34566153
Radiative Omega ---> Xi - gamma decay and physics beyond the standard model.
Inst. de Fis. Teorica Universidade Estadual Paulista, Rua Pamplona, 145, 01405-900, Sao Paulo, SP
31120441
Relativistic Vlasov approach to normal modes of nuclear matter.
A description of small amplitude oscillations around a stationary state in nuclear matter is formulated in the context of the relativistic Vlasov equation. We obtain a set of stationary linear modes of excitation satisfying orthogonality and completeness relations. For longitudinal modes it is explicitly shown that the system, which is made up of relativistic particles in interaction with an external scalar meson field, behaves like a system of fermions very weakly coupled to the scalar meson field, even if the coupling constant is large.
121784739
MESONIC EXCITATIONS IN THE LINEAR SIGMA MODEL
A semiclassical version of the linear sigma model is studied in a variational approach. Specifically we study the bosonic spectroscopy for both bound states and resonances. We give a quantitative description of the pion and its two observed resonances.
119362477
The J / psi D D* vertex
We employ QCD sum rules to calculate the J/yDD* form factors and coupling constant by studying the threepoint J/yD*D correlation function. We find that the momentum dependence of the form factor depends on the off-shell meson. We get a value for the coupling which is in agreement with estimates based on constituent quark model.
118530282
CHARM 2013: X(4260) as a Mixed Charmonium-Tetraquark State
Using the QCD sum rule approach we study the X(4260) state assuming that it can be described by a mixed charmonium-tetraquark current with $J^{PC}=1^{--}$ quantum numbers. For the mixing angle around $\theta=(53.0 \pm 0.5)^0$, we obtain a value for the mass which is in good agreement with the experimental mass of the X(4260). For the decay width into the channel $X \to J/\psi \pi \pi$, we find the value $\Gamma_{X \to J/\psi\pi\pi}=(4.1 \pm 0.6)$ MeV, which is much smaller than the total experimental width $\Gamma = (108\pm 12)$ MeV. However, considering the experimental upper limits for the decay of the X(4260) into open charm, we conclude that we cannot rule out the possibility of describing this state as a mixed charmonium-tetraquark state.
118637291
Width of exotics from QCD sum rules : Tetraquarks or molecules?
(4250) using QCD sum rules. Extending previous analyses regarding these states as diquark-antiquark states or molecules of D mesons, we introduce the Breit-Wigner function in the pole term.We ﬁnd that introducing the width increases the mass at small Borel window region. Using theoperator-product expansion up to dimension 8, we ﬁnd that the sum rules based on interpolatingcurrent with molecular components give a stable Borel curve from which both the masses andwidths of these resonances can be well obtained. Thus the QCD sum rule approach strongly favorsthe molecular description of these states.
12483632
Casimir energy for a three-piece relativistic string.
The Casimir energy for the transverse oscillations of a piecewise uniform closed string is calculated. The string consists of three pieces I, II, III of equal length, endowed with different tensions and mass densities, but adjusted in such a way that the velocity of sound always equals the velocity of light. In this sense the string forms a relativistic mechanical system. In the present paper the string is subjected to the following analysis: the dispersion function is derived and the zero-point energy is regularized using (i) a contour integration technique, being most convenient for the generalization of the theory to the case of finite temperatures, and (ii) the Hurwitz {zeta}-function technique, being usually the most compact method when the purpose is to calculate the Casimir energy numerically at {ital T}=0. The energy, being always nonpositive, is shown graphically in some cases as functions of the tension ratios I/II and II/III. The generalization to finite temperature theory is also given. {copyright} {ital 1996 The American Physical Society.}
46520640
Comparison of low-PT photon production in high- and low-multiplicity collisions at the CERN ISR.
Low-transverse-momentum photon production at the CERN ISR is compared in high- and low-multiplicity events. High-transverse-energy pp collisions and low-multiplicity ..cap alpha cap alpha.. and pp collisions are studied. Relative photon-to-charged-track production is found to be the same in pp minimum bias, ..cap alpha cap alpha.. minimum bias, and pp high-transverse-energy collisions, to within 15%. No low-P/sub T/ excess is seen; the limits are dominated by systematic uncertainties.