14,258 research outputs found
Neutral and charged pion production in the S-matrix approach
The S-matrix approach is applied to charged and neutral pion production in pp
collisions, in which the spin/isospin channels filter differently the
rescattering mechanism. The chiral perturbation theory rescattering amplitude
is employed. The contributions from the single-nucleon, Z-diagrams and
Delta-isobar mechanisms are also included. For the reactions investigated, the
convergence of the partial wave series is quite satisfactory and J=0 is enough
to describe the data close to threshold.Comment: To appear in the proceedings of the 6th International Conference on
Nuclear Physics at Storage Rings (STORI'05), Julich - Bonn, Germany, 23-26
May 200
A new approach to the asymptotics for Sobolev orthogonal polynomials
In this paper we deal with polynomials orthogonal with respect to an inner
product involving derivatives, that is, a Sobolev inner product. Indeed, we
consider Sobolev type polynomials which are orthogonal with respect to
where is a certain probability measure with unbounded support. For
these polynomials, we obtain the relative asymptotics with respect to
orthogonal polynomials related to , Mehler--Heine type asymptotics and
their consequences about the asymptotic behaviour of the zeros. To establish
these results we use a new approach different from the methods used in the
literature up to now. The development of this technique is highly motivated by
the fact that the methods used when is bounded do not work.Comment: 31 page
Short-range three-nucleon forces and low-energy constants
The 3N forces due to pi-rho, pi-sigma and pi-omega exchanges following from
the nucleon Born diagrams and diagrams with an intermediate N^{*}(1440) are
re-analyzed. The cancellation between pi-sigma and pi-omega forces is rather
sensitive to the values of the coupling constants and to the form of the piNN
vertex. Experimental uncertainties in the parameters of the TM pi-pi potential
are assessed. They lead to uncertainties in theoretical predictions of the
triton binding energy of about 0.4 MeV. The low-energy limit of pi-sigma and
pi-omega potentials is performed. It defines the coupling constants of
effective contact piNNNN vertices, which are compared with the corresponding
contact vertices of Chiral Perturbation Theory.Comment: 41 pages, 3 figures (4 *.eps files
Three-dimensional angular momentum projected relativistic point-coupling approach for the low-lying excited states in Mg
A full three-dimensional angular momentum projection on top of a triaxial
relativistic mean-Geld calculation is implemented for the first time. The
underlying Lagrangian is a point coupling model and pairing correlations are
taken into account by a monopole force. This method is applied for the
low-lying excited states in 24Mg. Good agreement with the experimental data is
found for the ground state properties. A minimum in the potential energy
surface for the 2+ state, with beta = 0.55, gamma = 10 deg, is used as the
basis to investigate the rotational energy spectrum as well as the
corresponding B(E2) transition probabilities as compared to the available data.Comment: 10 pages, 5 figure
Pion re-scattering operator in the S-matrix approach
The pion re-scattering operator for pion production, derived recently in
time-ordered perturbation theory, is compared with the one following from the
simple S-matrix construction. We show that this construction is equivalent to
the on-shell approximation introduced in previous papers. For a realistic NN
interaction, the S-matrix approach, and its simplified fixed
threshold-kinematics version, work well near threshold.Comment: 17 pages, 7 figure
Aspects of the T-duality construction for the Supermembrane theory
In this note we explicitly show how the generalization of the T-duality
symmetry of the supermembrane theory compactified in M9xT2 can be reduced to a
parabolic subgroup of SL(2,Z) that acts non-linearly on the moduli parameters
and on the KK and winding charges of the supermembrane. This is a first step
towards a deeper understanding of the dual relation between the parabolic type
II gauged supergravity in nine dimensions.Comment: 6 pages, Latex, Proceedings for the XIX Simposio Chileno de Fisica,
SOCHIFI 2014 Conference, 26-28 November 2014, held at Concepcion U., Chil
T-duality Invariance of the Supermembrane
We show that the supermembrane theory compactified on a torus is invariant
under T-duality. There are two different topological sectors of the
compactified supermembrane (M2) classified according to a vanishing or
nonvanishing second cohomology class. We find the explicit T-duality
transformation that acts locally on the supermembrane theory and we show that
it is an exact symmetry of the theory. We give a global interpretation of the
T-duality in terms of bundles. It has a natural description in terms of the
cohomology of the base manifold and the homology of the target torus. We show
that in the limit when the torus degenerate into a circle and the M2 mass
operator restricts to the string-like configurations, the usual closed string
T-duality transformation between the type IIA and type IIB mass operators is
recovered. Moreover if we just restrict M2 mass operator to string-like
configurations but we perform a generalized T-duality we find the SL(2,Z)
non-perturbative multiplet of IIA.Comment: 8pages, Latex. Proceeding of the XXI International Workshop on
Geometry and Physics held at U.Burgos, Spai
Characterizing the variability of Melotte 111 AV 1224: a new variable star in the Coma Berenices open cluster
A search for new pulsating stars in the Coma Berenices open cluster was
carried out. As a result of this search the cluster member Melotte 111 AV 1224
presented clear indications of photometric variability. In order to determine
its physical parameters Str\"omgren standard indices and low-resolution spectra
were acquired. In this work we present the preliminary results of these
observations.Comment: To be published in conference proceedings of IAU Symposium 301:
Precision Asteroseismology, held in Wroclaw, Poland, August 201
Charged and neutral pion production in the S-matrix approach
The S-matrix approach is used to calculate charged as well as neutral pion
production reactions from NN scattering, with the same set of underlying
processes and interactions. The chiral perturbation theory piN scattering
amplitude is used. For the nucleon-nucleon distortions a newly developed
realistic potential within the Bonn family of potentials, valid well above the
pion production threshold, is considered. In the pi+ production case, the NN
potential, the piN relative p-waves and the treatment of the exchanged pion
energy build up the observed cross-section strength.Comment: 8 pages, 5 figure
Searching for short-period variable stars in the direction of Coma Berenices and Upgren 1 open clusters: Melotte 111 AV 1224 a new eclipsing binary star
We report the results of CCD photometric observations in the direction of the
Coma Berenices and Upgren 1 open clusters with the aim at searching for new
short-period variable stars. A total of 35 stars were checked for variability.
As a result of this search the star designated in the SIMBAD database as
Melotte 111 AV 1224 was found to be a new eclipsing binary star. Follow-up
Str\"omgren photometric and spectroscopic observations allowed us to derive the
spectral type, distance, reddening and effective temperature of the star. A
preliminary analysis of the binary light curve was performed and the parameters
of the orbital system were derived. From the derived physical parameters we
conclude that Melotte 111 AV 1224 is most likely a W UMa eclipsing binary that
is not a member of the Coma Berenices open cluster. On other hand, we did not
find evidence of brightness variations in the stars NSV 5612 and NSV 5615
previously catalogued as variable stars in Coma Berenices open cluster.Comment: 9 pages, 9 figures, 4 tables, accepted for publication in New
Astronom
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