Disertacija Praznična glasba kapitljev na Krku in njena recepcija pri srednješolcih preučuje odnos mladih srednješolcev (od štirinajstega do osemnajstega leta) z otoka Krka do tradicijske glasbe ...otoka Krka v kontekstu praznovanja svetnikov zavetnikov krajev v cerkvenih enotah, imenovanih kapitlji.
Recently, a fully covariant version of the theory of F(T) torsion gravity has been introduced by M. Kršśák and E. Saridakis Classical Quantum Gravity 33, 115009 (2016). In covariant F(T) gravity, the ...Schwarzschild solution is not a vacuum solution for F(T)≠T, and therefore determining the spherically symmetric vacuum is an important open problem. Within the covariant framework, we perturbatively solve the spherically symmetric vacuum gravitational equations around the Schwarzschild solution for the scenario with F(T)=T+(α/2)T2, representing the dominant terms in theories governed by Lagrangians analytic in the torsion scalar. From this, we compute the perihelion shift correction to solar system planetary orbits as well as perturbative gravitational effects near neutron stars. This allows us to set an upper bound on the magnitude of the coupling constant, α, which governs deviations from general relativity. We find the bound on this nonlinear torsion coupling constant by specifically considering the uncertainty in the perihelion shift of Mercury. We also analyze a bound from a similar comparison with the periastron orbit of the binary pulsar PSR J0045-7319 as an independent check for consistency. Setting bounds on the dominant nonlinear coupling is important in determining if other effects in the Solar System or greater universe could be attributable to nonlinear torsion.
We consider static spherically symmetric self-gravitating configurations of the perfect fluid within the framework of the torsion-based extended theory of gravity. In particular, we use the covariant ...formulation of f(T) gravity with f(T)=T+α2T2, and for the fluid, we assume the polytropic equation of state with the adiabatic exponent Γ=2. The constructed solutions have a sharply defined radius as in General Relativity (GR) and can be considered as models of nonrotating compact stars. The particle number–to–stellar radius curves reveal that with positive (negative) values of α a smaller (greater) number of particles can be supported against gravity then in GR. For the interpretation of the energy density and the pressure within the star, we adopt the GR picture where the effects due to nonlinearity of f(T) are seen as a f(T) fluid, which together with the polytropic fluid contributes to the effective energy momentum. We find that sufficiently large positive α gives rise to an abrupt sign change (phase transition) in the energy density and in the principal pressures of the f(T) fluid, taking place within the interior of the star. The corresponding radial profile of the effective energy density is approximately constant over the central region of the star, mimicking an incompressible core. This interesting phenomenon is not found in configurations with negative α.
We consider extended covariant teleparallel (f(T)) gravity whose action is analytic in the torsion scalar and which is sourced by an su(2) valued Yang-Mills field. Specifically, we search for regular ...solutions to the coupled f(T)-Yang-Mills system. For f(T)=T, not surprisingly, the Bartnik-McKinnon solitons of Einstein Yang-Mills theory are recovered. However, interesting effects are discovered with the addition of terms in the action which are nonlinear in the torsion scalar, which are specifically studied up to cubic order. With the addition of the nonlinear terms the number of regular solutions becomes finite. As well, beyond critical values of the coupling constants it is found that there exist no regular solutions. These behaviors are asymmetric with respect to the sign of the nonlinear coupling constants and the elimination of regular solutions turns out to be extremely sensitive to the presence of the cubic coupling. It may be possible, therefore, that with sufficiently high powers of torsion in the action, there may be no regular Yang-Mills static solutions.
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