Parametrisations of the D -> K l nu form factor and the determination of \hat{g}

The vector form factor f_+(t) of the semileptonic decay D -> K l nu, measured recently with a high accuracy, can be used to determine the strong coupling constant g_{D_s^* D K}. The latter is related to the normalised coupling \hat{g} releveant in heavy-meson chiral perturbation theory. This determination relies on the estimation of the residue of the form factor at the D_s^* pole and thus on an extrapolation of the form factor in the unphysical region (m_D-m_K)^2<t<(m_D+m_K)^2. We test this extrapolation for several parametrisations of the form factors by determining the value of \hat{g}, whose value can be compared to other (experimental and theoretical) estimates. Several unsophisticated parametrisations, differing by the amount of physical information that they embed, are shown to pass this test. An apparently more elaborated parametrisation of form factors, the so-called z-expansion, is at variance with the other models, and we point out some significant shortcomings of this parametrisation for the problem under consideration.Comment: 16 pages, 2 figures. A few references added. Accepted for publication in JoP

BK from the lattice with Wilson quarks

We report our results for the bag-parameter BK obtained from the quenched simulations on the lattice with Wilson fermions at three values of the lattice spacing. We implemented the method by which no subtraction of the mixing with other four-fermion dS=2 operators is needed. Our final result, in terms of the renormalisation group invariant bag-parameter, is BK = 0.96 +/- 0.10.Comment: 12 pages, 3 figures [version published in Eur.Phys.J.C

Quark Masses and Renormalization Constants from Quark Propagator and 3-point Functions

We have computed the light and strange quark masses and the renormalization constants of the quark bilinear operators, by studying the large-p^2 behaviour of the lattice quark propagator and 3-point functions. The calculation is non-perturbatively improved, at O(a), in the chiral limit. The method used to compute the quark masses has never been applied so far, and it does not require an explicit determination of the quark mass renormalization constant.Comment: LATTICE99 (Improvement and Renormalization) - 3 pages, 2 figure

Lattice calculation of SU(3) flavor breaking ratios in B - anti-B mixing

We present an unquenched lattice calculation for the SU(3) flavor breaking ratios of the heavy-light decay constants and the $\Delta B = 2$ matrix elements. The calculation was performed on $16^3 \times 32$ lattices with two dynamical flavors of domain-wall quarks and inverse lattice spacing $1/a = 1.69(5)$ GeV. Heavy quarks were implemented using an improved lattice formulation of the static approximation. In the infinite heavy-quark mass limit we obtain $f_{B_s}/f_{B_d} = 1.29(4)(6)$, $B_{B_s}/B_{B_d} = 1.06(6)(4)$, $\xi = 1.33(8)(8)$ where the first error is statistical and the second systematic.Comment: 23 pages, 8 figures, RevTeX4; mentioned existence of 1/m_b corrections, minor changes improving readabilit

Power Corrections to Perturbative QCD and OPE in Gluon Green Functions

We show that QCD Green functions in Landau Gauge exhibit sizable $O(1/\mu^2)$ corrections to the expected perturbative behavior at energies as high as 10 GeV. We argue that these are due to a $$-condensate which does not vanish in Landau gauge.Comment: 3 pages 1 figure lattice2001 (gaugetheories

Masses and decay constants of Bc(∗)B_c^{(*)} mesons with Nf=2+1+1N_f=2+1+1 twisted mass fermions

We present a preliminary lattice determination of the masses and decay constants of the pseudoscalar and vector mesons $B_c$ and $B_c^*$. Our analysis is based on the gauge configurations produced by the European Twisted Mass Collaboration with $N_f = 2 + 1 + 1$ flavors of dynamical quarks. We simulated at three different values of the lattice spacing and with pion masses as small as 210 MeV. Heavy-quark masses are simulated directly on the lattice up to $\sim 3$ times the physical charm mass. The physical b-quark mass is reached using the ETMC ratio method. Our preliminary results are: $M_{B_c} = 6341\,(60)$ MeV, $f_{B_c} = 396\,(12)$ MeV, $M_{B_c^*} / M_{B_c} = 1.0037\,(39)$ and $f_{B_c^*} / f_{B_c} = 0.987\,(7)$.Comment: 7 pages, 3 figures, 1 table; contribution to the proceedings of the XXXVI Int'l Workshop on Lattice Field Theory (LATTICE2018), July 22-28, 2018, East Lansing, Michigan State University (Michigan, USA

A Theoretical Prediction of the Bs-Meson Lifetime Difference

We present the results of a quenched lattice calculation of the operator matrix elements relevant for predicting the Bs width difference. Our main result is (\Delta\Gamma_Bs/\Gamma_Bs)= (4.7 +/- 1.5 +/- 1.6) 10^(-2), obtained from the ratio of matrix elements, R(m_b)=/<\bar B_s^0|Q_L|B_s^0>=-0.93(3)^(+0.00)_(-0.01). R(m_b) was evaluated from the two relevant B-parameters, B_S^{MSbar}(m_b)=0.86(2)^(+0.02)_(-0.03) and B_Bs^{MSbar}(m_b) = 0.91(3)^(+0.00)_(-0.06), which we computed in our simulation.Comment: 21 pages, 7 PostScript figure

Improved estimates of rare K decay matrix-elements from Kl3 decays

The estimation of rare K decay matrix-elements from Kl3 experimental data is extended beyond LO in Chiral Perturbation Theory. Isospin-breaking effects at NLO (and partially NNLO) in the ChPT expansion, as well as QED radiative corrections are now accounted for. The analysis relies mainly on the cleanness of two specific ratios of form-factors, for which the theoretical control is excellent. As a result, the uncertainties on the K+ --> pi+ nu nubar and KL --> pi0 nu nubar matrix-elements are reduced by a factor of about 7 and 4, respectively, and similarly for the direct CP-violating contribution to KL --> pi0 l+ l-. They could be reduced even further with better experimental data for the Kl3 slopes and the K+l3 branching ratios. As a result, the non-parametric errors for B(K --> pi nu nubar) and for the direct CP-violating contributions to B(KL --> pi0 l+ l-) are now completely dominated by those on the short-distance physics.Comment: 16 pages, 1 figure. Numerical analysis updated to include the recent Kl3 data. To appear in Phys. Rev.

Chiral Corrections to the Hyperon Vector Form Factors

We present the complete calculation of the SU(3)-breaking corrections to the hyperon vector form factors up to O(p^4) in the Heavy Baryon Chiral Perturbation Theory. Because of the Ademollo-Gatto theorem, at this order the results do not depend on unknown low energy constants and allow to test the convergence of the chiral expansion. We complete and correct previous calculations and find that O(p^3) and O(1/M_0) corrections are important. We also study the inclusion of the decuplet degrees of freedom, showing that in this case the perturbative expansion is jeopardized. These results raise doubts on the reliability of the chiral expansion for hyperons.Comment: 20 pages, 4 figures, v2: published versio

D-meson decay constants and a check of factorization in non-leptonic B-decays

We compute the vector meson decay constants fD*, fDs* from the simulation of twisted mass QCD on the lattice with Nf = 2 dynamical quarks. When combining their values with the pseudoscalar D(s)-meson decay constants, we were able (i) to show that the heavy quark spin symmetry breaking effects with the charm quark are large, fDs*/fDs = 1.26(3), and (ii) to check the factorization approximation in a few specific B-meson non-leptonic decay modes. Besides our main results, fD* = 278 \pm 13 \pm 10 MeV, and fDs* = 311 \pm 9 MeV, other phenomenologically interesting results of this paper are: fDs*/fD* = 1.16 \pm 0.02 \pm 0.06, fDs*/fD = 1.46 \pm 0.05 \pm 0.06, and fDs/fD* = 0.89 \pm 0.02 \pm 0.03. Finally, we correct the value for B(B0 \rightarrow D+ pi-) quoted by PDG, and find B(B0 \rightarrow D+ pi-) = (7.8 \pm 1.4) \times 10-7. Alternatively, by using the ratios discussed in this paper, we obtain B(B0 \rightarrow D+ pi-) = (8.3 \pm 1.0 \pm 0.8)\times10-7.Comment: 16 pages, 4 eps figure