Following a suggestion by Aoki and Bär, c2 can be extracted by analyzing volume effects in 2-pion states. To this end we consider renormalized ratios of four point to two point correlation functions. We present the results from various CLS lattices, with pion masses ranging from 280 to 450 MeV and lattice spacings of 0.07 fm and 0.08 fm. This low energy constant is useful to understand discretization effects in chiral extrapolations with Wilson fermions, especially for quantities which vanish in the chiral limit, like the pion mass. Since our procedure is computationally cheap and straightforward, it is recommended as a routine study for any Wilson-type simulation, as a check of discretization effects.
First-principles lattice determinations of the Standard Model expectation for the leading order hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon have become sufficiently precise that further improvement requires including strong and electromagnetic isospin-breaking effects. We provide a continuum estimate of the strong isospin-breaking contribution, $a_μ^{SIB}$, using $SU(3)$ chiral perturbation theory. The result is shown to be dominated by resonance-region contributions encoded in a single low-energy constant whose value is known from flavor-breaking had…
I discuss the practical convergence of the SU(2) ChPT series in the meson sector, based on 2+1 flavor lattice data by the Wuppertal-Budapest and Budapest-Marseille-Wuppertal collaborations. These studies employ staggered and clover-improved Wilson fermions, respectively. In both cases large box volumes and several lattice spacings are used, and the pion masses reach down to the physical mass point. We conclude that LO and NLO low-energy constants can be determined with controlled systematics, if there is sufficient data between the physical mass point and about 350 MeV pion mass. Exploratory L…
We develop a strategy for the non-perturbative determination of the O(a)-improvement coefficient c_sw for Wilson fermions with massive sea quarks. The improvement condition is defined via the PCAC relation in the Schrödinger functional. It is imposed along a line of constant physics designed to be close to the correct mass of the charm quark. The numerical work uses the tree-level improved Lüscher-Weisz gauge action in N_f=3+1 Lattice QCD.
We present the comparison of the analytical microscopic spectral density for lattice QCD with $N_{\rm f}=2$ twisted mass fermions with the one obtained on the lattice utilizing configurations produced by the ETM collaboration. We extract estimates for the chiral condensate as well as the low-energy constant $W_8$ of Wilson $χ$-PT by employing spectral information of the Wilson Dirac operator with fixed index at finite volume.
Scattering lengths for two pseudoscalar meson systems, $ππ(I=2)$, $KK(I=1)$ and $πK(I=3/2,\ 1/2)$, are calculated from lattice QCD by using the finite size formula. We perform the calculation with $N_f=2+1$ gauge configurations generated on $32^3 \times 64$ lattice using the Iwasaki gauge action and non-perturbatively ${\cal O}(a)$-improved Wilson action at $a^{-1} = 2.19$ GeV. The quark masses correspond to $m_π= 0.17 - 0.71$ GeV. For $πK(I=1/2)$ system, we use the variational method with the two operators, $\bar{s}u$ and $πK$, to separate the contamination from the higher states. In order to…
A parametrization of the lattice spacing ($a$) in terms of the bare coupling ($β$) for the SU(3) Yang--Mills theory with the Wilson gauge action is given in a wide range of~$β$. The Yang--Mills gradient flow with respect to the flow time~$t$ for the dimensionless observable, $t\frac{d}{dt}t^2\langle E(t)\rangle$, is utilized to determine the parametrization. With fine lattice spacings ($6.3\leβ\le7.5$) and large lattice volumes ($N_{\rm s}=64$--$128$), the discretization and finite-volume errors are significantly reduced to the same level as the statistical error.
We present preliminary results for the charm quark mass in the $N_f=4$ RGI scheme. These were obtained using $N_f=2+1$ CLS ensembles with $\mathcal{O}(a)$ non-perturbatively improved Wilson fermions. We employed five different lattice spacings, ranging down to $a\lesssim 0.04$ fm and realized approximately physical pion and kaon masses, with ensembles spread out along three different trajectories in the quark mass plane, enabling a thorough study of the dependence on the lattice spacing and the light and strange sea quark masses. We sketch our analysis strategy and find that the dominant error…
First-Principles Determination of the QCD Contribution to the Axion-Photon Coupling Using Domain-Wall Fermions
School of Physics, Peking University（北京大学物理学院）；Collaborative Innovation Center of Quantum Matter（量子物质协同创新中心）；Center for High Energy Physics, Peking University（北京大学高能物理中心）；Southern Center for Nuclear-Science Theory (SCNT), Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所南方核科学理论中心（SCNT））；Department of Physics, University of Connecticut（康涅狄格大学物理系）
We determine non-perturbatively the normalisation constant Z_m*Z_P/Z_A as well as the Symanzik coefficients b_m and b_A-b_P, required in O(a) improved quark mass renormalisation with Wilson fermions. The strategy underlying their computation involves simulations in N_f=3 QCD with O(a) improved massless sea and non-degenerate valence quarks in the finite-volume Schroedinger functional scheme. Our results, which cover the typical gauge coupling range of large-volume N_f=2+1 QCD simulations with Wilson fermions at lattice spacings below 0.1 fm, are of particular use for the non-perturbative calcu…
We consider the determination of the finite temperature phase transition in the Yang--Mills SU(3) gauge theory. We compute the difference of the spatial and temporal energy density at a physical Wilson flow time. This difference is zero in the confined phase and becomes non zero in the deconfined phase. We locate the phase transition by using a new technique based on an exponential smoothing spline. This method is an alternative to the determination of the phase transition based on the Polyakov loop susceptibility and can also be used with dynamical fermions.
We derive chiral Ward identities for lattice QCD with Wilson quarks and $N_\mathrm{f} \geq 3$ flavours, on small lattices with Schrödinger functional boundary conditions and vanishingly small quark masses. These identities relate the axial variation of the non-singlet pseudoscalar density to the scalar one, thus enabling the non-perturbative determination of the scale-independent ratio $Z_\mathrm{S}/Z_\mathrm{P}$ of the renormalisation parameters of these operators. We obtain results for $N_\mathrm{f}=3$ QCD with tree-level Symanzik-improved gluons and Wilson-Clover quarks, for bare gauge coup…
We give a determination of the phenomenological value of the Wilson (or gradient) flow scales t0 and w0 for 2+1 flavours of dynamical quarks. The simulations are performed keeping the average quark mass constant, which allows the approach to the physical point to be made in a controlled manner. O(a) improved clover fermions are used and together with four lattice spacings this allows the continuum extrapolation to be taken.
A lot of progress has been made in the direct determination of nucleon sigma terms. Using similar methods, we consider the sigma terms of the other octet baryons as well. These are determined on CLS gauge field ensembles employing the Lüscher-Weisz gluon action and the Sheikholeslami-Wohlert fermion action with $N_\mathrm{f} = 2 + 1$. The ensembles have pion masses ranging from ${410}\,\mathrm{MeV}$ down to the physical value and lattice spacings covering a range between ${0.098}\,\mathrm{fm}$ and ${0.039}\,\mathrm{fm}$. We present some preliminary results for the pion and strange sigma terms …
A non-perturbative renormalisation prescription for the energy-momentum tensor, based on space-time symmetries along the Wilson flow, has been proposed recently in the context of 4-dimensional gauge theories. We extend this construction to the case of a scalar field theory, and investigate its numerical feasibility by studying Ward identities in 3-dimensional scalar field theory. After introducing the Wilson flow for the scalar field theory we discuss its renormalisation properties and the determination of the renormalisation constants for the energy-momentum tensor.
Experimental data from hadronic $τ$ decays allow for a precision determination of the slope of the $I=1$ vacuum polarization at zero momentum. We use this information to provide a value for the next-to-next-to-leading order (NNLO) low-energy constant $C_{93}$ in chiral perturbation theory. The largest systematic error in this determination results from the neglect of terms beyond NNLO in the effective chiral Lagrangian, whose presence in the data will, in general, make the effective $C_{93}$ determined in an NNLO analysis mass dependent. We estimate the size of this effect by using strange had…
The OpenLat initiative presents its results of lattice QCD simulations using Stabilized Wilson Fermions (SWF) using 2+1 quark flavors. Focusing on the $\mathrm{SU}(3)$ flavor symmetric point $m_π=m_K=412$ MeV, four different lattice spacings ($a=0.064,0.077,0.094,0.12$ fm) are used to perform the continuum limit to study cutoff effects. We present results on light hadron masses; for the determination we use a Bayesian analysis framework with constraints and model averaging to minimize the bias in the analysis.
Hadronic physics from a Wilson fermion mixed-action approach: Setup and scale setting
Humboldt Universität zu Berlin, Institut für Physik and IRIS Adlershof（柏林洪堡大学物理研究所与IRIS阿德勒霍夫）；Helmholtz Institute Mainz, Johannes Gutenberg University（美因茨亥姆霍兹研究所，约翰内斯·古腾堡大学）；GSI Helmholtz Centre for Heavy Ion Research（重离子研究亥姆霍兹中心（GSI））；John von Neumann-Institut für Computing NIC, Deutsches Elektronen-Synchrotron DESY（冯·诺依曼计算研究所，德国电子同步加速器（DESY））；Instituto de Física Teórica UAM-CSIC（马德里自治大学-西班牙高等科学研究理事会理论物理研究所）；Dpto. de Física Teórica, Universidad Autónoma de Madrid（马德里自治大学理论物理系）；INFN, Sezione di Torino（意大利国家核物理都灵分部）；Instituto de Física Corpuscular (IFIC), CSIC-Universitat de València（粒子物理研究所（IFIC），西班牙高等科学研究理事会-瓦伦西亚大学）
