Ghost poles in the nucleon propagator: Vertex corrections and form factors.
Vertex corrections are taken into account in the Schwinger-Dyson equation for the nucleon propagator in a relativistic field theory of fermions and mesons. The usual Hartree-Fock approximation for the nucleon propagator is known to produce the appearance of complex (ghost) poles which violate basic theorems of quantum field theory. In a theory with vector mesons there are vertex corrections that produce a strongly damped vertex function in the ultraviolet. One set of such corrections is known as the Sudakov form factor in quantum electrodynamics. When the Sudakov form factor generated by massive neutral vector mesons is included in the Hartree-Fock approximation to the Schwinger-Dyson equation for the nucleon propagator, the ghost poles disappear and consistency with basic requirements of quantum field theory is recovered.

title: CHARM 2013: X(4260) as a Mixed Charmonium-Tetraquark State
abstract: 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.

title: Width of exotics from QCD sum rules : Tetraquarks or molecules?
abstract: (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.

title: MESONIC EXCITATIONS IN THE LINEAR SIGMA MODEL
abstract: 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.

title: The J / psi D D* vertex
abstract: 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.

title: Relativistic Vlasov approach to normal modes of nuclear matter.
abstract: 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.

title: Casimir theory for the piecewise uniform string: Division into 2N pieces.
abstract: The Casimir energy for the transverse oscillations of a piecewise uniform string in Minkowski space is calculated. The string consists in general of 2[ital N] pieces of equal length, of alternating type I and type II material, endowed with different tensions [ital T][sub I], [ital T][sub II] and mass densities [rho][sub I], [rho][sub II] but adjusted in such a way that the velocity of sound always equals the velocity of light. This string model (with [ital N]=1) was introduced by the present authors in 1990. In the present paper, the governing equations are formulated in the case of arbitrary integers [ital N], although detailed calculations are restricted to the case [ital N]=2, i.e., a four-piece string. The Casimir energy is regularized using (i) the contour integration technique introduced by van Kampen, Nijboer, and Schram, and (ii) the Hurwitz [zeta]-function technique introduced by Li, Shi, and Zhang. The energy is found as a function of the tension ratio [ital x]=[ital T][sub I]/[ital T][sub II]. The finite temperature version of the theory is also given.

title: Casimir energy for a piecewise uniform string.
abstract: 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.