arXiv subjects

Ahmad Mohamadnejad

Publications and source records attributed to Ahmad Mohamadnejad.

22 records · Page 2Linked to original sources

arXiv2015

Appearance of vortices and monopoles in a decomposition of an SU(2) Yang-Mills field

We show how vortices can appear in the low energy limit of a pure SU(2) Yang-Mills theory as topological solitons. Motivated by Abelian dominance, we suppose that in the infrared regime of the SU(2) Yang-Mills theory, the field strength tensor can be obtained by multiplying two parts: $ G_{μν} $ and $ \textbf{n} $ such that $ \textbf{G}_{μν}=G_{μν} \textbf{n} $. The first part, $ G_{μν} $, is a space-time tensor and the second part, $ \textbf{n} $, is an isotriplet unit vector field which gives the Abelian direction at each space-time point. This leads to a decomposition for the SU(2) Yang-Mills field in the infrared regime. We show that vortices as well as monopoles can appear as a result of this decomposition where we have started with a pure Yang-Mills theory and we have ended up with a theory with an Abelian gauge field coupled to a scalar field. The effect of this scalar field on monopoles is also discussed.

hep-ph↗

arXiv2014

Abelian-Higgs model from Cho-Faddeev-Niemi decomposition

Applying Cho-Faddeev-Niemi decomposition for SU(2) Yang-Mills field, we obtain the Abelian-Higgs Lagrangian by some approximation. Abelian-Higgs Lagrangian with a spontaneous symmetry breaking potential has vortex solutions known as Nielsen-Olesen solutions. We conclude that vortices as well as magnetic monopoles can exist in Cho-Faddeev-Niemi decomposition of SU(2) Yang-Mills field.

hep-th↗

arXiv2012

The thermodynamic properties of weakly interacting quark gluon plasma via the one gluon exchange interaction

The thermodynamic properties of the quark gluon plasma($QGP$) as well as its phase diagram are calculated as a function of baryon density (chemical potential) and temperature. The $QGP$ is assumed to be composed of the light quarks only, i.e. the up and the down quarks, which interact weakly and the gluons which are treated as they are free. The interaction between quarks is considered in the framework of the one gluon exchange model which is obtained from the Fermi liquid picture. The bag model is used, with fixed bag pressure (${\cal B}$) for the nonperturbative part and the quantum chromodynamics ($QCD$) coupling is assumed to be constant i.e. no dependence on the temperature or the baryon density. The effect of weakly interacting quarks on the $QGP$ phase diagram are shown and discussed. It is demonstrated that the one gluon exchange interaction for the massless quarks has considerable effect on the $QGP$ phase diagram and it causes the system to reach to the confined phase at the smaller baryon densities and temperatures. The pressure of excluded volume hadron gas model is also used to find the transition phase-diagram. Our results depend on the values of bag pressure and the $QCD$ coupling constant which the latter does not have a dramatic effect on our calculations . Finally, we compare our results with the thermodynamic properties of strange quark matter and the lattice $QCD$ prediction for the $QGP$ transition critical temperature.

hep-ph↗

arXiv2012

Confinement in G(2) Gauge Theories Using Thick Center Vortex Model and domain structures

The thick center vortex model with the idea of using domain structures is used to calculate the potentials between two G(2) heavy sources in the fundamental, the adjoint and the 27 dimensional representations. The potentials are screened at large distances. This behavior is expected from the thick center vortex model since G(2) has only a trivial center element which makes no contribution to the average Wilson loop at the large distance regime. A linear potential is obtained at intermediate distances for all representations. This behavior can be explained by the thickness of the vortices (domains) and by defining a flux for the trivial center element of G(2). The role of the SU(3) subgroup of G(2) in the linear regime is also discussed. The string tensions are in rough agreement with the Casimir operators of the corresponding representations.

hep-ph↗