Herry J. Kwee

Phenomenology of the Pentaquark Antidecuplet

Abstract 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.

Phenomenology of Lorentz-conserving noncommutative QED

Recently a version of Lorentz-conserving noncommutative field theory (NCFT) has been suggested. The underlying Lie algebra of the theory is the same as that of Doplicher, Fredenhagen, and Roberts. In Lorentz-conserving NCFT the matrix parameter {theta}^{mu nu} which characterizes the canonical NCFTs is promoted to an operator {theta hat}^{mu nu} that transforms as a Lorentz tensor. In this paper, we calculate phenomenological consequences of the QED version of this theory by looking at various collider processes. In particular we calculate modifications to Moller scattering, Bhabha scattering, e^+e^- --> mu^+ mu^- and e^+e^- --> gamma gamma. We obtain bounds on the noncommutativity scale from the existing experiments at LEP and make predictions for what may be seen in future collider experiments.

Unusual high-energy phenomenology of Lorentz-invariant noncommutative field theories

It has been suggested that one may construct a Lorentz-invariant noncommutative field theory by extending the coordinate algebra to additional, fictitious coordinates that transform nontrivially under the Lorentz group. Integration over these coordinates in the action produces a four-dimensional effective theory with Lorentz invariance intact. Previous applications of this approach, in particular to a specific construction of noncommutative QED, have been studied only in a low-momentum approximation. Here we discuss Lorentz-invariant field theories in which the relevant physics can be studied without requiring an expansion in the inverse scale of noncommutativity. Qualitatively, we find that tree-level scattering cross sections are dramatically suppressed as the center-of-mass energy exceeds the scale of noncommutativity, that cross sections that are isotropic in the commutative limit can develop a pronounced angular dependence, and that nonrelativistic potentials (for example, the Coloumb potential) become nonsingular at the origin. We consider a number of processes in noncommutative QED that may be studied at a future linear collider. We also give an example of scattering via a four-fermion operator in which the noncommutative modifications of the interaction can unitarize the tree-level amplitude, without requiring any other new physics in the ultraviolet.

A naturally narrow positive-parity Θ +

We present a consistent color-flavor-spin-orbital wave function for a positive-parity

1/Nc Corrections in Meson-Baryon scattering

{\ensuremath{\Theta}}^{+}

Photoproduction of the \Theta^+ resonance on the nucleon in a Regge model

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

The pion form factor in AdS/QCD

{\ensuremath{\Theta}}^{+}

An identity on SU(2) invariants

lighter than its negative-parity counterpart. We consider decays of the

{pi}N{yields} multi-{pi}N scattering in the 1/N{sub c} expansion

{\ensuremath{\Theta}}^{+}

πN→multi-πNscattering in the1/Ncexpansion

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.