107 research outputs found
Dynamical solution of the strong CP problem within QCD ?
The strong CP problem is inseparably connected with the topology of gauge
fields and the mechanism of color confinement, which requires nonperturbative
tools to solve it. In this talk I present results of a recent lattice
investigation of QCD with the term in collaboration with Yoshifumi
Nakamura. The tool we are using to address the nonperturbative properties of
the theory is the gradient flow, which is a particular realization of momentum
space RG transformations. The novel result is that within QCD the vacuum angle
is renormalized, together with the strong coupling constant, and flows
to in the infrared limit. This means that CP is conserved by the
strong interactions.Comment: 12 pages, 10 figures, invited talk given at `XVth Quark Confinement
and the Hadron Spectrum Conference', Stavanger, August 202
Dynamical solution of the strong CP problem within QCD?
The strong CP problem is inseparably connected with the topology of gauge fields and the mechanism of color confinement, which requires nonperturbative tools to solve it. In this talk I present results of a recent lattice investigation of QCD with the θ term in collaboration with Yoshifumi Nakamura [1, 2]. The tool we are using to address the nonperturbative properties of the theory is the gradient flow, which is a particular realization of momentum space RG transformations. The novel result is that within QCD the vacuum angle θ is renormalized, together with the strong coupling constant, and flows to θ = 0 in the infrared limit. This means that CP is conserved by the strong interactions
Efficient operators for studying higher partial waves
An extended multi-hadron operator is developed to extract the spectra of
irreducible representations in the finite volume. The irreducible
representations of the cubic group are projected using a coordinate-space
operator. The correlation function of this operator is computationally
efficient to extract lattice spectra. In particular, this new formulation only
requires propagator inversions from two distinct locations, at fixed physical
separation. We perform a proof-of-principle study on a lattice
volume with ~MeV by isolating the spectra of ,
and of the system with isospin-2 in the rest frame.Comment: 8 pages, 3 figures, Contribution to the conference Lattice201
Improved determination of hadron matrix elements using the variational method
The extraction of hadron form factors in lattice QCD using the standard two-
and three-point correlator functions has its limitations. One of the most
commonly studied sources of systematic error is excited state contamination,
which occurs when correlators are contaminated with results from higher energy
excitations. We apply the variational method to calculate the axial vector
current gA and compare the results to the more commonly used summation and
two-exponential fit methods. The results demonstrate that the variational
approach offers a more efficient and robust method for the determination of
nucleon matrix elements.Comment: 7 pages, 6 figures, talk presented at Lattice 2015, PoS (LATTICE2015
Nucleon distribution amplitudes from lattice QCD
We calculate low moments of the leading-twist and next-to-leading twist
nucleon distribution amplitudes on the lattice using two flavors of clover
fermions. The results are presented in the MSbar scheme at a scale of 2 GeV and
can be immediately applied in phenomenological studies. We find that the
deviation of the leading-twist nucleon distribution amplitude from its
asymptotic form is less pronounced than sometimes claimed in the literature.Comment: 5 pages, 3 figures, 2 tables. RevTeX style. Normalization for
\lambda_i corrected. Discussion of the results extended. To be published in
PR
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