We present a calculation of the matrix elements of the most general set of ∆S = 2 dimension-six four-fermion operators. The values of the matrix elements are given in terms of the corresponding B-parameters. Our results can be used in many phenomenological applications, since the operators considered here give important contributions to K0–K̄0 mixing in several extensions of the Standard Model (supersymmetry, left-right symmetric models, multi-Higgs models etc.). The determination of the matrix elements improves the accuracy of the phenomenological analyses intended to put bounds on basic parameters of the different models, as for example the pattern of the sfermion mass matrices. The calculation has been performed on the lattice, using the tree-level improved Clover action at two different values of the strong coupling constant (β = 6/g2 0(a) = 6.0 and 6.2, corresponding to a −1 = 2.1 and 2.7 GeV respectively), in the quenched approximation. The renormalization constants and mixing coefficients of the lattice operators have been obtained non-perturbatively.

We discuss a lattice QCD computation of the $B$-meson decay constants by the ETM collaboration where suitable ratios allow to reach the bottom quark sector by combining simulations around the charm-quark mass with an exactly known static limit. The different steps involved in this ratio method are discussed together with an account of the assessment of various systematic effects. A comparison of results from simulations with two and four flavour dynamical quarks is presented.

We present a lattice QCD calculation of the up, down, strange and charm quark masses performed using the gauge configurations produced by the European Twisted Mass Collaboration with Nf=2+1+1 dynamical quarks, which include in the sea, besides two light mass degenerate quarks, also the strange and charm quarks with masses close to their physical values. The simulations are based on a unitary setup for the two light quarks and on a mixed action approach for the strange and charm quarks. The analysis uses data at three values of the lattice spacing and pion masses in the range 210–450 MeV, allowing for accurate continuum limit and controlled chiral extrapolation. The quark mass renormalization is carried out non-perturbatively using the RI′-MOM method. The results for the quark masses converted to the MS¯ scheme are: mud(2 GeV)=3.70(17) MeV, ms(2 GeV)=99.6(4.3) MeV and mc(mc)=1.348(46) GeV. We obtain also the quark mass ratios ms/mud=26.66(32) and mc/ms=11.62(16). By studying the mass splitting between the neutral and charged kaons and using available lattice results for the electromagnetic contributions, we evaluate mu/md=0.470(56), leading to mu=2.36(24) MeV and md=5.03(26) MeV.

We present the first unquenched lattice QCD results for the bag parameters controlling the short distance contribution to D meson oscillations in the standard model and beyond. We have used the gauge configurations produced by the European Twisted Mass collaboration with N-f = 2 dynamical quarks, at four lattice spacings and light meson masses in the range 280-500 MeV. Renormalization is carried out nonperturbatively with the regularization-independent momentum subtraction method. The bag-parameter results have been used to constrain new physics effects in D-0 - (D) over bar (0) mixing, to put a lower bound to the generic new physics scale and to constrain off-diagonal squark mass terms for TeV-scale supersymmetry.

We present a lattice QCD determination of the $b$-quark mass and of the $f_{B_s}$ and $f_B$ decay constants performed with $N_f = 2 + 1 + 1$ twisted mass Wilson fermions. We have used simulations at three values of the lattice spacing generated by ETMC with pion masses ranging from 210 to 440 MeV. To obtain physical quantities we performed a combined chiral and continuum limit and an extrapolation in the heavy quark mass from the charm to the $b$-quark region using suitable ratios calculated at nearby heavy-quark masses having an exactly known static limit. Our results are: $m_b(m_b) = 4.29 (13)$ GeV, $f_B = 196 (9)$ MeV, $f_{B_s} = 235 (9)$ MeV, $f_{B_s} / f_B = 1.201 (25)$, $(f_{B_s}/f_B)/(f_K/f_π) = 1.007 (16)$ and $(f_{B_s}/f_B)/(f_{D_s}/f_D) = 1.008 (13)$.

Matrix elements of the four fermion (4f) operators play an important rôle in the studies of CP-violation in the Standard Model and beyond. Of particular interest are the matrix elements describing the B − B̄ and K − K̄ mixing amplitudes. Lattice QCD is at present the best suited method to compute such quantities non-perturbatively (NP). To keep the theoretical uncertainties under control, it is of vital interest to renormalise the corresponding 4f-operators non-perturbatively. An additional difficulty arises when working with Wilson fermions on the lattice, namely all the parity even (∆F = 2) operators mix among themselves. Therefore, besides the overall renormalisation, the spurious mixing should be subtracted.

We present a lattice QCD computation of the b -quark mass, the B and B s decay constants, the B -mixing bag prameters for the full four-fermion operator basis as well as determinations for ξ and f Bq √(B_i^(q) ) extrapolated to the continuum limit and to the physical pion mass. We used N f = 2 twisted mass Wilson fermions at four values of the lattice spacing with pion masses ranging from 280 to 500 MeV. Extrapolation in the heavy quark mass from the charm to the bottom quark region has been carried out on ratios of physical quantities computed at nearby quark masses, exploiting the fact that they have an exactly known infinite mass limit. Our results are m b ( m b , MS ) = 4 . 29(12) GeV, f Bs = 228(8) MeV, f B = 189(8) MeV and f Bs /f B = 1 . 206(24). Moreover with our results for the bag-parameters we find ξ = 1 . 225(31), B_1^(s) / B_1^(d) . = 1 . 01(2), f Bd √(B_1^(d) ) = 216(10) MeV and 1 f Bs √(B_1^(s) ) = 262(10) MeV. We also computed the bag parameters for the complete basis of the four-fermion operators which are required in beyond the SM theories. By using these results for the bag parameters we are able to provide a refined Unitarity Triangle analysis in the presence of New Physics, improving the bounds coming from B ( s ) − B_(s) mixing.

We present an accurate lattice QCD computation of the b-quark mass, the B and Bs decay constants, the B-mixing bag-parameters for the full four-fermion operator basis, as well as estimates for \xi and f_{Bq}\sqrt{B_q} extrapolated to the continuum limit and the physical pion mass. We have used Nf = 2 dynamical quark gauge configurations at four values of the lattice spacing generated by ETMC. Extrapolation in the heavy quark mass from the charm to the bottom quark region has been carried out using ratios of physical quantities computed at nearby quark masses, having an exactly known infinite mass limit.

Abstract We present the first unquenched, continuum limit, lattice QCD results for the matrix elements of the operators describing neutral kaon oscillations in extensions of the Standard Model. Owing to the accuracy of our calculation on ∆S = 2 weak Hamiltonian matrix elements, we are able to provide a refined Unitarity Triangle analysis improving the bounds coming from model independent constraints on New Physics. In our nonperturbative computation we use a combination of N f = 2 maximally twisted sea quarks and Osterwalder-Seiler valence quarks in order to achieve both O(a)-improvement and continuum-like renormalization properties for the relevant four-fermion operators. The calculation of the renormalization constants has been performed non-perturbatively in the RI-MOM scheme. Based on simulations at four values of the lattice spacing and a number of quark masses we have extrapolated/interpolated our results to the continuum limit and physical light/strange quark masses.

We present a precise lattice QCD determination of the b-quark mass, of the B and Bs decay constants and first results for the B-meson bag parameters. For our computation we employ the so-called ratio method and our results benefit from the use of improved interpolating operators for the B-mesons. QCD calculations are performed with Nf = 2 dynamical light-quarks at four values of the lattice spacing and the results are extrapolated to the continuum limit. The preliminary results are mb(mb) = 4.35(12) GeV for the MSbar b-quark mass, fBs = 234(6) MeV and fB = 197(10) MeV for the B-meson decay constants, BBs(mb) = 0.90(5) and BB(mb) = 0.87(5) for the B-meson bag parameters.

Dip. di Fisica, Università “La Sapienza” and INFN-Roma I, P.le A. Moro 2, I-00185 Rome, Italy Laboratoire de Physique Théorique (bât.210), Université de Paris XI, 91405 Orsay Cedex, France Dep. de F́ıs.Teòrica and IFIC, Univ. de València, Dr. Moliner 50, E-46100, Burjassot, València, Spain Department of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, England Dip. di Fisica, Univ. di Roma Tre and INFN Roma III, Via della V. Navale 84, I-00146 Rome, Italy DESY, Theory Group, Notkestrasse 85, D-22607 Hamburg, Germany

We present the ETMC results for the bag parameters describing the neutral kaon mixing in the Standard Model and beyond and preliminary results for the bag parameters controlling the short distance contributions in the D^0-\bar{D}^0 oscillations. We also present preliminary results for the B_{Bd}, B_{Bs}, B_{Bs}/B_{Bd} and \xi -parameter controlling B^0_-\bar{B}^0 oscillations in the Standard Model employing the so-called ratio method. Using Nf=2 maximally twisted sea quarks and Osterwalder-Seiler valence quarks we achieve both O(a)-improvement and continuum like renormalization pattern. Simulations are performed at three-values of the lattice spacing and several values of quark masses in the light, strange, charm region and above charm up to ~2.5m_c. Our results are extrapolated to the continuum limit and extrapolated/interpolated to the physical quark masses.

We present preliminary results of the non-perturbative computation of the RI-MOM renormalisation constants in a mass-independent scheme for the action with Iwasaki glue and four dynamical Wilson quarks employed by ETMC. Our project requires dedicated gauge ensembles with four degenerate sea quark flavours at three lattice spacings and at several values of the standard and twisted quark mass parameters. The RI-MOM renormalisation constants are obtained from appropriate O(a) improved estimators extrapolated to the chiral limit.

We present preliminary results at β = 1.95 (a = 0.077 fm) on the first unquenched N f = 2 + 1 + 1 lattice computation of the B K parameter which controls the neutral kaon oscillations in the Standard Model.Using N f = 2 + 1 + 1 maximally twisted sea quarks and Osterwalder-Seiler valence quarks we achieve O(a) improvement and a continuum-like renormalization pattern for the four-fermion operator.Our results are extrapolated/interpolated to the physical light/strange quark mass but not yet to the continuum limit.The computation of the relevant renormalization constants is performed non perturbatively in the RI'-MOM scheme using dedicated simulations with N f = 4 degenerate sea quark flavours produced by the ETM collaboration.We get B RGI K (a = 0.077) = 0.747(18), which when compared to our previous unquenched N f = 2 determination and most of the existing results, suggests a rather weak B RGI K dependence on the number of dynamical flavours.We are at the moment analysing lattice data at two additional β values which will allow us to perform an extrapolation to the continuum limit.

We present a precise lattice QCD determination of the b-quark mass, of the B and Bs decay constants and first preliminary results for the B-mesons bag parameter. Simulations are performed with Nf = 2 Wilson twisted mass fermions at four values of the lattice spacing and the results are extrapolated to the continuum limit. Our calculation benefits from the use of improved interpolating operators for the B-mesons and employs the so-called ratio method. The latter allows a controlled interpolation at the b-quark mass between the relativistic data around and above the charm quark mass and the exactly known static limit.