348 research outputs found
Mixing of scalar tetraquark and quarkonia states in a chiral approach
A chiral invariant Lagrangian describing the tetraquark-quarkonia interaction
is considered at the leading and subleading order in the large-
expansion. Spontaneous chiral symmetry breaking generates mixing of scalar
tetraquark and quarkonia states and non-vanishing tetraquark condensates. In
particular, the mixing strength is related to the decay strengths of tetraquark
states into pseudoscalar mesons. The results show that scalar states below 1
GeV are mainly four-quark states and the scalars between 1 and 2 GeV
quark-antiquark states, probably mixed with the scalar glueball in the
isoscalar sector.Comment: 30 pages, 3 figures, 6 tables, to appear in Phys. Rev.
Linear growth of the trace anomaly in Yang-Mills thermodynamics
In the lattice work by Miller [1,2] and in the work by Zwanziger [3] a linear
growth of the trace anomaly for high temperatures was found in pure SU(2) and
SU(3) Yang-Mills theories. These results show the remarkable property that the
corresponding systems are strong interacting even at high temperatures. We show
that within an analytical approach to Yang-Mills thermodynamics this linear
rise is obtained and is directly connected to the presence of a
temperature-dependent ground state, which describes (part of) the
nonperturbative nature of the Yang-Mills system. Our predictions are in
approximate agreement with [1,2,3]Comment: 9 pages and 2 figure
Nonperturbative screening of the Landau pole
Based on the trace anomaly for the energy-momentum tensor, an effective
theory for the thermodynamics of the deconfining phase, and by assuming the
asymptotic behavior to be determined by one-loop perturbation theory we compute
the nonperturbative beta function for the fundamental coupling in SU(2) and
SU(3) Yang-Mills theory. With increasing temperature we observe a very rapid
approach to the perturbative running. The Landau pole is nonperturbatively
screened.Comment: 11 pages, 3 figure
Dynamical generation and dynamical reconstruction
A definition of `dynamical generation', a hotly debated topic at present, is
proposed and its implications are discussed. This definition, in turn, leads to
a method allowing to distinguish in principle tetraquark and molecular states.
The different concept of `dynamical reconstruction' is also introduced and
applies to the generation of preexisting mesons (quark-antiquark, glueballs,
>...) via unitarization methods applied to low-energy effective Lagrangians.
Large arguments play an important role in all these investigations. A
simple toy model with two scalar fields is introduced to elucidate these
concepts. The large behavior of the parameters is chosen in order that
the two scalar fields behave as quark-antiquark mesons. When the heavier field
is integrated out, one is left with an effective Lagrangian with the lighter
field only. A unitarization method applied to the latter allows to
`reconstruct' the heavier `quarkonium-like' field, which was previously
integrated out. It is shown that a Bethe-Salpeter (BS) analysis is capable to
reproduce the preformed quark-antiquark state. However, when only the lowest
term of the effective Lagrangian is retained, the large limit of the
reconstructed state is not reproduced: instead of the correct large
quarkonium limit, it fades out as a molecular state would do. Implications of
these results are presented: it is proposed that axial-vector, tensor and
(some) scalar mesons just above 1 GeV obtained via the BS approach from the
corresponding low-energy, effective Lagrangian in which only the lowest term is
kept, are quarkonia states, in agreement with the constituent quark model,
although they might fade away as molecular states in the large limit.Comment: 14 pages, 3 figure
Decays of tensor mesons and the tensor glueball in an effective field approach
The strong and electromagnetic decays of the ground-state tensor mesons are
studied in an effective field approach. A fit to the well-known experimental
data is performed. The decay ratios of the tensor glueball are evaluated and
possible candidates are discussed.Comment: 12 page
The Relationships between Companies and Bank System: An Analysis of Italian Context
The purpose of our research is to propose to model which could suggest to Italian small and medium companies the
best appropriate funding resources to their economic and financial situation. The framework of this paper is
represented by Giacosa and Mazzoleni (2016), in which a model classifies the companies into six groups according
to different elements, such as attitude to repay financial debts, company’s growth, and profitability. The sample is
composed of 39.400 Italian companies. In particular, companies could be divided in these categories: i) star
companies; ii) companies at the beginning of decline; and iii) companies in crisis.
It emerged that, in a medium-term vision, it’s necessary to change the management behavior and to try to reach
economic fundamentals expected by the bank system, while in the short-term vision the companies have to learn
how to use a non-bank financial instruments
On the two-photon decay width of the sigma meson
We shortly report on the two-photon decay width of the light -meson
interpreted as a quarkonium state. Results are given in dependence on the
-mass and the constituent mass of the light quark. The triangle
quark-loop diagram, responsible for the two-photon transition, is carefully
evaluated: a term in the transition amplitude, often omitted in literature,
results in destructive interference with the leading term. As a result we show
that the two-photon decay width of the in the quarkonium picture is
less than 1 keV for the physical range of parameters.Comment: 6 pages, 4 figure
QCD Tests of the Puzzling Scalar Mesons
Motivated by several recent data, we test the QCD spectral sum rules (QSSR)
predictions based on different proposals (\bar qq, \bar q\bar q qq, and
gluonium) for the nature of scalar mesons. In the I=1 and 1/2 channels, the
unusual (wrong) splitting between the a_0(980) and \kappa(900) and the a_0(980)
width can be understood from QSSR within a \bar qq assignement. However, none
of the \bar qq and \bar q\bar q qq results can explain the large \kappa width,
which may suggest that it can result from a strong interference with
non-resonant backgrounds. In the I=0 channel, QSSR and some low-energy theorems
(LET) require the existence of a low mass gluonium \sigma_B(1 GeV) coupled
strongly to Goldstone boson pairs which plays in the U(1)_V channel, a similar
role than the \eta' for the value of the U(1)_A topological charge. The
observed \sigma(600) and f_0(980) mesons result from a maximal mixing between
the gluonium \sigma_B and \bar qq(1 GeV) mesons, a mixing scheme which passes
several experimental tests. OZI violating J/\psi--> \phi\pi^+\pi^-, D_s--> 3\pi
decays and J/\psi--> \gamma S glueball filter processes may indicate that most
of the I=0 mesons above 1 GeV have important gluonium in their wave functions.
We expect that the f_0(1500), f_0(1710) and f_0(1790) have significant gluonium
component in their wave functions, while the f_0(1370) is mostly \bar qq. Tests
of these results can be provided by the measurements of the pure gluonium
\eta'\eta and 4\pi specific U(1)_A decay channels.Comment: Version to appear in Phys. Rev. D (one previous figure corrupted
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