2,248 research outputs found
Relativistic Quark Model Calculation of the l1, l2 Coefficients of the Chiral Lagrangian
We briefly report on a relativistic quark model scheme to calculate the
O(P^4) pion-pion vertex in the planar approximation and in the chiral limit.
The calculation is reduced to the solution of simple integral equations
(Bethe-Salpeter like) by an effective use of chiral Ward Identities. Specific
model computations are provided.Comment: Proc. V Intnal. Conf. on Quark Confinement and the Hadron Spectrum,
Gargnano,Italy 200
Chiral symmetry breaking for fermions charged under large Lie groups
We reexamine the dynamical generation of mass for fermions charged under
various Lie groups with equal charge and mass at a high Grand Unification
scale, extending the Renormalization Group Equations in the perturbative regime
to two-loops and matching to the Dyson-Schwinger Equations in the strong
coupling regime.Comment: 8 pages, 12 plot
Soft interactions in jet quenching
We study the collisional aspects of jet quenching in a high energy nuclear
collision, especially in the final state pion gas. The jet has a large energy,
and acquires momentum transverse to its axis more effectively by multiple soft
collisions than by few hard scatterings (as known from analogous systems such
as J/\psi production at Hera). Such regime of large E and small momentum
transfer corresponds to Regge kinematics and is characteristically dominated by
the pomeron. From this insight we estimate the jet quenching parameter in the
hadron medium (largely a pion gas) at the end of the collision, which is
naturally small and increases with temperature in line with the gas density.
The physics in the quark-gluon plasma/liquid phase is less obvious, and here we
revisit a couple of simple estimates that suggest indeed that the
pomeron-mediated interactions are very relevant and should be included in
analysis of the jet quenching parameter. Finally, the ocasional hard collisions
produce features characteristic of a L\`evy flight in the q_perp^2 plane
perpendicular to the jet axis. We suggest one- and two-particle q_perp
correlations as interesting experimental probes.Comment: 14 pages, 16 figure
Relativistic Many-Body Hamiltonian Approach to Mesons
We represent QCD at the hadronic scale by means of an effective Hamiltonian,
, formulated in the Coulomb gauge. As in the Nambu-Jona-Lasinio model,
chiral symmetry is explicity broken, however our approach is renormalizable and
also includes confinement through a linear potential with slope specified by
lattice gauge theory. This interaction generates an infrared integrable
singularity and we detail the computationally intensive procedure necessary for
numerical solution. We focus upon applications for the and quark
flavors and compute the mass spectrum for the pseudoscalar, scalar and vector
mesons. We also perform a comparative study of alternative many-body techniques
for approximately diagonalizing : BCS for the vacuum ground state; TDA and
RPA for the excited hadron states. The Dirac structure of the field theoretical
Hamiltonian naturally generates spin-dependent interactions, including tensor,
spin-orbit and hyperfine, and we clarify the degree of level splitting due to
both spin and chiral symmetry effects. Significantly, we find that roughly
two-thirds of the - mass difference is due to chiral symmetry and
that only the RPA preserves chiral symmetry. We also document how hadronic mass
scales are generated by chiral symmetry breaking in the model vacuum. In
addition to the vacuum condensates, we compute meson decay constants and detail
the Nambu-Goldstone realization of chiral symmetry by numerically verifying the
Gell-Mann-Oaks-Renner relation. Finally, by including D waves in our charmonium
calculation we have resolved the anomalous overpopulation of states
relative to observation
Is the Theta+ a K pi N bound state?
Following a recent suggestion that the could be a bound
state we perform an investigation under the light of the meson meson and meson
baryon dynamics provided by the chiral Lagrangians and using methods currently
employed to dynamically generate meson and baryon resonances by means of
unitary extensions of chiral perturbation theory. We consider two body and
three body forces and examine the possibility of a bound state below the three
particle pion-kaon-nucleon and above the kaon-nucleon thresholds. Although we
find indeed an attractive interaction in the case of isospin I=0 and
spin-parity , the interaction is too weak to bind the system. If we
arbitrarily add to the physically motivated potential the needed strength to
bind the system and with such strong attraction evaluate the decay width into
, this turns out to be small. A discussion on further work in this
direction is done.Comment: Change of title and few sentences, size of two graphs. References
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