Physics

We revisit the evolution of the scale factor in a flat FRW spacetime with a new generalized decay rule for the dynamic Λ -term under modified theories of gravity. It analyses certain cosmological parameters and examines their behaviours in this generalized setting which includes several decay laws in the literature. We have also obtained observational constraints on various model parameters and estimated the present values of cosmological parameters { Ω m 0 , Ω Λ 0 , q 0 , t 0 , ω 0 } and have discussed with various observational results. Finite time past and future singularities in this model are also discussed. \end{abstract}

We propose a new path integral for QED in the presence of magnetic monopoles on the formalism of Geometric Algebra of Hestenes-Haddamard-Rodrigues written in terms of Dirac Matrices

In the present article, we discuss relativistic anisotropic solutions of the Einstein field equation for the spherically symmetric line element under the class I condition. To do so we apply the embedding class one technique using Eisland condition. Within this approach, one arrives at a particular differential equation that links the two metric components e ν and e λ . In order to obtain the full space-time description inside the stellar configuration we ansatz the generalized form of metric component g rr corresponding to the Finch-Skea solution. Once the space-time geometry is specified we obtain the complete thermodynamic description i.e. the matter density ρ , the radial, and tangential pressures p r and p t , respectively. Graphical analysis shows that the obtained model respects the physical and mathematical requirements that all ultra-high dense collapsed structures must obey. The M−R diagram suggests that the solution yields stiffer EoS as parameter n increases. The M−I graph is in agreement with the concepts of Bejgar et al. \cite{bej} that the mass at I max is lesser by few percent (for this solution ∼3% ) from M max . This suggests that the EoSs is without any strong high-density softening due to hyperonization or phase transition to an exotic state.

The existence of "dark matter", inferred from the observed rotation curves of galaxies, is a hypothesis which is widely regarded as problematic. This paper proposes an alternative hypothesis based on the space-time geometry near a rotating body and formulated in terms of the dragging of inertial frames. This hypothesis is true in a certain linear approximation to General Relativity (D Sciama, Mon. Not. Roy. Astron. Soc. 113 (1953) 34--42) and is justified in general by Mach's principle. Dark matter corrects the rotation curve but does not predict the ubiquitous spiral structure of galaxies. The geometric alternative suggested here deals with both problems and allows the construction of a simple model for the dynamics of spiral galaxies which fits observations well.

The operator of elementary particle mass spectrum is constructed on the basis of the postulate of a six-dimensional space-time manifold having a Riemann-Cartan space structure, proceeding only from its geometric properties. Special solutions found for this operator well describe the mass spectrum of the known quark triplet and hence of some baryon supermultiplets.

The Jeans instability is regarded as important tool for analyzing dynamical of a self-gravitating system. However, the astronomical observation data show that some Bok globules, which mass are less than the Jeans mass still have stars or at least experience the star formation process. In this paper, we investigate the effects of higher order generalized uncertainty principle on the Jeans mass of collapsing molecular cloud. It is found that the higher order generalized uncertainty principle has a very significant effect on the canonical energy and gravitational potential of idea gas, and final leads to modified Jeans mass lower than the original case, this result can be used to explain the problem of Bok globules. Furthermore, we first constrain the upper limits of the GUP parameter β 0 by using the different data of Bok globules, which range from 10 15 to 10 17 .

The angular distribution of the Cosmic Microwave Background Radiation (CMBR) in sky shows a dipole asymmetry, ascribed to the observer's motion (peculiar velocity of the solar system!), relative to the local comoving coordinates. The peculiar velocity thus determined turns out to be 370 km s −1 in the direction RA = 168 ∘ , Dec =− 7 ∘ . On the other hand, a dipole asymmetry in the sky distribution of radio sources in the NRAO VLA Sky Survey (NVSS) catalog, comprising 1.8 million sources, yielded a value for the observer's velocity to be ∼4 times larger than the CMBR value, though the direction turned out to be in agreement with that of the CMBR dipole. This large difference in observer's speeds with respect to the reference frames of NVSS radio sources and of CMBR, confirmed since by many independent groups, is rather disconcerting as the observer's motion with respect to local comoving coordinates should be independent of the technique used to determine it. A genuine difference in relative speeds of two cosmic reference frames could jeopardize the cosmological principle, thence it is crucial to confirm such discrepancies using independent samples of radio sources. We here investigate the dipole in the sky distribution of radio sources in the recent TIFR GMRT Sky Survey (TGSS) dataset, comprising 0.62 million sources, to determine observer's motion. We find a significant disparity in observer's speeds relative to all three reference frames, determined from the radio source datasets and the CMBR, which does not fit with the cosmological principle, a starting point for the standard modern cosmology.

We develop a mathematical theory of quantization of multidimensional variational principles, and compare it with traditional constructions of quantum field theory. We conjecture that mathematical realization of quantum field theory axioms, in general, does not exist.

To avoid the infinitesimal rotation nature of the Cauchy-Stokes decomposition of velocity gradient, the letter proposes an new additive decomposition in which one part is a SO(3) rotation tensor Q=expW .

These are notes on the square root of 4×4 identity matrix and associated quantum fields of spin one half. The method is illustrated by constructing a new mass dimension one fermionic field. The presented field is local. The field energy is bounded from below. It is argued that these fermions are a first-principle candidate for dark matter with an unsuppressed quartic self interaction.