The role of gauge symmetry in spintronics

In this work we employ a field theoretical approach to explain the nature of the non-conserved spin current in spintronics. In particular, we consider the usual U(1) gauge theory for the electromagnetism at classical level in order to obtain the broken continuity equation involving the spin current and spin-transfer torque. Inspired by the recent work of A. Vernes, B. L. Gyorffy and P. Weinberger where they obtain such an equation in terms of relativistic quantum mechanics, we formalize their result in terms of the well known currents of field theory such as the Bargmann–Wigner current and the chiral current. Thus, an interpretation of spintronics is provided in terms of Noether currents (conserved or not) and symmetries of the electromagnetism. In fact, the main result of the present work is that the non-conservation of the spin current is associated with the gauge invariance of physical observables where the breaking term is proportional to the chiral current. Moreover, we generalize their result by including the electromagnetic field as a dynamical field instead of an external one.     

The Gribov–Zwanziger action in the presence of the gauge invariant,nonlocal mass operator Tr∫d<Superscript>4</Superscript>xF<Subscript>μν</Subscript>(D<Superscript>2</Superscript>)<Superscript>-1</Superscript>F<Subscript>μν</Subscript> in the Landau gauge

We prove that the nonlocal gauge invariant mass dimension 2 operator F_μν(D²)^-1F_μν can be consistently added to the Gribov–Zwanziger action, which implements the restriction of the path integral’s domain of integration to the first Gribov region when the Landau gauge is considered. We identify a local polynomial action and prove the renormalizability to all orders of perturbation theory by employing the algebraic renormalization formalism. Furthermore, we also pay attention to the breaking of the BRST invariance, and to the consequences that this has for the Slavnov–Taylor identity. PACS 11.15.-q; 11.15.Tk     

Cosmology from a gauge induced gravity

The main goal of the present work is to analyze the cosmological scenario of the induced gravity theory developed in previous works. Such a theory consists on a Yang–Mills theory in a four-dimensional Euclidian spacetime with \({ SO}(m,n)\) such that \(m+n=5\) and \(m\in \{0,1,2\}\) as its gauge group. This theory undergoes a dynamical gauge symmetry breaking via an Inönü–Wigner contraction in its infrared sector. As a consequence, the \({ SO}(m,n)\) algebra is deformed into a Lorentz algebra with the emergency of the local Lorentz symmetries and the gauge fields being identified with a vierbein and a spin connection. As a result, gravity is described as an effective Einstein–Cartan-like theory with ultraviolet correction terms and a propagating torsion field. We show that the cosmological model associated with this effective theory has three different regimes. In particular, the high curvature regime presents a de Sitter phase which tends towards a \(\Lambda \)CDM model. We argue that \({ SO}(m,n)\) induced gravities are promising effective theories to describe the early phase of the universe.     

Bulk Viscous Cosmological Model with Interacting Dark Fluids

We study a cosmological model for a spatially flat Universe whose constituents are a dark energy field and a matter field comprising baryons and dark matter. The constituents are assumed to interact with each other, and a non-equilibrium pressure is introduced to account for irreversible processes. We take the non-equilibrium pressure to be proportional to the Hubble parameter within the framework of a first-order thermodynamic theory. The dark energy and matter fields are coupled by their barotropic indexes, which depend on the ratio between their energy densities. We adjust the free parameters of the model to optimize the fits to the Hubble parameter data. We compare the viscous model with the non-viscous one, and show that the irreversible processes cause the dark-energy and matter-density parameters to become equal and the decelerated–accelerated transition to occur at earlier times. Furthermore, the density and deceleration parameters and the distance modulus have the correct behavior, consistent with a viable scenario of the present status of the Universe.     

On the topological reduction from the affine to the orthogonal gauge theory of gravity

Making use of the fibre bundle theory to describe metric–affine gauge theories of gravity we are able to show that metric–affine gauge theory can be reduced to the Riemann–Cartan one. The price we pay for simplifying the geometry is the presence of matter fields associated with the nonmetric degrees of freedom of the original setup. Also, a possible framework for the construction of a quantum gravity theory is developed in the text.     

Gribov horizon in the presence of dynamical mass generation in Euclidean Yang–Mills theories in the Landau gauge

We find the Goldstino action descending from the N=1 Goldstone–Maxwell superfield action associated with the spontaneous partial supersymmetry breaking, N=2 to N=1, in superspace. The new Goldstino action has higher (second-order) spacetime derivatives, while it can be most compactly described as a solution to the simple recursive relation. Our action seems to be related to the standard (having only the first-order derivatives) Akulov–Volkov action for Goldstino via a field redefinition.     

Remarks on the Renormalization Properties of Lorentz- and CPT-Violating Quantum Electrodynamics

In this work, we employ algebraic renormalization technique to show the renormalizability to all orders in perturbation theory of the Lorentz- and CPT-violating QED. Essentially, we control the breaking terms by using a suitable set of external sources. Thus, with the symmetries restored, a perturbative treatment can be consistently employed. After showing the renormalizability, the external sources attain certain physical values, which allow the recovering of the starting physical action. The main result is that the original QED action presents the three usual independent renormalization parameters. The Lorentz-violating sector can be renormalized by 19 independent parameters. Moreover, vacuum divergences appear with extra independent renormalization. Remarkably, the bosonic odd sector (Chern-Simons-like term) does not renormalize and is not radiatively generated. One-loop computations are also presented and compared with the existing literature.     

de Sitter gauge theories and induced gravities

The European Physical Journal C - Pure de Sitter, anti de Sitter, and orthogonal gauge theories in four-dimensional Euclidean spacetime are studied. It is shown that, if the theory is...