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arXiv 2201.04638hep-phhep-ex
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矢量轻夸克-标量盒图在类矢量族Pati-Salam统一中的重要性

Importance of vector leptoquark-scalar box diagrams in Pati-Salam unification with vector-like families

Syuhei Iguro, Junichiro Kawamura, Shohei Okawa, Yuji Omura

摘要:

研究了矢量轻夸克(LQ)和标量场在Pati-Salam(PS)类矢量族统一中的盒图诱导的轻子味破坏介子衰变.矢量LQ对应于与PS规范对称性破缺相关的质量规范玻色子,而标量场是PS破缺场的物理自由度。LQ通常在树水平上引起快速变味衰变,如$K_L \to μe$,除非其质量尺度高于PeV尺度。引入类矢量族来抑制由LQ介导的树级贡献,并解释现实的费米子质量矩阵。本文指出,即使抑制了树能级的贡献,由一个LQ和一个标量场介导的盒形图也不可避免地对这些介子衰变有单圈贡献。我们考虑了一个具体的模型进行论证,发现当单圈诱导介子衰变与实验极限一致时,对于给定的LQ质量,类矢量费米子质量存在一个上界。对于20 TeV的LQ,如果耦合的组合不能抑制$K_L \to μe$衰变,则类矢量费米子质量应该小于3 TeV。我们的研究结果将说明箱形图的重要性,涉及LQ和物理模式的对称性破缺标量的一般模型。

英文摘要:

We study lepton flavor violating meson decays induced by box diagrams involving a vector leptoquark (LQ) and scalar fields in Pati-Salam (PS) unification with vector-like families. The vector LQ corresponds to the massive gauge boson associated with the PS gauge symmetry breaking and the scalar fields are the physical degrees of freedom of the PS breaking field. The LQ generally causes the rapid flavor violating decays, such as $K_L \to μe$, at the tree-level unless its mass scale is higher than PeV scale. The vector-like families are introduced to suppress the tree-level contributions mediated by the LQ and explain the realistic fermion mass matrices. In this paper, we point out that there are inevitable one-loop contributions to those meson decays from the box diagrams mediated by both one LQ and one scalar field, even if the tree-level contributions are suppressed. We consider a concrete model for demonstration, and find that the vector-like fermion masses have an upper bound for a given LQ mass when the one-loop induced meson decays are consistent with the experimental limits. The vector-like fermion mass should be lighter than 3 TeV for 20 TeV LQ, if a combination of the couplings does not suppress $K_L \to μe$ decay. Our findings would illustrate importance of the box diagrams involving both LQ and physical modes of symmetry breaking scalars in generic models.

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