We consider the mass splittings and strong decays of members of the lowest-lying pentaquark multiplet, which we take to be a parity-odd antidecuplet. We derive useful decompositions of the quark model wave functions that allow for easy computation of color-flavor-spin matrix elements. We compute mass splittings within the antidecuplet including spin-color and spin-isospin interactions between constituents and point out the importance of hidden strangeness in rendering the nucleon-like states heavier than the S = 1 state. Using recent experimental data on a possible S = 1 pentaquark state, we make decay predictions for other members of the antidecuplet.

We extend a recent numerical calculation of the pion electromagnetic form factor F π (Q 2 ) in holographic QCD to study two important issues regarding the behavior of fields in the bulk. First, we show that using a chiral symmetry-breaking field formally satisfying the boundary conditions of the "soft-wall" model changes numerical results very little from the earlier calculation that ignores these constraints. Second, we use a background field that interpolates between "hard-wall" and "soft-wall" models to obtain an improved model that reproduces the desirable phenomenological features of both. In all cases, F π for large Q 2 is shallower than data, an effect that can be cured by relaxing the fit to one of the static observables, particularly the decay constant f π .

We present a consistent color-flavor-spin-orbital wave function for a positive-parity ⌰ ϩ that naturally explains the observed narrowness of the state. The wave function is totally symmetric in its flavor-spin part and totally antisymmetric in its color-orbital part. If flavor-spin interactions dominate, this wave function renders the positive-parity ⌰ ϩ lighter than its negative-parity counterpart. We consider decays of the ⌰ ϩ and compute the overlap of this state with the kinematically allowed final states. Our results are numerically small. We note that dynamical correlations between quarks are not necessary to obtain narrow pentaquark widths.The recent discovery of pentaquark states ͓1-7͔ has stimulated a significant body of theoretical ͓8-37͔ and experimental research. Pentaquarks are baryons whose minimal Fock components consist of four quarks and an antiquark. The first observed pentaquark was the ⌰ ϩ (1540) with strangeness Sϭϩ1, and with quark content ududs. More recently, the NA49 Collaboration ͓7͔ has reported a narrow ⌶ 5ϪϪ (1860) baryon with SϭϪ2 and quark content dsdsū , together with evidence for its isoquartet partner ⌶ 5 0 at the same mass.The existence of the ⌰ ϩ , as well as its flavor quantum numbers, seems to be well established ͑for a different view, see Ref.͓38͔͒. If the ⌰ ϩ were a member of an isovector or isotensor multiplet, then one would expect to observe its doubly charged partner experimentally. The SAPHIR Collaboration ͓4͔ searched for a ⌰ ϩϩ in ␥p→⌰ ϩϩ K Ϫ →pK ϩ K Ϫ , with negative results. They concluded that the ⌰ ϩ is an isosinglet and hence a member of a pentaquark antidecuplet. All but one theoretical paper ͓8͔ treat the ⌰ ϩ as an isosinglet.The spin and parity quantum numbers of the ⌰ ϩ have yet to be determined experimentally. The spin of ⌰ ϩ is taken to be 1/2 by all theory papers to our knowledge and various estimates show that spin-3/2 pentaquarks must be heavier ͓9͔. A more controversial point among theorists is the parity of the state. For example, QCD sum rule calculations ͓10͔, quenched lattice QCD ͓11͔, and a minimal constituent quark treatment by the present authors ͓12͔ predict that the lightest ⌰ ϩ is a negative-parity isosinglet. All chiral soliton papers ͓13,14͔, some correlated quark models ͓15,16͔, and some works within the constituent quark model ͓17-19͔ including a second work by the present authors ͓20͔, predict the lightest ⌰ ϩ pentaquark as a positive-parity isosinglet.The photoproduction and the pion-induced production cross sections of the ⌰ ϩ were studied in ͓21͔. It was shown in both cases that the production cross sections for a negative-parity ⌰ ϩ are much smaller than those for the positive-parity state ͑for a given ⌰ ϩ width͒. In Ref. ͓21͔, results for the ⌰ ϩ production cross section in photon-proton reactions were compared with estimates of the cross section based on data obtained by the SAPHIR Collaboration ͓4͔, and odd-parity pentaquark states were argued to be disfavored.Here, we present new results following from a consistent treatment of t...