Search results for "Renormalization"
showing 10 items of 470 documents
Quark exchange in deep inelastic scattering
1995
We use a model for baryons that links the constituent structure to the deep inelastic (current) properties. The approach consists in a laboratory partonic description (based on a model of hadron structure), to which a low momentum scaleQ 0 is adscribed, which is evolved to high momenta by means of the renormalization group. A generalization of the model by means of the hadronic quark cluster decomposition, provides a description of the structure functions of nuclei and is the starting point to study the effects that the antisymmetrization at the quark level has on the structure function of a model deuteron. The analysis contains conventional and high momentum partonic components. We next st…
Lattice quark masses: a non-perturbative measurement
1998
We discuss the renormalization of different definitions of quark masses in the Wilson and the tree-level improved SW-Clover fermionic action. For the improved case we give the correct relationship between the quark mass and the hopping parameter. Using perturbative and non-perturbative renormalization constants, we extract quark masses in the $\MSbar$ scheme from Lattice QCD in the quenched approximation at $\beta=6.0$, $\beta=6.2$ and $\beta=6.4$ for both actions. We find: $\bar{m}^{\MSbar}(2 GeV)=5.7 \pm 0.1 \pm 0.8$ MeV, $m_s^{\MSbar}(2GeV)= 130 \pm 2 \pm 18 $ MeV and $m_c^{\MSbar}(2 GeV) = 1662\pm 30\pm 230$ MeV.
Non-perturbative renormalisation of left left four-fermion operators with Neuberger fermions
2006
We outline a general strategy for the non-perturbative renormalisation of composite operators in discretisations based on Neuberger fermions, via a matching to results obtained with Wilson-type fermions. As an application, we consider the renormalisation of the four-quark operators entering the Delta S=1 and Delta S=2 effective Hamiltonians. Our results are an essential ingredient for the determination of the low-energy constants governing non-leptonic kaon decays.
New results from lattice QCD: Non-perturbative renormalization and quark masses
1998
For the first time, we compute non-perturbatively, i.e. without lattice perturbation theory, the renormalization constants of two-fermion operators in the quenched approximation at $\beta=6.0$, 6.2 and 6.4 using the Wilson and the tree-level improved SW-Clover actions. We apply these renormalization constants to fully non-perturbatively estimate quark masses in the $\bar{MS}$ scheme from lattice simulations of both the hadron spectrum and the Axial Ward Identity in the quenched approximation. Some very preliminary unquenched Wilson results obtained from the gluon configurations generated by the T$\chi$L Collaboration at $\beta=5.6$ and $N_{f}=2$ are also discussed.
Pion parton distributions in a nonlocal Lagrangian
2005
We use phenomenological nonlocal Lagrangians, which lead to non trivial forms for the quark propagator, to describe the pion. We define a procedure, based on the Dyson-Schwinger equations, for the calculation of the pion parton distributions at low Q^2. The obtained parton distributions fulfill all the wishful properties. Using a convolution approach we incorporate the composite character of the constituent quarks in the formalism. We evolve, using the Renormalization Group, the calculated parton distributions to the experimental scale and compare favorably with the data and draw conclusions.
Mesonic decay of 5ΛHe with quark-model-based hypernuclear wave function
1993
Abstract We have evaluated the mesonic decay of the 5 Λ He hypernucleus by using a Λ wave function generated from the quark cluster model. As a consequence of the Λ N repulsion at short distances we obtain a Λ wave function in the nucleus with a large radius. The smaller overlap with the 4 He core with respect to simpler wave functions and the effect of the pion renormalization increase the mesonic width considerably and one obtains a good reproduction of the experimental data.
Top quark mass from radiative corrections to the Z --> bb−− decay
1991
19 páginas, 3 figuras, 4 tablas.-- CERN-TH-5931-90 ; FTUV-90-49 ; IFIC-90-45.
Nonperturbative renormalization of quark bilinears
1998
We compute non-perturbatively the renormalization constants of quark bilinears on the lattice in the quenched approximation at three values of the coupling beta=6/g_0^2=6.0,6.2,6.4 using both the Wilson and the tree-level improved SW-Clover fermion action. We perform a Renormalization Group analysis at the next-to-next-to-leading order and compute Renormalization Group invariant values for the constants. The results are applied to obtain a fully non-perturbative estimate of the vector and pseudoscalar decay constants.
Nonperturbative renormalization and O(a) -improvement of the nonsinglet vector current with Nf=2+1 Wilson fermions and tree-level Symanzik improved g…
2019
In calculating hadronic contributions to precision observables for tests of the Standard Model in lattice QCD, the electromagnetic current plays a central role. Using a Wilson action with $\mathrm{O}(a)$ improvement in QCD with ${N}_{\mathrm{f}}$ flavors, a counterterm must be added to the vector current in order for its on-shell matrix elements to be $\mathrm{O}(a)$ improved. In addition, the local vector current, which has support on one lattice site, must be renormalized. At $\mathrm{O}(a)$, the breaking of the $\mathrm{SU}({N}_{\mathrm{f}})$ symmetry by the quark mass matrix leads to a mixing between the local currents of different quark flavors. We present a nonperturbative calculation…
Determination of m¯b/m¯c and m¯b from nf=4 lattice QCD+QED
2021
We extend HPQCD's earlier ${n}_{f}=2+1+1$ lattice-QCD analysis of the ratio of $\overline{\mathrm{MS}}$ masses of the $b$ and $c$ quark to include results from finer lattices (down to 0.03 fm) and a new calculation of QED contributions to the mass ratio. We find that ${\overline{m}}_{b}(\ensuremath{\mu})/{\overline{m}}_{c}(\ensuremath{\mu})=4.586(12)$ at renormalization scale $\ensuremath{\mu}=3\text{ }\text{ }\mathrm{GeV}$. This result is nonperturbative. Combining it with HPQCD's recent lattice $\mathrm{QCD}+\mathrm{QED}$ determination of ${\overline{m}}_{c}(3\text{ }\text{ }\mathrm{GeV})$ gives a new value for the $b$-quark mass: ${\overline{m}}_{b}(3\text{ }\text{ }\mathrm{GeV})=4.513(2…