We present a calculation of the vector-isovector timelike form factors of the pion and the kaon using lattice quantum chromodynamics. We calculate two-point correlation functions with 𝑚𝜋∼280  MeV, extracting both the finite-volume spectrum and matrix elements for these states created from the vacuum by a vector current. After determining the coupled-channel 𝜋⁢𝜋,𝐾⁢¯𝐾 scattering amplitudes, we perform the necessary correction for the significant finite-volume effects present in the current matrix elements, leading to the timelike form factors. We find these to be dominated by the presence of the 𝜌 resonance, and we extract its decay constant by an analytic continuation of the amplitudes to the resonance pole. In addition, the spacelike pion form factor is determined on the same lattice configurations, and a dispersive parametrization is used to simultaneously describe the spacelike and elastic timelike regions.

中文翻译：

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晶格 QCD 弹性区域之外的类时间介子形状因子


我们提出了使用晶格量子色动力学计算 pion 和 kaon 的向量-等向量时间模拟形式因子。我们用 mπ∼280 MeV 计算两点相关函数，提取矢量电流从真空中产生的这些状态的有限体积光谱和矩阵元素。在确定耦合通道 ππ，K ̄K 散射幅度后，我们对当前矩阵单元中存在的显着有限体积效应进行必要的校正，从而产生类似时间的形状因子。我们发现这些是由 ρ 谐振的存在主导的，我们通过振幅到谐振极点的解析延续来提取其衰减常数。此外，在相同的晶格构型上确定类空间 pion 形状因子，并使用色散参数化同时描述类空间和弹性类时间区域。