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arXiv 0908.1754hep-ph
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标准模型以外轻夸克的半轻子衰变

Semileptonic decays of light quarks beyond the Standard Model

Vincenzo Cirigliano, Martín González-Alonso, James Jenkins

摘要:

我们用SU(2)_L × U(1)_Y不变的有效拉格朗日量在弱标度下以模型无关的方式描述了半轻子过程的非标准贡献,由此导出了控制μ子和β衰变的低能有效拉格朗日量.我们发现对Cabibbo普适性的偏离Δ_CKM = |V_ud| ^2 + |V_us| ^2 + |V_ub| ^2 - 1得到了四个有效算子的贡献.Δ CKM =-1 E-4 +-6 E-4的唯象界对所有四个算符提供了强约束,对应于大于11 TeV(90%CL)的有效尺度.取决于操作员,该约束与Z极可观测量处于相同水平或更好。相反,仅精确的电弱约束将允许普适性违背大到Δ_CKM = -0.01(90%CL)。在这个水平上观察到的非零Δ_CKM可以用一个单一的四费米子算符来解释,这个算符受电弱精密测量的约束相对较差。

英文摘要:

We describe non-standard contributions to semileptonic processes in a model independent way in terms of an SU(2)_L X U(1)_Y invariant effective lagrangian at the weak scale, from which we derive the low-energy effective lagrangian governing muon and beta decays. We find that the deviation from Cabibbo universality, Δ_CKM = |V_ud|^2 + |V_us|^2 + |V_ub|^2 - 1, receives contributions from four effective operators. The phenomenological bound of Δ_CKM = -1E-4 +- 6E-4 provides strong constraints on all four operators, corresponding to an effective scale greater than 11 TeV (90% CL). Depending on the operator, this constraint is at the same level or better then the Z pole observables. Conversely, precision electroweak constraints alone would allow universality violations as large as Δ_CKM = -0.01 (90% CL). An observed nonzero Δ_CKM at this level could be explained in terms of a single four-fermion operator which is relatively poorly constrained by electroweak precision measurements.

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