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A guide to functional methods beyond one-loop order
DOI:10.1007/JHEP08(2025)099.png)
Abstract
En 中文
Functional methods can be applied to the quantum effective action to efficiently determine counterterms and matching conditions for effective field theories. We extend the toolbox to two-loop order and beyond and show how to evaluate the expansion of the path integral in a manifestly gauge-covariant manner. We also generalize the method to theories with mixed spin statistics and prove the validity of the hard-region matching formula to all loop orders. The methods are exemplified with a two-loop matching calculation of the Euler–Heisenberg Lagrangian resulting from decoupling the electron in QED.
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