A proposal for B-physics on current lattices Blossier, B.; Dimopoulos, P.; Frezzotti, R. ...
The journal of high energy physics,
04/2010, Letnik:
2010, Številka:
4
Journal Article
Recenzirano
Odprti dostop
A method to extract
B
-physics parameters (
b
-quark mass and
f
B
,
decay constants) from currently available lattice data is presented and tested. The approach is based on the idea of constructing ...appropriate ratios of heavy-light meson masses and decay constants, respectively, possessing a precisely known static limit, and evaluating them at various pairs of heavy quark masses around the charm. Via a smooth interpolation in the heavy quark mass from the easily accessible charm region to the asymptotic point,
B
-physics parameters are computed with a few percent (statistical + systematic) error using recently produced
N
f
= 2 maximally twisted Wilson fermions data.
Leading isospin breaking effects on the lattice de Divitiis, G. M.; Frezzotti, R.; Lubicz, V. ...
Physical review. D, Particles, fields, gravitation, and cosmology,
06/2013, Letnik:
87, Številka:
11
Journal Article
Odprti dostop
We present a method to evaluate on the lattice the leading isospin breaking effects due to both the small mass difference between the up and down quarks and the QED interaction. Our proposal is ...applicable in principle to any QCD + QED gauge invariant hadronic observable that can be computed on the lattice. It is based on the expansion of the path integral in powers of the small parameters (m sub(d) - m sub(u))/LambdaQCD and alpha sub(em), where m sub(functionof) is the renormalized quark mass and alpha sub(em) the renormalized fine structure constant. In this paper we discuss in detail the general strategy of the method and the conventional, although arbitrary, separation of QCD from QED isospin breaking corrections. We obtain results for the pion mass splitting, (ProQuest: Formulae and/or non-USASCII text omitted), for the Dashen's theorem breaking parameter varepsilon sub( gamma ) = 0.79(18)(18), for the light quark masses, m sub(d) - m sub(u)(MS, 2 GeV) = 2.39(8)(17) MeV, m sub(u)/m sub(d)(MS, 2 GeV) = 0.50(2)(3), and for the flavor symmetry breaking parameters R and Q. We also update our previous results for the QCD isospin breaking corrections to the K sub(l2) decay rate and for the QCD contribution to the neutron-proton mass splitting. The numerical results of this paper have been obtained by using the gluon field configurations produced by the ETMC Collaboration with n sub(functionof) = 2 dynamical quarks. We treated the dynamical quarks as electrically neutral particles (electroquenched approximation) and neglected a disconnected diagram in the charged and neutral pion mass splitting. We provide all the formulas necessary to remove these approximations and discuss in detail the estimate of the associated systematic uncertainties.
The phase structure of zero temperature twisted mass lattice QCD is investigated. We find strong metastabilities in the plaquette observable in correspondence of which the untwisted quark mass ...assumes positive or negative values. We provide interpretations of this phenomenon in terms of chiral symmetry breaking and the effective potential model of Sharpe and Singleton.
We present results on the nucleon scalar, axial, and tensor charges as well as on the momentum fraction, and the helicity and transversity moments. The pion momentum fraction is also presented. The ...computation of these key observables is carried out using lattice QCD simulations at a physical value of the pion mass. The evaluation is based on gauge configurations generated with two degenerate sea quarks of twisted mass fermions with a clover term. We investigate excited states contributions with the nucleon quantum numbers by analyzing three sink-source time separations. We find that, for the scalar charge, excited states contribute significantly and to a less degree to the nucleon momentum fraction and helicity moment. Our result for the nucleon axial charge agrees with the experimental value. Furthermore, we predict a value of 1.027(62) in the MS scheme at 2 GeV for the isovector nucleon tensor charge directly at the physical point. The pion momentum fraction is found to be left angle bracketxright angle bracket(ProQuest: Formulae and/or non-USASCII text omitted) = 0.214(15)((ProQuest: Formulae and/or non-USASCII text omitted)) in the MS at 2 GeV.
We study matrix elements of the "chromomagnetic" operator on the lattice. This operator is contained in the strangeness-changing effective Hamiltonian which describes electroweak effects in the ...Standard Model and beyond. Having dimension 5, the chromomagnetic operator is characterized by a rich pattern of mixing with other operators of equal and lower dimensionality, including also non gauge invariant quantities; it is thus quite a challenge to extract from lattice simulations a clear signal for the hadronic matrix elements of this operator. We compute all relevant mixing coefficients to one loop in lattice perturbation theory; this necessitates calculating both 2-point (quark-antiquark) and 3-point (gluon-quark-antiquark) Green's functions at nonzero quark masses. We use the twisted mass lattice formulation, with Symanzik improved gluon action. We also provide a nonperturbative method to compute mixing with lower dimensional operators; we use this method in numerical simulations, and extract the mixing with the 3-dimensional scalar density, finding good agreement with one-loop results.
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