7361514
Continuum Study of Deconfinement at Finite Temperature.
Deconfinement and chiral symmetry restoration are explored in a confining, renormalizable, Dyson-Schwinger equation model of two-flavor QCD.An order parameter for deconfinement is introduced and used to establish that, in the chiral limit, deconfinement and chiral symmetry restoration are coincident at {ital T}{sub {ital c}}{approx_equal}150 MeV. The transitions are second order and each has the same critical exponent: {beta}{approx_equal}0.3. The deconfinement transition exhibits sensitivity to the current-quark mass. {ital f}{sub {pi}} and {ital m}{sub {pi}} change by less than 10{percent} for {ital T}{lt}0.7{ital T}{sub {ital c}}; however, as {ital T}{r_arrow}{ital T}{sub {ital c}}, thermal fluctuations cause the pion bound state contribution to the four-point quark-antiquark correlation function to disappear. {copyright} {ital 1996 The American Physical Society.}
17985637
ASPECTS OF DYNAMICAL CHIRAL SYMMETRY BREAKING
Dynamical chiral symmetry breaking is a nonperturbative phenomenon that may be studied using QCD's gap equation. Model-independent results can be obtained with a nonperturbative and symmetry preserving truncation. The gap equation yields the massive dressed-quark propagator, which has a spectral representation when considered as a function of the current-quark mass. This enables an explication of the connection between the infrared limit of the QCD Dirac operator's spectrum and the quark condensate appearing in the operator product expansion.
14819649
Electromagnetic from factors of charged and neutral kaons
Abstract The charged and neutral kaon form factors are calculated as a phenomenological application of model QCD Dyson-Schwinger equations. The results are compared with the pion form factor calculated in the same framework and yield FK±(Q2) > Fπ±(Q2) on Q2 ϵ [0, 3] GeV2; and a negative charge radius for the neutral kaon. These results are sensitive to the difference between the kaon and pion Bethe-Salpeter amplitude and the u- and s-quark propagation characteristics.
119204026
Abelian anomaly and neutral pion production
We show that in fully self-consistent treatments of the pion, namely, its static properties and elastic and transition form factors, the asymptotic limit of the product Q{sup 2}G{sub {gamma}}{sup *}{sub {gamma}{pi}}{sup 0}(Q{sup 2}), determined a priori by the interaction employed, is not exceeded at any finite value of spacelike momentum transfer. Furthermore, in such a treatment of a vector-vector contact-interaction one obtains a {gamma}{sup *{gamma}{yields}{pi}0} transition form factor that disagrees markedly with all available data. We explain that the contact interaction produces a pion distribution amplitude that is flat and nonvanishing at the endpoints. This amplitude characterizes a pointlike pion bound state. Such a state has the hardest possible form factors (i.e., form factors that become constant at large momentum transfers and hence are in striking disagreement with completed experiments). However, interactions with QCD-like behavior produce soft pions, a valence-quark distribution amplitude that vanishes as {approx}(1-x){sup 2} for x{approx}1, and results that agree with the bulk of existing data. Our analysis supports a view that the large-Q{sup 2} data obtained by the BaBar Collaboration is not an accurate measure of the {gamma}*{gamma}{yields}{pi}{sup 0} form factor.
16592262
Dyson-Schwinger equations: connecting small and large length-scales.
The phenomenological application of Dyson-Schwinger equations to the calculation of meson properties observable at TJNAF is illustrated. Particular emphasis is given to the ability of this framework to unify long-range effects constrained by chiral symmetry with short-range effects prescribed by perturbation theory, and interpolate between them.
118382521
Flavour symmetry breaking in the kaon parton distribution amplitude
Abstract We compute the kaon's valence-quark (twist-two parton) distribution amplitude (PDA) by projecting its Poincare-covariant Bethe–Salpeter wave-function onto the light-front. At a scale ζ = 2 GeV , the PDA is a broad, concave and asymmetric function, whose peak is shifted 12–16% away from its position in QCD's conformal limit. These features are a clear expression of SU ( 3 ) -flavour-symmetry breaking. They show that the heavier quark in the kaon carries more of the bound-state's momentum than the lighter quark and also that emergent phenomena in QCD modulate the magnitude of flavour-symmetry breaking: it is markedly smaller than one might expect based on the difference between light-quark current masses. Our results add to a body of evidence which indicates that at any energy scale accessible with existing or foreseeable facilities, a reliable guide to the interpretation of experiment requires the use of such nonperturbatively broadened PDAs in leading-order, leading-twist formulae for hard exclusive processes instead of the asymptotic PDA associated with QCD's conformal limit. We illustrate this via the ratio of kaon and pion electromagnetic form factors: using our nonperturbative PDAs in the appropriate formulae, F K / F π = 1.23 at spacelike- Q 2 = 17 GeV 2 , which compares satisfactorily with the value of 0.92 ( 5 ) inferred in e + e − annihilation at s = 17 GeV 2 .
41501121
Can four-quark states be easily detected in baryon-antibaryon scattering?
We attempt to explain the experimental sparsity of diquonia candidates given the theoretical abundance of such states. We do this by investigating the lowest-order contributions of such states as intermediates in {ital p{bar p}} scattering into exclusive baryon-antibaryon final states. We find that the contributions depend on the partial widths for the meson-meson decays of the diquonia, and that resonant effects can be easily made to disappear. We conclude that if the meson-meson widths of diquonia are larger than about 50 MeV, most of these states will be extremely difficult to observe in {ital p{bar p}} scattering, for instance. We note that diquonia may offer a convenient means of describing some aspects of the dynamics of baryon-antibaryon scattering.
11167229
Simple tests of the factorization assumption.
We suggest simple experimental tests to determine whether or not the factorization assumption is valid for the two-body, nonleptonic decays of heavy hadrons, when both daughter hadrons are also heavy.
23690451
Systematics of inclusive pion double charge exchange in the delta resonance region.
A systematic study of inclusive pion double charge exchange is reported for nuclei between A=16 and A=208. The doubly differential cross sections for the A(${\mathrm{\ensuremath{\pi}}}^{+}$,${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$) and A(${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$,${\mathrm{\ensuremath{\pi}}}^{+}$) reactions in $^{16}\mathrm{O}$, $^{40}\mathrm{Ca}$, $^{103}\mathrm{Rh}$, and $^{208}\mathrm{Pb}$ were measured at incident energies between 120 and 270 MeV at three to five outgoing pion angles. Pion spectra were measured over the energy range from 10 MeV to the kinematic limit for double charge exchange. Integrating these spectra over outgoing pion energy generated angular distributions, and subsequently integrating these angular distributions generated total reaction cross sections. The shapes of the measured spectra are compared with those determined by the distribution of events in four-body phase space and with those predicted by a model in which the pion undergoes two sequential single charge exchanges on nucleons in a Fermi gas. The cross sections are compared with predictions of cascade calculations in which more than two interactions, including pion absorption and scattering without charge exchange, may occur.
34021352
Color-singlet quark-pair transmutation: Helicity amplitudes and partial-wave analysis.
Quark-pair transmutation via two gluons is the lowest-order, color-singlet process. In this paper the helicity amplitudes for this process are evaluated and a partial-wave analysis performed. The amplitudes for these annihilations are infrared divergent and this divergence is removed by giving the gluons a confinement mass. The results are generally dependent on this mass. Many of the features are similar to those of quark-pair annihilation into two gluons. Somewhat surprisingly, there is a large proportion of a ${1}^{+}$ partial wave. Threshold effects are understood in terms of threshold effects in pair annihilation into two gluons. However, there is a ``competition'' effect that depends on the ratio of masses of the initial- and final-quark pairs. For similar masses, singlet production dominates as expected, but for very dissimilar masses, singlet annihilation of the heavier pair competes with triplet production of the lighter pair. Some comments about the possible applications and extensions of this work are made. Obvious applications are to the Okubo-Zweig-Iizuka-rule-suppressed decays of quarkonia. Other applications include development of a quark-pair-creation model that differs from the usual $^{3}\mathrm{P}_{0}$ and $^{3}\mathrm{S}_{1}$ models.
41503347
Heavy quark symmetries and the decays B--> baryon+antibaryon.
We enumerate the form factors necessary to describe the two-body baryonic decays of B mesons.We use the symmetries of the heavy quark effective theory to arrive at some relations among these form factors, when at least one of the daughter baryons is heavy.