Abstract:
Classical and quantum aspects of physical systems that can be described by Riemannian non degenerate superspaces are analyzed from the topological and geometrical points of view. For the N=1 case the simplest supermetric introduced in [Physics Letters B \textbf{661}, (2008),186] have the correct number of degrees of freedom for the fermion fields and the super-momentum fulfil the mass shell condition, in sharp contrast with other cases in the literature where the supermetric is degenerate. This fact leads a deviation of the 4-impulse (e.g. mass constraint) that can be mechanically interpreted as a modification of the Newton's law. Quantum aspects of the physical states and the basic states and the projection relation between them, are completely described due the introduction of a new Majorana-Weyl representation of the generators of the underlying group manifold. A new oscillatory fermionic effect in the $B_{0}$ part of the vaccum solution involving the chiral and antichiral components of this Majorana bispinor is explicitly shown.

Abstract:
Improved computation of the dielectric function considering excitonic effects and long wavelength is performed and compared with the nearly free electron band approximation, similarly with the Penn's model case. New expressions for the real and imaginary part of the dielectric function are presented and the real part compared with the Penn's result. The obtained functions satisfy the Kramers-Kr\"onig relations, in contrast with earlier results in the literature. In addition, our improved dielectric function presents a coeficient of 2/3 for small gap approximation (different from the value of 1 in the original Penn model) is very close to the value 0.62 obtained in [Can. J. Phys.53,(1975) p.2549] from pure numerical procedures. The obtained dielectric function also is used in a rough and stimative analysis of the metal-insulator transition in molecular hydrogen being the critical densities determined near the experimental values for the hydrogen coming from other approach. The approximated expressions and critical values are given and the usefulness of the rough methods involved in the determination of the critical points briefly discussed.

Abstract:
We briefly give a very simple picture about one of the most remarkable results of Matvej Petrovich Bronstein concerning the quantization of the gravitational waves showing also that the linearized Einstein equations of the paper: Phys.Rev. D65 (2002) 104005 are the same Bronstein's equations given 66 years before.

Abstract:
The 2-dimensional charge transport with parallel (in plane) magnetic field is considered from the physical and mathematical point of view. To this end, we start with the magnetic field parallel to the plane of charge transport, in sharp contrast to the configuration described by the theorems of Aharonov and Casher where the magnetic field is perpendicular. We explicitly show that the specific form of the arising equation enforce the respective field solution to fulfil the Majorana condition. Consequently, as soon any physical system is represented by this equation, the rise of fields with Majorana type behaviour is immediately explained and predicted. In addition, there exists a quantized particular phase that removes the action of the vector potential producing interesting effects. Such new effects are able to explain due the geometrical framework introduced, several phenomenological results recently obtained in the area of spintronics and quantum electronic devices. The quantum ring as spin filter is worked out in this framework and also the case of the quantum Hall effect.

Abstract:
In previous work [1] new bounded coherent states construction, based on a Keldysh conjecture, was introduced. As was shown in [1] the particular group structure arising from the model leads to new symmetry transformations for the coherent states system. As was shown, the emergent new symmetry transformation is reminiscent of the Bogoliubov ones and was successfully applied to describe an excitonic system showing that is intrinsically related to the stability and its general physical behavior. The group theoretical structure of the model permits to analyze its thermal properties in theoretical frameworks that arise as a consequence of the definition of the squeezed-coherent states as transformed vacua under the automorphism group of the commutation relations, as the thermofield dynamics case given by Umezawa and other similar developments [5]. On the other hand, the idea of a possible Bose--Einstein condensation (BEC) of excitons in semiconductors has attracted the attention of both experimentalists and theoreticians for more than three decades being one of the main questions what happens with the influence of non zero temperature in the case that such condensation really exists [2]. In this paper we considered the theoretical treatment of the excitonic behaviour by mean a new coherent state construction of bounded states in a quantum field theoretical context.

Abstract:
Starting from a Unified Field Theory (UFT) proposed previously by the author, the possible fermionic representations arising from the same spacetime are considered from the algebraic and geometrical viewpoint. We specifically demonstrate in this UFT general context that the underlying basis of the single geometrical structure P (G,M) (the principal fiber bundle over the real spacetime manifold M with structural group G) reflecting the symmetries of the different fields carry naturally a biquaternionic structure instead of a complex one. This fact allows us to analyze algebraically and to interpret physically in a straighforward way the Majorana and Dirac representations and the relation of such structures with the spacetime signature and non-hermitian (CP) dynamic operators. Also, from the underlying structure of the tangent space, the existence of hidden (super) symmetries and the possibility of supersymmetric extensions of these UFT models are given showing that Rothstein's theorem is incomplete for that description. The importance of the Clifford algebras in the description of all symmetries, mainly the interaction of gravity with the other fields, is briefly discussed.

Abstract:
It is commonly claimed in the recent literature that certain solutions to wave equations of positive energy of Dirac-type with internal variables are characterized by a non-thermal spectrum. As part of that statement, it was said that the transformations and symmetries involved in equations of such type correspond to a particular representation of the Lorentz group. In this paper we give the general solution to this problem emphasizing the interplay between the group structure, the corresponding algebra and the physical spectrum. This analysis is completed with a strong discussion and proving that: i) the physical states are represented by coherent states; ii) the solutions in previous references [1] are not general, ii) the symmetries of the considered physical system in [1] (equations and geometry) do not correspond to the Lorentz group but to the fourth covering: the Metaplectic group Mp(n).

Abstract:
Geometrical analysis of a new type of Unified Field Theoretical models follow the guidelines of previous works of the authors is presented. These new unified theoretical models are characterized by an underlying hypercomplex structure, zero non-metricity and the geometrical action is determined fundamentally by the curvature provenient of the breaking of symmetry of a group manifold in higher dimensions. This mechanism of Cartan-MacDowell-Mansouri type, permits us to construct geometrical actions of determinantal type leading a non topological physical Lagrangian due the splitting of a reductive geometry. Our goal is to take advantage of the geometrical and topological properties of this theory in order to determine the minimal group structure of the resultant spacetime Manifold able to support a fermionic structure. From this fact, the relation between antisymmetric torsion and Dirac structure\ of the spacetime is determined and the existence of an important contribution of the torsion to the giromagnetic factor of the fermions, shown. Also we resume and analyze previous cosmological solutions in this new UFT where, as in our work [Class. Quantum Grav. 22 (2005) 4987--5004] for the non abelian Born-Infeld model, the Hosoya and Ogura ansatz is introduced for the important cases of tratorial, totally antisymmetric and general torsion fields. In the case of spacetimes with torsion the real meaning of the spin-frame alignment is find and the question of the minimal coupling is discussed.

Abstract:
In this work, the solution of the Einstein equations for a slowly rotating black hole with Born-Infeld charge is obtained. Geometrical properties and horizons of this solution are analyzed. The conditions when the ADM mass (as in the nonlinear static cases) and the ADM angular momentum of the system have been modified by the non linear electromagnetic field of the black hole, are considered.

Abstract:
The coherent states for a quantum particle on a M\"{o}bius strip are constructed and their relation with the natural phase space for fermionic fields is shown. The explicit comparison of the obtained states with previous works where the cylinder quantization was used and the spin 1/2 was introduced by hand is given, and the relation between the geometrical phase space, constraints and projection operators is analyzed and discussed.