We present a comprehensive study of the electromagnetic form factor, the decay constant and the mass of the pion computed in lattice QCD with two degenerate O(a)-improved Wilson quarks at three different lattice spacings in the range 0.05-0.08fm and pion masses between 280 and 630MeV at m_pi L >~ 4. Using partially twisted boundary conditions and stochastic estimators, we obtain a dense set of precise data points for the form factor at very small momentum transfers, allowing for a model-independent extraction of the charge radius. Chiral Perturbation Theory (ChPT) augmented by terms which model lattice artefacts is then compared to the data. At next-to-leading order the effective theory fails to produce a consistent description of the full set of pion observables but describes the data well when only the decay constant and mass are considered. By contrast, using the next-to-next-to-leading order expressions to perform global fits result in a consistent description of all data. We obtain <r^2_pi>=0.481(33)(13)fm^2 as our final result for the charge radius at the physical point. Our calculation also yields estimates for the pion decay constant in the chiral limit, F_pi/F=1.080(16)(6), the quark condensate, Sigma^{1/3}_MSbar(2GeV)=261(13)(1)MeV and several low-energy constants of SU(2) ChPT.
We present lattice QCD calculations of valence parton distribution function (PDF) of pion employing next-to-next-leading-order (NNLO) perturbative QCD matching. Our calculations are based on three gauge ensembles of 2+1 flavor highly improved staggered quarks and Wilson--Clover valance quarks, corresponding to pion mass $m_π=140$~MeV at a lattice spacing $a=0.076$~fm and $m_π=300$~MeV at $a=0.04, 0.06$~fm. This enables us to present, for the first time, continuum-extrapolated lattice QCD results for NNLO valence PDF of the pion at the physical point. Applying leading-twist expansion for renorm…
We construct a relativistic chiral nucleon-nucleon interaction up to the next-to-next-to-leading order in covariant baryon chiral perturbation theory. We show that a good description of the $np$ phase shifts up to $T_\mathrm{lab}=200$ MeV and even higher can be achieved with a $\tildeχ^2/\mathrm{d.o.f.}$ less than 1. Both the next-to-leading order results and the next-to-next-to-leading order results describe the phase shifts equally well up to $T_\mathrm{lab}=200$ MeV, but for higher energies, the latter behaves better, showing satisfactory convergence. The relativistic chiral potential provi…
We discuss finite volume effects and partial quenching for Chiral Perturbation Theory in the mesonic sector. The effects are computed in terms of analytical expressions for masses, decay constants and vacuum expectation values (VEVs) to two-loop order. Numerical examples are presented for a number of interesting and relevant cases. All numerical programs are publically available, the prospects of a combination of these studies with lattice gauge theory computations are discussed briefly.
Extraction of the nucleon axial form factor from Lattice QCD using NNLO chiral perturbation theory
GSI Helmholtzzentrum für Schwerionenforschung GmbH(GSI重离子研究中心有限公司);Instituto de Física Corpuscular (IFIC), CSIC‐Universitat de València(粒子物理研究所(IFIC),西班牙国家研究委员会-瓦伦西亚大学)
In this paper, we consider two-flavor QCD at zero temperature and finite isospin chemical potential ($μ_I$) using a model-independent analysis within chiral perturbation theory at next-to-leading order. We calculate the effective potential, the chiral condensate and the pion condensate in the pion-condensed phase at both zero and nonzero pionic source. We compare our finite pionic source results for the chiral condensate and the pion condensate with recent (2+1)-flavor lattice QCD results and find that they are in excellent agreement.
We present results for the leading hadronic contribution to the muon $g-2$ from configurations with 2+1+1 flavors of HISQ quarks. The ensembles have been generated by the MILC collaboration at three lattice spacings. Using the time-momentum representation of the electromagnetic current correlator, we calculate the finite volume effects up to next-to-next-to-leading-order in Chiral Perturbation Theory.
We extend the standard second order effective chiral Lagrangian of pions and nucleons by considering the coupling to an external gravitational field. As an application we calculate one-loop corrections to the one-nucleon matrix element of the energy-momentum tensor to fourth order in chiral counting, and next-to-leading order tree-level amplitude of the pion-production in an external gravitational field. We discuss the relation of the obtained results to experimentally measurable observables. Our expressions for the chiral corrections to the nucleon gravitational form factors differ from those…
Next-to-next-to-leading order QCD corrections to pion (kaon)-induced exclusive Drell-Yan process
South China Normal University(华南师范大学);Guangdong Basic Research Center of Excellence for Structure and Fundamental Interactions of Matter(广东省物质结构与基本相互作用卓越研究中心);Guangdong Provincial Key Laboratory of Nuclear Science(广东省核科学重点实验室);École polytechnique, Institut Polytechnique de Paris(巴黎综合理工学院,巴黎理工学院);Zhengzhou University(郑州大学);Institute of High Energy Physics, Chinese Academy of Sciences(中国科学院高能物理研究所);School of Physical Sciences, University of Chinese Academy of Sciences(中国科学院大学物理科学学院)