New extended model of hadrons

Abstract

We propose that a strongly interacting particle is a finite region of space to which fields are confined. The confinement is accomplished in a Lorentz-invariant way by endowing the finite region with a constant energy per unit volume, B. We call this finite region a "bag. " The contained fields may be either fermions or bosons and may have any spin; they may or may not be coupled to one another. Equations of motion and boundary conditions are obtained from a variational principle. The confining region has no dynamical freedom but constrains the fields inside: There are no excitations of the coordinates determining the confining region. The model possesses many desirable features of hadron dynamics: (i) a parton interpretation and presumably Bjorken scaling; the confined fields are free or weakly interacting except close to the boundary; (ii) infinitely rising Begge trajectories as a consequence of the bag's finite extent; (iii) the Hagedorn degeneracy or limiting temperature; (iv) all physical hadrons are singlets under hadronic gauge s~~etries. For example, in a theory of fractionally charged, "colored" quarks interacting with colored, massless gauge vector gluons, if both quark and gluon fields are confined to the bag, only color-singlet solutions exist. In addition to establishing these general properties, we present complete classical and quantum solutions for free scalars and also for free fermions inside a bag of one space and one time dimension. Both systems have linear mass-squared spectra. We demonstrate Poincare invariance at the classical level in any dimension and at the quantum level for the above-mentioned explicit solutions in two dimensions. We discuss the behavior of specific solutions in one and three space dimensions. We also discuss in detail the problem of fermlon boundary conditions, which follow only indirectly from the variational principle.

The quark gluon plasma equation of state and the expansion of the early Universe

“…One of the first equations of state of the quark gluon plasma was the one derived from the MIT bag model [12]. Because of its simplicity it has been widely used in astrophysics and cosmology.…”

The hadron-quark phase transition in neutron stars

“…One of these constraints is the phenomenological observation that in heavy ion collisions at intermediate energies (10 MeV/A E/A 200 MeV/A) no evidence for a transition to a quark-gluon plasma has been found up to about 3 times the saturation density ρ 0 . We have taken this constraint in due consideration, and used an extended MIT bag model [ 12] (including the possibility of a density dependent bag "constant") and the color dielectric model [ 13], both compatible with this condition [ 14]. For completeness, we have also used the Nambu-Jona-Lasinio model [ 15].…”

Neutron Star Structure with Hyperons and Quarks

“…The MIT bag model [19] provides a simple example for the description of the bulk properties of uniform quark matter, deconfined from the beta-stable hadronic matter mentioned in the previous section. The energy density of the f = u, d, s quark gas can be expressed as a sum of the kinetic term and the one-gluon-exchange term [20] proportional to the QCD coupling constant α s ,…”