https://fisica.ufop.br/publications/using-cosmological-perturbation-theory-distinguish-between-gr-and-unimodular
Fabris JC, Alvarenga MH, Velten H. Using Cosmological Perturbation Theory to Distinguish between GR and Unimodular Gravity. Symmetry [Internet]. 2023;15 (7).
perturbation theoryusingcosmologicaldistinguishgr
https://www.arxiv.org/abs/nucl-th/9807035
Abstract page for arXiv paper nucl-th/9807035: Bethe-Salpeter Approach for Meson-Meson Scattering in Chiral Perturbation Theory
thsalpeterapproachmesonscattering