1,462 research outputs found
f_0(600), kappa(800), rho(770) and K*(892), quark mass dependence from unitarized SU(3) Chiral Perturbation Theory
We study the strange and non-strange quark mass dependence of the parameters
of the f_0(600), kappa(800), rho(770) and K*(892) resonances generated from
elastic meson-meson scattering using unitarized one-loop Chiral Perturbation
Theory. We fit simultaneously all experimental scattering data up to 0.8-1 GeV
together with lattice results on decay constants and scattering lengths up to a
pion mass of 440 MeV. Then, the strange and non-strange quark masses are varied
from the chiral limit up to values of interest for lattice studies. In these
amplitudes, the mass and width of the rho(770) and K*(892) present a similar
and smooth quark mass dependence. In contrast, both scalars present a similar
non-analyticity at high quark masses. Nevertheless the f_0(600) dependence on
both quark masses is stronger than for the kappa(800) and the vectors. We also
confirm the lattice assumption of quark mass independence of the vector
two-meson coupling that, in contrast, is violated for scalars.Comment: To appear in the proceedings of the XIII International Conference on
Hadron Spectroscopy Nov.29-Dec.4, 2009. Tallahassee, Florida, USA. 5 page
Dependence on the quark masses of elastic phase shifts and light resonances within standard and unitarized Chiral Perturbation Theory
We study the dependence of the pion-pion scattering phase shifts on the light
quark mass in both standard and unitarized SU(2) Chiral Perturbation Theory
(ChPT) to one and two loops. We then use unitarized SU(3) ChPT to study the
elastic f_0(600), kappa(800), rho(770) and K*(892) resonances. The quark masses
are varied up to values of interest for lattice studies. We find a very soft
dependence on the light quark mass of the pion-pion phase shifts at one loop
and slightly stronger at two loops and a good agreement with lattice results.
The SU(3) analysis shows that the properties of the rho(770) and K*(892) depend
smoothly on the quark mass whereas the scalar resonances present a
non-analyticity at high quark masses. We also confirm the lattice assumption of
quark mass independence of the vector two-meson coupling that, however, is
violated for scalars.Comment: To appear in the proceedings of the 12th International Conference on
Meson-Nucleon Physics and the Structure of the Nucleon, College of William
and Mary Williamsburg, Virginia, May 31-June 4, 201
Strange and non-strange quark mass dependence of elastic light resonances from SU(3) Unitarized Chiral Perturbation Theory to one loop
We study the light quark mass dependence of the f_0(600), kappa(800),
rho(770) and K*(892) resonance parameters generated from elastic meson-meson
scattering using unitarized one-loop Chiral Perturbation Theory. First, we show
that it is possible to fit simultaneously all experimental scattering data up
to 0.8-1 GeV together with lattice results on decay constants and scattering
lengths up to a pion mass of 400 MeV, using chiral parameters compatible with
existing determinations. Then, the strange and non-strange quark masses are
varied from the chiral limit up to values of interest for lattice studies. In
these amplitudes, the mass and width of the rho(770) and K*(892) present a
similar and smooth quark mass dependence. In contrast, both scalars present a
similar non-analyticity at high quark masses. Nevertheless, the f_0(600)
dependence on the non-strange quark mass is stronger than for the kappa(800)
and the vectors. We also confirm the lattice assumption of quark mass
independence of the vector two-meson coupling that, in contrast, is violated
for scalars. As a consequence, vector widths are very well approximated by the
KSRF relation, and their masses are shown to scale like their corresponding
meson decay constants.Comment: 20 pages, 13 figures. References added to new version and region of
applicability slightly modified. Typos corrected
In silico transitions to multicellularity
The emergence of multicellularity and developmental programs are among the
major problems of evolutionary biology. Traditionally, research in this area
has been based on the combination of data analysis and experimental work on one
hand and theoretical approximations on the other. A third possibility is
provided by computer simulation models, which allow to both simulate reality
and explore alternative possibilities. These in silico models offer a powerful
window to the possible and the actual by means of modeling how virtual cells
and groups of cells can evolve complex interactions beyond a set of isolated
entities. Here we present several examples of such models, each one
illustrating the potential for artificial modeling of the transition to
multicellularity.Comment: 21 pages, 10 figures. Book chapter of Evolutionary transitions to
multicellular life (Springer
Efficient vasculature investment in tissues can be determined without global information
Cells are the fundamental building blocks of organs and tissues. Information and mass flow through cellular contacts in these structures is vital for the orchestration of organ function. Constraints imposed by packing and cell immobility limit intercellular communication, particularly as organs and organisms scale up to greater sizes. In order to transcend transport limitations, delivery systems including vascular and respiratory systems evolved to facilitate the movement of matter and information. The construction of these delivery systems has an associated cost, as vascular elements do not perform the metabolic functions of the organs they are part of. This study investigates a fundamental trade-off in vascularization in multicellular tissues: the reduction of path lengths for communication versus the cost associated with producing vasculature. Biologically realistic generative models, using multicellular templates of different dimensionalities, revealed a limited advantage to the vascularization of two-dimensional tissues. Strikingly, scale-free improvements in transport efficiency can be achieved even in the absence of global knowledge of tissue organization. A point of diminishing returns in the investment of additional vascular tissue to the increased reduction of path length in 2.5- and three-dimensional tissues was identified. Applying this theory to experimentally determined biological tissue structures, we show the possibility of a co-dependency between the method used to limit path length and the organization of cells it acts upon. These results provide insight as to why tissues are or are not vascularized in nature, the robustness of developmental generative mechanisms and the extent to which vasculature is advantageous in the support of organ function
Identification of non-ordinary mesons from the dispersive connection between their poles and their Regge trajectories: the f0(500) resonance
We show how the Regge trajectory of a resonance can be obtained from its pole
in a scattering process and analytic constraints in the complex angular
momentum plane. The method is suited for resonances that dominate an elastic
scattering amplitude. In particular, from the rho(770) resonance pole in
pion-pion scattering, we obtain its linear Regge trajectory, characteristic of
ordinary quark-antiquark states. In contrast, the f0(500) pole -the sigma
meson- which dominates scalar isoscalar pion-pion scattering, yields a
non-linear trajectory with a much smaller slope at the f0(500) mass.
Conversely, imposing a linear Regge trajectory for the f0(500), with a slope of
typical size, yields an elastic amplitude at odds with the data. This provides
strong support for the non-ordinary nature of the sigma meson.Comment: 8 pages, 4 figure
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