Chemical potential as a source of stability for gravitating Skyrmions

A discussion of the stability of self gravitating Skyrmions, with a large winding number N, in a Schwarzschild type of metric, is presented for the case where an isospin chemical potential is introduced. It turns out that the chemical potential stabilizes the behavior of the Skyrmion discussed previously in the literature. This analysis is carried on in the framework of a variational approach using different ansaetze for the radial profile of the Skyrmion. We found a divergent behavior for the size of the Skyrmion, associated to a certain critical value $\mu_c$ of the chemical potential. At this point, the mass of the Skyrmion vanishes. $\mu_c$ is essentialy independent of gravitating effects. The stability of a large N skyrmion against decays into single particles is also discussed.Comment: 10 pages, 4 figures Small changes to the previous version and a new referenc

Skyrmions, Hadrons and isospin chemical potential

Using the Hamiltonian formulation, in terms of collective variables, we explore the evolution of different skyrmionic parameters as function of the isospin chemical potential ($\mu$), such as the energy density, the charge density, the isoscalar radius and the isoscalar magnetic radius. We found that the radii start to grow very fast for $\mu \gtrsim 140$ MeV, suggesting the occurrence of a phase transition.Comment: 10 pages, 5 figure

Skyrme model and Isospin Chemical Potential

We discuss the stability of the Skyrmion solution in the presence of a finite isospin chemical potential $\mu$. Solving numerically the mass of the Skyrmion as function of $\mu$, we find a critical value $\mu_c=222.8$ MeV where the Skyrmion mass vanishes. We compare the exact numerical treatment with an analytical discussion based on a special shape for the profile of the Skyrmion due to Atiyah and Manton. The extension of this ansatz for finite $\mu$ works quite well for $\mu<121$ MeV. Then, for small values of $\mu$, where the analytical approach is valid, we consider the possibility of having an angular deformation for the Skyrmionic profile, which is possible for finite values of $\mu$. This is however, a small effect. Finally we introduce finite temperature corrections, which strength the instability induced by the chemical potential, finding the dependence of the critical temperature on $\mu$.Comment: 13 pages, 7 figure

Background field method at finite temperature and density

In this letter we make use of the Background Field Method (BFM) to compute the effective potential of an SU(2) gauge field theory, in the presence of chemical potential and temperature. The main idea is to consider the chemical potential as the background field. The gauge fixing condition required by the BFM turns out to be exactly the one we found in a previous article in a different context.Comment: 6 pages, no figure

On the role of soft gluons in collinear parton densities

The role of soft (non-perturbative) gluons in collinear parton densities is investigated with the Parton Branching method as a solution of the DGLAP evolution equations. It is found that soft gluons contribute significantly to collinear parton densities. Within the Parton Branching frame, the Sudakov form factor can be split into a perturbative and non-perturbative part. The non-perturbative part can be calculated analytically under certain conditions. It is shown that the inclusion of soft (non-perturbative) gluons to the parton density evolution is essential for the proper cancellation of divergent terms. It is argued that the non-perturbative part of the Sudakov form factor has its correspondence in Transverse Momentum Dependent parton distributions. Within the Parton Branching approach, this non-perturbative Sudakov form factor is constrained by fits of inclusive, collinear parton densities. We show that the non-perturbative Sudakov form factor and soft gluon emissions are essential for inclusive distributions (collinear parton densities and Drell-Yan transverse momentum spectra), while those soft gluons play essentially no role in final state hadron spectra.Comment: Significantly updated including studies on parton shower and hadronizatio

Weinberg-Salam model at finite temperature and density

We present a new gauge fixing condition for the Weinberg-Salam electro-weak theory at finite temperature and density. After spontaneous symmetry breaking occurs, every unphysical term in the Lagrangian is eliminated with our gauge fixing condition. A new and simple Lagrangian can be obtained where we can identify the propagators and vertices. Some consequences are discussed, as the new gauge dependent masses of the gauge fields and the new Faddeev-Popov Lagrangian. After obtaining the quadratic terms, we calculate exactly the 1-loop effective potential identifying the contribution of every particular field.Comment: 4 pages, no figures. New references added. Typo correcte