We compute the leading QED corrections to the hadronic vacuum polarization (HVP) of the photon, relevant for the determination of leptonic anomalous magnetic moments, al. We work in the ...electroquenched approximation and use dynamical QCD configurations generated by the CLS initiative with two degenerate flavors of nonperturbatively O(a)-improved Wilson fermions. We consider QEDL and QEDM to deal with the finite-volume zero modes. We compare results for the Wilson loops with exact analytical determinations. In addition we make sure that the volumes and photon masses used in QEDM are such that the correct dispersion relation is reproduced by the energy levels extracted from the charged pions two-point functions. Finally we compare results for pion masses and the HVP between QEDL and QEDM. For the vacuum polarization, corrections with respect to the pure QCD case, at fixed pion masses, turn out to be at the percent level.
We present our first set of results for charm physics, using the mixed-action setup introduced in a companion paper
1
. Maximally twisted Wilson valence fermions are used on a sea of ...non-perturbatively
O
(
a
)-improved Wilson fermions, made up by CLS
N
f
=
2
+
1
ensembles. Our charm-sector observables are free from
O
(
a
m
c
)
discretisation effects, without need of tuning any improvement coefficient, and show continuum-limit scaling properties consistent with leading cutoff effects of
O
(
a
2
)
. We consider a subset of CLS ensembles – including four values of the lattice spacing and pion masses down to 200 MeV – allowing to take the continuum limit and extrapolate to the physical pion mass. A number of techniques are incorporated in the analysis in order to estimate the systematic uncertainties of our results for the charm quark mass and the
D
(
s
)
-meson decay constants. This first study of observables in the charm sector, where the emphasis has been on the control of the methodology, demonstrates the potential of our setup to achieve high-precision results.
On reweighting for twisted boundary conditions Bussone, Andrea; Della Morte, Michele; Hansen, Martin ...
Computer physics communications,
October 2017, 2017-10-00, Letnik:
219
Journal Article
Recenzirano
Odprti dostop
We consider the possibility of using reweighting techniques in order to correct the breaking of unitarity when twisted boundary conditions are imposed on valence fermions in simulations of lattice ...gauge theories. We start by studying the properties of reweighting factors and their variances at tree-level. This leads us to the introduction of a factorization for the fermionic reweighting determinant. In the numerical, stochastic implementation of the method, we find that the effect of reweighting is negligible in the case of large volumes but it is sizeable when the volumes are small and the twisting angles are large. More importantly, we find that for un-improved Wilson fermions, and in small volumes, the dependence of the critical quark mass on the twisting angle is quite pronounced and results in large violations of the continuum dispersion relation.
Abstract We present our first set of results for charm physics, using the mixed-action setup introduced in a companion paper 1. Maximally twisted Wilson valence fermions are used on a sea of ...non-perturbatively O(a)-improved Wilson fermions, made up by CLS $$N_\mathrm {\scriptstyle f}=2+1$$ N f = 2 + 1 ensembles. Our charm-sector observables are free from $$O(am_c)$$ O ( a m c ) discretisation effects, without need of tuning any improvement coefficient, and show continuum-limit scaling properties consistent with leading cutoff effects of $$O(a^2)$$ O ( a 2 ) . We consider a subset of CLS ensembles – including four values of the lattice spacing and pion masses down to 200 MeV – allowing to take the continuum limit and extrapolate to the physical pion mass. A number of techniques are incorporated in the analysis in order to estimate the systematic uncertainties of our results for the charm quark mass and the $$D_{(s)}$$ D ( s ) -meson decay constants. This first study of observables in the charm sector, where the emphasis has been on the control of the methodology, demonstrates the potential of our setup to achieve high-precision results.
We compute the leading QED corrections to the hadronic vacuum polarization (HVP) of the photon, relevant for the determination of leptonic anomalous magnetic moments,
a
l
. We work in the ...electroquenched approximation and use dynamical QCD configurations generated by the CLS initiative with two degenerate flavors of nonperturbatively O(
a
)-improved Wilson fermions. We consider QED
L
and QED
M
to deal with the finite-volume zero modes. We compare results for the Wilson loops with exact analytical determinations. In addition we make sure that the volumes and photon masses used in QED
M
are such that the correct dispersion relation is reproduced by the energy levels extracted from the charged pions two-point functions. Finally we compare results for pion masses and the HVP between QED
L
and QED
M
. For the vacuum polarization, corrections with respect to the pure QCD case, at fixed pion masses, turn out to be at the percent level.
We present some aspects of high precision calculations in the context of Lattice Quantum Field Theory. This work is a collection of three studies done during my Ph.D. period. First we present how to ...use the reweighting technique to compensate for the breaking of unitarity due to the use of different boundary conditions in the valence and sea sector. In particular when twisted boundary conditions are employed, with \(\theta\) twisting angle. In large volume we found that the breaking is negligible, while in rather small volumes an effect is present. The quark mass appears to change with \(\theta\) as a cutoff effect. In the second part of the dissertation we present an optimization method for Hybrid Monte Carlo performances. The work is based on the existence of a shadow Hamiltonian, an exactly conserved quantity along the Molecular Dynamics trajectory. The optimization method is economic since it only requires the forces to be measured, which are already used for the evolution from one configuration to the new one. We found predictions for the cost of the simulations with an accuracy of 10% and we could estimate the optimal parameters for the Omelyan integrator with mass-preconditioning and multi time-scale. In the last part of the work we address the calculation of electromagnetic corrections to the hadronic contribution to the \((g-2)\) anomaly of the muon. A long standing discrepancy between theoretical calculations and experimental results is present. But before invoking New Physics we need to clear the sight from possible effects within the Standard Model. In this exploratory study we carefully matched the masses of the charged pions in the theory with and without QED. We found a visible effect at the percent level although consistent with zero within two sigmas.
We present our first set of results for charm physics, using the mixed-action
setup introduced in a companion paper. Maximally twisted Wilson valence
fermions are used on a sea of non-perturbatively ...$O(a)$-improved Wilson
fermions, made up by CLS $N_{\mathrm{\scriptstyle f}}=2+1$ ensembles. Our
charm-sector observables are free from $O(am_c)$ discretisation effects,
without need of tuning any improvement coefficient, and show continuum-limit
scaling properties consistent with leading cutoff effects of $O(a^2)$. We
consider a subset of CLS ensembles -- including four values of the lattice
spacing and pion masses down to 200 MeV -- allowing to take the continuum limit
and extrapolate to the physical pion mass. A number of techniques are
incorporated in the analysis in order to estimate the systematic uncertainties
of our results for the charm quark mass and the $D_{(s)}$-meson decay
constants. This first study of observables in the charm sector, where the
emphasis has been on the control of the methodology, demonstrates the potential
of our setup to achieve high-precision results.
The first phase of a heavy quark program based on twisted mass valence quarks has been presented at last years's lattice conference. The CLS \(N_f=2+1\) ensembles were used for their fine lattice ...spacing, while twisting the masses is expected to reduce discretisation errors even further and allow for a fully relativistic calculation. We present our strategy and preliminary results on three point functions, corresponding to \(D\to K\) and \(D\to\pi\) semileptonic decays. The form factors for \(m_u=m_d=m_s\) quark masses obtained as a first step are shown here to be at the percent level in statistical precision at \(q^2=0\).
We compute the leading QED corrections to the hadronic vacuum polarization (HVP) of the photon, relevant for the determination of leptonic anomalous magnetic moments, \(a_\ell\). We work in the ...electroquenched approximation and use dynamical QCD configurations generated by the CLS initiative with two degenerate flavors of non-perturbatively O(\(a\))-improved Wilson fermions. We consider QED\(_{\rm L}\) and QED\(_{\rm M}\) to deal with the finite-volume zero modes. We compare results for the Wilson loops with exact analytical determinations. In addition we make sure that the volumes and photon masses used in QED\(_{\rm M}\) are such that the correct dispersion relation is reproduced by the energy levels extracted from the charged pions two-point functions. Finally we compare results for pion masses and the HVP between QED\(_{\rm L}\) and QED\(_{\rm M}\). For the vacuum polarization, corrections with respect to the pure QCD case, at fixed pion masses, turn out to be at the percent level.
A mixed action composed of valence quark flavours regularized with a
fully-twisted tmQCD action and of $N_f=2+1$ flavours of non-perturbatively
${\rm O}(a)$-improved Wilson sea quarks is described. ...Two procedures for the
matching of sea and valence quark masses are discussed. We report about a
comparison of the continuum-limit scaling of pseudoscalar meson observables and
of quark masses using the sea and valence actions.
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