42 research outputs found
Nucleon-Nucleon Scattering and Large N(c) QCD
Nucleon-nucleon scattering observables are discussed in the context of large
Nc QCD. As is well known, the baryon spectrum in the large Nc limit exhibits
contracted SU(2Nf) spin-flavor sym- metry. This symmetry can be used to derive
model-independent relations between proton-proton and proton-neutron total
cross sections. These relations are valid in the kinematic regime in which the
relative momentum of two nucleons is of order of Nc. In this semiclassical
regime the nucleon-nucleon scattering can be described in the time-dependent
mean field approximation. These model-independent results are compared to
experimental data for spin-independent and polarized total nucleon-nucleon
cross sections.Comment: 9 pages, 3 figures. Invited talk, Xth Quark Confinement and the
Hadron Spectrum, October 201
Heavy Baryons: A Combined Large N_c and Heavy Quark Expansion for Electroweak Currents
The combined large N_c and heavy quark limit for baryons containing a single
heavy quark is discussed. The combined large N_c and heavy quark expansion of
the heavy quark bilinear operators is obtained. In the combined expansion the
corrections proportional to m_N/m_Q are summed to all orders. In particular,
the combined expansion can be used to determine semileptonic form factors of
heavy baryons in the combined limit.Comment: 8 pages. Presented at The Phenomenology of Large N_c QCD, Tempe,
Arizona, 9-11 Jan 200
Classical Strongly Coupled QGP II: Screening and Equation of State
We analyze the screening and bulk energy of a classical and strongly
interacting plasma of color charges, a model we recently introduced for the
description of a quark-gluon plasma at T=(1-3)Tc. The partition function is
organized around the Debye-Huckel limit. The linear Debye-Huckel limit is
corrected by a virial expansion. For the pressure, the expansion is badly
convergent even in the dilute limit. The non-linear Debye-Huckel theory is
studied numerically as an alternative for moderately strong plasmas. We use
Debye theory of solid to extend the analysis to the crystal phase at very
strong coupling. The analytical results for the bulk energy per particle
compare well with the numerical results from molecular dynamics simulation for
all couplings.Comment: 9 pages, 5 figure
New near-threshold mesons
We show that under a number of rather plausible assumptions QCD spectrum may
contain a number of mesons which have not been predicted or observed. Such
states will have the quantum numbers of two existing mesons and masses very
close to the dissociation threshold into the two mesons. Moreover, at least one
of the two mesonic constituents itself must be very close to its dissociation
threshold. In particular, one might expect the existence of loosely bound
systems of and \D; similarly, and \ff, and \ff, and
and and can be bound. The mechanism for binding in these
cases is the S-wave kaon exchange. The nearness of one of the constituents to
its decay threshold into a kaon plus a remainder, implies that the range of the
kaon exchange force becomes abnormally long--significantly longer than
which greatly aids the binding.Comment: 5 page
Nucleon-Nucleon Scattering Observables in Large- QCD
Nucleon-nucleon scattering observables are considered in the context of the
large limit of QCD for initial states with moderately high momenta (). The scattering is studied in the framework of the time-dependent
mean-field approximation. We focus on the dependence of those observables on
the spin and isospin of the initial state which may be computed using
time-dependent mean-field theory. We show that, up to corrections, all such
observables must be invariant under simultaneous spin and isospin flips ({\it
i.e.} rotations through in both spin and isospin) acting on either
particle. All observables of this class obtained from spin unpolarized
measurements must be isospin independent up to corrections. Moreover,
it can be shown that the leading correction is of relative order
rather than .Comment: 4 page
Yields of weakly bound light nuclei as a probe of the statistical hadronization model
The statistical hadronization model successfully describes the yields of hadrons and light nuclei from central heavy-ion collisions over a wide range of energies. It is a simple and efficient phenomenological framework in which the relative yields for very high energy collisions are essentially determined by a single model parameter—the chemical freeze-out temperature. Recent measurements of yields of hadrons and light nuclei covering over nine orders of magnitudes from the ALICE collaboration at the Large Hadron Collider were described by the model with remarkable accuracy with a chemical freeze-out temperature of 156.5 ± 1.5 MeV. A key physical question is whether (at least to a good approximation) the freeze-out temperature can be understood, literally, as the temperature at which the various species of an equilibrated gas of hadrons (including resonances) and nuclei chemically freeze out, as the model assumes, or whether it successfully parametrizes the yield data for a different reason. This paper analyzes the yields of weakly bound light nuclei—the deuteron and the hypertriton—to probe this issue. Such nuclei are particularly sensitive to assumptions of the model because their binding energies are at a scale far below both typical hadronic scales and the freeze-out temperature. The analysis depends only on outputs of the statistical hadronization model, known hadronic properties and standard assumptions of kinetic theory while making no additional dynamical assumptions about the dynamics of heavy-ion collisions. The analysis indicates that a key assumption underlying the model—that hadrons (and nuclei), just prior to chemical freeze-out temperature, are in thermal equilibrium and are sufficiently dilute as to have particle distributions accurately described statistically by a nearly ideal gas of hadrons and nuclei with masses given by their free space values—appears to be inconsistent with the chemical freeze-out temperature output by the model, at least for these weakly bound nuclei. Implications of this analysis for the interpretation of parameters extracted from the model are discussed
Model-Independent Predictions for Low Energy Isoscalar Heavy Baryon Observables in the Combined Heavy Quark and Large Expansion
Model-independent predictions for excitation energies, semileptonic form
factors and electromagnetic decay rates of isoscalar heavy baryons and their
low energy excited states are discussed in terms of the combined heavy quark
and large expansion. At leading order, the observables are completely
determined in terms of the known excitation energy of the first excited state
of . At next-to-leading order in the combined expansion all heavy
baryon observables can be expressed in a model-independent way in terms of two
experimentally measurable quantities. We list predictions at leading and
next-to-leading order.Comment: 7 pages, LaTe