8144700
QCD sum rules for Sigma hyperons in nuclear matter.
Within the finite-density QCD sum-rule approach we investigate the self-energies of [Sigma] hyperons propagating in nuclear matter from a correlator of [Sigma] interpolating fields evaluated in the nuclear matter ground state. We find that the Lorentz vector self-energy of the [Sigma] is similar to the nucleon vector self-energy. The magnitude of Lorentz scalar self-energy of the [Sigma] is also close to the corresponding value for nucleon; however, this prediction is sensitive to the strangeness content of the nucleon and to the assumed density dependence of certain four-quark condensate. The scalar and vector self-energies tend to cancel, but not completely. The implications for the couplings of [Sigma] to the scalar and vector mesons in nuclear matter and for the [Sigma] spin-orbit force in a finite nucleus are discussed.
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.
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.
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.
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.
44544605
Casimir energy for a piecewise uniform string.
The Casimir energy for the transverse oscillations of a piecewise uniform closed string is calculated. The string consists of two parts I and II, endowed in general with different tensions and mass densities, although adjusted in such a way that the velocity of sound always equals the velocity of light. The dispersion equation is worked out under general conditions and the frequency spectrum is determined in special cases. When the ratio {ital L}{sub II}/L{sub I} between the string lengths is an integer, it is in principle possible to determine the frequency spectrum through solving algebraic equations of increasingly high degree. The Casimir energy relative to the uniform string is in general found to be negative, although in the special case {ital L}{sub I}=L{sub II} the energy is equal to zero. Delicate points in the regularization procedure are discussed; in particular, it turns out that a straightforward use of the Riemann {zeta}-function regularization method leads to an incorrect expression for the Casimir energy.
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.