Pole analysis on unitarized $SU(3)\times SU(3)$ one loop $\chi$PT amplitudes

TL;DR

This paper investigates meson resonances using unitarized chiral perturbation theory, identifying the nature of various scalar and vector mesons through pole analysis and N_c trajectories.

Contribution

It provides a detailed pole analysis of coupled channel amplitudes in unitarized SU(3) chiral perturbation theory, clarifying the nature of several meson resonances.

Findings

K*(892) and rho(770) are confirmed as Breit-Wigner resonances.

f0(980) is identified as a molecular state.

a0(980) maintains a twin pole structure despite N_c variations.

Abstract

We analyze $\pi\pi-K\bar{K}$ and $\pi\eta-K\bar{K}$ couple channel [1,1] matrix Pad\'e amplitudes of $SU(3)\times SU(3)$ chiral perturbation theory. By fitting phase shift and inelasticity data, we determine pole positions in different channels ($f_0(980)$, $a_0(980)$,$f_0(600)$, $K_0^*(800)$, $K^*(892)$, $\rho(770)$) and trace their $N_c$ trajectories. We stress that a couple channel Breit--Wigner resonance should exhibit two poles on different Riemann sheets and meet each other on the real axis when $N_c=\infty$. Poles are hence classified using this criteria and we conclude that $K^*(892)$ and $\rho(770)$ are unambiguous Breit--Wigner resonances. For scalars the situation is much less clear. We find that $f_0(980)$ is a molecular state rather than a Breit--Wigner resonance, while $a_0(980)$, though behaves oddly when varying $N_c$, does maintain a twin pole structure.