104 research outputs found
Chiral Ward identities, automatic O(a) improvement and the gradient flow
Non-singlet chiral Ward identities for fermionic operators at positive
flow-time are derived using standard techniques based on local chiral
variations of the action and of local operators. The gradient flow formalism is
applied to twisted mass fermions and it is shown that automatic O(a)
improvement for Wilson twisted mass fermions at maximal twist is a property
valid also at positive flow-time. A definition of the chiral condensate that is
multiplicatively renormalizable and automatically O(a) improved is then
derived.Comment: 25 pages; v2: few typos corrected, one reference added, it matches
the published versio
Cutoff effects of the gradient flow for fermions
I analyze cutoff effects of the gradient flow for Wilson-type fermions. I
show that with a proper choice of the higher dimensional fields in the Symanzik
effective theory, O() improvement of the action is achieved changing the
initial conditions of the gradient flow equation.Comment: 8 pages. Proceedings contribution to the "39th International
Symposium on Lattice Field Theory (Lattice 2022)
Moments of parton distribution functions of any order from lattice QCD
We describe a procedure to determine moments of parton distribution functions
of any order in lattice QCD. The procedure is based on the gradient flow for
fermion and gauge fields. The flowed matrix elements of twist-2 operators
renormalize multiplicatively, and the matching with the physical matrix
elements can be obtained using continuum symmetries and the irreducible
representations of Euclidean 4-dimensional rotations. We calculate the matching
coefficients at one-loop in perturbation theory for moments of any order in the
flavor non-singlet case. We also give specific examples of operators that could
be used in lattice QCD computations. It turns out that it is possible to choose
operators with identical Lorentz indices and still have a multiplicative
matching. One can thus use twist-2 operators exclusively with temporal indices,
thus substantially improving the signal-to-noise ratio in the computation of
the hadronic matrix elements.Comment: 7 pages, 1 figur
The nucleon electric dipole moment with the gradient flow: the -term contribution
We propose a new method to calculate electric dipole moments induced by the
strong QCD -term. The method is based on the gradient flow for gauge
fields and is free from renormalization ambiguities. We test our method by
computing the nucleon electric dipole moments in pure Yang-Mills theory at
several lattice spacings, enabling a first-of-its-kind continuum extrapolation.
The method is rather general and can be applied for any quantity computed in a
vacuum. This first application of the gradient flow has been
successful and demonstrates proof-of-principle, thereby providing a novel
method to obtain precise results for nucleon and light nuclear electric dipole
moments.Comment: 32 pages, 14 figures, 2 tables. v2: added 1 plot, 1 table and 1
reference. Typos corrected. Published versio
Massive Photons: An Infrared Regularization Scheme for Lattice QCD plus QED
Standard methods for including electromagnetic interactions in lattice quantum chromodynamics calculations result in power-law finite-volume corrections to physical quantities. Removing these by extrapolation requires costly computations at multiple volumes. We introduce a photon mass to alternatively regulate the infrared, and rely on effective field theory to remove its unphysical effects. Electromagnetic modifications to the hadron spectrum are reliably estimated with a precision and cost comparable to conventional approaches that utilize multiple larger volumes. A significant overall cost advantage emerges when accounting for ensemble generation. The proposed method may benefit lattice calculations involving multiple charged hadrons, as well as quantum many-body computations with long-range Coulomb interactions
Topological susceptibility from twisted mass fermions using spectral projectors
We discuss the computation of the topological susceptibility using the method
of spectral projectors and dynamical twisted mass fermions. We present our
analysis concerning the O(a)-improvement of the topological susceptibility and
we show numerical results for Nf=2 and Nf=2+1+1 flavours, performing a study of
the quark mass dependence in terms of leading order chiral perturbation theory.Comment: 7 pages, 3 figures; presented at the 31st International Symposium on
Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz, German
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