Solution

ID: past-exam-of-the-gauge-field-theory-course-of-the-university-of-cambridge/2013/paper-1/3/c/solution

The operator has mass dimension , giving . It is not power-counting renormalizable as a fundamental interaction treated to arbitrary energy. It is a perfectly usable dimension-five effective operator below its suppression scale. Successive orders in that effective field theory require a derivative and operator expansion rather than one finite set of parameters valid at every order.

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