Searcharxiv⌕ Search

arXiv subjects

D. Becirevic

Publications and source records attributed to D. Becirevic.

At least 37 records · Page 2Linked to original sources
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↗
arXiv2002

Heavy to light vector meson semileptonic decays

New (preliminary) results for the form factors relevant for the semileptonic decays of heavy pseudoscalar to a light vector meson are presented. In particular, we discuss the form factors for D --> K* and B --> rho modes.

hep-lat↗
arXiv2002

A lattice estimate of the g_{D^* D pi} coupling

We present the results of the first direct determination of the g_{D^* D pi} coupling using lattice QCD. From our simulations in the quenched approximation, we obtain g_{D^* D pi} = 18.8 +/- 2.3^{+1.1}_{-2.0} and hat(g) = 0.67 +/- 0.08^{+0.04}_{-0.06}. It is in agreement with a recent experimental result from CLEO.

hep-lat↗
arXiv2002

First lattice QCD estimate of the g_{D^* D pi} coupling

We present the results of the first lattice QCD study of the strong coupling g_{D^* D pi}. From our simulations in the quenched approximation, we obtain g_{D^* D pi} = 18.8 +/- 2.3^{+1.1}_{-2.0} and hat(g)_c = 0.67 +/- 0.08^{+0.04}_{-0.06}. Whereas previous theoretical studies gave different predictions, our result favours a large value for hat(g)_c. It agrees very well with the recent experimental value by CLEO. hat(g) varies very little with the heavy mass and we find in the infinite mass limit hat(g)_infinity = 0.69(18).

hep-ph↗
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↗
arXiv2001

Matrix elements of (delta S=2) operators with Wilson fermions

We test the recent proposal of using the Ward identities to compute the K0-K0bar mixing amplitude with Wilson fermions, without the problem of spurious lattice subtractions. From our simulations, we observe no difference between the results obtained with and without subtractions. In addition, from the standard study of the complete set of (delta S=2) operators, we quote the following (preliminary) results (in the MS(NDR) scheme): Bk(2 GeV)=0.70(10), < O7^{3/2}>_{K->pi pi} = 0.10(2)(1) GeV^3, < O8^{3/2}>_{K->pi pi} = 0.49(6)(0) GeV^3.

hep-lat↗
arXiv2001

Combined Relativistic and static analysis for all Delta B=2 operators

We analyse matrix elements of Delta B=2 operators by combining QCD results with the ones obtained in the static limit of HQET. The matching of all the QCD operators to HQET is made at NLO order. To do that we have to include the anomalous dimension matrix up to two loops, both in QCD and HQET, and the one loop matching for all the Delta B=2 operators. The matrix elements of these operators are relevant for the prediction of the B-\bar B mixing, B_s meson width difference and supersymmetric effects in Delta B=2 transitions.

hep-lat↗
arXiv2001

B-parameters of the complete set of matrix elements of (Delta B = 2) operators from the lattice

We compute on the lattice the ``bag'' parameters of the five (Delta B = 2) operators of the supersymmetric basis, by combining their values determined in full QCD and in the static limit of HQET. The extrapolation of the QCD results from the accessible heavy-light meson masses to the B-meson mass is constrained by the static result. The matching of the corresponding results in HQET and in QCD is for the first time made at NLO accuracy in the MSbar(NDR) renormalization scheme. All results are obtained in the quenched approximation.

hep-lat↗
arXiv2001

Heavy --> Light semileptonic decays of pseudoscalar mesons from lattice QCD

We have computed the form factors for B --> pi and D --> K(pi) semileptonic decays on the lattice by using full non-perturbative O(a) improvement, in the quenched approximation. Our results are expressed in terms of few parameters which describe the q^2-dependence and normalization of the form factors.

hep-lat↗
arXiv2001

Asymptotic behaviour of the gluon propagator from lattice QCD

We study the flavorless gluon propagator in the Landau gauge from high statistics lattice calculations. Hypercubic artifacts are efficiently eliminated by taking the $\sum p_μ^4 \to 0$ limit. The propagator is fitted to the three-loops perturbative formula in an energy window ranging form $\sim$ 2.5 GeV up to $\sim$ 5.5 GeV. $α_s$ is extracted from the best fit in a continuous set of renormalisation schemes. The fits are very good, with a $χ^2$ per d.o.f smaller than 1. We propose a more stringent test of asymptotic scaling based on scheme independence of the resulting $Λ_{\bar MS}$. This method shows that asymptotic scaling at three loops is not reached by the gluon propagator although we use rather large energies. We are only able to obtain an effective flavorless three-loops estimate $Λ_{\bar MS}^{(3)}= 353 \pm 2 ^{+25}_{-10} $ MeV. We argue that the real asymptotic value for $Λ_{\bar MS}$ should plausibly be smaller.

hep-ph↗
arXiv2000

First Lattice Calculation of the Electromagnetic Operator Amplitude

We present the first lattice calculation of the matrix element of the electromagnetic operator , where Q+ = (Q_d e/16 pi^2)* (\bar s_L sigma{mu,nu} F{mu,nu} d_R + \bar s_R sigma{mu,nu} F{mu,nu} d_L). This matrix element plays an important role, since it contributes to enhance the CP violating part of the K_L -> pi0 e+ e- amplitude in supersymmetric extensions of the Standard Model.

hep-ph↗
arXiv2000

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 (ΔΓ_Bs/Γ_Bs)= (4.7 +/- 1.5 +/- 1.6) 10^(-2), obtained from the ratio of matrix elements, R(m_b)=<\bar B_s^0|Q_S|B_s^0>/<\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.

hep-ph↗
arXiv2000

K0-K0bar Mixing with Wilson Fermions without Subtractions

By using suitable Ward identities, we show that it is possible to compute K0-K0bar mixing without subtracting the terms generated by explicit chiral symmetry breaking present in Wilson-like lattice actions. The accuracy in the determination of the amplitudes is of O(a), which is the best one attainable in the absence of improvement.

hep-lat↗
arXiv2000

Mixing of B mesons and Decay Constants with the Non-Perturbatively Improved Action

Several quantities relevant to phenomenological studies of the mixing of neutral B mesons are computed on the lattice. Our main results are: f_{Bd} sqrt(B_{Bd})=206(28)(7) MeV, f_{Bs} sqrt(B_{Bs})/f_{Bd}sqrt(B_{Bd})=1.16(7). We also obtain the related quantities f_{Bs}sqrt(B{Bs})=237(18)(8) MeV, f_{Bd}= 174(22)(+7-0)(-4-0) MeV, f_{Bs}= 204(15)(+7-0)(+3-0) MeV, f_{Bs}/f_{Bd}=1.17(4)(+0-1), f_{Bd}/f_{Ds}=0.74(5). After combining our results with the experimental world average (Delta m_d), we predict (Delta m_s)=15.8(2.1)(3.3) ps^{-1}. We have also computed the relevant parameters for mixing of neutral D mesons which may be useful in some extensions of the Standard Model. All the quantities were obtained from a quenched simulation with a non-perturbatively improved Clover action at beta=6.2, corresponding to a lattice spacing 1/a=2.7(1) GeV, on a sample of 200 gauge-field configurations. A discussion of the main systematic errors is also presented.

hep-lat↗
arXiv1999

Decays of Heavy Mesons

We present preliminary results for heavy to light transitions of pseudoscalar mesons, induced by the vector and tensor operators. This lattice study is performed in quenched approximation, by using the nonperturbatively improved Wilson action and operators. We also update the values of the heavy-light meson decay constants.

hep-lat↗