F. Myhrer

The baryon masses and the chiral quark bag model

Abstract The baryon octet and decuplet mass spectrum is calculated within the chiral bag model. To zeroth order, this reduces to the MIT bag model. To the next order, baryon self-energies coming from coupling to pions enter. These are about as important as terms from gluon exchange; their inclusion decreases somewhat the colour coupling constant α s needed to fit the empirical baryon splittings. We show that mass splittings resulting from our calculation obey well the Gell-Mann-Okubo mass formulae, although certain terms included would individually violate them. Also the absolute value of the Λ magnetic moment comes out very well. In our theory, part of the mass splitting is a manifestation of the spontaneous breaking of chiral symmetry in the region outside the bag, resulting from the Goldstone pion which is introduced to conserve the axial current at the bag boundary. With inclusion of pionic interactions, the phenomenological zero-point energy introduced through the constant Z 0 in the MIT work is much smaller in order to fit the empirical masses, the pionic self-energies replacing most of it.

Neutrino-deuteron reactions at solar neutrino energies

Abstract In interpreting the SNO experiments, accurate estimates of the νd reaction cross sections are of great importance. We improve the previous estimates of our group by updating some of its inputs and by taking into account the results of a recent effective-field-theoretical calculation. The new cross sections are slightly (∼1%) larger than the previously reported values. It is shown to be reasonable to assign 1% uncertainty to the νd cross sections reported here; this error estimate does not include radiative corrections, for which we refer to the literature.

Chiral perturbation approach to the p p ---> p p pi0 reaction near threshold

The usual theoretical treatments of the near-threshold

The μ−d capture rate in effective field theory

pp \rightarrow pp\pi^0

Effective kaon mass in baryonic matter and kaon condensation

reaction are based on various phenomenological Lagrangians. In this work we examine the relationship between these approaches and a systematic chiral perturbation method. Our chiral perturbation calculation indicates that the pion rescattering term should be significantly enhanced as compared with the traditional phenomenological treatment, and that this term should have substantial energy and momentum dependence. An important consequence of this energy-momentum dependence is that, for a representative threshold kinematics and within the framework of our semiquantitative calculation, the rescattering term interferes destructively with the Born-term in sharp contrast to the constructive interference obtained in the conventional treatment. This destructive interference makes theoretical cross sections for

Chiral perturbation approach to the {ital pp}{r_arrow}{ital pp}{pi}{sup 0} reaction near threshold

pp \rightarrow pp\pi^0

A next-to-next-to-leading-order pp→ppπ0 transition operator in chiral perturbation theory

much smaller than the experimental values, a feature that suggests the importance of the heavy-meson exchange contributions to explain the experimental data.

Interference of dibaryon resonances with Faddeev amplitudes for elastic πd scattering

Abstract Muon capture on the deuteron is studied in a framework that essentially incorporates heavy baryon chiral perturbation theory (HBχPT). It is found that by far the dominant contribution to μd capture comes from a region of the final three-body phase-space in which the energy of the two neutrons is sufficiently small for HBχPT to be applicable. The single unknown low-energy constant having been fixed from the tritium beta decay rate, our calculation contains no free parameter. Our estimate of the μd capture rate is consistent with the existing data. The relation between μd capture and the νd reactions, which are important for the SNO experiments, is briefly discussed.

On mass corrections and the axial coupling constant in the chiral quark model

Abstract The effective kaon mass m K ∗ in dense baryonic matter is calculated based on PCAC, current algebra and the Weinberg smoothness hypothesis. The off-shell behavior of the KN scattering amplitudes is treated consistently with PCAC, and the effects of the subthreshold KN resonances are also included. The m K ∗ is foundd to depend crucially on the KN sigma term, ΣKN. Since the current estimates of ΣKN are very uncertain, we discuss various scenarios treating ΣKN as an input parameter; for certain values of ΣKN a collective mode of a hyperon-particle-nucleon-hole state appears at high densities, possibly leading to kaon condensation.

A possible resolution of the proton spin problem

The usual theoretical treatments of the near-threshold