Particle horizon

About: Particle horizon is a research topic. Over the lifetime, 2096 publications have been published within this topic receiving 69137 citations.

Determining the expansion history of the universe with the three dimensional cosmic shear

Abstract: We define a new observable that depends on finite redshift differences of the spin-weighted angular moments of the two point function of the three dimensional cosmic shear and on luminosity distance It is shown that precise measurements of our observable will be able to tightly constrain the expansion history of the universe

A weak cosmological constant due to residual gravity in a multiply connected universe

Abstract: Context. Two of the biggest open questions in physical cosmology are the physical interpretation of the measured density of dark energy, and the still uncertain global shape of comoving space, especially including its topology. It was previously shown that multiple connectedness, via the twin paradox of special relativity, provides physical justification for an otherwise arbitrary assumption of the standard FLRW model: it implies a favoured space-time splitting (comoving coordinates). Aims. Could cosmic topology also imply dark energy (e.g. a cosmological constant)? Methods. We use a weak field (Newtonian) approximation of gravity and consider the gravitational effect from distant, multiple copies of a large, collapsed (virialised) object today (i.e. a massive galaxy cluster), taking into account the finite propogation speed of gravity, in a flat, multiply connected universe, and assume that due to a prior epoch of fast expansion (e.g. inflation), the gravitational effect of the distant copies is felt locally, from beyond the näıvely calculated horizon. Results. We find that the residual newtonian gravitational force provides an effect that repels test particles from the cluster, proportionally to the distance from the cluster. This effect is algebraically similar to that of a cosmological constant and could be interpreted as an effect repelling a test object at comoving distance χ from the nearest dense nodes of the cosmic web of density perturbations. The amplitude of the effect, expressed in terms of the pressure-to-density ratio w of the equation of state in an FLRW universe, is w ∼ −(χ/L), where L is the size of the fundamental domain, i.e. of the Universe. Clearly, |w| ≪ 1. Conclusions. Provided that at least a modest amount of inflation occurred in the early Universe, and given some other conditions, multiple connectedness does generate an effect similar to that of dark energy, but the amplitude of the effect at the present epoch is too small to explain the observed dark energy density.

Static universe and cosmic field

Abstract: It is found that in the presence of the cosmic field, which singles out a time-like direction, a static closed homogeneous isotropic universe of the Einstein type is possible, provided matter is present. On the other hand, a universe of the de Sitter type is not permitted by the field equations.

Anisotropic cosmology with vector field in the Noether approach

Abstract: In this Letter, based on Bianchi-I type cosmological model, we have studied the evolution of universe in terms of a vector field coupled to the scalar field. The symmetries of the system are calculated in the Noether approach, the scalar potential and the gauge kinetic function are also obtained following these symmetries. The dynamical equations are integrated numerically and the behaviors of cosmological evolution are presented certainly. Furthermore, the early-time and late-time scenarios are also reached asymptotically, that is, the universe is during the period of decelerating expansion in the early time while during the period of accelerating expansion in the late time. Moreover, we have also studied the expansion isotropization of the universe during evolution. There is no Kasner solution in the present case, while the universe would approach an isotropic Robertson-Walker one, concretely, a de Sitter type one in the late time.