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H. Walliser

Publications and source records attributed to H. Walliser.

11 recordsLinked to original sources
arXiv2005

Bound State versus Collective Coordinate Approaches in Chiral Soliton Models and the Width of the $Θ^+$ Pentaquark

We thoroughly compare the bound state and rigid rotator approaches to three--flavored chiral solitons. We establish that these two approaches yield identical results for the baryon spectrum and kaon--nucleon $S$--matrix in the limit that the number of colors ($N_C$) tends to infinity. After proper subtraction of the background phase shift the bound state approach indeed exhibits a clear resonance behavior in the strangeness $S=+1$ channel. We present a first dynamical calculation of the widths of the $Θ^+$ and $Θ^*$ pentaquarks for finite $N_C$ in a chiral soliton model.

hep-ph↗
arXiv2003

Exotic baryon states in topological soliton models

The novel observation of an exotic strangeness S=+1 baryon state at 1.54 GeV will trigger an intensified search for this and other baryons with exotic quantum numbers. This state was predicted long ago in topological soliton models. We use this approach together with the new datum in order to investigate its implications for the baryon spectrum. In particular we estimate the positions of other pentaquark and septuquark states with exotic and with non-exotic quantum numbers.

hep-ph↗
arXiv2001

Comment on "Reverse Brazil Nut Problem: Competition between Percolation and Condensation"

In a recent paper [Phys. Rev. Lett. 86, 3423 (2001)] D.C. Hong, P.V. Quinn and S. Luding investigated the Brazil nut problem and the reverse Brazil nut problem at fixed temperature. A new condensation versus percolation driven segregation mechanism was put forward, which has attracted much attention in the press. The proposed mechanism is incorrect.

cond-mat.stat-mech↗
arXiv2001

Effective action for quantum Hall skyrmions

Recently, an O(3) type of effective action was proposed for the quantum Hall ferromagnet, which accounts for bag formation observed in microscopic Hartree- Fock calculations. We apply this action in the soliton sector and compare with Hartree-Fock results. We find good agreement over the whole parameter range where skyrmions exist. The standard minimal O(3) model cannot explain the bag and has further shortcomings connected with that fact.

cond-mat.mes-hall↗
arXiv1999

The Casimir energy of skyrmions in the 2+1-dimensional O(3)-model

One-loop quantum corrections to the classical vortices in 2+1 dimensional O(3)-models are evaluated. Skyrme and Zeeman potential terms are used to stabilize the size of topological solitons. Contributions from zero modes, bound-states and scattering phase-shifts are calculated for vortices with winding index n=1 and n=2. For both cases the S-matrix shows a pronounced series of resonances for magnon-vortex scattering in analogy to the well-established baryon resonances in hadron physics, while vortices with n>2 are already classically unstable against decay. The quantum corrections destabilize the classically bound n=2 configuration. Approximate independence of the results with respect to changes in the renormalization scale is demonstrated.

hep-ph↗
arXiv1999

Soliton formation in the Nambu-Jona-Lasinio model

The soliton formation is considered in the Nambu-Jona-Lasinio model with local four quark interaction and various schemes to regularize the energy contribution of the polarized vacuum. No additional constraints are admitted in order to stabilize the soliton. While solitons are unstable in the proper-time regularized version the three momentum cut-off regularization apparently is more appropriate. Using a semi-classical approach multi-quark solitons obtained from that scheme are discussed. However, no self-consistent non-trivial unit baryon number configuration has been found. We also study a renormalizable extension of the model. In this case no stable multi-quark solitons are obtained within the semi-classical approach.

nucl-th↗
arXiv1997

1-loop corrections to the SU(3) symmetric chiral soliton

Masses of the SU(3) chiral soliton in tree approximation turn out at much too high energies typically around 2 GeV. It is shown that 1-loop corrections reduce this value drastically with results in the region of the empirical nucleon mass.

hep-ph↗
arXiv1997

Hot Nucleons in Chiral Soliton Models

Chiral lagrangians as effective field theories of QCD are most suitable for the study of nucleons in a hot pion gas because they contain pions and also baryons as solitons of the same action. The semiclassical treatment of the soliton solutions must be augmented by pionic fluctuations which requires renormalisation to 1-loop, and finite temperatures do not introduce new ultraviolet divergencies and may easily be considered. Alternatively, a renormalisation scheme based on the renormalisation group equation at finite temperature comprises and extends the rigorous results of chiral perturbation theory and renders the low energy constants temperature-dependent which allows the construction of temperature-dependent solitons below the critical temperature. The temperature-dependence of the baryon energy and the pion-nucleon coupling is studied. There is no simple scaling law for the temperature-dependence of these quantities.

hep-ph↗
arXiv1996

Electro-excitation amplitudes of the Delta-isobar in the Skyrme model

Electro magnetic transition form factors for the excitation of the Delta33-resonance are evaluated in the Skyrme model. They crucially rely on rotationally induced deformations of the hedgehog soliton which are suppressed by two N_C-orders as compared to the leading parts of the isovector current. Partial photon coupling through vector mesons is included in a schematic way. Recoil corrections are approximated by a boost to the equal-velocity frame. The results for the photodecay amplitudes agree with experimental numbers and the shapes of M1, E2, C2 - transition form factors show essential features as observed in electro-excitation experiments.

hep-ph↗