Where are the missing members of the baryon antidecuplet?

We analyze what consequences has the observation of exotic pentaquark baryons on the location of the non-exotic baryons belonging to the antidecuplet. We suggest that there must be a new nucleon state at 1650-1690 MeV and a new Sigma baryon at 1760-1810 MeV.Comment: 5 pages, 1 figure. Missing reference adde

Semi-spheroidal Quantum Harmonic Oscillator

A new single-particle shell model is derived by solving the Schr\"odinger equation for a semi-spheroidal potential well. Only the negative parity states of the $Z(z)$ component of the wave function are allowed, so that new magic numbers are obtained for oblate semi-spheroids, semi-sphere and prolate semi-spheroids. The semi-spherical magic numbers are identical with those obtained at the oblate spheroidal superdeformed shape: 2, 6, 14, 26, 44, 68, 100, 140, ... The superdeformed prolate magic numbers of the semi-spheroidal shape are identical with those obtained at the spherical shape of the spheroidal harmonic oscillator: 2, 8, 20, 40, 70, 112, 168 ...Comment: 4 pages, 3 figures, 1 tabl

Spectrum of the Y=2 Pentaquarks

By assuming a mass formula for the spectrum of the Y=2 pentaquarks, where the chromo-magnetic interaction plays a main role, and identifying the lightest state with the Theta^+(1540), we predict a spectrum in good agreement with the few I=0 and I=1 candidates proposed in the past.Comment: 12 pages, 4 figures, LaTe

Some (further) Comments on the Theta(1540) Pentaquark

Additional broader I=0 states in the KN channel near $\Theta^+$(1540) are expected in many models, making the absence of any signature in the K$^+$-deuteron scattering data even more puzzling. In an ideal "three-body" picture the $\Theta$ is viewed as two compact ud(1)ud(2) $\bar{3}$ color diquarks and an $\bar{s}$ quark. A "QCD-type" inequality involving $m(\Theta^+), m(\Lambda)$, the mass of the $\Lambda(1/2^-)$ L=1 excitation and that of a new I=0 tetraquark vector meson then follows. The inequality suggests a very light new vector meson, and is violated. We note that "associated production" of the pentaquark with another quadriquark or anti-pentaquark may be favored. This along with some estimates of the actual production cross sections suggest that the $\Theta$ can be found in BaBar or Belle e$^+$-e$^-$ colliders.Comment: 6 page

Light-Front Approach for Heavy Pentaquark Transitions

Assuming the two diquark structure for the pentaquark state as advocated in the Jaffe-Wilczek model, there exist exotic parity-even anti-sextet and parity-odd triplet heavy pentaquark baryons. The theoretical estimate of charmed and bottom pentaquark masses is quite controversial and it is not clear whether the ground-state heavy pentaquark lies above or below the strong-decay threshold. We study the weak transitions of heavy pentaquark states using the light-front quark model. In the heavy quark limit, heavy-to-heavy pentaquark transition form factors can be expressed in terms of three Isgur-Wise functions: two of them are found to be normalized to unity at zero recoil, while the third one is equal to 1/2 at the maximum momentum transfer, in accordance with the prediction of the large-Nc approach or the quark model. Therefore, the light-front model calculations are consistent with the requirement of heavy quark symmetry. Numerical results for form factors and Isgur-Wise functions are presented. Decay rates of the weak decays Theta_b+ to Theta_c0 pi+ (rho+), Theta_c0 to Theta+ pi- (rho-), Sigma'_{5b}+ to Sigma'_{5c}0 pi+ (rho+) and Sigma'_{5c}0 to N_8+ pi- (rho-) with Theta_Q, Sigma'_{5Q} and N_8 being the heavy anti-sextet, heavy triplet and light octet pentaquarks, respectively, are obtained. For weakly decaying Theta_b+ and Theta_c0, the branching ratios of Theta_b+ to Theta_c0 pi+, Theta_c0 to Theta+ pi- are estimated to be at the level of 10^{-3} and a few percents, respectively.Comment: 33 pages, 3 figures, version to be published in Phys. Rev.

Nonquasiparticle states in half-metallic ferromagnets

Anomalous magnetic and electronic properties of the half-metallic ferromagnets (HMF) have been discussed. The general conception of the HMF electronic structure which take into account the most important correlation effects from electron-magnon interactions, in particular, the spin-polaron effects, is presented. Special attention is paid to the so called non-quasiparticle (NQP) or incoherent states which are present in the gap near the Fermi level and can give considerable contributions to thermodynamic and transport properties. Prospects of experimental observation of the NQP states in core-level spectroscopy is discussed. Special features of transport properties of the HMF which are connected with the absence of one-magnon spin-flip scattering processes are investigated. The temperature and magnetic field dependences of resistivity in various regimes are calculated. It is shown that the NQP states can give a dominate contribution to the temperature dependence of the impurity-induced resistivity and in the tunnel junction conductivity. First principle calculations of the NQP-states for the prototype half-metallic material NiMnSb within the local-density approximation plus dynamical mean field theory (LDA+DMFT) are presented.Comment: 27 pages, 9 figures, Proceedings of Berlin/Wandlitz workshop 2004; Local-Moment Ferromagnets. Unique Properties for Moder Applications, ed. M. Donath, W.Nolting, Springer, Berlin, 200