128 research outputs found
Triangle Singularities and XYZ Quarkonium Peaks
We discuss analytical properties of partial waves derived from projection of
a 4-legged amplitude with crossed-channel exchanges in the kinematic region of
the direct channel that corresponds to the XYZ peaks in charmonium and
bottomonium. We show that in general partial waves can develop anomalous branch
points in the vicinity of the direct channel physical region. In a specific
case, when these branch points lie on the opposite side of the unitary cut they
pinch the integration contour in a dispersion relation and if the pinch happens
close to threshold, the normal threshold cusp is enhanced. We show that this
effect only occurs if masses of resonances in the crossed channel are in a
specific, narrow range. We estimate the size of threshold enhancements
originating from these anomalous singularities in reactions where the Zc(3900)
and the Zb(10610) peaks have been observed.Comment: 10 pages, 9 figures, Version v3 to appear in Phys. Lett.
Schwinger-Dyson equations and disorder
Using simple models in D=0+0 and D=0+1 dimensions we construct partition
functions and compute two-point correlations. The exact result is compared with
saddle-point approximation and solutions of Schwinger-Dyson equations. When
integrals are dominated by more than one saddle-point we find Schwinger-Dyson
equations do not reproduce the correct results unless the action is first
transformed into dual variables.Comment: 7 pages, 6 figure
Energy spectrum of the low-lying gluon excitations in the Coulomb gauge
We compute the energy spectrum of low-lying gluonic excitations in the
presence of static quark-antiquark sources using Coulomb gauge and the
quasi-particle representation. Within the valence sector of the Fock space we
reproduce both, the overall normalization and the ordering of the spin-parity
multiplets. We discus how the interactions induced by the non-abelian Coulomb
kernel are central in to fine structure of the spectrum.Comment: 8 pages, 8 figure
Chiral symmetry restoration and deconfinement in Coulomb Gauge QCD
In the framework of Coulomb Gauge QCD we explore dynamical breaking of chiral
symmetry and screening of the confinement potential at finite density. The
screened potential is applied in study of charmonium dissociation.Comment: 7 pages, 8 figure
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