Abstract
We present the open-source package openQ*D-1.0 (openQ*D. GitLab: https://gitlab.com/rcstar/openQxD. CSIC: https://dx.doi.org/10.20350/digitalCSIC/8591. https://hdl.handle.net/10261/173334, 2019), which has been primarily, but not uniquely, designed to perform lattice simulations of QCD+QED and QCD, with and without mathrm {C}^* boundary conditions, and O(a) improved Wilson fermions. The use of mathrm {C}^* boundary conditions in the spatial direction allows for a local and gauge-invariant formulation of QCD+QED in finite volume, and provides a theoretically clean setup to calculate isospin-breaking and radiative corrections to hadronic observables from first principles. The openQ*D code is based on openQCD-1.6 (Simulation program for lattice QCD (openQCD code). https://cern.ch/luscher/openQCD, 2016) and NSPT-1.4 (Numerical Stochastic Perturbation Theory (NSPT code). https://cern.ch/luscher/NSPT, 2017). In particular it inherits from openQCD-1.6 several core features, e.g. the highly optimized Dirac operator, the locally deflated solver, the frequency splitting for the RHMC, or the 4th order OMF integrator.
Highlights
A recent review [4] of the results obtained by the different lattice groups shows that leptonic and semileptonic decay rates of π and K mesons are presently known at the sub-percent level of accuracy
The code implements the proposal of Ref. [18] and allows to choose C∗ boundary conditions along the spatial directions and periodic boundary conditions can be simulated efficiently
We presented the main functionalities of the code and discussed the theoretical motivations behind the algorithmic choices and their specific implementations
Summary
An overview of the main algorithmic choices made in the code will be given . Eq (2.12), the pseudofermion field f, is natively defined on the extended lattice, i.e. f, (x) are truly independent variables for each x in the extended lattice It satisfies the same boundary conditions as ψ f in Eqs. Simulations close to the physical point are dominated by the inversion of the Dirac operator and the overhead due to the evolution of the gauge field is expected to be negligible Evidence of this fact has been presented in [41]. The functions that impose the orbifold constraint on gauge and momentum fields are trivial, shifted boundary conditions (by half lattice) are implemented by a simple redefinition of the map of nearest neighbouring MPI processes, and gauge action and forces need to be multiplied by a factor 1/2. On the other hand the Dirac operators and the solvers are completely untouched by the orbifold construction
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