Mannque Rho

The little bag

Abstract A quark bag model for nucleons and isobars is made with pions existing only outside the bag. The pion field is introduced so as to ensure continuity of the axial-vector current at the boundary of the bag. It is argued that the bag can be quite small, of radius ∼ħ/ m n c where m n is the nucleon mass. The energy of the small bag is much larger than m n c 2 , but self-energy processes, especially those involving the pion, are invoked in order to bring the nucleon energy down to its physical value. The resulting theory looks very much like the old Yukawa theory for a pion with a small distributed source, the source now being described in terms of quarks.

From kaon-nuclear interactions to kaon condensation

Abstract An effective chiral lagrangian in heavy-fermion formalism whose parameters are constrained by kaon-nucleon and kaon-nuclear interactions next to the leading order in chiral expansion is used to describe kaon condensation in dense “neutron star” matter. The critical density is found to be robust with respect to the parameters of the chiral lagrangian and is found to be ρ c ~ (3–4)ρ 0 . Once kaon condensation sets in, the system is no longer composed of neutron matter but of nuclear matter. Possible consequences on stellar collapse with the formation of compact “nuclear stars” or light mass black holes are pointed out.

Chiral dynamics of baryons from string theory

We study baryons in a holographic model of QCD by Sakai and Sugimoto, realized as small instantons with fundamental string hairs. We introduce an effective field theory of the baryons in the five-dimensional setting, and show that the instanton interpretation implies a particular magnetic coupling. Dimensional reduction to four dimensions reproduces the usual chiral effective action, and, in particular, we estimate the axial coupling

Chiral pion dynamics for spherical nucleon bags

{g}_{A}

Chiral restoration in hot and/or dense matter

between baryons and pions and the magnetic dipole moments, both of which are proportional to

The giant Gamow-Teller resonance

{N}_{c}

Quenching of axial-vector coupling constant in β-decay and pion-nucleus optical potential☆

. We extrapolate to finite

On the manifestation of chiral symmetry in nuclei and dense nuclear matter

{N}_{c}

Little bag dynamics

and discuss subleading corrections.

Strangeness condensation and “clearing” of the vacuum☆

Abstract A chirally symmetric quark-bag model for the nucleon is obtained by introducing an explicit, classical, pion field exterior to the bag. The coupling at the bag surface is determined by the requirement of a conserved axial-vector current. The pion field satisfies equations of motion corresponding to the non-linear σ-model. We study in this paper the simplified case where the bag and the pion field are spherically symmetric. Corrections due to gluon exchange between the quarks are ignored along with other interactions which split the N- and Δ-masses. The equations of motion for the pion field are solved and we find a substantial pion pressure at the bag surface, along with an attractive contribution to the nucleon self-energy. The total energy of the system, bag plus meson cloud, turns out to be approximately M n c 2 for a wide range of bag radii, from 1.5 fm down to about 0.5 fm. Introduction of a form factor for the pion would extend the range of possible radii to even smaller values. We propose that the bag with the smallest allowed radius be identified with the “little bag” discussed before. One surprising result of the paper is that as long as one restricts to spherically symmetric bags, restoring chiral symmetry to the bag model makes the axial-vector current coupling constant g A to be always too large compared with the experimental value for any bag radius, suggesting a deviation from spherical symmetry for the intrinsic bag wave functions of the “ground-state” hadrons.