavor changing Yukawa couplings in the leptonic sector. We also obtain lower bounds for the mass of the Higgs pseudoscalar ${(m}_{{A}^{0}})$ as a function of the parameters of the model.
TL;DR: In this article, the authors present a study of the flavor asymmetry of polarized anti-quarks in the nucleon using the meson cloud model, including contributions both from the vector mesons and the interference terms of pseudoscalar and vector meshes.
Abstract: We present a study of the flavor asymmetry of polarized anti-quarks in the nucleon using the meson cloud model. We include contributions both from the vector mesons and the interference terms of pseudoscalar and vector mesons. Employing the bag model, we first give the polarized valence quark distribution of the $\rho$
meson and the interference distributions. Our calculations show that the interference effect mildly increases the prediction for $\Delta{\bar d}(x)- \Delta{\bar u}(x)$
at intermediate x region. We also discuss the contribution of “Pauli blocking” to the asymmetry.
TL;DR: In this article, it was shown that chirally enhanced corrections can be included consistently in the framework of QCD factorization only if the twist-3 distribution amplitudes are symmetric.
TL;DR: In this article, the authors present a study of the flavour asymmetry of polarized anti-quarks in the nucleon using the meson cloud model, including contributions both from the vector mesons and the interference terms of pseudoscalar and vector meshes.
Abstract: We present a study of the flavour asymmetry of polarized anti-quarks in the nucleon using the meson cloud model. We include contributions both from the vector mesons and the interference terms of pseudoscalar and vector mesons. Employing the bag model, we first give the polarized valence quark distribution of the $\rho$ meson and the interference distributions. Our calculations show that the interference effect mildly increases the prediction for $\Delta \dbar(x)-\Delta \ubar(x)$ at intermediate $x$ region. We also discuss the contribution of `Pauli blocking' to the asymmetry.
TL;DR: In this article, the role of the Zweig rule violation in the scalar channel for the determination of low-energy constants and condensates arising in the effective chiral lagrangian of QCD was discussed.
Abstract: We discuss the role of the Zweig rule (ZR) violation in the scalar channel for the determination of low-energy constants and condensates arising in the effective chiral lagrangian of QCD. The analysis of the Goldstone boson masses and decay constants shows that the three-flavor condensate and some low-energy constants are very sensitive to the value of the ZR violating constant L6. A similar study is performed in the case of the decay constants. A chiral sum rule based on experimental data in the 0++ channel is used to constrain L6, indicating a significant decrease between the two- and the three-flavor condensates. The analysis of the scalar form factors of the pion at zero momentum suggests that the pseudoscalar decay constant could also be suppressed from Nf = 2 to 3.
TL;DR: In this paper, the authors revisited the isovector pseudoscalar sum rule determination of mu+md, using families of finite energy sum rules known to be very accurately satisfied in the ISV channel.
TL;DR: In this paper, it was shown that isospin symmetry breaking effects on pseudoscalar mesons naturally induces correspondingly effects within the physics of vector mesons, through kaon loops.
Abstract: We study the way isospin symmetry violation can be generated within the Hidden Local Symmetry (HLS) Model. We show that isospin symmetry breaking effects on pseudoscalar mesons naturally induces correspondingly effects within the physics of vector mesons, through kaon loops. In this way, one recovers all features traditionally expected from $\rho-\omega$
mixing and one finds support for the Orsay phase modelling of the $e^+e^- \rightarrow \pi^+ \pi^-$
amplitude. We then examine an effective procedure which generates mixing in the whole $\rho, \omega, \phi$
sector of the HLS Model. The corresponding model allows us to account for all two body decays of light mesons accessible to the HLS model in modulus and phase, leaving aside the $\rho \rightarrow \pi \pi$
and $K^* \rightarrow K \pi$
modes only, which raise a specific problem. Comparison with experimental data is performed and covers modulus and phase information; this represents 26 physics quantities successfully described with very good fit quality within a constrained model which accounts for SU(3) breaking, nonet symmetry breaking in the pseudoscalar sector and, now, isospin symmetry breaking.