H. Høgaasen

Chromomagnetic mechanism for the X(3872) resonance

The chromomagnetic interaction, with proper account for flavor-symmetry breaking, is shown to explain the mass and coupling properties of the X(3872) resonance as a J{sup PC}=1{sup ++} state consisting of a heavy quark-antiquark pair and a light one. It is crucial to introduce all the spin-color configurations compatible with these quantum numbers and diagonalize the chromomagnetic interaction in this basis. This approach thus differs from the molecular picture DD* and from the diquark-anti-diquark picture.

Chromomagnetism, flavour symmetry breaking and S-wave tetraquarks

The chromomagnetic interaction, with full account for flavour-symmetry breaking, is applied to S-wave configurations containing two quarks and two antiquarks. Phenomenological implications are discussed for light, charmed, charmed and strange, hidden-charm and double-charm mesons, and extended to their analogues with beauty.

Strong and electromagnetic decays of excited heavy mesons

Abstract. We discuss a model for heavy mesons where the light quark (u or d) moves in the colour-electric field from a heavy quark (c or b) placed in the center of a bag. We calculate energy spectra for pionic and photonic transitions from excited states. The transition amplitudes and the branching ratios between electromagnetic and pionic transitions compare favorably with the limited amount of known experimental data.

Bag model with residual interaction for the quarks

Abstract We propose a modified version of the MIT bag in which the quarks are subject to a central potential. As in other models, the continuity of the axial current is assured by introducing a pionic cloud surrounding the bag, but it is no longer necessary to allow the pion field to penetrate the bag to obtain reasonable values of the axial charge, the magnetic moment and the charge radius of the nucleon. The magnetic moments of the hyperons are also well described.

Recoil Corrected Bag Model Calculations for Semileptonic Weak Decays

We develop recoil corrections to various bag model results for strangeness changing weak decay amplitudes. It is shown that the spurious reference frame dependence of earlier calculations is reduced. The second class currents are generally less important than obtained by calculations in the static approximation. Finally, theoretical results are compared to observations. The agreement is quite good, although the values for the Cabibbo angle obtained by fits to the decay rates are somewhat too large.

Hidden colour and the isobar content of the deuteron

We show how experiments concerning the isobar content of the deuteron that apparently are contradicitng each other can be reconciled by the quark model with hidden colour.

Two-electron atoms, ions, and molecules

The quantum mechanics of two-electron systems is reviewed, starting with the ground state of the helium atom and heliumlike ions with central charge Z. The case of Z≥2 is rather straightforward. In contrast, for negative hydrogen ion with Z=1, the stability of H− cannot be achieved using a product of individual electron wavefunctions and requires explicit account of the anticorrelation among the two electrons. The wavefunction proposed by Chandrasekhar is revisited, where the permutation symmetry is first broken and then restored by a counterterm. More difficult problems can be studied using the same strategy such as the stability of hydrogenlike ions for any value of the proton-to-electron mass ratio M/m, the energy of the lowest spin-triplet state of helium and heliumlike ions, and the stability of the doubly excited hydrogen ion with unnatural parity. The positronium molecule, which was predicted years ago and discovered recently, can also be shown to be stable against spontaneous dissociation. Emphasi...

Nucleon resonances and the quark model

Abstract We study the level ordering of the nucleon resonances in the non-relativistic quark model. With any plausible phenomenological potential, the orbital excitation with negative parity always turns out to have the lowest mass contrary to the experimental situation where the Roper resonance with positive parity comes first.

Isovector and hidden-beauty partners of the X(3872)

Article history: The isovector partners of the X(3872), recently found at BES III, Belle and CLEO-c were predicted in a simple model based on the chromomagnetic interaction among quarks. The extension to the hidden- beauty sector is discussed.

Isgur-Wise functions for confined light quarks in a colour electric potential

We explore the influence on the Isgur-Wise function of the colour electric potential between heavy and light quarks in mesons. It is shown that in bag models, its inclusion tends to restore light quark flavour symmetry relative to the MIT bag predictions, and that relative to this model it flattens the Isgur-Wise function. Results compare very well with observations.