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arXiv · 0904.4128

Gauge invariance in the presence of a cutoff

A. N. Kvinikhidze·B. Blankleider·E. Epelbaum·C. Hanhart·M. Pavón Valderrama
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Abstract

We use the method of gauging equations to construct the electromagnetic current operator for the two-nucleon system in a theory with a finite cutoff. The employed formulation ensures that the two-nucleon T-matrix and corresponding five-point function, in the cutoff theory, are identical to the ones formally defined by a reference theory without a cutoff. A feature of our approach is that it effectively introduces a cutoff into the reference theory in a way that maintains the long-range part of the exchange current operator; for applications to effective field theory (EFT), this property is usually sufficient to guarantee the predictive power of the resulting cutoff theory. In addition, our approach leads to Ward-Takahashi (WT) identities that are linear in the interactions. From the point of view of EFT's where such a WT identity is satisfied in the reference theory, this ensures that gauge invariance in the cutoff theory is maintained order by order in the expansion.

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A. N. Kvinikhidze, B. Blankleider, E. Epelbaum, C. Hanhart, M. Pavón Valderrama. 2009-04-27. Gauge invariance in the presence of a cutoff. https://doi.org/10.1103/physrevc.80.044004

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