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We consider field equations of spinors with torsional interactions having higher-order dimension: by applying the Velo-Zwanziger method, we obtain that it is always possible to find situations where the propagation is affected by non-causal behavior. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the phase-space of a model of dark energy in which a non-canonical scalar field (tachyon) non-minimally coupled to torsion scalar in the framework of teleparallelism. Scalar field potential and non-minimal coupling function are chosen as V( ϕ) = V ϕ and f( ϕ) = ϕ, respectively. We obtain a critical point that behaves like a stable or saddle point depending on the values of N and n. Additionally we find an unstable critical line. We have shown such a behavior of critical points using numerical computations and phase-space trajectories explicitly. [ABSTRACT FROM AUTHOR]

In this paper a classification of proper teleparallel homothetic vector field in spherically symmetric static space-times is given using the direct integration technique. From the above study we show that the above space-times do not admit proper teleparallel homothetic vector fields. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the dynamical instability of a spherically symmetric collapsing star in the context of f( T) gravity. For this purpose, we assume power-law f( T) model with non-dissipative anisotropic fluid distribution under expansion-free condition. The perturbation scheme is applied to all matter, metric and f( T) functions. We formulate dynamical equations using contracted Bianchi identities to investigate dynamical instability ranges in Newtonian and post-Newtonian regimes. It is found that the instability ranges of expansion-free fluid are independent of adiabatic index but depend on radial density profile, anisotropic pressure and torsion terms. [ABSTRACT FROM AUTHOR]

The f( T) theory is recently proposed to explain the present cosmic accelerating expansion of the universe. f( T) theory is an extension of Teleparallel theory of gravity, where T is the torsion scalar. This paper contains the construction of f( T) models within the Kantowski-Sachs universe. For this purpose, we use conservation equation and equation of state parameter, which represents the different phases of the universe. We discuss possible cases for the matter dominated era, radiation dominated era, present dark energy phase and their combinations. Particularly, a constant solution has been obtained which may correspond to the cosmological constant. Further, we consider two well known f( T) models and derive the equation of state parameter and discuss the cosmic acceleration. Also, the Hubble parameter and average scale factor have been evaluated. [ABSTRACT FROM AUTHOR]

We investigate warm intermediate scenario of the cosmological inflation in F( T) gravity in the limit of high dissipation. The inflationary expansion is driven by the scalar inflaton while the gravitational dynamics follow from the F( T) gravity. We calculate the relevant inflationary observables such as scalar-tensor ratio, power-spectrum indices of density perturbations and gravitational waves and the e-folding parameter. We obtain a ratio of slow-roll parameters to be constant. Our calculations support the warm-intermediate inflationary scenario in a spacetime with torsion. Moreover our results are compatible with the astrophysical observations of cosmic microwave background and Planck data. [ABSTRACT FROM AUTHOR]

We consider the torsional completion of gravity with electrodynamics for Dirac matter fields; we will see that these Dirac matter field equations will develop torsionally-induced non-linear interactions, which can be manipulated in order to be rearranged in the form of self-fermion potentials of a specific structure: we will see that this structure is formally equivalent to the one arising from quantum properties. [ABSTRACT FROM AUTHOR]

One of the main features of unified models, based on affine geometries, is that all possible interactions and fields naturally arise under the same standard. Here, we consider, from the effective Lagrangian of the theory, the torsion induced 4-fermion interaction. In particular, how this interaction affects the cosmological term, supposing that a condensation occurs for quark fields during the quark-gluon/hadron phase transition in the early universe. We explicitly show that there is no parity-violating pseudo-scalar density, dual to the curvature tensor (Holst term) and the spinor-bilinear scalar density has no mixed couplings of A-V form. On the other hand, the space-time dimensionality cannot be constrained from multidimensional phenomenological models admitting torsion. [ABSTRACT FROM AUTHOR]

Inthe present work we show that the existence of non-vanishing torsion field may solve, at least, one of the problems FRW-cosmology, the particle horizons problem. The field equations of general relativity (GR) are written in a space having non-vanishing torsion, the absolute parallelism (AP) space. An AP-Structure, satisfying the cosmological principle, is used to construct a world model. Energy density and pressure, purely induced by torsion, are defined from the building blocks of the AP-geometry using GR. When these quantities are used in the FRW-dynamical equations, we get a world model free from particle horizons. [ABSTRACT FROM AUTHOR]

We consider the most general axial torsion completion of gravity with electrodynamics for $\frac{1}{2}$-spin spinors in an 8-dimensional representation of the Dirac matter field: this theory will allow to define antimatter as matter with all quantum numbers reversed, where also the sign of the mass beside that of the charge is inverted: we shall see that matter and antimatter solutions of the Dirac field equations coincide with the known ones with respect to all observables, that despite the inversion of the sign of the mass term only positive-mass states are present and only positive-energy densities are given; the present and the common approach will be compared, and some experimental implications will be discussed. [ABSTRACT FROM AUTHOR]

In this paper, we find the teleparallel version of the cylindrically symmetric stiff fluid space-time. The expressions for torsion vector and torsion axial-vector are obtained. We show that the value of torsion axial-vector depends on the choice of tetrad fields. Furthermore, we calculate the energy and momentum densities and show that these values do not depend on the choice of tetrad fields. Finally, we find the equation determining trajectory and spin precession of a Dirac equation in the space-time under consideration and show that the corresponding Hamiltonian depends on the choice of tetrad fields. [ABSTRACT FROM AUTHOR]

In this paper we explored teleparallel conformal vector fields in cylindrically symmetric static space-times in the teleparallel theory of gravitation by using the direct integration technique. It turns out that the dimension of teleparallel conformal vector fields are 8, 9, 10 or 11. The case VI in which the space-time becomes conformally flat admits eleven independent teleparallel conformal vector fields. [ABSTRACT FROM AUTHOR]

We study Dirac field equations coupled to electrodynamics with metric and torsion fields: we discuss how special spinorial solutions are incompatible with torsion; eventually these results will be used to sketch a discussion on the problem of renormalizability of point-like particles. [ABSTRACT FROM AUTHOR]

In this paper we consider the most general least-order derivative theory of gravity in which not only curvature but also torsion is explicitly present in the Lagrangian, and where all independent fields have their own coupling constant: we will apply this theory to the case of ELKO fields, which is the acronym of the German Eigenspinoren des LadungsKonjugationsOperators designating eigenspinors of the charge conjugation operator, and thus they are a Majorana-like special type of spinors; and to the Dirac fields, the most general type of spinors. We shall see that because torsion has a coupling constant that is still undetermined, the ELKO and Dirac field equations are endowed with self-interactions whose coupling constant is undetermined: we discuss different applications according to the value of the coupling constants and the different properties that consequently follow. We highlight that in this approach, the ELKO and Dirac field's self-interactions depend on the coupling constant as a parameter that may even make these non-linearities manifest at subatomic scales. [ABSTRACT FROM AUTHOR]

The integrability condition that must be formally fulfilled by any Infeld-Van der Waerden spin-affine connexion is derived explicitly. Some geometric properties of the action of torsionless covariant-derivative commutators on arbitrary spin tensors and densities are then brought out. The relevant calculations supply a set of new differential expressions which will presumably ensure the consistency of any formulation that involves utilizing normally the traditional two-component spinor methods for classical general relativity. [ABSTRACT FROM AUTHOR]

In this work the underlying structure of new type of Unified Field Theoretical model introduced in by the authors is elucidated and analyzed from the geometrical and group theoretical point of view. 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 important physical consequences enumerated. In the case of spacetime with torsion the real meaning of the spin-frame alignment is find and the question of the minimal coupling is discussed based in the important cases of tratorial, totally antisymmetric and general torsion fields. [ABSTRACT FROM AUTHOR]

We consider a geometric approach to field theory in which torsion is present beside gravity and also electrodynamics for the matter field equations, and we develop the consequences of the torsion-spin coupling for the spinor fields; we show that these interactions have the structure of the weak interactions acting among leptons: we discuss the implications for the standard model of fundamental interactions of elementary fields in the perspective of the foundations of unification in theoretical physics. [ABSTRACT FROM AUTHOR]

The interaction energy is studied for the coupling of axial torsion fields with photons in the presence of an external electromagnetic field. To this end, we compute the static quantum potential. Our discussion is carried out using the gauge-invariant but path-dependent variables formalism, which is alternative to the Wilson loop approach. Our results show that the static potential is a Yukawa correction to the usual static Coulomb potential. Interestingly, when this calculation is done by considering a mass term for the gauge field, the Coulombic piece disappears leading to a screening phase. [ABSTRACT FROM AUTHOR]

We show that it is possible to formulate the classical Einstein-Maxwell-Dirac theory of spinors interacting with the gravitational and electromagnetic fields as the Einstein-Cartan-Kibble-Sciama theory with the Ricci scalar of the traceless torsion, describing gravity, and the torsion trace acting as the electromagnetic potential. [ABSTRACT FROM AUTHOR]

The existence and stability under linear perturbation of closed timelike curves in the spacetime associated to Schwarzschild black hole pierced by a spinning string are studied. Due to the superposition of the black hole, we find that the spinning string spacetime is deformed in such a way to allow the existence of closed timelike geodesics. [ABSTRACT FROM AUTHOR]

In addition to introducing matter injection through a scalar field determined by Pryce-Hoyle tensor, we also combine it with a BCDE (Brans-Dicke-Einstein-Cartan) theory with lambda-term developed earlier by Berman (Astrophys. Space Sci. 314:79–82, 2008), for inflationary scenario. It involves a variable cosmological constant, which decreases with time, jointly with energy density, cosmic pressure, shear, vorticity, and Hubble’s parameter, while the scale factor, total spin and scalar field increase exponentially. The post-inflationary fluid resembles a perfect one, though total spin grows, but not the angular speed (Berman, in Astrophys. Space Sci. 312:275, 2007). The Pryce-Hoyle tensor, which can measured by the number of injected particles per unit proper volume and time, as well as shear and vorticity, can be neglected in the aftermath of inflation (“no-hair”). [ABSTRACT FROM AUTHOR]

By summarizing and extending the Lagrangian densities of general relativity and the Kibble’s gauge theory of gravitation,a further generalized Lagrangian density for a gravitational system is obtained and analyzed in greater detail, which will extend the studying range for the theory of gravitation. Many special cases can be derived from this generalized Lagrangian density, and the general characteristics and some peculiarities of them will be described and discussed. [ABSTRACT FROM AUTHOR]

The movement of topological or deformable surfaces was shown to create a helicoid surface. The description of dynamics in the parametric space of helicoid introduces a new understanding to quantum mechanics and field theory. The different equations of quantum mechanics can be obtained from a general equation of motion derived from helicoidal dynamics. It was shown that space and time can be transformed into each other in parametric space. [ABSTRACT FROM AUTHOR]

A two spinor lagrangian formulation of field equations for massive particle of arbitrary spin is proposed in a curved space-time with torsion. The interaction between fields and torsion is expressed by generalizing the situation of the Dirac equation. The resulting field equations are different (except for the spin-1/2 case) from those obtained by promoting the covariant derivatives of the torsion free equations to include torsion. The non linearity of the equations, that is induced by torsion, can be interpreted as a self-interaction of the particle. The spin-1 and spin-3/2 cases are studied with some details by translating into tensor form. There result the Proca and Rarita-Schwinger field equations with torsion, respectively. [ABSTRACT FROM AUTHOR]

A novel analysis of the Mathisson-Papapetrou-Dixon equations is presented employing mathematical tools that do not rely on the torsion free geometries used in previous literature. A system of differential algebraic equations that can be used to describe the motion of spinning particles in an arbitrary geometry is derived. The curvature in these equations can involve non-Riemannian contributions. Subsequently, this particular system of equations can accommodate modification to geodesic motion from both scalar fields and the spin of the particle. [ABSTRACT FROM AUTHOR]

We study theories of gravitation that are based on the Einstein – Hilbert action that are not projectively invariant and can therefore completely determine their connections. We are thus lead to the conclusion that the geometry is necessarily Riemann – Cartan and at least the trace part of a torsion field must be present. We examine the consequence of including these torsion fields in cosmological models. Our results differ from those obtained earlier in the Einstein – Cartan – Sciama – Kibble theory. We also consider a model that includes a series of quadratic torsion terms. This series leads to a potential function that has the effect of “turning on” the cosmological constant. This potential function then acts like dark energy. This model also shows that the torsion field can produce an inflationary period. [ABSTRACT FROM AUTHOR]

In the Einstein–Cartan space U4, an axial vector torsion together with a scalar field connected to a local scale factor have been considered. By combining two particular terms from the SO(4, 1) Pontryagin density and then modifying it in a SO(3, 1) invariant way, we get a Lagrangian density with Lagrange multipliers. Then under FRW-cosmological background, where the scalar field is connected to the source of gravitation, the Euler–Lagrange equations ultimately give the constancy of the gravitational constant together with only three kinds of energy densities representing mass, radiation and cosmological constant. The gravitational constant has been found to be linked with the geometrical Nieh-Yan density. [ABSTRACT FROM AUTHOR]

We use a class of generalized relative entropies on density matrices to obtain one-parameter families of torsion-free affine connections. [ABSTRACT FROM AUTHOR]

A general interaction scheme is formulated in a general space–time with torsion from the action principle by considering the gravitational, the Dirac, and the torsion field as independent fields. Some components of the torsion field come out to be automatically zero. Both the resulting Einstein-like and the Dirac-like fields equations contain nonlinear terms given by a self-interaction of the Dirac spinor and originally produced by torsion. The theory is specialized to the Robertson–Walker space–time without torsion. To solve he corresponding equations, that still have a complex structure, the spin coefficients have to be calculated explicitly from the tetrad employed. A solution, even if simple and elementary, is then determined. [ABSTRACT FROM AUTHOR]