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Showing papers on "Pseudoscalar published in 2008"


Journal ArticleDOI
TL;DR: In this article, light scalar mesons in the holographic QCD soft-wall model with a background dilaton field were studied and the masses and decay constants were compatible with experiment and QCD determinations.
Abstract: We study light scalar mesons in the holographic QCD soft-wall model with a background dilaton field. The masses and decay constants are compatible with experiment and QCD determinations if a{sub 0}(980) and f{sub 0}(980) are identified as the lightest scalar mesons; moreover, the states are organized in linear Regge trajectories with the same slope of vector mesons. Comparing the two-point correlation function of scalar operators derived on the anti-de Sitter side and in QCD, information about the condensates can be derived. Strong couplings of scalar states to pairs of light pseudoscalar mesons turn out to be small, at odds with experiment and QCD estimates: we discuss how this discrepancy is related to the description of chiral symmetry breaking in this model, and the possible solutions.

213 citations


Journal ArticleDOI
TL;DR: In this article, the authors considered only the scalar torsion and showed that this mode can contribute an oscillating aspect to the expansion rate of the universe. And they showed that for suitable ranges of the parameters, the dynamic scalar Torsion model can display features similar to those of the presently observed accelerating universe.
Abstract: Investigations of the dynamic modes of the Poincar\'e gauge theory of gravity found only two good propagating torsion modes; they are effectively a scalar and a pseudoscalar. Cosmology affords a natural situation where one might see observational effects of these modes. Here, we consider only the ``scalar torsion'' mode. This mode has certain distinctive and interesting qualities. In particular, this type of torsion does not interact directly with any known matter, and it allows a critical nonzero value for the affine scalar curvature. Via numerical evolution of the coupled nonlinear equations we show that this mode can contribute an oscillating aspect to the expansion rate of the Universe. From the examination of specific cases of the parameters and initial conditions we show that for suitable ranges of the parameters the dynamic ``scalar torsion'' model can display features similar to those of the presently observed accelerating universe.

136 citations


Journal ArticleDOI
TL;DR: In this paper, the electromagnetic form factors of vector mesons are calculated in an explicitly Poincare covariant formulation, based on the Dyson-Schwinger equations of QCD.
Abstract: The electromagnetic form factors of vector mesons are calculated in an explicitly Poincare covariant formulation, based on the Dyson-Schwinger equations of QCD, that respects electromagnetic current conservation and unambiguously incorporates effects from vector meson poles in the quark-photon vertex. This method incorporates a two-parameter effective interaction, where the parameters are constrained by the experimental values of chiral condensate and f{sub {pi}}. This approach has successfully described a large amount of light-quark meson experimental data, including ground-state pseudoscalar masses and their electromagnetic form factors and ground-state vector meson masses and strong and electroweak decays. Here we apply it to predict the electromagnetic properties of vector mesons. The results for the static properties of the {rho} meson are as follows: charge radius =0.54 fm{sup 2}, magnetic moment {mu}=2.01, and quadrupole moment Q=-0.41. We investigate the quark-mass dependence of these static properties and find that our results at the charm quark mass are in agreement with recent lattice simulations. The charge radius decreases with increasing quark mass, but the magnetic moment is almost independent of the quark mass.

119 citations


Journal ArticleDOI
TL;DR: A review of the experimental status of glueballs can be found in this paper, where theoretical expectations of phenomenological models and QCD on the lattice are briefly discussed.
Abstract: Glueballs and other resonances with large gluonic components are predicted as bound states by Quantum Chromodynamics (QCD). The lightest (scalar) glueball is estimated to have a mass in the range from 1 to 2 GeV/c**2; a pseudoscalar and tensor glueball are expected at higher masses. Many different experiments exploiting a large variety of production mechanisms have presented results in recent years on light mesons with J(PC) = 0(++), 0(-+), and 2(++) quantum numbers. This review looks at the experimental status of glueballs. Good evidence exists for a scalar glueball which is mixed with nearby mesons, but a full understanding is still missing. Evidence for tensor and pseudoscalar glueballs are weak at best. Theoretical expectations of phenomenological models and QCD on the lattice are briefly discussed.

105 citations


Journal ArticleDOI
TL;DR: In this paper, a relativistic invariant pseudoscalar alpha-tilde was derived from the magnetoelectric moduli of chromium sesquioxide Cr2O3.
Abstract: The magnetoelectric effect of chromium sesquioxide Cr2O3 has been determined experimentally as a function of temperature. One measures the electric field-induced magnetization on Cr2O3 crystals or the magnetic field-induced polarization. From the magnetoelectric moduli of Cr2O3 we extract a four-dimensional relativistic invariant pseudoscalar alpha-tilde. It is temperature dependent and of the order of ~10−4/Z0, with Z0 as vacuum impedance. We show that the new pseudoscalar is odd under parity transformation and odd under time inversion. Moreover, alpha-tilde is for Cr2O3 what Tellegen's gyrator is for two port theory, the axion field for axion electrodynamics, and the PEMC (perfect electromagnetic conductor) for electrical engineering.

101 citations


Journal ArticleDOI
TL;DR: In this article, the back-coupling of the pion onto the quark propagator within the nonperturbative continuum framework of Schwinger-Dyson equations (SDE) and Bethe-Salpeter equations (BSE) is considered.
Abstract: We investigate hadronic unquenching effects in light quarks and mesons. To this end, we take into account the back-coupling of the pion onto the quark propagator within the nonperturbative continuum framework of Schwinger-Dyson equations (SDE) and Bethe-Salpeter equations (BSE). We improve on a previous approach by explicitly solving both the coupled system of SDEs and BSEs in the complex plane and the normalization problem for Bethe-Salpeter kernels depending on the total momentum of the meson. As a result of our study, we find considerable unquenching effects in the spectrum of light pseudoscalar, vector and axial-vector mesons.

79 citations


Journal ArticleDOI
TL;DR: The KLOE detector at DAϕNE, the Frascati ϕ, and its physics program is described in this article, where the authors verify the validity of Cabibbo unitarity and lepton universality.
Abstract: We describe the KLOE detector at DAϕNE, the Frascati ϕ, and its physics program. We begin with a brief description of the detector design and operation. Kaon physics is a major topic of investigation with KLOE thanks in part to the unique availability of pure KS, KL, K± beams at a ϕ.We have measured all significant branching ratios of all kaon species, the KL and K± lifetimes and the K →π form factor’s t dependence. From the measurements we verify the validity of Cabibbo unitarity and lepton universality. We have studied properties of light scalar and pseudoscalar mesons with unprecedented accuracy. We have measured the e+e- → π+π- cross-section necessary for computing the major part of the hadronic contribution to the muon anomaly. The methods employed in all the above measurements as well as the ϕ leptonic width, precision mass measurements and searches for forbidden or extremely rare decays of kaons and η-mesons are described. The impact of our results on flavor and hadron physics to date, as well as an outlook for further improvement in the near future, are discussed.

77 citations


Journal ArticleDOI
TL;DR: In this article, a 4-dimensional relativistic invariant pseudoscalar (alpha) over tilde was derived from the magnetoelectric moduli of chromium sesquioxide Cr2O3.

57 citations


Journal ArticleDOI
TL;DR: In this article, the mass of the singlet pseudoscalar meson with N_f = 2 flavors of light quarks has been derived using lattice QCD, and the phenomenological status of this meson has been discussed.
Abstract: We study the flavour singlet pseudoscalar mesons from first principles using lattice QCD. With N_f=2 flavours of light quark, this is the so-called eta_2 meson and we discuss the phenomenological status of this. Using maximally twisted-mass lattice QCD, we extract the mass of the eta_2 meson at two values of the lattice spacing for lighter quarks than previously discussed in the literature. We are able to estimate the mass value in the limit of light quarks with their physical masses.

50 citations


Journal ArticleDOI
TL;DR: In this paper, the introduction of a finite baryon density may trigger spontaneous parity violation in the hadronic phase of QCD, and a σ model that retains the two lowest scalar and pseudoscalar multiplets is proposed.

49 citations


Posted Content
TL;DR: In this paper, the potential of the lightest scalar (h1) and pseudoscalar (a1) Higgs bosons to cover the parameter space of the NMSSM at the Large Hadron Collider (LHC) was studied.
Abstract: We study the potential of the h1 ? a1a1 ? 4 signal from the lightest scalar (h1) and pseudoscalar (a1) Higgs bosons to cover the parameter space of the Next-to- Minimal Supersymmetric Standard Model (NMSSM) at the Large Hadron Collider (LHC). We exploit a 2? + 2jets signature from four ’s decays (accompanied by missing transverse energy), resorting to both Higgs-strahlung (HS), by triggering on leptonic W± decays, and Vector Boson Fusion (VBF), by triggering on two same sign non-isolated muons.

Journal ArticleDOI
TL;DR: In this paper, a linear sigma model containing one chiral nonet transforming under the SU(3) invariant limit for two scalar octets and an excited pion octet was studied.
Abstract: We present a detailed study of a linear sigma model containing one chiral nonet transforming under $\mathrm{U}(1{)}_{\mathrm{A}}$ as a quark-antiquark composite and another chiral nonet transforming as a diquark-antidiquark composite (or, equivalently from a symmetry point of view, as a two meson molecule). The model provides an intuitive explanation of a current puzzle in low energy QCD: Recent work has suggested the existence of a lighter than 1 GeV nonet of scalar mesons which behave like four quark composites. On the other hand, the validity of a spontaneously broken chiral symmetric description would suggest that these states be chiral partners of the light pseudoscalar mesons, which are two quark composites. The model solves the problem by starting with the two chiral nonets mentioned and allowing them to mix with each other. The input of physical masses in the SU(3) invariant limit for two scalar octets and an excited pion octet results in a mixing pattern wherein the light scalars have a large four quark content while the light pseudoscalars have a large two quark content. One light isosinglet scalar is exceptionally light. In addition, the pion pion scattering is also studied and the current algebra theorem is verified for massless pions which contain some four quark admixture.

Posted Content
TL;DR: In this article, the physics of purely leptonic decays of pi-, K-, D+, Ds+, and B- pseudoscalar mesons are reviewed. But the interplay between theory and experiment is different for each particle, and theoretical predictions that are necessary in the B sector can be tested, for example, in the charm sector.
Abstract: We review here the physics of purely leptonic decays of pi-, K-, D+, Ds+, and B- pseudoscalar mesons. The measured decay rates are related to the product of the relevant weak interaction based CKM matrix element of the constituent quarks and a strong interaction parameter related to the overlap of the quark and anti-quark wave-functions in the meson, called the decay constant fP. The interplay between theory and experiment is different for each particle. Theoretical predictions that are necessary in the B sector can be tested, for example, in the charm sector. One such measurement, that of fDs, differs from the most precise unquenched lattice calculation and may indicate the presence of new intermediate particles, or the theoretical prediction could be misleading. The lighter pi and K mesons provide stringent comparisons due to the accuracy of both the measurements and the theoretical predictions. This review was prepared for the Particle Data Group's 2008 edition.

Journal ArticleDOI
TL;DR: In this paper, the authors present the results of a lattice QCD calculation of the average up-down and strange quark masses and of the light meson pseudoscalar decay constants with Nf=2 dynamical fermions.
Abstract: We present the results of a lattice QCD calculation of the average up-down and strange quark masses and of the light meson pseudoscalar decay constants with Nf=2 dynamical fermions. The simulation is carried out at a single value of the lattice spacing with the twisted mass fermionic action at maximal twist, which guarantees automatic O(a)-improvement of the physical quantities. Quark masses are renormalized by implementing the non-perturbative RI-MOM renormalization procedure. Our results for the light quark masses are m_ud^{msbar}(2 GeV)= 3.85 +- 0.12 +- 0.40 MeV, m_s^{msbar}(2 GeV) = 105 +- 3 +- 9 MeV and m_s/m_ud = 27.3 +- 0.3 +- 1.2. We also obtain fK = 161.7 +- 1.2 +- 3.1 MeV and the ratio fK/fpi=1.227 +- 0.009 +- 0.024. From this ratio, by using the experimental determination of Gamma(K-> mu nu (gamma))/Gamma(pi -> mu nu (gamma)) and the average value of |Vud| from nuclear beta decays, we obtain |Vus|=0.2192(5)(45), in agreement with the determination from Kl3 decays and the unitarity constraint.

Journal ArticleDOI
TL;DR: In this article, the reconstruction theorem of Stern, Sazdjian, and Fuchs is generalized to the case of the (2,yields) scattering of all the pseudoscalar octet mesons.
Abstract: We generalize the reconstruction theorem of Stern, Sazdjian, and Fuchs based on the dispersion relations to the case of the (2{yields}2) scattering of all the pseudoscalar octet mesons ({pi},K,{eta}). We formulate it in a general way and include also a discussion of the assumptions of the theorem. It is used to obtain the amplitudes of all such processes in the isospin limit to the one-loop order (and can be straightforwardly extended to two loops) independently on the particular power-counting scheme of the chiral perturbation theory in question. The results in this general form are presented.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the warped deformed conifold has two bosonic massless modes, a pseudoscalar and a scalar, that are dual to the phase and the modulus of the baryonic condensates in the cascading gauge theory.
Abstract: As shown in arXiv:hep-th/0405282, the warped deformed conifold has two bosonic massless modes, a pseudoscalar and a scalar, that are dual to the phase and the modulus of the baryonic condensates in the cascading gauge theory. We reconsider the scalar mode sector, mixing fluctuations of the NS-NS 2-form and the metric, and include non-zero 4-d momentum kμ. The resulting pair of coupled equations produce a discrete spectrum of m42 = −kμ2 which is interpreted as the spectrum of JPC = 0+− glueballs in the gauge theory. Similarly, we derive the spectrum of certain pseudoscalar glueballs with JPC = 0−−, which originate from the decoupled fluctuations of the RR 2-form. We argue that each of the massive scalar or pseudoscalar modes we find belongs to a 4-d massive axial vector or vector supermultiplet. We also discuss our results in the context of a finite length throat embedded into a type IIB flux compactification.

Book ChapterDOI
TL;DR: The role of the U(1)A anomaly in QCD phenomenology is reviewed in this article, focusing on the relation between quark dynamics and gluon topology, and the first moment sum rule for g 1 р (the ‘proton spin’ problem) is confronted with new data from COMPASS and HERMES on the deuteron structure function and shown to be quantitatively explained in terms of topological charge screening.
Abstract: The role of the U(1)A anomaly in QCD phenomenology is reviewed, focusing on the relation between quark dynamics and gluon topology. Topics covered include a generalisation of the Witten–Veneziano formula for the mass of the η′, the determination of pseudoscalar meson decay constants, radiative pseudoscalar decays and the U(1)A Goldberger–Treiman relation. Sum rules are derived for the proton and photon structure functions g 1 р and g 1 γ measured in polarised deep inelastic scattering (DIS). The first moment sum rule for g1 р (the ‘proton spin’ problem) is confronted with new data from COMPASS and HERMES on the deuteron structure function and shown to be quantitatively explained in terms of topological charge screening. Proposals for experiments on semi-inclusive DIS and polarised two-photon physics at future eр and high-luminosity e+ e- colliders are discussed.

Journal ArticleDOI
TL;DR: In this paper, the authors calculate the radiative decay width of scalar mesons under the Chiral Unitary Approach (CUA) and provide results for all the possible charge channels and obtain results, with uncertainties, which differ significantly from quark loops models.
Abstract: We calculate the radiative decay widths of the $a_0(980)$ and $f_0(980)$ scalar mesons into $\rho\gamma$ and $\omega\gamma$ considering the dynamically generated nature of these scalar resonances within the realm of the Chiral Unitary Approach. The main ingredient in the evaluation of the radiative width of the scalar mesons are the loops coming from the decay into their constituent pseudoscalar-pseudoscalar components and the subsequent radiation of the photon. The dominant diagrams with only pseudoscalar mesons in the loops are found to be convergent while the divergence of those with a vector meson in the loop are written in terms of the two meson loop function easily regularizable. We provide results for all the possible charge channels and obtain results, with uncertainties, which differ significantly from quark loops models and some version of vector meson dominance.

Journal ArticleDOI
TL;DR: In this article, the s-wave interaction of the vector meson nonet with the octet of pseudoscalar Goldstone Bosons is described within the chiral unitary approach, and it is shown that the main component of the axial vector mesons does not follow the QCD dependence on the number of colors for ordinary qqbar mesons.
Abstract: By describing within the chiral unitary approach the s-wave interaction of the vector meson nonet with the octet of pseudoscalar Goldstone Bosons, we find that the main component of the axial vector mesons b_1(1235), h_1(1170), h_1(1380), a_1(1260), f_1(1285) and the two states associated to the K_1(1270) does not follow the QCD dependence on the number of colors for ordinary qqbar mesons.

Journal ArticleDOI
TL;DR: In this paper, the spinor-spinor Bethe-Salpeter equation is solved in Euclidean space using hyperspherical harmonics, and an appropriate extension to form a new basis of spin-angular harmonics is proposed for a representation of the vertex functions.
Abstract: To solve the spinor-spinor Bethe-Salpeter equation in Euclidean space we propose a novel method related to the use of hyperspherical harmonics. We suggest an appropriate extension to form a new basis of spin-angular harmonics that is suitable for a representation of the vertex functions. We present a numerical algorithm to solve the Bethe-Salpeter equation and investigate in detail the properties of the solution for the scalar, pseudoscalar and vector meson exchange kernels including the stability of bound states. We also compare our results to the nonrelativistic ones and to the results given by light-front dynamics.

Journal ArticleDOI
TL;DR: In this article, an efficient interpolating field for lattice spectroscopy of mesons was constructed by applying covariant derivatives on Jacobi-smeared quark sources.
Abstract: We construct efficient interpolating fields for lattice spectroscopy of mesons by applying covariant derivatives on Jacobi-smeared quark sources These interpolators are tested in a quenched calculation of excited mesons based on the variational method We present results for pseudoscalar, scalar, vector and pseudovector mesons

Journal ArticleDOI
TL;DR: In this paper, the authors calculate the radiative decay width of scalar mesons by considering the dynamically generated nature of these scalar resonances within the realm of the chiral unitary approach.
Abstract: We calculate the radiative decay widths of the a 0(980) and f 0(980) scalar mesons into ργ and ωγ considering the dynamically generated nature of these scalar resonances within the realm of the chiral unitary approach. The main ingredient in the evaluation of the radiative width of the scalar mesons are the loops coming from the decay into their constituent pseudoscalar-pseudoscalar components and the subsequent radiation of the photon. The dominant diagrams with only pseudoscalar mesons in the loops are found to be convergent while the divergence of those with a vector meson in the loop are written in terms of the two-meson loop function easily regularizable. We provide results for all the possible charge channels and obtain results, with uncertainties, which differ significantly from quark loops models and some version of vector meson dominance.

Journal ArticleDOI
TL;DR: In this paper, the weak form factors of the nucleon, including the induced pseudoscalar form factor and second class terms, were constrained using a microscopic calculation of the weak capture process He 3 ( μ −, ν μ ) H 3.

Journal ArticleDOI
TL;DR: In this article, the role of diquarks in light baryons through point-to-point baryon correlators was studied. But the authors did not find any isolated diquark with the third light quark.
Abstract: We study the role of diquarks in light baryons through point-to-point baryon correlators. We contrast results from quenched simulations with ones with two flavors of dynamical overlap fermions. The scalar, pseudoscalar, and axial vector diquarks are combined with light quarks to form color singlets. The quenched simulation shows large zero-mode effects in correlators containing the scalar and pseudoscalar diquark. The two scalar diquarks created by ${\ensuremath{\gamma}}_{5}$ and ${\ensuremath{\gamma}}_{0}{\ensuremath{\gamma}}_{5}$ lead to different behavior in baryon correlators, showing that the interaction of diquarks with the third light quark matters: we do not see an isolated diquark. In our quark mass range, the scalar diquark created by ${\ensuremath{\gamma}}_{5}$ seems to play a greater role than the others.

Journal ArticleDOI
TL;DR: In this paper, a new method of the solution of the Bethe-Salpeter equation for a pseudoscalar quark-antiquark bound state is proposed with the help of an integral representation.
Abstract: A new method of the solution of the Bethe–Salpeter equation for a pseudoscalar quark–antiquark bound state is proposed. With the help of an integral representation, the results are directly obtained in Minkowski space. Dressing of Green's functions is naturally taken into account, thus providing the possible inclusion of a running coupling constant as well as quark propagators. First numerical results are presented for a simplified ladder approximation.

Journal ArticleDOI
TL;DR: In this paper, the effect of photon and ultralight pseudoscalar mixing on the propagation of electromagnetic radiation through the extragalactic medium is studied and an analytic expression for the different Stokes parameters in the limit of a small mixing angle is obtained.
Abstract: We study the effect of photon and ultralight pseudoscalar mixing on the propagation of electromagnetic radiation through the extragalactic medium. The medium is modeled as a large number of uncorrelated magnetic domains. We obtain an analytic expression for the different Stokes parameters in the limit of a small mixing angle. Stokes parameters are found to change linearly with the number of domains. We verify this result by direct numerical simulations. We use the formalism to estimate the effect of pseudoscalar-photon mixing on the cosmic microwave background (CMB) polarization. We impose limits on the model parameters consistent with CMB observations. We find that the currently allowed parameter range admits a CMB circular polarization up to order ${10}^{\ensuremath{-}7}$.

Posted Content
TL;DR: In this paper, the SU(2) gauge theory with two fermions in the adjoint representation has been proposed as a possible technicolor candidate, and simulations are performed on 8^3x16 lattices, at fixed lattice spacing.
Abstract: We discuss the lattice formulation of gauge theories with fermions in arbitrary representations of the color group, and present the implementation of the RHMC algorithm for simulating dynamical Wilson fermions. A first dataset is presented for the SU(2) gauge theory with two fermions in the adjoint representation, which has been proposed as a possible technicolor candidate. Simulations are performed on 8^3x16 lattices, at fixed lattice spacing. The PCAC mass, the pseudoscalar, vector and axial meson masses, the pseudoscalar meson decay constant are computed. The extrapolation to the chiral limit is discussed. However more extensive investigations are needed in order to control the systematic errors in the numerical results, and then understand in detail the phase structure of these theories.

Journal ArticleDOI
TL;DR: In this article, it is argued that it is valid to use QCD sum rules to determine the scalar and pseudoscalar two-point functions at zero momentum, which in turn determine the ratio of the strange to nonstrange quark condensates Rsu = s/q with (q = u, d).
Abstract: It is argued that it is valid to use QCD sum rules to determine the scalar and pseudoscalar two-point functions at zero momentum, which in turn determine the ratio of the strange to non-strange quark condensates Rsu = s/q with (q = u, d). This is done in the framework of a new set of QCD Finite Energy Sum Rules (FESR) that involve as integration kernel a second degree polynomial, tuned to reduce considerably the systematic uncertainties in the hadronic spectral functions. As a result, the parameters limiting the precision of this determination are ΛQCD, and to a major extent the strange quark mass. From the positivity of Rsu there follows an upper bound on the latter: (2 GeV) ≤ 121 (105) MeV, for ΛQCD = 330 (420) MeV.

Journal ArticleDOI
TL;DR: In this article, the first 2+1 flavor lattice QCD calculations of pseudoscalar flavor-singlet propagators using improved staggered fermions were presented, where the disconnected correlator is shown to have a highly non-Gaussian distribution and reliable estimates of the errors require care.
Abstract: We present the first 2+1 flavor lattice QCD calculations of pseudoscalar flavor-singlet propagators using improved staggered fermions We explore the relevant techniques and discuss prospects for the larger scale studies now in progress The disconnected correlator is shown to have a highly non-Gaussian distribution and reliable estimates of the errors require care

Journal ArticleDOI
05 Jul 2008-Pramana
TL;DR: In this paper, the general problem of mixing of electromagnetic and scalar or pseudoscalar fields coupled by axion-type interactions was solved, and the results were applied to the mixing of light propagating in a background magnetic field of varying directions.
Abstract: We solve the general problem of mixing of electromagnetic and scalar or pseudoscalar fields coupled by axion-type interactions L int = g ϕ ϕe μναβ F μν F αβ . The problem depends on several dimensionful scales, including the magnitude and direction of background magnetic field, the pseudoscalar mass, plasma frequency, propagation frequency, wave number, and finally the pseudoscalar coupling. We apply the results to the first consistent calculations of the mixing of light propagating in a background magnetic field of varying directions, which show a great variety of fascinating resonant and polarization effects.