Isgur-Wise functions from the MIT bag model

The Isgur-Wise functions for the ground state to ground state semileptonic decays involvingb→c transitions are calculated from the (modified) MIT bag model. It is checked that the results for the decays \(\bar B \to Dl\bar v\) and \(\bar B \to D^* l\bar v\) agree well with experiment. Predictions for the decays \(\Lambda _b \to \Lambda _c l\bar v,\bar B_s \to D_s^* l\bar v\) and \(\bar B_s \to D_s^* l\bar v\) are given and discussed.     

Proton polarizability in the MIT bag model

The polarizability of the proton is calculated in a simplified MIT bag model and compared with an analysis of Compton scattering. Qualitative agreement is obtained for the sum of the electric and magnetic polarizabilities, which is found to be within 30% of the experiment.     

Properties of hybrid stars in an extended MIT bag model

The properties of hybrid stars are investigated in the framework of the relativistic mean field theory (RMFT) and an MIT bag model with density-dependent bag constant to describe the hadron phase (HP) and quark phase (QP), respectively. We find that the density-dependent B(p) decreases with baryon density p; this decrement makes the strange quark matter become more energetically favorable than ever, which makes the threshold densities of the hadron-quark phase transition lower than those of the original bag constant case. In this case, the hyperon degrees of freedom can not be considered. As a result, the equations of state of a star in the mixed phase (MP) become softer whereas those in the QP become stiffer, and the radii of the star obviously decrease. This indicates that the extended MIT bag model is more suitable to describe hybrid stars with small radii.     

Properties of hybrid stars in an extended MIT bag model

The properties of hybrid stars are investigated in the framework of the relativistic mean field theory （RMFT） and an MIT bag model with density-dependent bag constant to describe the hadron phase （HP） and quark phase （QP）, respectively. We find that the density-dependent B（p） decreases with baryon density p; this decrement makes the strange quark matter become more energetically favorable than ever, which makes the threshold densities of the hadron-quark phase transition lower than those of the original bag constant case. In this case, the hyperon degrees of freedom can not be considered. As a result, the equations of state of a star in the mixed phase （MP） become softer whereas those in the QP become stiffer, and the radii of the star obviously decrease. This indicates that the extended MIT bag model is more suitable to describe hybrid stars with small radii.     

Bose analogs of the MIT bag model of hadrons in coherent precession

It has recently been demonstrated that magnon condensation in the trap exhibits the phenomenon of self-localization [1]. When the number of magnons in the textural trap increases, they drastically modify the profile of the gap and highly increase its size. The trap gradually transforms from the initial harmonic one to the box with walls almost impenetrable for magnons. The resulting texture-free “cavity” filled with the magnon condensate wavefunction becomes the bosonic analog of the MIT bag, in which hadron is seen as a cavity surrounded by the QCD vacuum, in which the free quarks are confined in the ground or excited state. Here, we consider the bosonic analog of the MIT bag with quarks on the ground and excited levels.     

Electroweak properties of nucleons in the MIT bag model with approximate chiral symmetry

Zeitschrift für Physik C Particles and Fields - Corrections to magnetic moments, axial coupling constantg A and root mean square charge radii of nucleons, resulting from specific quark-pion...     

Recoil corrections to magnetic moments of octet baryons in the MIT bag model

The presence of certain recoil corrections in the determination of baryon magnetic moments is described and taken into account for the octet members. Inclusion of these recoil corrections makes the MIT bag model, even in its zeroth-order version, very appealing, if the sum of many other corrections is not important by comparison.     

Radiative transitions of baryons in the MIT bag

Resonance photoproduction is studied via the MIT bag model and comparison is made with a single quark transition SU(6)_θ analysis. Correspondence is found between the two pictures. The bag model predictions are shown to be in good qualitative agreement with experiment; however, specific numerical results are rather model dependent and in general less successful.     

Semileptonic decays of heavy to light mesons from an MIT bag model

Using the (modified) MIT bag model we calculated formfactors and decay widths for pseudoscalar-pseudoscalar and pseudoscalar-vector semileptonic decays of heavy to light mesons. We discuss the physical phenomena which are important in these processes and their influence on the measurable quantities. Our results are consistent with the available experimental data. A comparison with the results of other models is also given.Work supported by the KBN grant no. 2P30207607     

Magnetic moments of the strange baryons in the bag model

We break SU(3) symmetry in the bag model by giving the singlet quark a mass m. The magnetic moment ratios of the strange baryons are calculated and compared with exact SU(6) predictions and with experiment.     

Vacuum structure of a modified MIT bag

An alternative to introducing and subsequently renormalizing classical parameters in the expression for the vacuum energy of the MIT bag for quarks is proposed in the massless case by appealing to the QCD trace anomaly and scale separation due to asymptotic freedom. The explicit inclusion of gluons implies an unrealistically low separation scale. Received: 4 April 2000 / Published online: 6 July 2000     

Magnetic superconductors

The old problem of the coexistence of superconductivity and magnetism has obtained new interest since the discovery of the unusual magnetic and superconducting properties of some ternary compounds. In this report I want to discuss the influence of antiferromagnetic order on the superconducting state and, in particular, will compare different pairing approximations which have been proposed in the literature. Furthermore I will investigate the influence of fluctuations on the stability of the periodic spin structure and other superconducting phases at the onset of ferromagnetic order.     

Magnetic superconductors

Simultaneous occurence of magnetism and superconductivity in Mo₅SnGa_0.5S₆ has been reported by Alekseevskii, Dobrovol'skii and Tsebro. X-ray studies show that this results from two phase mixtures of Mo₃Sn_0.5S₄ and Mo₂Ga_0.5S₄ which have previously been reported to be superconducting and ferromagnetic respectively.     

Magnetic moments of the nucleon octet calculated in the cloudy bag model

The formalism of the cloudy bag model is used to calculate the pion coupling to the strange members of the nucleon octet (and delta decuplet). We then calculate the magnetic moments of all members of the octet, including lowest-order pionic corrections. Results are presented as a function of the radius of the bag, R, which is the only true free parameter of the model. Excellent agreement is obtained with experiment for bag radii ranging from 0.8 to 1.1 fm.