1,897 research outputs found
A 2-set-up Routley-Meyer Semantics for the 4-valued Relevant Logic E4
The logic BN4 can be considered as the 4-valued logic of the relevant conditional and the logic E4, as the 4-valued logic of (relevant) entailment. The aim of this paper is to endow E4 with a 2-set-up Routley-Meyer semantics. It is proved that E4 is strongly sound and complete w.r.t. this semantics
Odd Parity Light Baryon Resonances
We use a consistent SU(6) extension of the meson-baryon chiral Lagrangian
within a coupled channel unitary approach in order to calculate the T-matrix
for meson-baryon scattering in s-wave. The building blocks of the scheme are
the pion and nucleon octets, the rho nonet and the Delta decuplet. We identify
poles in this unitary T-matrix and interpret them as resonances. We study here
the non exotic sectors with strangeness S=0,-1,-2,-3 and spin J=1/2, 3/2 and
5/2. Many of the poles generated can be associated with known N, Delta, Sigma,
Lambda and Xi resonances with negative parity. We show that most of the
low-lying three and four star odd parity baryon resonances with spin 1/2 and
3/2 can be related to multiplets of the spin-flavor symmetry group SU(6). This
study allows us to predict the spin-parity of the Xi(1620), Xi(1690), Xi(1950),
Xi(2250), Omega(2250) and Omega(2380) resonances, which have not been
determined experimentally yet.Comment: New appendix and references adde
Spectroscopic search for binaries among EHB stars in globular clusters
We performed a spectroscopic search for binaries among hot Horizontal Branch
stars in globular clusters. We present final results for a sample of 51 stars
in NGC6752, and preliminary results for the first 15 stars analyzed in M80. The
observed stars are distributed along all the HBs in the range 8000 < Teff <
32000 K, and have been observed during four nights. Radial velocity variations
have been measured with the cross-correlation technique. We carefully analyzed
the statistical and systematic errors associated with the measurements in order
to evaluate the statistical significance of the observed variations. No close
binary system has been detected, neither among cooler stars nor among the
sample of hot EHB stars (18 stars with Teff > 22000 K in NGC6752). The data
corrected for instrumental effects indicate that the radial velocity variations
are always below the 3sigma level of ~15 km/s. These results are in sharp
contrast with those found for field hot subdwarfs, and open new questions about
the formation of EHB stars in globular clusters, and possibly of the field
subdwarfs.Comment: To appear in Baltic Astronomy. Proceedings of the 2nd meeting on Hot
Subdwarf Stars, La Palma, June 2005. 4 pages, 2 figure
Charmed hadrons in nuclear medium
We study the properties of charmed hadrons in dense matter within a
coupled-channel approach which accounts for Pauli blocking effects and meson
self-energies in a self-consistent manner. We analyze the behaviour in this
dense environment of dynamically-generated baryonic resonances as well as the
open-charm meson spectral functions. We discuss the implications of the
in-medium properties of open-charm mesons on the and the
predicted X(3700) scalar resonances.Comment: 4 pages, 5 figures, invited parallel talk in the 5th International
Conference on Quarks and Nuclear Physics (QNP09), Beijing, September 21-26,
200
Strange and charm mesons at FAIR
We study the properties of strange and charm mesons in hot and dense matter
within a self-consistent coupled-channel approach for the experimental
conditions of density and temperature expected for the CBM experiment at
FAIR/GSI. The in-medium solution at finite temperature accounts for Pauli
blocking effects, mean-field binding of all the baryons involved, and meson
self-energies. We analyze the behaviour in this hot and dense environment of
dynamically-generated baryonic resonances together with the evolution with
density and temperature of the strange and open-charm meson spectral functions.
We test the spectral functions for strange mesons using energy-weighted sum
rules and finally discuss the implications of the properties of charm mesons on
the D_{s0}(2317) and the predicted X(3700) scalar resonances.Comment: 12 pages, 9 figures, invited talk at XXXI Mazurian Lakes Conference
on Physics: Nuclear Physics and the Road to FAIR, August 30-September 6,
2009, Piaski, Polan
The link between chemical anomalies along the red giant branch and the horizontal branch extension in globular clusters
We find a strong correlation between the extension of the Na-O
anticorrelation observed in red giant branch (RGB) stars and the high
temperature extension of the horizontal branch (HB) blue tails of Galactic
globular clusters (GCs). The longer is the O-depleted tail of the Na-O
anticorrelation observed in the RGB stars, the higher is the maximum
temperature reached by the bluest HB stars in the GC. This result provides a
clear, empirical evidence of a link between the extension of the HB and the
presence of star-to-star abundance variations of proton-capture elements in GC
stars. We discuss the possible interpretation of this correlation.Comment: Comments: 6 pages, 1 figure, uses emulateapj.cls; accepted for
publication in the Astrophysical Journal Letter
Rotation of Hot Horizontal Branch Stars in the Globular Clusters NGC 1904, NGC 2808, NGC 6093 and NGC 7078
We present high resolution UVES+VLT spectroscopic observations of 56 stars in
the extended horizontal branch (EHB) of the Galactic globular clusters NGC
1904, NGC 2808, NGC 6093, and NGC 7078. Our data reveal for the first time the
presence in NGC 1904 of a sizable population of fast (vsini > 20 km/s)
horizontal branch (HB) rotators, confined to the cool end of the EHB, similar
to that found in M13. We also confirm the fast rotators already observed in NGC
7078. The cooler stars (Teff < 11,500 K) in these three clusters show a range
of rotation rates, with a group of stars rotating at ~ 15 km/s or less, and a
fast rotating group at ~ 30 km/s. Apparently, the fast rotators are relatively
more abundant in NGC 1904 and M13, than in NGC 7078. No fast rotators have been
identified in NGC 2808 and NGC 6093. All the stars hotter than Teff ~ 11,500 K
have projected rotational velocities vsini < 12 km/s, but less than 20% have
vsini < 2 km/s. The connection between photometric gaps in the HB and the
change in the projected rotational velocities is not confirmed by the new data.
However, our data are consistent with a relation between this discontinuity and
the HB jump. We discuss a number of possibilities for the origin of the stellar
rotation distribution along the HB. We conclude that none of them can yet
provide a satisfactory explanation of the observations.Comment: 12 pages, 3 figures, ApJ Letter, accepte
- …