264 research outputs found
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
Zero temperature properties of mesons in a vector meson extended linear sigma model
A three flavor linear sigma model with vector and axial-vector mesons is
discussed. Preliminary results concerning on the symmetry breaking pattern, the
question of parameterization, as well as the resulting meson masses are
presented.Comment: 4 pages, 0 figures, submitted to the Hot and Cold Baryonic Matter
(HCBM 2010) conference proceeding
Scalar mesons in a linear sigma model with (axial-)vector mesons
The structure of the scalar mesons has been a subject of debate for many
decades. In this work we look for states among the physical
resonances using an extended Linear Sigma Model that contains scalar,
pseudoscalar, vector, and axial-vector mesons both in the non-strange and
strange sectors. We perform global fits of meson masses, decay widths and
amplitudes in order to ascertain whether the scalar states are below
or above 1 GeV. We find the scalar states above 1 GeV to be preferred as
states.Comment: 6 pages, 1 figure, To appear in the proceedings of the XII. Hadron
Physics Conference, Bento Goncalves, Brasil, April, 22 - 27, 201
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
Vacuum Properties of Mesons in a Linear Sigma Model with Vector Mesons and Global Chiral Invariance
We present a two-flavour linear sigma model with global chiral symmetry and
vector and axial-vector mesons. We calculate pion-pion scattering lengths and
the decay widths of scalar, vector, and axial-vector mesons. It is demonstrated
that vector and axial-vector meson degrees of freedom play an important role in
these low-energy processes and that a reasonable theoretical description
requires globally chirally invariant terms other than the vector meson mass
term. An important question for meson vacuum phenomenology is the quark content
of the physical scalar f0(600) and a0(980) mesons. We investigate this question
by assigning the quark-antiquark sigma and a0 states of our model with these
physical mesons. We show via a detailed comparison with experimental data that
this scenario can describe all vacuum properties studied here except for the
decay width of the sigma, which turns out to be too small. We also study the
alternative assignment f0(1370) and a0(1450) for the scalar mesons. In this
case the decay width agrees with the experimental value, but the pion-pion
scattering length is too small. This indicates the necessity to
extend our model by additional scalar degrees of freedom.Comment: 22 pages, 6 figure
Vacuum phenomenology of the chiral partner of the nucleon in a linear sigma model with vector mesons
We investigate a linear sigma model with global chiral symmetry. The mesonic degrees of freedom are the standard scalar and
pseudoscalar mesons and the vector and axial-vector mesons. The baryonic
degrees of freedom are the nucleon, , and its chiral partner, , which
is usually identified with N(1535). The chiral partner is incorporated in the
so-called mirror assignment, where the nucleon mass is not solely generated by
the chiral condensate but also by a chirally invariant mass term, . The
presence of (axial-) vector fields modifies the expressions for the axial
coupling constants of the nucleon, , and its partner,
. Using experimental data for the decays and
, as well as lattice results for we infer
MeV, i.e., an appreciable amount of the nucleon mass originates
from sources other than the chiral condensate. We test our model by evaluating
the decay and the s-wave nucleon-pion scattering lengths
.Comment: 16 pages, 2 figures. To appear in Phys. Rev.
The Glueball in a Chiral Linear Sigma Model with Vector Mesons
We present a two-flavour linear sigma model with global chiral symmetry and
(axial-)vector mesons as well as an additional glueball degree of freedom. We
study the structure of the well-established scalar resonances f0(1370) and
f0(1500): by a fit to experimentally known decay widths we find that f0(1370)
is predominantly a \bar{q}q state and f0(1500) is predominantly a glueball
state. The overall phenomenology of these two resonances can be well described.
Other assignments for our mixed quarkonium-glueball states are also tested, but
turn out to be in worse agreement with the phenomenology. As a by-product of
our analysis, the gluon condensate is determined.Comment: 8 page
Structure of the Southern Patagonian Andes at 49ºS, Argentina
This paper describes Late Paleozoic Gondwanan and Late Cretaceous to Early Cenozoic Andean structures in the Southern Patagonian Andes and an associated Extra-Andean region between lakes San MartÃn and Viedma. The study area encompasses a 200-km-long W-E section between the Patagonian icefield and the 72ºW longitude meridian, in Argentine Patagonia. The oldest structures are of Late Paleozoic age and developed through at least two deformation phases during the Gondwanan Orogeny. The first deformation phase (Dg1) includes isoclinal and N-overturned WNW trending folds and associated thrusts, including duplexes. The second deformation phase includes NNE trending open folds (Dg2). Deformation occurred in non-metamorphic to very low-grade metamorphic conditions. A spaced rough cleavage is found near the first phase fold hinges. The Eocene and Miocene Andean structural compression resulted in a N-S oriented fold and thrust belt. This belt is comprised of three morphostructural zones from W to E, with distinctive topographic altitudes and structural styles: Andean; Sub-Andean; and Extra-Andean zones. The first corresponds to the inner fold and thrust belt, while the last two are part of the outer fold and thrust belt. The Andean zone (3400–2000m above sea level) is characterized by N-S to NNE trending, E-vergent, Cenozoic reverse faults and associated minor thrusts. The northern part of the Sub- Andean zone (2000–1500m above sea level) consists of W-vergent reverse faults and some NNE open folds. The southern part of the Andean zone includes tight folds with box and kink geometries, related to thrusts at deeper levels. In the Extra-Andean zone, with maximum heights of 1500m, the deformation is less intense, and gentle folds deform the Upper Cretaceous sediments. An inherited Jurassic N-S extensional fault system imposed a strong control on this morphostructural zonation. Also the variation of the Austral Basin sedimentary thickness in the N-S direction seems to have influenced the structural styles of the outer fold and thrust belt. Those differences in sedimentary thickness may be related to S-dipping transfer zones associated to W-E Jurassic extension. In turn, the transfer zones may have been controlled by the N-vergent WNW, Dg1, Gondwanan structural fabric
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