Global superscaling analysis of quasielastic electron scattering with relativistic effective mass

We present a global analysis of the inclusive quasielastic electron scattering data with a superscaling approach with relativistic effective mass. The SuSAM* model exploits the approximation of factorization of the scaling function $f^*(\psi^*)$ out of the cross section under quasifree conditions. Our approach is based on the relativistic mean field theory of nuclear matter where a relativistic effective mass for the nucleon encodes the dynamics of nucleons moving in presence of scalar and vector potentials. Both the scaling variable $\psi^*$ and the single nucleon cross sections include the effective mass as a parameter to be fitted to the data alongside the Fermi momentum $k_F$. Several methods to extract the scaling function and its uncertainty from the data are proposed and compared. The model predictions for the quasielastic cross section and the theoretical error bands are presented and discussed for nuclei along the periodic table from $A=2$ to $A=238$: $^2$H, $^3$H, $^3$He, $^4$He, $^{12}$C, $^{6}$Li, $^{9}$Be, $^{24}$Mg, $^{59}$Ni, $^{89}$Y, $^{119}$Sn, $^{181}$Ta, $^{186}$W, $^{197}$Au, $^{16}$O, $^{27}$Al, $^{40}$Ca, $^{48}$Ca, $^{56}$Fe, $^{208}$Pb, and $^{238}$U. We find that more than 9000 of the total $\sim 20000$ data fall within the quasielastic theoretical bands. Predictions for $^{48}$Ti and $^{40}$Ar are also provided for the kinematics of interest to neutrino experiments.Comment: 26 pages, 20 figures and 4 table

Chiral Lagrangian at finite temperature from the Polyakov-Chiral Quark Model

We analyze the consequences of the inclusion of the gluonic Polyakov loop in chiral quark models at finite temperature. Specifically, the low-energy effective chiral Lagrangian from two such quark models is computed. The tree level vacuum energy density, quark condensate, pion decay constant and Gasser-Leutwyler coefficients are found to acquire a temperature dependence. This dependence is, however, exponentially small for temperatures below the mass gap in the full unquenched calculation. The introduction of the Polyakov loop and its quantum fluctuations is essential to achieve this result and also the correct large $N_c$ counting for the thermal corrections. We find that new coefficients are introduced at ${\cal O}(p^4)$ to account for the Lorentz breaking at finite temperature. As a byproduct, we obtain the effective Lagrangian which describes the coupling of the Polyakov loop to the Goldstone bosons.Comment: 16 pages, no figure

Dimension two vacuum condensates in gauge-invariant theories

Gauge dependence of the dimension two condensate in Abelian and non-Abelian Yang-Mills theory is investigated.Comment: 10 page

Center of mass momentum dependence of short-range correlations with the coarse-grained Granada potential

The effect of the center of mass motion on the high-momentum distributions of correlated nucleon pairs is studied by solving the Bethe-Goldstone equation in nuclear matter with the Granada nucleon-nucleon potential. We show that this coarse-grained potential reduces the problem to an algebraic linear system of five (ten) equations for uncoupled (coupled) partial waves that can be easily solved. The corresponding relative wave functions of correlated pn, pp and nn pairs are computed for different values of their CM momentum. We find that the pn pairs dominate the high-momentum tail of the relative momentum distribution, and that this only depends marginally on center of mass momentum. Our results provide further justification and agreement for the factorization approximation commonly used in the literature. This approximation assumes that the momentum distribution of nucleon pairs can be factorized as the product of the center of mass momentum distribution and the relative momentum distribution.Comment: 27 pages, 12 figures, corrected the treatment of the coupled nucleon-nucleon partial waves, new authors adde

Photon distribution amplitudes and light-cone wave functions in chiral quark models

The leading- and higher-twist distribution amplitudes and light-cone wave functions of real and virtual photons are analyzed in chiral quark models. The calculations are performed in the nonlocal quark model based on the instanton picture of QCD vacuum, as well as in the spectral quark model and the Nambu--Jona-Lasinio model with the Pauli-Villars regulator, which both treat interaction of quarks with external fields locally. We find that in all considered models the leading-twist distribution amplitudes of the real photon defined at the quark-model momentum scale are constant or remarkably close to the constant in the $x$ variable, thus are far from the asymptotic limit form. The QCD evolution to higher momentum scales is necessary and we carry it out at the leading order of the perturbative theory for the leading-twist amplitudes. We provide estimates for the magnetic susceptibility of the quark condensate $\chi_m$ and the coupling $f_{3\gamma}$, which in the nonlocal model turn out to be close to the estimates from QCD sum rules. We find the higher-twist distribution amplitudes at the quark model scale and compare them to the Wandzura-Wilczek estimates. In addition, in the spectral model we evaluate the distribution amplitudes and light-cone wave functions of the $\rho$-meson.Comment: 24 pages, 15 figure

Chiral phase transition in a covariant nonlocal NJL model

The properties of the chiral phase transition at finite temperature and chemical potential are investigated within a nonlocal covariant extension of the Nambu-Jona-Lasinio model based on a separable quark-quark interaction. We consider both the situation in which the Minkowski quark propagator has poles at real energies and the case where only complex poles appear. In the literature, the latter has been proposed as a realization of confinement. In both cases, the behaviour of the physical quantities as functions of T and \mu is found to be quite similar. In particular, for low values of T the chiral transition is always of first order and, for finite quark masses, at certain "end point" the transition turns into a smooth crossover. In the chiral limit, this "end point" becomes a "tricritical" point. Our predictions for the position of these points are similar, although somewhat smaller, than previous estimates. Finally, the relation between the deconfining transition and chiral restoration is also discussed.Comment: 11 pages, 2 figures. Figures modified, minor changes in the text. To be published in Phys. Lett.