Solution

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

The operator has mass dimension , so . It is not power-counting renormalizable. Hermiticity may require a suitable conjugate or a symmetrized derivative, and electromagnetic gauge invariance would require a further consistent completion; neither repair changes its engineering dimension. Such derivative interactions can occur in an effective field theory, subject to its symmetries and operator redundancies.

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