357 research outputs found
Large Weinberg-Tomozawa interaction and spin-flavor symmetry
The construction of an extended version of the Weinberg-Tomozawa Lagrangian,
in which baryons and mesons form spin-flavor multiplets, is reviewed and some
of its properties discussed, for an arbitrary number of colors and flavors. The
coefficient tables of spin-flavor irreducible representations related by
crossing between the -, - and -channels are explicitly constructed.Comment: 3 pages, no figures. Presented at the IVth International Conference
on Quarks and Nuclear Physics, Madrid, June 5th-10th 200
Entangled spinning particles in charged and rotating black holes
Spin precession for an EPR pair of spin-1/2 particles in equatorial orbits
around a Kerr-Newman black hole is studied. Hovering observers are introduced
to ensure fixed reference frames in order to perform the Wigner rotation. These
observers also guarantee a reliable direction to compare spin states in
rotating black holes. The velocity of the particle due frame-dragging is
explicitly incorporated by addition of velocities with respect the hovering
observers and the corresponding spin precession angle is computed. The
spin-singlet state is observed to be mixed with the spin-triplet by dynamical
and gravity effects, thus it is found that a perfect anti-correlation of
entangled states for these observers is deteriorated. Finally, an analysis
concerning the different limit cases of parameters of spin precession including
the frame-dragging effects is carried out.Comment: 25+1 pages, 7 eps figures. Major changes were made through all the
manuscript. Clarifications regarding modifications were introduced through
the draft. Figures were changed and reduced in number. arXiv admin note: text
overlap with arXiv:quant-ph/030711
Meson-Baryon s-wave Resonances with Strangeness -3
Starting from a consistent SU(6) extension of the Weinberg-Tomozawa (WT)
meson-baryon chiral Lagrangian (Phys. Rev. D74 (2006) 034025), we study the
s-wave meson-baryon resonances in the strangeness S=-3 and negative parity
sector. Those resonances are generated by solving the Bethe-Salpeter equation
with the WT interaction used as kernel. The considered mesons are those of the
35-SU(6)-plet, which includes the pseudoscalar (PS) octet of pions and the
vector (V) nonet of the rho meson. For baryons we consider the 56-SU(6)-plet,
made of the 1/2+ octet of the nucleon and the 3/2+ decuplet of the Delta.
Quantum numbers I(J^P)=0(3/2^-) are suggested for the experimental resonances
Omega*(2250)- and Omega*(2380)-. Among other, resonances with I=1 are found,
with minimal quark content sss\bar{l}l', being s the strange quark and l, l'
any of the the light up or down quarks. A clear signal for such a pentaquark
would be a baryonic resonance with strangeness -3 and electric charge of -2 or
0, in proton charge units. We suggest looking for K- Xi- resonances with masses
around 2100 and 2240 MeV in the sector 1(1/2^-), and for pi Omega- and K- Xi*-
resonances with masses around 2260 MeV in the sector 1(3/2^-).Comment: 3 pages, 1 Postscript figure, 7 table
Resonances and the Weinberg--Tomozawa 56-baryon --35-meson interaction
Vector meson degrees of freedom are incorporated into the
Weinberg-Tomozawa (WT) meson-baryon chiral Lagrangian by using a scheme which
relies on spin--flavor SU(6) symmetry. The corresponding Bethe-Salpeter
approximation successfully reproduces previous SU(3)--flavor WT results for the
lowest-lying s--wave negative parity baryon resonances, and it also provides
some information on the dynamics of the heavier ones. Moreover, it also
predicts the existence of an isoscalar spin-parity bound
state (strangeness +1) with a mass around 1.7--1.8 GeV, unstable through
decay. Neglecting d-wave KN decays, this state turns out to be quite narrow
( MeV) and it might provide clear signals in reactions like
by looking at the three body
invariant mass.Comment: Talk given at the IVth International Conference on Quarks an Nuclear
Physics, Madrid, June 5th-10th 2006. Minor correction
Internal rotation of red giants by asteroseismology
We present an asteroseismic approach to study the dynamics of the stellar
interior in red-giant stars by asteroseismic inversion of the splittings
induced by the stellar rotation on the oscillation frequencies. We show
preliminary results obtained for the red giant KIC4448777 observed by the space
mission Kepler.Comment: 3 pages, 4 figures, the 40th Liege International Astrophysical
Colloquium Liac40, 'Ageing low mass stars: from red giants to white dwarfs',
to be published on EPJ Web of Conference
The age-metallicity relation in the solar neighbourhood from a pilot sample of white dwarf-main sequence binaries
The age-metallicity relation (AMR) is a fundamental observational constraint for understanding how the Galactic disc formed and evolved chemically in time. However, there is not yet an agreement on the observational properties of the AMR for the solar neighbourhood, primarily due to the difficulty in obtaining accurate stellar ages for individual field stars. We have started an observational campaign for providing the much needed observational input by using wide white-dwarf-main-sequence (WDMS) binaries. White dwarfs are `natural' clocks and can be used to derive accurate ages. Metallicities can be obtained from the main-sequence companions. Since the progenitors of white dwarfs and the main-sequence stars were born at the same time, WDMS binaries provide a unique opportunity to observationally constrain in a robust way the properties of the AMR. In this work we present the AMR derived from analysing a pilot sample of 23 WDMS binaries and provide clear observational evidence for the lack of correlation between age and metallicity at young and intermediate ages (0-7 Gyr)
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