Theoretical Physics

4

Authors: M.A. Grado-Caffaro, M. Grado-Caffaro

We investigate satisfactorily the possible, under certain circumstances, fermionic nature of excitons in both parabolic and non-parabolic semiconductors. In this context, we discuss some key aspects dealing, on the one hand, with Fermi velocity and, on the other hand, with the particle-in-abox model. These aspects are discussed in the light of the role of excitons as bosons or fermions. Our investigation has a, say, a practical character so we may say that the method utilized here is more intuitive for the reader than some work published in the current literature.

6

Authors: V. G. Mete, V. D. Elkar, V.S. Deshmukh

In this paper we present a bulk viscous magnetized Bianchi type IX string cosmological model in general relativity. In order to find determinate solution of the investigated model, we assume the conditions :(i) Scalar expansion is proportional to shear scalar and (ii) ξθ = constant, where ξ is bulk viscosity and θ is scalar expansion. Some physical and geometrical properties of the investigated model are also discussed.

7

Authors: Mario Rabinowitz

Time dilation derived here from relativistic Least Action couples relativistic mass and time transformations. This is an argument against time dilation for other than the signal speed of light c . Because c is the paramount signal velocity in Special Relativity, we examine the extent to which limited relativistic transformations of time dilation and length contraction might occur for any signal velocity, C c < , provided that the relative frame velocity v C <<< . Such relativistic effects depending on C may be detectable in a narrow range. If allowed by nature and confirmed by experiment, this will alter our views of space-time. Known experiments do not rule this out. The total resultant velocity 3 v cannot exceed C in the Einstein addition of velocities due to the condition v C <<< . A derivation is presented which together with experiment rules out mass transformation unless the signal velocity is the speed of light.

10

Authors: A.Y.Shaikh, K.S.Wankhade

In the present study we investigate, Hypersurface-Homogeneous cosmological model in f(R,T) theory of gravity with a term Λ. We obtain the gravitational field equations in the metric formalism, which follow from the covariant divergence of the stress-energy tensor. The field equations correspond for a specific choice of f(R,T)=f1(R)+f2(T), with the individual superior functions f1(R)=λR and f2(T)=λT. In this paper, we consider a simple form of expansion history of Universe referred to as the hybrid expansion law − a product of power-law and exponential type of functions. Einstein’s field equations have been solved by taking into account the hybrid expansion law for scale factor that yields time dependent deceleration parameter (DP). Some physical and geometric properties of the model along with physical acceptability of the solutions have also been discussed in detail.