Effective free-fermionic form factors and the XY spin chain

  title={Effective free-fermionic form factors and the XY spin chain},
  author={Oleksandr Gamayun and N. Z. Iorgov and Yu. Yu. Zhuravlev},
  journal={arXiv: Statistical Mechanics},
We introduce effective form factors for one-dimensional lattice fermions with arbitrary phase shifts. We study tau functions defined as series of these form factors. On the one hand we perform the exact summation and present tau functions as Fredholm determinants in the thermodynamic limit. On the other hand simple expressions of form factors allow us to present the corresponding series as integrals of elementary functions. Using this approach we re-derive the asymptotics of static correlation… 

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