Are the CKM anomalies induced by vector-like quarks? Limits from flavor changing and Standard Model precision tests

A bstract Recent high precision determinations of V us and ud indicate towards anomalies in the first row CKM matrix. Namely, determination from beta decays kaon imply a violation unitarity at about 3 ? level. Moreover, there is tension between obtained leptonic K? 2 semileptonic K? decays. These discrepancies can be explained if exist extra vector-like quarks TeV scale, which have large enough mixings with lighter quarks. In particular, weak singlets thought as solution to problem an doublet principle resolve all tensions. The implications this kind are examined against flavour changing phenomena SM tests. We consider separately effects down-type isosinglet, up-type isosinglet isodoublet containing both up down type, determine available parameter spaces for each case. find that experimental constraints on flavor become more stringent larger masses, so species should masses no than few TeV. only one type multiplet cannot entirely explain discrepancies, some their combination required, e.g. two isodoublet, or (up type) isosinglet. show these scenarios testable future experiments. responsible anomalies, then least them found scale TeV, anomalous isospin violating Z -boson couplings light detected hadronic decay rate improved by factor so.