标题： 淬火penguins和Delta I=1/2规则 显示英文标题

标题： Quenched penguins and the Delta I=1/2 rule

摘要： 强penguin算符在味群作用下的变换性质在将其视为(部分)消去QCD中的算符而非未消去理论中的算符时会发生变化。 因此，在描述部分消去设置中非轻子K介子衰变矩阵元的有效理论中，会出现额外的算符和新的低能常数。 这些新的低能常数在未消去理论中没有对应项，因此应被视为消去近似的产物。 在此，我们考虑由两个左手味电流乘积组成的强penguin算符，并对K^0到真空和K^+到pi^+矩阵元在有效理论中的完整一环分析进行了研究。 我们发现，这些新的低能常数已经在这些矩阵元中在主导阶出现。 这意味着，例如对Delta I=1/2规则的部分消去格点计算在主导阶会受到消去近似内在不确定性的干扰。 唯一的例外是具有三个轻虚夸克的部分消去情况，这与一般预期一致。 当理论中保留魅夸克时，我们的结果同样适用。 显示英文摘要

摘要： The transformation properties of strong penguin operators under the action of the flavor group change when they are considered as operators in (partially) quenched QCD instead of the unquenched theory. As a result, additional operators and new low-energy constants appear in the effective theory describing non-leptonic kaon decay matrix elements in the partially quenched setting. These new low-energy constants do not have a counterpart in the unquenched theory, and should thus be considered as an artifact of the quenched approximation. Here we consider strong penguin operators consisting of products of two left-handed flavor currents, and give a complete one-loop analysis in the effective theory for K^0 to vacuum and K^+ to pi^+ matrix elements. We find that the new low-energy constants already appear in these matrix elements at leading order. This implies that (partially) quenched lattice computations of for instance the Delta I=1/2 rule are affected by ambiguities intrinsic to the use of the quenched approximation at leading order. The only exception is the partially quenched case with three light sea quarks, consistent with general expectations. Our results are also relevant when the charm quark is kept in the theory.