Abstract
We discuss a list of possible light gauge boson interpretations for the long- standing experimental anomaly in (g − 2)μ and also recent anomalous excess in KL→ π0 + (invisible) events at the J-PARC KOTO experiment. We consider two models: i) Lμ− Lτ gauge boson with heavy vector-like quarks and ii) (Lμ− Lτ) + є(B3− Lτ ) gauge boson in the presence of right-handed neutrinos. When the light gauge boson has mass close to the neutral pion in order to satisfy the Grossman-Nir bound, the models successfully explain the anomalies simultaneously while satisfying all known experimental constraints. We extensively provide the future prospect of suggested models.
Highlights
If we assume these events come from π0ννdecay channel
2.1 Decay widths and experimental limits We focus on the effective flavour changing neutral current (FCNC) couplings of X boson
In the two subsections, we i) introduce heavy vector-like quarks (VLQs) to enhance the coupling between Lμ − Lτ gauge boson and Standard Model (SM) quarks, especially for tree-level FCNC, or ii) consider a (Lμ−Lτ )+ (B3−Lτ ) gauge boson which dominantly contribute to the down-type FCNC at the loop-level
Summary
Where first term is relevant to the KOTO process, and both terms are correlated to each other under these two model frameworks that will be discussed in this work. We set mX m0π to evade the stringent constraint from Br(K+ → π+ + invisible) decay, which is suffered from overwhelming K+ → π+π0 background It can satisfy other upper bounds from current observations of rare K and B meson FCNC decays. Explaining the KOTO event excess through KL → π0 + X with light gauge boson mX m0π is still in accordance with other present experimental constraints. Further more, if this X boson carries the muonic force with coupling strength of O(10−3), it can explain the (g − 2)μ anomaly [36]
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