Chiral symmetry and its spontaneous breaking play an important role both in the light
hadron and heavy hadron systems. The chiral perturbation theory (χ PT) is the low energy …

The existence and properties of the sigma meson have been controversial for almost six
decades, despite playing a central role in the spontaneous chiral symmetry of QCD or in the …

We obtain a reliable cosmological bound on the axion mass ma by (1) deriving the
production rate directly from pion-pion scattering data, which overcomes the breakdown of …

A bstract We revisit from a modern bootstrap perspective the longstanding problem of
solving QCD in the large N limit. We derive universal bounds on the effective field theory of …

We review the structure of Roy–Steiner equations for pion–nucleon scattering, the solution
for the partial waves of the t-channel process π π→ N ̄ N, as well as the high-accuracy …

We improve our description of π π scattering data by imposing additional requirements on
our previous fits, in the form of once-subtracted Roy-like equations, while extending our …

Glueballs, hybrids and multiquark states are predicted as bound states in models guided by
quantum chromo dynamics (QCD), by QCD sum rules or QCD on a lattice. Estimates for the …

We demonstrate that near the threshold, the π π scattering amplitude contains a pole with
the quantum numbers of the vacuum—commonly referred to as the σ—and determine its …

We determine the energy-dependent amplitude for elastic π π P-wave scattering in isospin-1
by computing part of the discrete energy spectrum of QCD in finite cubic boxes. We observe …

We use our latest dispersive analysis of π π scattering data and the very recent K ℓ 4
experimental results to obtain the mass, width, and couplings of the two lightest scalar …