Search results for "Pseudoscalar"
showing 10 items of 189 documents
η−η′-glueball mixing
2010
We have revisited glueball mixing with the pseudoscalar mesons in the MIT bag model scheme. The calculation has been performed in the spherical cavity approximation to the bag using two different fermion propagators, the cavity and the free propagators. We obtain probabilities of mixing for the $\ensuremath{\eta}$ at the level of 0.006%--2.0%, while for the ${\ensuremath{\eta}}^{\ensuremath{'}}$ one at the level of 0.6%--40%, depending on the choice of bag radius and, therefore, of the strong coupling constant. Our results differ from previous calculations. The origin of our difference stems from the treatment of the time integrations. The comparison of our calculation with experimental dat…
First lattice calculation of the B-meson binding and kinetic energies
1995
We present the first lattice calculation of the B-meson binding energy $\labar$ and of the kinetic energy $-\lambda_1/2 m_Q$ of the heavy-quark inside the pseudoscalar B-meson. This calculation has required the non-perturbative subtraction of the power divergences present in matrix elements of the Lagrangian operator $\bar h D_4 h$ and of the kinetic energy operator $\bar h \vec D^2 h$. The non-perturbative renormalisation of the relevant operators has been implemented by imposing suitable renormalisation conditions on quark matrix elements, in the Landau gauge. Our numerical results have been obtained from several independent numerical simulations at $\beta=6.0$ and $6.2$, and using, for t…
Meson loops in the $f_0(980)$ and $a_0(980)$ radiative decays into $\rho$, $\omega$
2008
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 p…
Nonperturbative renormalization of quark bilinears
1998
We compute non-perturbatively the renormalization constants of quark bilinears on the lattice in the quenched approximation at three values of the coupling beta=6/g_0^2=6.0,6.2,6.4 using both the Wilson and the tree-level improved SW-Clover fermion action. We perform a Renormalization Group analysis at the next-to-next-to-leading order and compute Renormalization Group invariant values for the constants. The results are applied to obtain a fully non-perturbative estimate of the vector and pseudoscalar decay constants.
HQE parameters from unquenched lattice data on pseudoscalar and vector heavy-light meson masses
2017
We present a new lattice determination of some of the parameters appearing both in the Operator Product Expansion (OPE) analysis of the inclusive semileptonic $B$-meson decays and in the Heavy Quark Expansion (HQE) of the pseudoscalar (PS) and vector (V) heavy-light meson masses. We perform a lattice QCD (LQCD) computation of PS and V heavy-light meson masses for heavy-quark masses $m_h$ in the range from $m_c^{\rm phys}$ to $\simeq 4m_b^{\rm phys}$. We employed the $N_f = 2+1+1$ gauge configurations of the European Twisted Mass Collaboration (ETMC) at three values of the lattice spacing $a \simeq (0.062, 0.082, 0.089)$ fm with pion masses in the range $M_\pi \simeq (210 - 450)$ MeV. The he…
Electron and muon $g-2$ anomalies in general flavour conserving two Higgs doublets models
2020
In general two Higgs doublet models (2HDMs) without scalar flavour changing neutral couplings (SFCNC) in the lepton sector, the electron, muon and tau interactions can be decoupled in a robust framework, stable under renormalization group evolution. In this framework, the breaking of lepton flavour universality (LFU) goes beyond the mass proportionality, opening the possibility to accommodate a different behaviour among charged leptons. We analyze the electron and muon $(g-2)$ anomalies in the context of these general flavour conserving models in the leptonic sector (g$\ell$FC). We consider two different models, I-g$\ell$FC and II-g$\ell$FC, in which the quark Yukawa couplings coincide, res…
Inclusive production of neutral vector mesons in hadronic Z decays
1996
Data on the inclusive production of the neutral vector mesons rho(0)(770), omega(782), K*(0)(892), and phi (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 the p(0) production rate. An average p(0) multiplicity of 1.45 +/- 0.21 per event is obtained. The omega is detected via its three pion decay mode omega --> pi(+)pi(-)pi(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 the phi is 0.122 +/- 0.009, both measured using their charged decay modes. The measurements pro…
Probing the chiral weak Hamiltonian at finite volumes
2006
Non-leptonic kaon decays are often described through an effective chiral weak Hamiltonian, whose couplings ("low-energy constants") encode all non-perturbative QCD physics. It has recently been suggested that these low-energy constants could be determined at finite volumes by matching the non-perturbatively measured three-point correlation functions between the weak Hamiltonian and two left-handed flavour currents, to analytic predictions following from chiral perturbation theory. Here we complete the analytic side in two respects: by inspecting how small ("epsilon-regime") and intermediate or large ("p-regime") quark masses connect to each other, and by including in the discussion the two …
QCD isospin breaking in meson masses, decay constants and quark mass ratios
2001
The procedure to calculate masses and matrix-elements in the presence of mixing of the basis states is explained in detail. We then apply this procedure to the two-loop calculation in Chiral Perturbation Theory of pseudoscalar masses and decay constants including quark mass isospin breaking. These results are used to update our analysis of $K_{\ell4}$ done previously and obtain a value of $m_u/m_d$ in addition to values for the low-energy-constants $L_i^r$.
Flavour symmetry restoration and kaon weak matrix elements in quenched twisted mass QCD
2007
We simulate two variants of quenched twisted mass QCD (tmQCD), with degenerate Wilson quarks of masses equal to or heavier than half the strange quark mass. We use Ward identities in order to measure the twist angles of the theory and thus check the quality of the tuning of mass parameters to a physics condition which stays constant as the lattice spacing is varied. Flavour symmetry breaking in tmQCD is studied in a framework of two fully twisted and two standard Wilson quark flavours, tuned to be degenerate in the continuum. Comparing pseudoscalar masses, obtained from connected quark diagrams made of tmQCD and/or standard Wilson quark propagators, we confirm that flavour symmetry breaking…