Zobrazeno 1 - 10
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pro vyhledávání: '"Cotsakis, Spiros"'
Autor:
Cotsakis, Spiros
For a given nonlinear system of dynamical equations, the set of all stable perturbations of the system, the versal unfolding, is fully determined by bifurcation theory. This leads to a complete depiction of all possible qualitatively different soluti
Externí odkaz:
http://arxiv.org/abs/2412.04283
Autor:
Cotsakis, Spiros
We analyse the dynamics of the Friedmann-Lema\^itre universes taking into account the different roles played by the fluid parameter and the cosmological constant, as well as the degenerate character of the equations. We find that the Friedmann-Lema\^
Externí odkaz:
http://arxiv.org/abs/2411.17286
Autor:
Cotsakis, Spiros
Publikováno v:
Eur. Phys. J. C 84, 391 (2024)
The crease flow, replacing the Hamiltonian system used for the evolution of crease sets on black hole horizons, is introduced and its bifurcation properties for null hypersurfaces are discussed. We state the conditions of nondegeneracy and typicality
Externí odkaz:
http://arxiv.org/abs/2312.08023
Publikováno v:
Eur. Phys. J. C (2023) 83:433
We propose a new formulation of $f(R)$ gravity, dubbed scalarized $f(R)$ gravity, in which the Legendre transform is included as a dynamical term. This leads to a theory with second-order field equations that describes general relativity with a self-
Externí odkaz:
http://arxiv.org/abs/2305.04011
Publikováno v:
Eur. Phys. J. C. 83 (2023) 491
We construct a generic asymptotic solution for modified gravity near a sudden singularity. This solution contains a fluid source with no equation of state and is function-counting stable, that is it has eleven independent arbitrary functions of the s
Externí odkaz:
http://arxiv.org/abs/2304.13291
Publikováno v:
Eur. Phys. J. C 83, 735 (2023)
We discuss implications of the cosmological frame principle which states that cosmological effects of modified gravity must be stable as solutions of each of the corresponding sets of dynamical equations holding in the two conformally-related frames.
Externí odkaz:
http://arxiv.org/abs/2304.12733
Autor:
Cotsakis, Spiros, Miritzis, John
Publikováno v:
Mathematics 11 (2023) 633
We study the effects of trans-planckian censorship conjecture (TCC) bounds on geodesic completeness of spacetime and the associated existence for an infinite proper time. Using Gronwall's lemma, TCC bounds can be derived directly, leading to a result
Externí odkaz:
http://arxiv.org/abs/2301.00156
Autor:
Cotsakis, Spiros
Publikováno v:
Gen. Rel. Grav. 55 (2023) 61
We introduce consideration of dispersive aspects of standard perfect fluid Friedmann cosmology and study the new qualitative behaviours of cosmological solutions that emerge as the fluid parameter changes and zero eigenvalues appear in the linear par
Externí odkaz:
http://arxiv.org/abs/2208.07892
Autor:
Cotsakis, Spiros
Publikováno v:
Lett. HEP 322 (2023) 1
We consider the evolution of homogeneous cosmologies towards the future in a dynamical systems formulation. Using a variational equation approach, we show that there is a short period in which transient solutions between the end of a Mixmaster era an
Externí odkaz:
http://arxiv.org/abs/2208.07104
Publikováno v:
Eur. Phys. J. C82 (2022) 785
We study the problem of evolution of bulk 5-fluids having an embedded braneworld with a flat, de Sitter, or anti-de Sitter geometry. We introduce new variables to express the Einstein equations as a dynamical system that depends on the equation of st
Externí odkaz:
http://arxiv.org/abs/2205.08125