686 research outputs found
Light scalar mesons in NN decays in a chiral unitary approach
We study the four-body decays {\it meson meson} using
a chiral unitary approach to account for the meson meson final state
interaction (FSI). The calculation of the
process properly reproduces the experimental data after taking the FSI of
mesons and the contribution of intermediate meson into account. The
isoscalar resonances , and the isovector resonance
are generated through the FSI of the mesons in the channels
and ,
respectively. We also calculate the two mesons invariant mass distribution and
the partial decay width of and , on which there is still no experimental data available.Comment: 13 pages, 5 figures in LaTex, version accepted by Phys. Rev.
The two pion decay of the Roper resonance
We evaluate the two pion decay of the Roper resonance in a model where
explicit re-scattering of the two final pions is accounted for by the use of
unitarized chiral perturbation theory. Our model does not include an explicit
or scalar-isoscalar meson decay mode, instead it
generates it dynamically by means of the pion re-scattering. The two ways,
explicit or dynamically generated, of introducing this decay channel have very
different amplitudes.
Nevertheless, through interference with the other terms of the model we are
able to reproduce the same phenomenology as models with explicit consideration
of the meson.Comment: 17 latex pages, 11 eps figures. A few misprints corrected. A few new
references. Version accepted for publication in Phys. Rev.
Chiral unitary theory: application to nuclear problems
In this talk we briefly describe some basic elements of chiral perturbation
theory, , and how the implementation of unitarity and other novel
elements lead to a better expansion of the matrix for meson meson and meson
baryon interactions. Applications are then done to the interaction
in nuclear matter in the scalar and vector channels, antikaons in nuclei and
atoms, and how the meson properties are changed in a nuclear
medium.Comment: 15 pages, 9 figures, Invited talk in the International Symposium on
Nuclear Physics, Bombay, december 200
On the size of the sigma meson and its nature
In this work the nature of the \sigma or f_0(600) resonance is discussed by
evaluating its quadratic scalar radius, \la r^2\ra_s^\sigma. This allows one to
have a quantitative estimate for the size of this resonance. We obtain that the
\sigma resonance is a compact object with \la
r^2\ra_s^\sigma=(0.19\pm0.02)-i(0.06\pm0.02) fm^2. Within our approach,
employing unitary chiral perturbation theory, the \sigma is a dynamically
generated resonance that stems from the pion-pion interactions. Given its small
size we conclude that the two pions inside the resonance are merged. A
four-quark picture is then more appropriate. However, when the pion mass
increases, for pion masses somewhat above 400 MeV, the picture of a two-pion
molecule is the appropriate one. The \sigma is then a spread \pi\pi bound
state. These results are connected with other recent works that support a non
standard nature of the \sigma as well, while fulfilling strong QCD constraints,
as well as with lattice QCD. We offer a detailed study of the low-energy S-wave
\pi\pi scattering data from where we extract our values for the threshold
parameters of S-wave \pi\pi phase shifts, the {\cal O}(p^4) chiral perturbation
theory low energy constants as well as the \sigma pole position. From the
comparison with other accurate determinations in the literature we obtain the
average values for the isospin 0 S-wave \pi\pi threshold parameters,
, , and for the real and
imaginary parts of the \sigma pole position in \sqrt{s},
MeV. The quark mass dependence of the size of the \sigma, its mass and width
are considered too. The latter agree accurately with a previous lattice QCD
calculation. The fact that the mass of this resonance tends to follow the
threshold of two pions is a clear indication that the \sigma is a dynamically
generated meson-meson resonance.Comment: 31 pages, 21 figure
The nature of the Lambda(1405)
We present here some results supporting the nature of the
resonance as dynamically generated from the meson baryon interaction in coupled
channels and resulting from the superposition of two close-by poles. We find
support for this picture in the reaction,
which shows a different shape than the one obtained from the reaction. We also call the attention to the with in the region, which shows a narrow
peak in the calculations around 1420 MeV. We also report on recent calculations
of the radiative decay of the two states and on reactions to
obtain information on these decay modes. Finally, we present results for the
reaction recently measured at ANKE/COSY and compare
them with theoretical results.Comment: Talk given at the NSTAR2007 Workshop, Bonn September 200
Thermal rho and sigma mesons from chiral symmetry and unitarity
We study the temperature evolution of the rho and sigma mass and width, using
a unitary chiral approach. The one-loop pion-pion scattering amplitude in
Chiral Perturbation Theory at finite temperature is unitarized via the Inverse
Amplitude Method. Our results predict a clear increase with T of both the rho
and sigma widths. The masses decrease slightly for high T, while the
rho-pion-pion coupling increases. The rho behavior seems to be favored by
experimental results. In the sigma case, it signals chiral symmetry
restoration.Comment: 5 pages, 5 figures, revtex. References and brief comments added.
Final version to appear in Phys. Rev.
Chiral Symmetry and light resonances in hot and dense matter
We present a study of the scattering amplitude in the and
channels at finite temperature and nuclear density within a chiral
unitary framework. Meson resonances are dynamically generated in our approach,
which allows us to analyze the behavior of their associated scattering poles
when the system is driven towards chiral symmetry restoration. Medium effects
are incorporated in three ways: (a) by thermal corrections of the unitarized
scattering amplitudes, (b) by finite nuclear density effects associated to a
renormalization of the pion decay constant, and complementarily (c) by
extending our calculation of the scalar-isoscalar channel to account for finite
nuclear density and temperature effects in a microscopic many-body
implementation of pion dynamics. Our results are discussed in connection with
several phenomenological aspects relevant for nuclear matter and Heavy-Ion
Collision experiments, such as mass scaling vs broadening from dilepton
spectra and chiral restoration signals in the channel. We also
elaborate on the molecular nature of resonances.Comment: 14 pages, 14 figures. Contribution to Hard Probes 2008, Illa de A
Toxa, Spain, June 8th-14th 200
Recent Developments in Chiral Unitary Dynamics of Resonances
In this talk I summarize recent findings made on the description of axial
vector mesons as dynamically generated states from the interaction of
peseudoscalar mesons and vector mesons, dedicating some attention to the two
states. Then I review the generation of open and hidden charm
scalar and axial states. Finally, I present recent results showing that the low
lying baryon resonances for S=-1 can be obtained as bound states or
resonances of two mesons and one baryon in coupled channels dynamics.Comment: Talk at the International Conference on Hadron Physics, Troia07,
Canakkale, Turkey, Sep. 2007 and at the Chiral Symmetry in Hadron and Nuclear
Physics Workshop, Chiral07, Osaka, November 200
Baryon polarization in low-energy unpolarized meson-baryon scattering
We compute the polarization of the final-state baryon, in its rest frame, in
low-energy meson--baryon scattering with unpolarized initial state, in
Unitarized BChPT. Free parameters are determined by fitting total and
differential cross-section data (and spin-asymmetry or polarization data if
available) for , and scattering. We also compare our
results with those of leading-order BChPT
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