Systematic effects of the quenched approximation on the strong penguin contribution to epsilon'/epsilon

TL;DR

This paper examines how the quenched approximation impacts the calculation of strong penguin contributions to epsilon'/epsilon, revealing significant artifacts that affect only specific operators in chiral perturbation theory.

Contribution

It evaluates the large quenching artifacts in the Q_6 operator's contribution to epsilon'/epsilon using improved methods, clarifying the limitations of the quenched approximation.

Findings

Large quenching artifacts in Q_6 contribution to epsilon'/epsilon.

The quenched approximation does not affect Q_8 or the Delta I=1/2 rule.

Improved methods reduce power divergent corrections.

Abstract

We discuss the implementation and properties of the quenched approximation in the calculation of the left-right, strong penguin contributions (i.e. Q_6) to epsilon'/epsilon. The coefficient of the new chiral logarithm, discovered by Golterman and Pallante, which appears at leading order in quenched chiral perturbation theory is evaluated using both the method proposed by those authors and by an improved approach which is free of power divergent corrections. The result implies a large quenching artifact in the contribution of Q_6 to epsilon'/epsilon. This failure of the quenched approximation affects only the strong penguin operators and so does not affect the Q_8 contribution to epsilon'/epsilon nor Re A_0, Re A_2 and thus the Delta I=1/2 rule at tree level in chiral perturbation theory.