Belle II Constraints on the Non-Minimal Universal Extra Dimensional Model

Abstract

Recent measurements by the Belle II Collaboration report a branching ratio for the decay $B^+\to K^+ ν\barν$ with a 3.5$σ$ significance and deviating by 2.7$σ$ from Standard Model expectation. In this article, we interpret this experimental result through the lens of a Non-minimal Universal Extra Dimensional model, where the mass profiles and interactions among various Kaluza-Klein states differ remarkably from those in the minimal scenario. Our analysis indicates that, according to the model's parameters, the lower limit on the inverse of the compactification radius has been elevated to approximately 900 GeV. In contrast, conducting the same analysis within the model variant in which all boundary terms are nullified does not permit the determination of a lower bound on the inverse compactification radius.