Soft symmetry improvement of two particle irreducible effective actions

@article{Brown2017SoftSI,
  title={Soft symmetry improvement of two particle irreducible effective actions},
  author={Michael J. Brown and Ian B. Whittingham},
  journal={Physical Review D},
  year={2017},
  volume={95},
  pages={025018}
}
Two particle irreducible effective actions (2PIEAs) are valuable nonperturbative techniques in quantum field theory; however, finite truncations of them violate the Ward identities (WIs) of theories with spontaneously broken symmetries. The symmetry improvement (SI) method of Pilaftsis and Teresi attempts to overcome this by imposing the WIs as constraints on the solution; however, the method suffers from the nonexistence of solutions in linear response theory and in certain truncations in… 

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