24,655 research outputs found
The reaction in coupled channel chiral models up to next-to-leading order
We study the meson-baryon interaction in S-wave in the strangeness S=-1
sector using a chiral unitary approach based on a next-to-leading order chiral
SU(3) Lagrangian. We fit our model to the large set of experimental data in
different two-body channels. We pay particular attention to the reaction, where the effect of the next-to-leading order
terms in the Lagrangian are sufficiently large to be observed, since at tree
level the cross section of this reaction is zero. For these channels we improve
our approach by phenomenologically taking into account effects of the high spin
hyperonic resonances.Comment: 8 pages, 4 figures, presented at the II Russian-Spanish Congress
"Particle and Nuclear Physics at all Scales and Cosmology", Saint-Petersburg,
October 1-4, 2013. arXiv admin note: text overlap with arXiv:1311.5025; and
with arXiv:hep-ph/0505239 by other author
Explicit minimal Scherk saddle towers of arbitrary even genera in
Starting from works by Scherk (1835) and by Enneper-Weierstra\ss \ (1863),
new minimal surfaces with Scherk ends were found only in 1988 by Karcher (see
\cite{Karcher1,Karcher}). In the singly periodic case, Karcher's examples of
positive genera had been unique until Traizet obtained new ones in 1996 (see
\cite{Traizet}). However, Traizet's construction is implicit and excludes {\it
towers}, namely the desingularisation of more than two concurrent planes. Then,
new explicit towers were found only in 2006 by Martin and Ramos Batista (see
\cite{Martin}), all of them with genus one. For genus two, the first such
towers were constructed in 2010 (see \cite{Valerio2}). Back to 2009, implicit
towers of arbitrary genera were found in \cite{HMM}. In our present work we
obtain {\it explicit} minimal Scherk saddle towers, for any given genus ,
WISE morphological study of Wolf-Rayet nebulae
We present a morphological study of nebulae around Wolf-Rayet (WR) stars
using archival narrow-band optical and Wide-field Infrared Survey Explorer
(WISE) infrared images. The comparison among WISE images in different bands and
optical images proves to be a very efficient procedure to identify the nebular
emission from WR nebulae, and to disentangle it from that of the ISM material
along the line of sight. In particular, WR nebulae are clearly detected in the
WISE W4 band at 22 m. Analysis of available mid-IR Spitzer spectra shows
that the emission in this band is dominated by thermal emission from dust
spatially coincident with the thin nebular shell or most likely with the
leading edge of the nebula. The WR nebulae in our sample present different
morphologies that we classified into well defined WR bubbles (bubble -type nebulae), clumpy and/or disrupted shells (clumpy/disrupted -type nebulae), and material mixed with the diffuse medium (mixed -type nebulae). The variety of morphologies presented by WR nebulae shows a
loose correlation with the central star spectral type, implying that the
nebular and stellar evolutions are not simple and may proceed according to
different sequences and time-lapses. We report the discovery of an obscured
shell around WR35 only detected in the infrared.Comment: 11 pages, 6 figures, plus 23 appendix figures; to appear in Astronomy
and Astrophysic
Evidence for the two pole structure of the Lambda(1405) resonance
The K^- p --> pi^0 pi^0 Sigma^0 reaction is studied within a chiral unitary
model. The distribution of pi^0 Sigma^0 states forming the Lambda(1405) shows,
in agreement with a recent experiment, a peak at 1420 MeV and a relatively
narrow width of Gamma = 38 MeV. The mechanism for the reaction is largely
dominated by the emission of a pi^0 prior to the K^- p interaction leading to
the Lambda(1405). This ensures the coupling of the Lambda(1405) to the K^- p
channel, thus maximizing the contribution of the second state found in chiral
unitary theories, which is narrow and of higher energy than the nominal
Lambda(1405). This is unlike the pi^- p --> K^0 \pi Sigma reaction, which gives
more weight to the pole at lower energy and with a larger width. The data of
these two experiments, together with the present theoretical analysis, provides
a firm evidence of the two pole structure of the Lambda(1405).Comment: 4 pages, 6 figure
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