0000000000964088
AUTHOR
Vicente Giménez Gómez
An exploratory lattice study of Delta I=3/2 K ->pi pi decays at next-to-leading order in the chiral expansion
We present the first direct evaluation of Delta I = 3/2K -> 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 behavior in masses and momenta of our lattice results, with NLO chiral perturbation theory at lower masses. In…
Lattice B-parameters for Delta S=2 and Delta I=3/2 operators
We compute several matrix elements of dimension-six four-fermion operators and extract their B-parameters. The calculations have been performed with the tree-level Clover action at beta = 6.0. The renormalization constants and mixing coefficients of the lattice operators have been obtained non-perturbatively. In the renormalization scheme, at a renormalization scale mu similar or equal to 2 GeV, we find B-K(B-9(3/2))=0.66(11), B-7(3/2)=0.72(5) and B-8(3/2)=1.03(3). The result for B-8(3/2) has important implications for the calculation of epsilon'/epsilon.
Matrix elements of Delta I=3/2 K ->pi pi decays
We present a numerical computation of matrix elements of DeltaI = 3/2 K --> pipi 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,O-8 which can contribute significantly in the theoretical prediction of epsilon'/epsilon. The study is done at beta = 6.0 on a 24(3) x 64 lattice.
Width difference in the B-s(0)-(B)over-bar-(0)(s) system from lattice HQET
We present recent results for the prediction of the B-s(0)-(B) over bar (0)(s) lifetime difference from lattice Heavy Quark Effective Theory simulations. In order to get a next-to-leading order result we have calculated the matching between QCD and HQET and the two loop anomalous dimension in the HQET for all the DeltaB = 2 operators, in particular for the operators which enter in the width difference. me obtain far the B-s(0)-(B) over bar (0)(s) lifetime difference, Delta GammaB(s)/GammaB(s) = (5.1 +/- 1.9 +/- 1.7) x 10(-2).
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 similar or equal to 0.06 fm, are relatively heavy, i.e., they cover the range corresponding to 0.60 less than or similar to M-p/M-V less than or similar to 0.75. After implementing the non-perturbative RI-MOM method to renormalise quark masses, we obtain m(ud)((MS) over bar)(2 GeV)= 4.3 +/- 0.4(-0)(+1.1) MeV, and m(s)((MS) over bar)(2 GeV) = 101 +/- 8(-0)(+25) MeV, which are about 15% larger than they would be if renormalised perturbatively. In addition, we show that the above results are compatible wi…
D-0 - (D)over-bar(0) mixing in the standard model and beyond from N-f=2 twisted mass QCD
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…
Calculation of the continuum-lattice HQET matching for the complete basis of four-fermion operators: reanalysis of the B-0-(B)over-bar(0) mixing
In this work, we find the expressions of continuum HQET four-fermion operators in terms of lattice operators in perturbation theory. To do so, we calculate the one-loop continuum-lattice HQET matching for the complete basis of Delta B = 2 and Delta B = 0 operators (excluding penguin diagrams), extending and completing previous studies. We have also corrected some errors in previous evaluations of the matching for the operator O-LL. Our results are relevant to the lattice computation of the values of unknown hadronic matrix elements which enter in many very important theoretical predictions in B-meson phenomenology: B-0-(B) over bar(0) mixing, tau(B) and tau(B), lifetimes, SUSY effects in De…
K-0-(K)over-bar(0) mixing with Wilson fermions without subtractions
By using suitable Ward identities, we show that it is possible to compute K-0-(K) over bar(0) 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.
B-(B)over-bar mixing in the HQET
We present a high statistics, quenched lattice calculation of the B-parameters B-Bd and B-Bs, computed at lowest order in the HQET. The results were obtained using a sample of 600 quenched gauge field configurations, generated by Monte Carlo simulation at beta = 6.0 on a 24(3) x 40 lattice. For the light quarks the SW-Clover action was used; the propagator of the lattice HQET was also tree-level improved. Our best estimate of the renormalization scale independent B-parameter is (B) over cap(Bd) = 1.08 +/- 0.06 +/- 0.08. (B) over cap(Bd) has been obtained by using ''boosted'' perturbation theory to calculate the renormalization constants which relate the matrix elements of the lattice operat…
Up, down, strange and charm quark masses with N-f=2+1+1 twisted mass lattice QCD
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 N-f = 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 renorma…
B(d) - anti-B(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-(B) over bard mixing and to the CP asymmetry a(J)/psiK(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.