Structure of theΛ(1405)baryon resonance from its largeNcbehavior

Abstract

We study the behavior with the number of colors (Nc) of the two poles associated to the Λ(1405) resonance obtained dynamically within the chiral unitary approach. The leading order chiral mesonbaryon interaction manifests a nontrivial Nc dependence for SU(3) baryons, which gives a finite attractive interaction in some channels in the large Nc limit. As a consequence, the SU(3) singlet (KN ) component of the Λ(1405) survives in the large Nc limit as a bound state, while the other components dissolve into the continuum. The Nc dependence of the decay widths shows different behavior from the general counting rule for a qqq state, indicating the dynamical origin of the two poles for the Λ(1405) resonance. PACS numbers: 11.15.Pg, 14.20.Jn, 11.30.Rd The quest for the understanding of the nature of the hadronic spectrum is one of the most challenging issues in particle physics. Especially the structure of hadronic resonances is one of the cornerstones in this field. Recently it has been suggested that multiquark and/or hadronic components of some resonances in intermediate energies prevail over the simple mesonic qq and baryonic qqq components. For instance, the light scalar mesons have been investigated in the four-quark picture [1], in the mesonic molecular picture [2], and in lattice QCD [3]. Methods to clarify the internal structure of the hadrons are called for. This is one of the main aims of the present work, in the baryonic sector.Despite the success of QCD as the theory for the strong interactions, the inherent confinement properties of quarks and gluons make its direct applicability to investigate the hadron structure far from being feasible. One of the most powerful tools to investigate the properties of hadrons are the effective theories of QCD, such as chiral perturbation theory (ChPT) [4] and its recent development, chiral unitary approach [2,5,6,7]. ChPT provides hadronic interactions based on a systematic lowenergy expansion. The nonperturbative resummation of the low-energy interactions required by the unitarity condition leads to the success of the chiral unitary approaches in a variety of hadron scatterings with many hadronic resonances being dynamically generated.It is particularly interesting that the Λ(1405) is well reproduced in the chiral unitary approach as a dynamically generated resonance in the s-wave meson-baryon scattering with strangeness S = −1 and isospin I = 0 [5,6,7]. This finding unveils the structure of the Λ(1405) as a superposition of two states [6,8], which have been studied both theoretically and experimentally [9]. The structure of the Λ(1405) has a large impact for the study of thē KN interaction [10], which is eventually important for the study of the kaonic nuclei and kaon condensation in the neutron star [11]. The works based on the chiral unitary approach have shed new light on the understanding of the nature of the Λ(1405) resonance, reinforcing the dynamical or "molecular" origin versus the qqq picture.The expansion in the inverse of the number of colors, 1/N c , is a...

Charmed and strange baryon resonances with heavy-quark spin symmetry

“…Note that SU(3) WT counterpart in some channels also scale as O(1) because the coupling strength for some channels behaves as O(N C ), which compensates O(1/N C ) coming from the square of the meson decay constant [65]. However, the WT interaction behaves as O(1/N C ) within the 120 and 4752 baryon-meson spaces.…”

Λc(2595)resonance as a dynamically generated state: The compositeness condition and the largeNcevolution

“…Such corrections have been taken into account in the SU(3) chiral study of the Λ(1405) in Refs. [57,58], as well as in the study of negative parity s-wave resonances carried out in [55,56], where a SU(2N F ) SF extension of the chiral SU(3) WT interaction for an arbitrary number of flavors and colors is derived. In the present exploratory work on the Λ c (2595), we will present N c > 3 results for the chiral two coupled-channel scenario [12], and only in the strict N c → ∞ limit, in the case of the SU(6)×HQSS model [15,16].…”

“…Another approach 2 to probe the dominant component of a hadronic state is to study the N c dependence of the poles associated to resonances that appear in the unitarized meson-meson [45][46][47][48][49][50][51][52][53][54] or meson-baryon [55][56][57][58] scattering amplitudes, being N c the number of colors of quarks. The 1/N c expansion [59][60][61][62][63][64] is valid for the whole energy region and makes specific predictions for qq and qqq states.…”

Topics in low-energy QCD with strange quarks

“…The Λ(1405) with isospin I = 0 emerges from coupled-channels dynamics as a quasiboundKN state embedded in the πΣ continuum. A characteristic feature of the chiral SU (3) coupled-channels approach is the appearance of two poles in the T matrix (see [7] for a review and refs. therein).…”

“…The threshold points indicating the real and imaginary parts of the corresponding scattering length are constrained by the SIDDHARTA kaonic hydrogen measurement [5]. Upper panel: two-poles scenario of coupledKN and πΣ channels [7].…”