Strong Isospin Breaking in the Decay Constants of Heavy-Light Mesons from Local-Duality QCD Sum Rules

TL;DR

This paper investigates how small up-down quark mass differences affect the decay constants of heavy-light mesons using a specialized QCD sum rule approach, predicting a roughly 1 MeV difference for charmed and bottom mesons.

Contribution

It introduces a novel limit of QCD sum rules with an infinite Borel mass to analyze isospin breaking effects on meson decay constants.

Findings

Decay constants of charged and neutral heavy-light mesons differ by about 1 MeV.

The method provides a new way to quantify isospin breaking in QCD.

Results are relevant for precision tests of the Standard Model.

Abstract

We explore, by a rather peculiar limit of QCD sum rules subject to a Borel transformation (realized by allowing the related Borel mass parameter to approach infinity), how the small difference of the masses of up and down quark translates into the leptonic decay constants of pseudoscalar or vector heavy-light mesons. For the charmed and bottom mesons, we find that the decay constants of their lowest-lying charged and neutral representatives should differ by an amount of the order of 1 MeV.