Second moment of the pion distribution amplitude with the momentum smearing technique

Using the second moment of the pion distribution amplitude as an example, we investigate whether lattice calculations of matrix elements of local operators involving covariant derivatives may benefit from the recently proposed momentum smearing technique for hadronic interpolators. Comparing the momentum smearing technique to the traditional Wuppertal smearing we find—at equal computational cost—a considerable reduction of the statistical errors. The present investigation was carried out using N_{f}=2+1 dynamical non-perturbatively order a improved Wilson fermions on lattices of different volumes and pion masses down to 220 MeV

Scale setting and the light baryon spectrum in Nf=2+1N_f=2+1 QCD with Wilson fermions

We determine the light baryon spectrum on ensembles generated by the Coordinated Lattice Simulations (CLS) effort, employing $N_f=2+1$ flavours of non-perturbatively improved Wilson fermions. The hadron masses are interpolated and extrapolated within the quark mass plane, utilizing three distinct trajectories, two of which intersect close to the physical quark mass point and the third one approaching the SU(3) chiral limit. The results are extrapolated to the continuum limit, utilizing six different lattice spacings ranging from $a\approx 0.10\,$fm down to below $0.04\,$fm. The light pion mass varies from $M_{\pi}\approx 429\,$MeV down to $127\,$MeV. In general, the spatial extent is kept larger than four times the inverse pion mass and larger than $2.3\,$fm, with additional small and large volume ensembles to investigate finite size effects. We determine the Wilson flow scales $\sqrt{t_{0,{\rm ph}}}=0.1449^{(7)}_{(9)}\,$fm and $t_0^*\approx t_{0,{\rm ph}}$ from the octet cascade ($\Xi$ baryon). Determining the light baryon spectrum in the continuum limit, we find the nucleon mass $m_N=941.7^{(6.5)}_{(7.6)}\,$MeV and the other stable baryon masses to agree with their experimental values within sub-percent level uncertainties. Moreover, we determine SU(3) and SU(2) chiral perturbation theory low energy constants, including the octet and the $\Omega$ baryon sigma~terms $\sigma_{\pi N}=43.9(4.7)\,$MeV, $\sigma_{\pi\Lambda}=28.2^{(4.3)}_{(5.4)}\,$MeV, $\sigma_{\pi\Sigma}=25.9^{(3.8)}_{(6.1)}\,$MeV, $\sigma_{\pi\Xi}=11.2^{(4.5)}_{(6.4)}\,$MeV and $\sigma_{\pi\Omega}=6.9^{(5.3)}_{(4.3)}\,$MeV, as well as various parameters, renormalization factors and improvement coefficients that are relevant for simulations with our lattice action.Comment: 128 pages, many figure

Probing exotic phenomena at the interface of nuclear and particle physics with the electric dipole moments of diamagnetic atoms: A unique window to hadronic and semi-leptonic CP violation

The current status of electric dipole moments of diamagnetic atoms which involves the synergy between atomic experiments and three different theoretical areas -- particle, nuclear and atomic is reviewed. Various models of particle physics that predict CP violation, which is necessary for the existence of such electric dipole moments, are presented. These include the standard model of particle physics and various extensions of it. Effective hadron level combined charge conjugation (C) and parity (P) symmetry violating interactions are derived taking into consideration different ways in which a nucleon interacts with other nucleons as well as with electrons. Nuclear structure calculations of the CP-odd nuclear Schiff moment are discussed using the shell model and other theoretical approaches. Results of the calculations of atomic electric dipole moments due to the interaction of the nuclear Schiff moment with the electrons and the P and time-reversal (T) symmetry violating tensor-pseudotensor electron-nucleus are elucidated using different relativistic many-body theories. The principles of the measurement of the electric dipole moments of diamagnetic atoms are outlined. Upper limits for the nuclear Schiff moment and tensor-pseudotensor coupling constant are obtained combining the results of atomic experiments and relativistic many-body theories. The coefficients for the different sources of CP violation have been estimated at the elementary particle level for all the diamagnetic atoms of current experimental interest and their implications for physics beyond the standard model is discussed. Possible improvements of the current results of the measurements as well as quantum chromodynamics, nuclear and atomic calculations are suggested.Comment: 46 pages, 19 tables and 16 figures. A review article accepted for EPJ

Masses and decay constants of the η and η′ mesons from lattice QCD

Abstract We determine the masses, the singlet and octet decay constants as well as the anomalous matrix elements of the η and η′ mesons in N f = 2 + 1 QCD. The results are obtained using twenty-one CLS ensembles of non-perturbatively improved Wilson fermions that span four lattice spacings ranging from a ≈ 0.086 fm down to a ≈ 0.050 fm. The pion masses vary from M π = 420 MeV to 126 MeV and the spatial lattice extents L s are such that L s M π ≳ 4, avoiding significant finite volume effects. The quark mass dependence of the data is tightly constrained by employing two trajectories in the quark mass plane, enabling a thorough investigation of U(3) large-N c chiral perturbation theory (ChPT). The continuum limit extrapolated data turn out to be reasonably well described by the next-to-leading order ChPT parametrization and the respective low energy constants are determined. The data are shown to be consistent with the singlet axial Ward identity and, for the first time, also the matrix elements with the topological charge density are computed. We also derive the corresponding next-to-leading order large-N c ChPT formulae. We find F 8 = 115.0(2.8) MeV, θ 8 = −25.8(2.3)°, θ 0 = −8.1(1.8)° and, in the MS ¯ $$\overline{\mathrm{MS}}$$ scheme for N f = 3, F 0(μ = 2 GeV) = 100.1(3.0) MeV, where the decay constants read F η 8 $${F}_{\eta}^8$$ = F 8 cos θ 8, F η ′ 8 $${F}_{\eta \prime}^8$$ = F 8 sin θ 8, F η 0 $${F}_{\eta}^0$$ = −F 0 sin θ 0 and F η ′ 0 $${F}_{\eta \prime}^0$$ = F 0 cos θ 0. For the gluonic matrix elements, we obtain a η (μ = 2 GeV) = 0.0170(10) GeV3 and a η′ (μ = 2 GeV) = 0.0381(84) GeV3, where statistical and all systematic errors are added in quadrature

D and Ds decay constants in N f = 2 + 1 QCD with Wilson fermions

Abstract We present results for the leptonic decay constants of the D and Ds mesons from N f = 2 + 1 lattice QCD. We employ a set of 49 high statistics gauge ensembles generated by the Coordinated Lattice Simulations (CLS) effort utilising non-perturbatively improved Wilson fermions and the tree-level Symanzik improved gauge action at six values of the lattice spacing in the range a = 0.098 fm down to a = 0.039 fm, with pion masses varying from around 420 MeV down to below the physical point. The ensembles lie on three trajectories in the quark mass plane, two trajectories intersecting close to the physical quark mass point and the third one approaching the SU(3) chiral limit, enabling tight control of the light and strange quark mass dependence. We obtain f D s $${f}_{{\textrm{D}}_{\textrm{s}}}$$ = 246.8(1.3) MeV, f D = 208.4(1.5) MeV and f D s $${f}_{{\textrm{D}}_{\textrm{s}}}$$ /f D = 1.1842(36), where the precision of our results is mostly limited by the determination of the scale