Precision dispersive approaches versus unitarized chiral perturbation theory for the lightest scalar resonances σ/f0(500) and κ/K0∗(700)

• Published in: The European physical journal. ST, Special topics Vol. 230; no. 6; pp. 1539 - 1574
• Main Authors: Peláez, José R., Rodas, Arkaitz, Ruiz de Elvira, Jacobo
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.07.2021; Springer Nature B.V
• Subjects: Atomic; Chiral dynamics; Classical and Continuum Physics; Condensed Matter Physics; Dispersion; Materials Science; Measurement Science and Instrumentation; Mesons; Molecular; Optical and Plasma Physics; Parameters; Perturbation theory; Physics; Physics and Astronomy; Review; Topics in Light-Quark Physics
• DOI: 10.1140/epjs/s11734-021-00142-9
• ISSN: 1951-6355

For several decades, the σ / f 0 ( 500 ) and κ / K 0 ∗ ( 700 ) resonances have been subject to long-standing debate. Both their existence and properties were controversial until very recently. In this tutorial review, we compare model-independent dispersive and analytic techniques versus unitarized Chiral Perturbation Theory, when applied to the lightest scalar mesons σ / f 0 ( 500 ) and κ / K 0 ∗ ( 700 ) . Generically, the former have settled the long-standing controversy about the existence of these states, providing a precise determination of their parameters, whereas unitarization of chiral effective theories allows us to understand their nature, spectroscopic classification and dependence on QCD parameters. Here we review in a pedagogical way their uses, advantages and caveats.