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V. Gimenez

Publications and source records attributed to V. Gimenez.

At least 37 records · Page 2Linked to original sources
arXiv2007

Light quark masses and pseudoscalar decay constants from Nf=2 Lattice QCD with twisted mass fermions

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.

hep-lat↗
arXiv2007

Dynamical Twisted Mass Fermions with Light Quarks

We present results of dynamical simulations with 2 flavours of degenerate Wilson twisted mass quarks at maximal twist in the range of pseudo scalar masses from 300 to 550 MeV. The simulations are performed at one value of the lattice spacing a \lesssim 0.1 fm. In order to have O(a) improvement and aiming at small residual cutoff effects, the theory is tuned to maximal twist by requiring the vanishing of the untwisted quark mass. Precise results for the pseudo scalar decay constant and the pseudo scalar mass are confronted with chiral perturbation theory predictions and the low energy constants F, \bar{l}_3 and \bar{l}_4 are evaluated with small statistical errors.

hep-lat↗
arXiv2005

Non-perturbatively Renormalized Light Quark Masses with Two Dynamical Fermions

We present the results of a partially quenched lattice QCD calculation of light quark masses with $N_f=2$ degenerate dynamical flavors. Numerical simulations are carried out using the plaquette gauge action and the Wilson quark action at $β= 5.8$ ($a^{-1} \simeq 3.2\gev$). The spatial extension of the $24^3 \times 48$ lattice is about 1.5 fm. Configurations have been generated at four values of the sea quark masses, for which the ratio of pseudoscalar over vector meson masses is in the range $M_P/M_V \simeq 0.60 ÷0.75$. An important feature of the present study is the use of non-perturbative renormalization, performed with the $\ri$ method. The effects of dynamical sea quarks in the determination of light quark masses have been investigated by performing a quenched calculation on a similar lattice. Our results for the average up-down and strange quark masses are $m_{ud}^{MS} (2\gev) = 4.3(4) (^{+1.1}_{-0.4})\mev$ and $m_s^{MS}(2\gev)=101(8)(^{+25}_{-9}) \mev$. These values are larger than those obtained by evaluating the quark mass renormalization constants with one-loop (boosted) perturbation theory. Our results for the light quark masses are compatible with those obtained in the quenched simulation. No significant sea quark effects are seen, at the values of sea quark masses used in the present study.

hep-lat↗
arXiv2005

Kaon B-parameter with NF=2 dynamical Wilson fermions

We present a preliminary study of the neutral kaon mixing bag parameter BK using two flavors of dynamical Wilson fermions. We determine the matrix element of the relevant DeltaS=2 operator by using both the conventional approach and the so called ``non-subtraction method'', and find that the latter leads to results with smaller uncertainties. After having implemented non-perturbative renormalization, we study the dependence of BK on the see quark mass. At our relatively heavy values of quark masses (0.60<M_P/M_V<0.75) such a dependence is found to be negligible and the results, within the statistical accuracy, are consistent with a quenched determination. As a preliminary result for the renormalization group invariant parameter we quote BKRGI=1.02(25).

hep-lat↗
arXiv2005

Operator product expansion and quark condensate from LQCD in coordinate space

We perform an exploratory study of the operator product expansion of the quark propagator on the lattice at short distance in coordinate space. This permits a simple determination of the quark condensate, ^MS(2 GeV)=(-265\pm 5\pm 22 MeV)^3, and of the renormalization constant of the quark field, Z^MS(2 GeV)=0.871 \pm 0.003 \pm 0.020. This new method also provides a remarkable non-perturbative test of the OPE predictions at short distance in QCD.

hep-lat↗
arXiv2005

Non-perturbatively renormalised light quark masses from a lattice simulation with N_f=2

We present results for the light quark masses obtained from a lattice QCD simulation with N_f=2 degenerate Wilson dynamical quark flavours. The sea quark masses of our lattice, of spacing a ~ 0.06 fm, are relatively heavy, i.e., they cover the range corresponding to 0.60 <~ M_P/M_V <~ 0.75. After implementing the non-perturbative RI-MOM method to renormalise quark masses, we obtain m_{ud}^{MS}(2 GeV)=4.3 +- 0.4^{+1.1}_{-0} MeV, and m_s^{MS}(2 GeV)=101 +- 8^{+25}_{-0} MeV, which are about 15% larger than they would be if renormalised perturbatively. In addition, we show that the above results are compatible with those obtained in a quenched simulation with a similar lattice.

hep-lat↗
arXiv2005

An exploratory lattice study of DI=3/2 K -> pi pi decays at next-to-leading order in the chiral expansion

We present the first direct evaluation of DI = 3/2 K -> pi pi matrix elements with the aim of determining all the low-energy constants at NLO in the chiral expansion. Our numerical investigation demonstrates that it is indeed possible to determine the K -> pi pi matrix elements directly for the masses and momenta used in the simulation with good precision. In this range however, we find that the matrix elements do not satisfy the predictions of NLO chiral perturbation theory. For the chiral extrapolation we therefore use a hybrid procedure which combines the observed polynomial behaviour in masses and momenta of our lattice results, with NLO chiral perturbation theory at lower masses. In this way we find stable results for the quenched matrix elements of the electroweak penguin operators ( = (0.68 +- 0.09) GeV^3 and = (0.12 +- 0.02) GeV^3 in the NDR-MSbar scheme at the scale 2 GeV), but not for the matrix elements of O_4 (for which there are too many Low-Energy Constants at NLO for a reliable extrapolation). For all three operators we find that the effect of including the NLO corrections is significant (typically about 30%). We present a detailed discussion of the status of the prospects for the reduction of the systematic uncertainties.

hep-lat↗
arXiv2005

Operator product expansion and quark condensate from Lattice QCD in coordinate space

We present a Lattice QCD determination of the chiral quark condensate based on a new method. We extract the quark condensate from the operator product expansion of the quark propagator at short euclidean distances, where it represents the leading contribution in the chiral limit. From this study we obtain <\bar q q>^ms(2 GeV)=-(265+-5+-22 MeV)^3$, in good agreement with determinations of this quantity based on different approaches. The simulation is performed by using the O(a)-improved Wilson action at beta=6.45 on a volume 32^3\times70 in the quenched approximation.

hep-lat↗
arXiv2004

Light Hadron Spectrum, Renormalization Constants and Light Quark Masses with Two Dynamical Fermions

The results of a preliminary partially quenched (N_f=2) study of the light hadron spectrum, renormalization constants and light quark masses are presented. Numerical simulations are carried out with the LL-SSOR preconditioned Hybrid Monte Carlo with two degenerate dynamical fermions, using the plaquette gauge action and the Wilson quark action at beta = 5.8. Finite volume effects have been investigated employing two lattice volumes: 16^3 x 48 and 24^3 x 48. Configurations have been generated at four values of the sea quark mass corresponding to M_{PS}/M_V ~ 0.6 - 0.8.

hep-lat↗
arXiv2004

Non-perturbative renormalization of lattice operators in coordinate space

We present the first numerical implementation of a non-perturbative renormalization method for lattice operators, based on the study of correlation functions in coordinate space at short Euclidean distance. The method is applied to compute the renormalization constants of bilinear quark operators for the non-perturbative O(a)-improved Wilson action in the quenched approximation. The matching with perturbative schemes, such as MS-bar, is computed at the next-to-leading order in continuum perturbation theory. A feasibility study of this technique with Neuberger fermions is also presented.

hep-lat↗
arXiv2004

Renormalization Constants of Quark Operators for the Non-Perturbatively Improved Wilson Action

We present the results of an extensive lattice calculation of the renormalization constants of bilinear and four-quark operators for the non-perturbatively O(a)-improved Wilson action. The results are obtained in the quenched approximation at four values of the lattice coupling by using the non-perturbative RI/MOM renormalization method. Several sources of systematic uncertainties, including discretization errors and final volume effects, are examined. The contribution of the Goldstone pole, which in some cases may affect the extrapolation of the renormalization constants to the chiral limit, is non-perturbatively subtracted. The scale independent renormalization constants of bilinear quark operators have been also computed by using the lattice chiral Ward identities approach and compared with those obtained with the RI-MOM method. For those renormalization constants the non-perturbative estimates of which have been already presented in the literature we find an agreement which is typically at the level of 1%.

hep-lat↗
arXiv2004

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.

hep-lat↗
arXiv2003

Non perturbative renormalization in coordinate space

We present an exploratory study of a gauge-invariant non-perturbative renormalization technique. The renormalization conditions are imposed on correlation functions of composite operators in coordinate space on the lattice. Numerical results for bilinears obtained with overlap and O(a)-improved Wilson fermions are presented. The measurement of the quark condensate is also discussed.

hep-lat↗
arXiv2003

Matrix elements of DI=3/2 K-->pi pi decays

We present a numerical computation of matrix elements of DI=3/2 K-->pi pi decays by using Wilson fermions. In order to extrapolate to the physical point we work at unphysical kinematics and we resort to Chiral Perturbation Theory at the next-to-leading order. In particular we explain the case of the electroweak penguins O_{7,8} which can contribute significantly in the theoretical prediction of epsilon'/epsilon. The study is done at beta=6.0 on a 24^3x64 lattice.

hep-lat↗
arXiv2002

Non-perturbative renormalization constants and light quark masses

We present the results of an extensive non-perturbative calculation of the renormalization constants of bilinear quark operators for the non-perturbatively O(a)-improved Wilson action. The results are obtained at four values of the lattice coupling, by using the RI/MOM and the Ward identities methods. A new non-perturbative renormalization technique, which is based on the study of the lattice correlation functions at short distance in x-space, is also numerically investigated. We then use our non-perturbative determination of the quark mass renormalization constants to compute the values of the strange and the average up/down quark masses. After performing an extrapolation to the continuum limit, we obtain ms^msbar(2 GeV) = (106 +- 2 +- 8) MeV and ml^msbar(2 GeV)=(4.4 +- 0.1 +- 0.4) MeV.

hep-lat↗
arXiv2002

Kaon Weak Matrix Elements with Wilson Fermions

We present results of several numerical studies with Wilson fermions relevant for kaon physics. We compute the B_K parameter by using two different methods and extrapolate to the continuum limit. Our preliminary result is B_K(2 GeV)=0.66(7). Delta I=3/2 K->pi pi matrix elements are obtained by using the next-to-leading order expressions derived in chiral perturbation theory in which the low energy constants are determined by the lattice results computed at unphysical kinematics. From the simulation at beta=6.0 our (preliminary) results read: _{I=2}=0.14(1)(1) GeV^3 and _{I=2}=0.69(6)(6) GeV^3.

hep-lat↗
arXiv2001

B_d-Bbar_d Mixing and the B_d -> J/psi K_s Asymmetry in General SUSY Models

We present a next-to-leading order determination of the gluino-mediated SUSY contributions to B_d-Bbar_d mixing and to the CP asymmetry a_{J/psi K_s} in the framework of the mass-insertion approximation. Using hadronic matrix elements recently computed on the lattice, we obtain improved constraints on the squark-mass splittings.

hep-ph↗