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Particle horizon
About: Particle horizon is a research topic. Over the lifetime, 2096 publications have been published within this topic receiving 69137 citations.
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24 Jan 2023
TL;DR: In this paper , a two scalar field model that incorporates non Riemannian Measures of Integration (TMT) is introduced, in order to unify the early and present universe.
Abstract: A two scalar field model that incorporates non Riemannian Measures of integration or usually called Two Measures Theory (TMT) is introduced, in order to unify the early and present universe. In the Einstein frame a K-essence is generated and as a consequence for the early universe, we can have a Non Singular Emergent universe followed by Inflation and for the present universe dark epochs with consistent generation of dark energy (DE), dark matter (DM) and stiff matter. The scale invariance is introduced and then is spontaneously broken from the integration of the degrees of freedom associated with the modified measures. The resulting effective potentials and K-essence in the Einstein frame produce three flat regions corresponding to the different epochs mentioned before. For the first flat region we can associate an emergent and an inflationary universe. Here for a parameter-space region this flat plateau possesses a non singular stable emergent universe solution which characterizes an initial epoch of evolution that precedes the inflationary scenario. Also assuming this first plateau, we study the inflation in the framework of the slow-roll approximation. The corresponding cosmological perturbations in our model are determined and we also obtain the different constrains on the parameter-space from the Planck data.In the following flat region DE and also the DM, which does not need to be introduced separately, it is instead a result of a K-essence induced by the multi measures, multi field theory. Also stiff matter component is automatically generated from the K-essence theory from two scalar fields. From the perturbative analysis associated to the perturbation solution of background, we find a correlation between the two scalars. Besides, we obtain that our model during the dark epoch has a behavior of tracking freezing model.
01 Jan 2010
TL;DR: In this article, a complete solution to Projective General Relativity (PGR) equations in the De Sitter universe is provided, so as to establish univocal relations between the scale factor R(�) and cosmic time.
Abstract: In this work, we examine in depth the cosmological physical aspects of the archaic universe described by Euclidean 5-sphere geometry. (see Int. Jour. of Theor., Phys 2009, 48:1003-1018). We hypothesize that the big bang consisted of a spatially extended nucleation process which took place at the end of a pre-cosmic phase, characterized by the evolution parameter x0. This parameter, which can be considered a quantum precursor of ordinary physical time, is a coordinate of Euclidean 5-sphere metrics. We must now examine what the privileged role of the x0 axis consists in. The big bang is a sort of nucleation of matter and fields by vacuum; to try to understand it we must therefore make some assumptions regarding a pre-cosmic state of matter and energy. The introduction of an evolution parameter such as x0 which can be extended to pre-big bang situations is absolutely necessary if we are to define any pre-cosmic dynamics. A generalized Bekenstein relation is here proposed for archaic Universe. A complete solution to Projective General Relativity (PGR) equations in the De Sitter Universe is provided, so as to establish univocal relations between the scale factor R(�) and cosmic time �. In this way, the physics and geometry of the cosmological model are specified completely.
TL;DR: In this paper, the authors show that when the model is extended to incorporate an exponentially small 4D cosmological constant, the KK spectrum becomes continuous, even in the compactified case.
Abstract: Giant resonances of gravity Kaluza-Klein modes (with tensor couplings) in high energy collisions are expected in the Randall-Sundrum orbifold model that incorporates a plausible solution to the hierarchy problem. When the model is extended to incorporate an exponentially small 4-D cosmological constant, the KK spectrum becomes continuous, even in the compactified case. This is due to the presence of a particle horizon, which provides a way to evade Weinberg's argument of the need of fine-tuning to get a very small cosmological constant.
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TL;DR: In this article, the motion of a test Dq-brane in a Dpbrane background is studied and the induced metric on the test brane is then interpreted as the cosmology of the testbrane universe.
Abstract: The motion of a test Dq-brane in a Dp-brane background is studied The induced metric on the test brane is then interpreted as the cosmology of the test brane universe One is then able to resolve the resulting cosmological singularities In particular, for a D3-brane in a D5-brane background, one finds a 3+1 dimensional FRW universe with equation of state $p = \ed$ It has been argued that this may have been the dominant form of matter at very early times