8,128 research outputs found
Non-perturbative renormalization of tensor currents: strategy and results for and QCD
Tensor currents are the only quark bilinear operators lacking a
non-perturbative determination of their renormalisation group (RG) running
between hadronic and electroweak scales. We develop the setup to carry out the
computation in lattice QCD via standard recursive finite-size scaling
techniques, and provide results for the RG running of tensor currents in and QCD in the continuum for various Schr\"odinger Functional
schemes. The matching factors between bare and renormalisation group invariant
currents are also determined for a range of values of the lattice spacing
relevant for large-volume simulations, thus enabling a fully non-perturbative
renormalization of physical amplitudes mediated by tensor currents.Comment: 50 pages, 14 Figure
X(3872) as a D-D* molecule bound by quark exchange forces
The Bethe-Salpeter equation for the T-Matrix of D-D* scattering is solved
with a meson-meson potential that results from 2nd order Born approximation of
quark exchange processes. This potential turns out to be complex and energy
dependent due to the pole contribution from the coupling to the intermediate
J/psi-rho meson pair propagator. As a consequence, a bound state with a mass
close to 3.872 GeV occurs in the J/psi-rho continuum. This result suggests that
quark exchange forces may provide the solution to the puzzling question for the
origin of the interaction which leads to a binding of D and D* mesons in the
X(3872) state.Comment: 6 pages, 3 figures, contribution to the Proceedings of the 28th
Max-Born-Symposium on "Three days on quarkyonic island", Wroclaw, Poland, May
19-21, 201
A tmQCD mixed-action approach to flavour physics
We discuss a mixed-action approach in which sea quarks are regularised using
non-perturbatively improved Wilson fermions, while a fully-twisted
tmQCD action is used for valence quarks. In this setup, automatic
improvement is preserved for valence observables, apart from small residual
effects from the sea. A strategy for matching sea and valence is
set up, and carried out for CLS ensembles with open boundary
conditions at several simulation points. The scaling of basic light-quark
observables such as the pseudoscalar meson decay constant is studied, as well
as the isospin splitting of pseudoscalar meson masses.Comment: 11 pages, 5 figures, Proceedings of the 35th International Symposium
on Lattice Field Theory (Lattice 2017), 18-24 June 2017, Granada, Spai
Non-perturbative running of quark masses in three-flavour QCD
We present our preliminary results for the computation of the
non-perturbative running of renormalized quark masses in QCD, between
the electroweak and hadronic scales, using standard finite-size scaling
techniques. The computation is carried out to very high precision, using
massless -improved Wilson quarks. Following the strategy
adopted by the ALPHA Collaboration for the running coupling, different schemes
are used above and below a scale , which differ by using either
the Schr\"odinger Functional or Gradient Flow renormalized coupling. We discuss
our results for the running in both regions, and the procedure to match the two
schemes.Comment: 7 pages, 3 figures, 34th annual International Symposium on Lattice
Field Theor
Non-perturbative quark mass renormalisation and running in QCD
We determine from first principles the quark mass anomalous dimension in Nf=3
QCD between the electroweak and hadronic scales. This allows for a fully
non-perturbative connection of the perturbative and non-perturbative regimes of
the Standard Model in the hadronic sector. The computation is carried out to
high accuracy, employing massless O(a)-improved Wilson quarks and finite-size
scaling techniques. We also provide the matching factors required in the
renormalisation of light quark masses from lattice computations with
O(a)-improved Wilson fermions and a tree-level Symanzik improved gauge action.
The total uncertainty due to renormalisation and running in the determination
of light quark masses in the SM is thus reduced to about 1%.Comment: 41 pages, 10 tables, 7 figures, published version (minimal text
improvements
- …