Zobrazeno 1 - 10
of 596
pro vyhledávání: '"Harkó T"'
Publikováno v:
Physics of the Dark Universe, 2022, 101131 (Available online 26 October 2022)
Particle creation (or annihilation) mechanisms, described by either quantum field theoretical models, or by the thermodynamics of irreversible processes, play an important role in the evolution of the early Universe, like, for example, in the warm in
Externí odkaz:
http://arxiv.org/abs/2203.08907
Autor:
Ghilencea, D. M., Harko, T.
We discuss the cosmological evolution of the Weyl conformal geometry and its associated Weyl quadratic gravity. The Einstein gravity (with a positive cosmological constant) is recovered in the spontaneously broken phase of Weyl gravity; this happens
Externí odkaz:
http://arxiv.org/abs/2110.07056
Publikováno v:
Journal of Applied Mathematics and Engineering Vol 8 (2016) Part I, pages 25-34
In this work we obtain an approximate solution of the strongly nonlinear second order differential equation $\frac{d^{2}u}{dt^{2}}+\omega ^{2}u+\alpha u^{2}\frac{d^{2}u}{dt^{2}}+\alpha u\left( \frac{du}{dt}\right)^{2}+\beta \omega ^{2}u^{3}=0$, descr
Externí odkaz:
http://arxiv.org/abs/1707.05369
Scalar-tensor gravitational theories are important extensions of standard general relativity, which can explain both the initial inflationary evolution, as well as the late accelerating expansion of the Universe. In the present paper we investigate t
Externí odkaz:
http://arxiv.org/abs/1612.05446
Autor:
Harko, T., Mak, M. K.
Publikováno v:
Astrophysics and Space Science, 361(9), 1-19 (2016)
Obtaining exact solutions of the spherically symmetric general relativistic gravitational field equations describing the interior structure of an isotropic fluid sphere is a long standing problem in theoretical and mathematical physics. The usual app
Externí odkaz:
http://arxiv.org/abs/1607.06877
Publikováno v:
Astrophys Space Sci (2016) 361:52
In this paper, we investigate the Noether symmetries of a generalized scalar-tensor, Brans-Dicke type cosmological model, in which we consider explicit scalar field dependent couplings to the Ricci scalar, and to the scalar field kinetic energy, resp
Externí odkaz:
http://arxiv.org/abs/1512.08054
Autor:
Harko, T., Mak, M. K.
Publikováno v:
J. Math. Phys. 56, 111501 (2015)
We consider quasi-stationary (travelling wave type) solutions to a general nonlinear reaction-convection-diffusion equation with arbitrary, autonomous coefficients. The second order nonlinear equation describing one dimensional travelling waves can b
Externí odkaz:
http://arxiv.org/abs/1510.08163
Autor:
Mak, M. K., Harko, T.
Publikováno v:
The European Physical Journal C, 73, 2585 (2013)
We present a general solution of the Einstein gravitational field equations for the static spherically symmetric gravitational interior spacetime of an isotropic fluid sphere. The solution is obtained by transforming the pressure isotropy condition,
Externí odkaz:
http://arxiv.org/abs/1309.5123
Autor:
Mak, M. K., Harko, T.
Publikováno v:
Applied Mathematics and Computation 219 (2013), pp. 7465-7471
New further integrability conditions of the Riccati equation $dy/dx=a(x)+b(x)y+c(x)y^{2}$ are presented. The first case corresponds to fixed functional forms of the coefficients $a(x)$ and $c(x)$ of the Riccati equation, and of the function $F(x)=a(x
Externí odkaz:
http://arxiv.org/abs/1301.5720
We present an extension of general relativity in which an $f(R)$ term \`{a} la Palatini is added to the usual metric Einstein-Hilbert Lagrangian. Expressing the theory in a dynamically equivalent scalar-tensor form, we show that it can pass the Solar
Externí odkaz:
http://arxiv.org/abs/1301.2209