Decay Constants of the Heavy-Light Mesons $D^{(*)}$ and $B^{(*)}$: Isospin Breaking

TL;DR

This paper uses QCD sum rules to analyze the decay constants of heavy-light mesons, focusing on isospin-breaking effects caused by up and down quark mass differences, and compares results with previous studies.

Contribution

It reconstructs the quark-mass dependence of effective thresholds in QCD sum rules to study isospin-breaking effects on meson decay constants.

Findings

Good agreement with previous studies for most mesons.

Significant disagreement with lattice-QCD predictions for B mesons.

Highlights the impact of up-down quark mass differences on decay constants.

Abstract

QCD sum rules are analytic predictions of hadron observables from quantum chromodynamics. In the so-called local-duality limit of their Borel-transformed form, all nonperturbative contributions are encompassed by just a single quantity, an effective threshold beyond which, by assumption, all hadronic contributions are reliably described by perturbative QCD. Reconstructing its quark-mass dependence enables us to investigate the differences of the leptonic decay constants of heavy-light mesons effectuated by the tiny isospin-violating discrepancy of the masses of up and down quarks. By and large, our findings enjoy excellent agreement with the outcomes of earlier studies, the only exception being a lattice-QCD prediction for the $B$ mesons, where we find dramatic disagreement.