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Sedigheh Deldar

Publications and source records attributed to Sedigheh Deldar.

33 records · Page 2Linked to original sources
arXiv2013

Interaction between Vortices in CFL Phase

We try to calculate the interaction between vortices in the color-flavor locked (CFL) phase of Quantum Chromodynamics (QCD). The most fundamental strings in high density color superconductivity are the non-abelian semi-super fluid strings. Using Abrikosov ansatz, one can show that the interaction between these vortices has a universal repulsion form when they are far from each other. The Ginzburg-Landau (GL) Lagrangian of CFL phase may be compared with the Lagrangian of Quantum Electrodynamics (QED) with three condensation states. The behavior of vortices of multi-component superconductivity, within the framework of GL theory was done for two condensation states ($\rm{MgB_2}$ superconductors) by variational method. The interaction between these vortices is attractive when they are far from each other and repulsive when they get close. We attempt to obtain the interaction between these vortices in such substances using numerical variational method for three condensation states (Fe-based superconductors). The ultimate aim of the research is to apply these calculations to the vortices in the color-flavor locked phase of QCD to be able to study the interaction between them.

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↗
arXiv2010

Center vortex model and the G(2) gauge group

The thick center vortex model is applied to G(2) gauge group to obtain the potentials between static sources of the fundamental and adjoint representations. The group G(2) has only one trivial center element and therefore it does not have any vortices which are defined based on non trivial center elements. To obtain the potential from the thick center vortex model, the idea of the vacuum domain structure is used. The intermediate string tensions from this model are in rough agreement with the G(2) lattice results and the Casimir ratio. We argue that the SU(3) subgroup of G(2) may be responsible for the linear potential at the intermediate distances.

hep-ph↗
arXiv2010

Removing the concavity of the thick center vortex potentials by fluctuating the vortex profile

The thick center vortex model reproduces important aspects of the potentials between static quark sources as seen in lattice Yang-Mills calculations: Both the intermediate distance behavior, governed by Casimir scaling, as well as the long distance behavior, governed by N-ality, are obtained. However, when a fixed vortex profile is used, these two distance regimes do not connect naturally to each other. The transition in general violates concavity constraints on the potential, especially for higher representations of the gauge group. We demonstrate how this issue can be alleviated when the vortex profile is allowed to fluctuate within this simple model.

hep-ph↗
arXiv2009

Short distance potential and the thick center vortex model

The short distance potentials between heavy SU(3) and SU(4) sources are calculated by increasing the role of vortex fluxes piercing Wilson loops with contributions close to the trivial center element and by fluctuating the vortex core size in the model of thick center vortices. By this method, a Coulombic potential consistent with Casimir scaling is obtained. In addition, all other features of the potential including a linear intermediate potential in agreement with Casimir scaling and a large distance potential proportional to the $N$-ality of the representation are restored. Therefore, the model of thick center vortices may be used as a phenomenological model, which is able to describe the potential for all regimes.

hep-ph↗
arXiv2007

Confinement and the second vortex of the SU(4) gauge group

We study the potential between static SU(4) sources using the Model of Thick Center Vortices. Such vortices are characterized by the center elements $z_1=\mathrm i$ and $z_2=z_1^2$. Fitting the ratios of string tensions to those obtained in Monte-Carlo calculations of lattice QCD we get $f_2>f_1^2$, where $f_n$ is the probability that a vortex of type $n$ is piercing a plaquette. Because of $z_2=z_1^2$ vortices of type two are overlapping vortices of type one. Therefore, $f_2>f_1^2$ corresponds to the existence of an attractive force between vortices of type one.

hep-ph↗
arXiv2006

A new lattice measurement for potentials between static SU(3) sources

In this article, a new calculation of static potentials between sources of different representations in SU(3) gauge group is presented. The results of author's previous study \cite{Deld00} at the smallest lattice spacing $a_{s}\simeq0.11$~ fm are shown to have been affected by finite volume effects. Within statistical errors, the new results obtained here are still in agreement with both, Casimir scaling and flux tube counting. There is also no contradiction to the results obtained in Ref.~ \cite{Bali00} which however exclude flux counting.

hep-lat↗
arXiv2005

SU(4) string tensions from the fat-center-vortices model

The thick- or fat-center-vortices model has been applied to a calculation of the potentials between static sources of various SU(4) representations. For intermediate distances, a linear potential is obtained. For this region the string tensions agree qualitatively with both flux tube counting and Casimir scaling, even though for some representations it favors flux tube counting more. In addition, our results confirm the existence of two different string tensions for non-zero 4-ality representations at large distances. In this area, zero 4-ality representations are screened. In our computations, we have used only the first non-trivial vortex of SU(4).

hep-ph↗
arXiv2004

Flux tube counting or Casimir scaling

QCD confines quarks in all representations. From lattice calculations and fat center vortices model, we discuss that the coefficient of the linear term in the potential is proportional to both casimir scaling and the number of fundamental strings.

hep-lat↗
arXiv2004

Confinement and fat-center-vortices model

In this paper I review shortly potentials obtained for SU(2), SU(3) and SU(4) static sources from fat-center-vortices model. Results confirm the confinement of quarks in all three gauge groups. Proportionality of string tensions with flux tube counting is better than Casimir scaling especially for SU(4).

hep-ph↗
arXiv2001

Potentials between static SU(3) sources in the fat-center-vortices model

The potentials between static sources in various representaions in SU(3) are calculated based on the fat-center-vortices model of Faber, Greensite and Olejnik. At intermediate distances, most distributions of the flux within vortices lead to potentials that are qualitatively in agreement with ``Casimir scaling,'' which says that the string tension is proportional to the quadratic operator of the representation. However, at the quantitative level, violations of Casimir scaling are generally much larger than those seen in numerical simulations, indicating that additional physical input to the fat-center-vortices model is required. At large distances, screening occurs for zero-triality representations; for the representations with non-zero triality the string tension equals that of the fundamental representation. Some rather ``unphysical,'' flux distributions can lead to violations of Casimir scaling at intermediate distances and violations of the expected ordering of representations at large distances.

hep-ph↗
arXiv2000

Static SU(3) potentials for sources in various representations

The potentials and string tensions between static sources in a variety of representations (fundamental, 8, 6, 15-antisymmetric, 10, 27 and 15-symmetric) have been computed by measuring Wilson loops in pure gauge SU(3). The simulations have been done primarily on anisotropic lattices, using a tadpole improved action improved to O(a_{s}^4). A range of lattice spacings (0.43 fm, 0.25 fm and 0.11 fm) and volumes ($8^3\times 24$, $10^3 \times 24$, $16^3 \times 24$ and $18^3 \times 24$) has been used in an attempt to control discretization and finite volume effects. At intermediate distances, the results show approximate Casimir scaling. Finite lattice spacing effects dominate systematic error, and are particularly large for the representations with the largest string tensions.

hep-lat↗
arXiv1999

Pure SU(3) Potentials

The string tensions for fundamental and a variety of representations: adjoint, 6, 10, 15-symmetric, 15-antisymmetric, and 27 have been measured in pure gauge SU(3). The calculations have been done on anisotropic lattices, using an $O(a^2)$ tadpole improved action. A range of lattice spacings and lattice sizes has been used to control finite volume and finite lattice spacing effects. Potentials between quarks in various representations have also been calculated with the fat center vortices model. At intermediate distances, the results show approximate Casimir scaling. From my lattice calculations, no color screening has been observed so far, even for distances as large as about 2.5 fm.

hep-lat↗
arXiv1998

The string tensions of SU(3) representations

I report on the status of a computation of fundamental and some higher representation string tensions in pure gauge SU(3). An order a^2 tadpole improved action and an anisotropic lattice are used. At present, the static quark potentials and the string tensions are calculated by measuring Wilson loops on an 8^3 x 24 lattice. Wilson loops for higher representations are measured in terms of Wilson loops of the fundamental representation. At the small and intermediate distances available, rough agreement with Casimir scaling is observed, and no color screening for the 8 representation is seen.

hep-lat↗