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Chiral perturbation theory, the 1/N_c expansion and Regge behavior determine the structure of the lightest scalar meson Peláez Sagredo, José Ramón Pennington, M. R. Ruiz De Elvira Carrascal, Jacobo Wilson, D. J. ©2011 American Physical Society. M. R. P is grateful to Bob Jaffe for discussions about the issues raised at the start of this study. The authors (J. R. de E, M. R. P and D. J. W) acknowledge partial support of the EU-RTN Programme, Contract No. MRTN–CT-2006-035482, ‘‘Flavianet’’ for this work, while at the IPPP in Durham. D. J. W is grateful to the UK STFC for the award of a postgraduate studentship and to Jefferson Laboratory for hospitality while this work was completed. This work was supported in part by DOE Contract No. DE-AC05-06OR23177, under which Jefferson Science Associates, LLC, operates Jefferson Laboratory. The leading 1=N_c behavior of unitarized chiral perturbation theory distinguishes the nature of the ρ and the : The is a qq̅ meson, while the σ is not. However, semilocal duality between resonances and Regge behavior cannot be satisfied for larger N_c, if such a distinction holds. While the σ at N_c = 3 is inevitably dominated by its di-pion component, unitarized chiral perturbation theory also suggests that as N_c increases above 6–8, the σ may have a subdominant qq̅ fraction up at 1.2 GeV. Remarkably this ensures semilocal duality is fulfilled for the range of Nc ≤ 15–30, where the unitarization procedure adopted applies. 2023-06-20T04:01:19Z 2023-06-20T04:01:19Z 2011-11-09 journal article 1550-7998 10.1103/PhysRevD.84.096006 https://hdl.handle.net/20.500.14352/44814 http://dx.doi.org/10.1103/PhysRevD.84.096006 http://journals.aps.org/ eng MRTN–CT-2006-035482 DE-AC05-06OR23177 open access Amer Physical Soc