643 research outputs found
Amplitudes Fitted to Experimental Data and to Roy's Equations
The scalar-isoscalar, scalar-isotensor and vector-isovector pi-pi amplitudes
are fitted simultaneously to experimental data and to Roy's equations. The
resulting amplitudes are compared with those fitted only to experimental data.
No additional constraints for the pi-pi threshold behaviour of the amplitudes
are imposed. Threshold parameters are calculated for the amplitudes in the
three waves. Spectrum of scalar mesons below 1.8 GeV is found from the analysis
of the analytical structure of the fitted amplitudes.Comment: 3 pages, 1 figure. Talk given at MESON 2004: 8th International
Workshop on Meson Production, Properties and Interactions, Cracow, Poland,
4-8 Jun 2004. Submitted to Int.J.Mod.Phys.
Forward dispersion relations and Roy equations in pi-pi scattering
We review results of an analysis of pipi interactions in S, P and D waves for
two-pion effective mass from threshold to about 1.4 GeV. In particular we show
a recent improvement of this analysis above the K anti-K threshold using more
data for phase shifts and including the S0 wave inelasticity from pipi -> K
anti-K. In addition, we have improved the fit to the f2(1270) resonance and
used a more flexible P wave parametrization above the K anti-K threshold and
included an estimation of the D2 wave inelasticity. The better accuracy thus
achieved also required a refinement of the Regge analysis above 1.42 GeV. We
have checked that the pipi scattering amplitudes obtained in this approach
satisfy remarkably well forward dispersion relations and Roy's equations.Comment: 6 pages, invited talk to the IV International Conference on Quarks
and Nuclear Physics QNP06, Madrid 5th-10th June 200
Properties of scalar--isoscalar mesons from multichannel interaction analysis below 1800 MeV
Scalar-isoscalar mesons are studied using an unitary model in three channels:
pi-pi, K-anti K and an effective 2pi-2pi.
All the solutions, fitted to the pi-pi and K-anti K data, exhibit a wide
f0(500), a narrow f0(980) and two relatively narrow resonances, lying on
different sheets between 1300 MeV and 1500 MeV.
These latter states are similar to the f0(1370) and f0(1500) seen in
experiments at CERN. Branching ratios are compared with available data. We have
started investigations of some crossing symmetry and chiral constraints imposed
near the pi-pi threshold on the scalar-isoscalar, scalar-isotensor and P-wave
pi-pi amplitudes.Comment: Talk given at XVth Particles and Nuclei Int. Conf. (PANIC99),
Uppsala, Sweden, June 10-16, 1999; 4 pages, 3 figures, file espcrc1.sty
include
Direct vs. final state tensor meson photoproduction - amplitude analysis
Tensor meson photoproduction is described as either a direct production
process or a consequence of the final state \pi\pi interactions. We calculate
the mass distributions for selected partial waves and confront our predictions
with the measurements of the CLAS experiment. We also point out the structures
in the photoproduction amplitudes which may result in observable effects able
to indicate the dominant tensor meson photoporduction mechanism
photoproduction in the coupled channel model
We calculated the coupled channel photoproduction amplitudes of the scalar
isovector resononace , which include the , and
intermediate states. Based on them we obtained the mass
distribution in the channel at photon energy =7 GeV,
corresponding to energy accissible in new JLab experiments CLAS12 and GlueX. We
also analyzed the shape of mass distribution as a function of the phase of the
background amplitude.Comment: 5 pages, 3 figure
Optical spectropolarimetry of V4332 Sagittarii
The eruption of V4332 Sgr was observed in 1994. During the outburst, the
object became extremely red, so it has been considered as to belong to red
transients of the V838 Mon type. Optical spectroscopy obtained a few years
after the eruption showed a faint M-type stellar spectrum underlying numerous
molecular and atomic emission features. It has recently been suggested that the
central object in V4332 Sgr is now hidden in a dusty disc and that the
photospheric spectrum of this object observed in the optical results from
scattering of the radiation of the central star on dust grains in the
circumstellar matter. Recent polarimetric photometry has shown that the optical
radiation of the object is indeed strongly polarized. We present and analyse
our spectropolarimetric observations of V4332 Sgr obtained with the VLT in the
optical region. The optical continuum of V4332 Sgr is linearly polarized with a
typical degree of 16.6%. A clear depolarization is observed in the spectral
regions where emission features contribute significantly to the observed flux.
The only prominent exception is the CaI 6573 emission line, which is polarized
in 21%. The results of our spectropolarimetric observations are in accord with
the proposed geometry of the system and the advocated nature of the observed
optical spectrum of V4332 Sgr. The continuum is not seen directly but results
from scattering on dust within the disc and polar outflow, while most of the
gas emission comes from the polar outflow excited by the radiation field of the
central source. Additionally, the observed polarization patterns suggest a
stratification of the outflow.Comment: accepted for publication in Astronomy & Astrophysic
Evolution of the stellar-merger red nova V1309 Scorpii: SED analysis
One very important object for understanding the nature of red novae is V1309
Sco. Its pre-outburst observations showed that, before its red-nova eruption in
2008, it was a contact binary quickly evolving to the merger of the components.
It thus provided us with a direct evidence that the red novae result from
stellar mergers. We analyse the spectral energy distribution (SED) of the
object and its evolution with time. From various optical and infrared surveys
and observing programmes carried out with OGLE, HST, VVV, Gemini South, WISE,
Spitzer, and Herschel we constructed observed SED in 2010 and 2012. Some
limited data are also available for the red-nova progenitor in 2007. We analyse
the data with our model of a dusty envelope surrounding a central star. Dust
was present in the pre-outburst state of V1309 Sco. Its high temperature
(900-1000 K) suggests that this was a freshly formed dust in a presumable
mass-loss from the spiralling-in binary. Shortly after its 2008 eruption,
V1309~Sco became almost completely embedded in dust. The parameters
(temperature, dimensions) of the dusty envelope in 2010 and 2012 evidence that
we then observed matter lost by the object during the 2008 outburst. Its mass
is at least . The object remains quite luminous, although
since its maximum brightness in September 2008, it has faded in luminosity by a
factor of ~50 (in 2012). Far infrared data from Herschel reveal presence of a
cold (~30 K) dust at a distance of a few thousand AU from the object. This
conclusion could be verified by submillimeter interferometric observations.Comment: 12 pages, 7 figures, accepted in Astronomy & Astrophysisc
Multichannel Interaction Analysis of Scalar Mesons Below 1800 MeV
Properties of scalar--isoscalar mesons in a mass range from pi-pi threshold
up to 1800 MeV are analysed using an unitary model with separable interactions
in three decay channels: pi-pi, K-anti K and an effective 2pi-2pi. Different
solutions are obtained by fitting pi-pi and K-anti K data. Analytical structure
of the meson-meson multichannel amplitudes is studied with a special emphasis
on the important role played by the S-matrix zeroes. The dependence of the
positions of S-matrix singularities on the interchannel coupling strength is
investigated. Poles, located in the complex energy plane not too far from the
physical region, are interpreted as scalar resonances: a wide f0(500), a narrow
f0(980) and a relatively narrow f0(1400). In all our solutions two resonances,
lying on different sheets, in the energy region between 1300 MeV and 1500 MeV
are found. These states may be compared with the resonances f0(1370) and
f0(1500) seen in the experiments at CERN. Total, elastic and inelastic channel
cross sections, branching ratios and coupling constants are evaluated and
compared with available data.Comment: Talk given at Workshop on Hadron Spectroscopy, Frascati (Rome) -
Italy, March 8-12, 1999. To be published in Frascati Physics Series, 8 pages,
4 figures, included file frascatiphys.st
The pion-pion scattering amplitude. II: Improved analysis above threshold
We improve, in the energy region between threshold and
GeV, the energy-dependent phase shift analysis of scattering presented
in a previous paper. For the S0 wave we have included more data above
threshold and we have taken into account systematically the
elasticity data on the reaction . We here made a coupled
channel fit. For the D0 wave we have considered information on low energy
parameters, and imposed a better fit to the resonance. For both waves the
expressions we now find are substantially more precise than the previous ones.
We also provide slightly improved D2 and P waves, including the estimated
inelasticity for the first, and a more flexible parametrization between 1 and
1.42 GeV for the second. The accuracy of our amplitudes is now such that it
requires a refinement of the Regge analysis, for GeV, which
we also carry out. We show that this more realistic input produces
scattering amplitudes that satisfy better forward dispersion relations,
particularly for scattering.Comment: Plain TeX. 12 figures. Minor anomaly in the K-matrix fit corrected by
moving matching point to 932 MeV, and pole to 910.6 MeV. Results
unaltere
High-resolution optical spectroscopy of V838 Monocerotis in 2009
V838 Mon erupted at the beginning of 2002. In the course of the outburst the
object evolved to low effective temperatures and declined as a very late M-type
supergiant. Among various scenarios proposed to explain the nature of the
outburst, the most promising is a stellar merger event. We aim at studying the
structure and evolution of the object in the decline from the 2002 eruption. We
obtained spectroscopic observations of V838 Mon in January--March 2009 with
UVES/VLT. The results are analysed and compared with similar observations
obtained in October 2005 with HIRES/Keck. The most striking difference between
2009 and 2005 is a complete absence of the B3V component and of the [FeII]
emission lines in 2009. The present spectrum displays only the spectrum of the
2002 eruption remnant. It resembles that of an M6 giant, although the molecular
bands in V838 Mon are deeper than those in standard stellar spectra of a
similar spectral class. Several atomic lines, which displayed P-Cyg profiles in
2005, are now dominated by pure absorptions. Some of these lines, however, show
a narrow emission component, which, as we argue, measures the radial velocity
of V838 Mon. The resulting heliocentric velocity is 71 km/s, which very well
agrees with the velocity obtained from SiO maser observations. The atomic lines
and the molecular bands show very complex kinematics. In some atomic lines and
high-excitation molecular bands we observe matter infalling in the object
atmosphere. The infall components were already observed in 2005, but were less
pronounced and present in fewer lines than in 2009. We argue that the most
negative radial velocity components seen in the resonance atomic lines and in
the low-excitation molecular bands were formed in the ejecta of the 2002
eruption. The B3V companion most probably became engulfed in an opaque dusty
matter of the 2002 V838 Mon ejecta.Comment: A&A, in pres
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