34 research outputs found
The BES f_0(1810): a new glueball candidate
We analyze the f_0(1810) state recently observed by the BES collaboration via
radiative J/\psi decay to a resonant \phi\omega spectrum and confront it with
DM2 data and glueball theory. The DM2 group only measured \omega\omega decays
and reported a pseudoscalar but no scalar resonance in this mass region. A
rescattering mechanism from the open flavored KKbar decay channel is considered
to explain why the resonance is only seen in the flavor asymmetric \omega\phi
branch along with a discussion of positive C parity charmonia decays to
strengthen the case for preferred open flavor glueball decays. We also
calculate the total glueball decay width to be roughly 100 MeV, in agreement
with the narrow, newly found f_0, and smaller than the expected estimate of
200-400 MeV. We conclude that this discovered scalar hadron is a solid glueball
candidate and deserves further experimental investigation, especially in the
K-Kbar channel. Finally we comment on other, but less likely, possible
assignments for this state.Comment: 11 pages, 4 figures. Major substantive additions, including an
ab-initio, QCD-based computation of the glueball inclusive decay width,
evaluation of final state effects, and enhanced discussion of several
alternative possibilities. Our conclusions are unchanged: the BES f_0(1810)
is a promising glueball candidat
Two-meson cloud contribution to the baryon antidecuplet self-energy
We study the self-energy of the SU(3) antidecuplet coming from two-meson
virtual clouds. Assuming that the exotic Theta+ belongs to an antidecuplet
representation with N(1710) as nucleon partner, we derive effective Lagrangians
that describe the decay of N(1710) into N pi pi with two pions in s- or p-wave.
It is found that the self-energies for all members of the antidecuplet are
attractive, and the larger strangeness particle is more bound. From two-meson
cloud, we obtain about 20 % of the empirical mass splitting between states with
different strangeness.Comment: 4 pages, 2 figures, 1 table, Talk given at the 10th International
Conference on Baryons (Baryons04), Palaiseau (France), October 25-29, 200
Quark mass dependence of the pion vector form factor
We examine the quark mass dependence of the pion vector form factor, particularly the curvature (mean quartic radius). We focus our study on the consequences of assuming that the coupling constant of the rho to pions, g(rho pi pi), is largely independent of the quark mass while the quark mass dependence of the rho mass is given by recent lattice data. By employing the Omnes representation we can provide a very clean estimate for a certain combination of the curvature and the square radius, whose quark mass dependence could be determined from lattice computations. This study provides an independent access to the quark mass dependence of the rho pi pi coupling and in this way a non-trivial check of the systematics of chiral extrapolations. We also provide an improved value for the curvature for physical values for the quark masses. namely (r(4)) = 0.73 +/- 0.09 fm(4) or equivalently c(v) = 4.00 +/- 0.50 GeV-4. (C) 2009 Elsevier B.V. All rights reserved
Fermion family recurrences in the Dyson-Schwinger formalism
We study the multiple solutions of the truncated propagator Dyson-Schwinger
equation for a simple fermion theory with Yukawa coupling to a scalar field.
Upon increasing the coupling constant , other parameters being fixed, more
than one non-perturbative solution breaking chiral symmetry becomes possible
and we find these numerically. These ``recurrences'' appear as a mechanism to
generate different fermion generations as quanta of the same fundamental field
in an interacting field theory, without assuming any composite structure. The
number of recurrences or flavors is reduced to a question about the value of
the Yukawa coupling, and has no special profound significance in the Standard
Model. The resulting mass function can have one or more nodes and the
measurement that potentially detects them can be thought of as a collider-based
test of the virtual dispersion relation for the charged
lepton member of each family. This requires three independent measurements of
the charged lepton's energy, three-momentum and off-shellness. We illustrate
how this can be achieved for the (more difficult) case of the tau lepton
Meson and tetra-quark mixing
The mixing between q-qbar meson and qqbar-qqbar tetra-quark states is
examined within an effective QCD Coulomb gauge Hamiltonian model. Mixing matrix
elements of the Hamiltonian are computed and then diagonalized yielding an
improved prediction for the low-lying J^{PC} = 0^{+/- +}, 1^{--} isoscalar
spectra. Mixing effects were found significant for the scalar hadrons but not
for the 1^{--} states, which is consistent with the ideal mixing of vector
mesons. A perturbative assessment of the exact QCD kernel is also reported.Comment: 7 pages, 6 figure
Vertex functions and infrared fixed point in Landau gauge SU(N) Yang-Mills theory
The infrared behaviour of vertex functions in an SU(N) Yang-Mills theory in
Landau gauge is investigated employing a skeleton expansion of the
Dyson-Schwinger equations. The three- and four-gluon vertices become singular
if and only if all external momenta vanish while the dressing of the
ghost-gluon vertex remains finite in this limit. The running coupling as
extracted from either of these vertex functions possesses an infrared fixed
point. In general, diagrams including ghost-loops dominate in the infrared over
purely gluonic ones.Comment: 14 pages, 8 figures, v2: typos corrected, version to be published in
PL
Coulomb gauge approach to (qqg)over-bar hybrid mesons
An effective Coulomb gauge Hamiltonian, H-eff, is used to calculate the light ( u (u) over barg), strange ( s (s) over barg) and charmed (c (c) over barg) hybrid meson spectra. For the same two parameter H-eff providing glueball masses consistent with lattice results and a good description of the observed u, d, s and c quark mesons, a large-scale variational treatment predicts that the lightest hybrid has J(PC) = 0(++) and mass 2.1 GeV. The lightest exotic 1(-+) state is just above 2.2 GeV, near the upper limit of lattice and flux tube predictions. These theoretical formulations all indicate that the observed 1(-+) pi(1)(1600) and, more clearly, pi(1)(1400) are not hybrid states. The Coulomb gauge approach further predicts that in the strange and charmed sectors, respectively, the ground state hybrids have 1(+-) with masses 2.1 and 3.8 GeV, while the. rst exotic 1( +) states are at 2.4 and 4.0 GeV. Finally, using our hybrid wavefunctions and the Franck-Condon principle, a novel experimental signature is presented to assist heavy hybrid meson searches
The ratio of viscosity to entropy density in a pion gas satisfies the KSS holographic bound
We evaluate the ratio of shear viscosity to entropy density in a pion gas
employing the Uehling-Uehlenbeck equation and experimental phase-shifts
parameterized by means of the SU(2) Inverse Amplitude Method. We find that the
ratio for this monocomponent gas stays well above the KSS 1/(4 pi) bound. We
find similar results with other sets of phase shifts and conclude the bound is
nowhere violated.Comment: 2 page text, three figures. V2: short comment and graph added to
assert that a minimum of eta/s is not discarded from the hadron, low T side
in a heavy-ion collisio
Analytical approach to chiral symmetry breaking in Minkowsky space
The mass gap equation for spontaneous chiral symmetry breaking is studied
directly in Minkowsky space. In hadronic physics, spontaneous chiral symmetry
breaking is crucial to generate a constituent mass for the quarks, and to
produce the Partially Conserved Axial Current theorems, including a small mass
for the pion. Here a class of finite kernels is used, expanded in Yukawa
interactions. The Schwinger-Dyson equation is solved with an analytical
approach. This improves the state of the art of solving the mass gap equation,
which is usually solved with the equal-time approximation or with the Euclidean
approximation. The mapping from the Euclidean space to the Minkowsky space is
also illustrated.Comment: 7 pages, 3 figure
Analysis of the triply heavy baryon states with QCD sum rules
In this article, we study the and
triply heavy baryon states in an systematic way by subtracting the
contributions from the corresponding and
triply heavy baryon states with the QCD sum rules, and make reasonable
predictions for their masses.Comment: 14 pages, 25 figures, revised versio