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Lepton Universality, Rare Decays and Split Fermions

We-Fu Chang·I-Lin Ho·John N. Ng
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Abstract

We investigate the constraint on the split fermions in extra dimensions by considering the universality of $W$ leptonic decays $W\to l_i ν_i$, the charged lepton decays $l_i \ra l_jν_i\barν_j$, and the lepton flavor violating process $l_i\ra \bar{l}_j l_k l_h$ where $l_i= e,μ$ or $τ$. For the Standard Model (SM) background of $W\ra l_i ν_i$, we extended the one loop quantum correction to include effects of order $m_l^2/M_W^2$ and the Higgs mass dependence. We find that in general the split fermion scenarios give rise to a 4D effective Yukawa matrix of the Kaluza-Klein Higgs bosons is misaligned with respect to the fermion mass matrix. This holds true also for gauge bosons as well. This leads to decays of $l_i\ra \bar{l_j}l_k l_h$ at tree level and muonium antimuonium conversion. Interestingly the leptonic universality of $W$ boson decays are not affected at this level.

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We-Fu Chang, I-Lin Ho, John N. Ng. 2002-06-20. Lepton Universality, Rare Decays and Split Fermions. https://doi.org/10.1103/physrevd.66.076004

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