Improved Ke3 radiative corrections sharpen the Kμ2–Kl3 discrepancy

Abstract

The measurements of Vus in leptonic (Kμ2) and semileptonic (Kl3) kaon decays exhibit a 3σ disagreement, which could originate either from physics beyond the Standard Model or some large unidentified Standard Model systematic effects. Clarifying this issue requires a careful examination of all existing Standard Model inputs. Making use of a newly-proposed computational framework and the most recent lattice QCD results, we perform a comprehensive re-analysis of the electroweak radiative corrections to the Ke3 decay rates that achieves an unprecedented level of precision of 10−4, which improves the current best results by almost an order of magnitude. No large systematic effects are found, which suggests that the electroweak radiative corrections should be removed from the “list of culprits” responsible for the Kμ2–Kl3 discrepancy.

Neutron Stars with Baryon Number Violation, Probing Dark Sectors

“…[62,63]. Moreover, both electromagnetic and isospin corrections are also key to determining consistent values of |V us | from K 2 and K 3 decays [65,66], with the current scale factor of S = 2.7 [30] seemingly indicating the need for further theoretical and experimental work [67][68][69][70]. Here we focus on the V − A structure of neutron decay in the SM, and the concomitant ties between its observables, as this constrains the possibility that the neutron lifetime anomaly comes from new physics [35]-and we refer to Refs.…”

Full $K_{\ell 3}$ radiative corrections and implications on $|V_{us}|$

“…It is rather meaningless to copy everything from the existing literature, so most of the time we simply refer the reader to the notations, formulas and descriptions in specific sections of Ref. [24].…”

“…where the integration region D 3 is defined in Appendix A of Ref. [24], while the function H(a, b) is defined in Eq. (2.7) of the same reference.…”

“…In a follow-up work [20] we outlined an efficient approach for lattice Quantum Chromodynamics (QCD) to help fixing the large theory uncertainties in the K ℓ3 RC that originate from non-perturbative QCD, which was then partially put into practice [21]. With these new theory basis and lattice inputs, we improved the existing theory precision of the K e3 RC [22] by almost an order of magnitude [23,24], and presented an updated global analysis to the value of the top-row CKM matrix element |V us | extracted from semileptonic kaon decays [25]. This new analysis supports the current top-row CKM unitarity violation, and further sharpens a previously-observed discrepancy between the values of |V us | obtained from K ℓ3 and the leptonic kaon decay (K µ2 ) [9].…”

“…In Section III we outline the theory framework of the O(α) virtual corrections, most of them are similar to Refs. [23,24] except a novel and more rigorous treatment of the RCs to f − (t). In Section IV we discuss the bremsstrahlung contributions.…”