Use and misuse of ChPT in the heavy-light systems

TL;DR

This paper evaluates the applicability of chiral perturbation theory (ChPT) to heavy-light meson systems, highlighting limitations and proposing conditions under which certain ChPT forms remain valid for lattice QCD extrapolations.

Contribution

It critically assesses the validity of standard and heavy-meson ChPT in heavy-light systems, especially considering recent experimental findings and the impact of positive parity states.

Findings

Standard ChPT with Nf=3 is not suitable for lattice extrapolations.

HMChPT with Nf=2 remains valid for pions lighter than 350 MeV.

Positive parity states influence the chiral behavior of heavy-light mesons.

Abstract

We discuss the range of validity of ChPT when applied to the systems of heavy-light mesons. Having in mind the recent experimental evidence according to which the heavy-light scalar and axial states are closer to the ground states than anticipated, we revisited the prediction for the chiral behavior of the B-Bbar mixing amplitude and examined the impact of nearness of the positive parity states. We conclude that the standard ChPT expressions with Nf=3 light flavours are not useful in guiding the extrapolation of hadronic quantities computed on the lattice. Instead those derived in HMChPT with Nf=2, i.e., including only the pion loops, are still adequate as long as they are applied to the pions lighter than 350 MeV, or the quarks lighter than a third of the physical strange quark mass.