Particle horizon

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

Universe acceleration and nonlinear electrodynamics

Abstract: A new model of nonlinear electrodynamics with a dimensional parameter $\beta$ coupled to gravity is considered. We show that an accelerated expansion of the universe takes place if the nonlinear electromagnetic field is the source of the gravitational field. A pure magnetic universe is investigated and the magnetic field drives the universe to accelerate. In this model, after the big bang, the universe undergoes inflation, and the accelerated expansion and then decelerates approaching Minkowski spacetime asymptotically. We demonstrate the causality of the model and a classical stability at the deceleration phase.

Constraints on anisotropic cosmic expansion from supernovae

Abstract: Aims. We test the isotropy of the expansion of the Universe by estimating the hemispherical anisotropy of supernova type Ia (SN Ia) Hubble diagrams at low redshifts (z< 0.2). Methods. We compare the best fit Hubble diagrams in pairs of hemisphere s and search for the maximal asymmetric orientation. For an isotropic Universe, we expect only a small asymmetry due to noise and the presence of nearby structures. This test does not depend on the assumed content of the Universe, the assumed model of gravity, or the spatial curvature of the Universe. The expect ation

Can the Universe Create Itself

Abstract: The question of first-cause has troubled philosophers and cosmologists alike. Now that it is apparent that our universe began in a big bang explosion, the question of what happened before the big bang arises. Inflation seems like a very promising answer, but as Borde and Vilenkin have shown, the inflationary state preceding the big bang could not have been infinite in duration---it must have had a beginning also. Where did it come from? Ultimately, the difficult question seems to be how to make something out of nothing. This paper explores the idea that this is the wrong question---that that is not how the Universe got here. Instead, we explore the idea of whether there is anything in the laws of physics that would prevent the Universe from creating itself. Because spacetimes can be curved and multiply connected, general relativity allows for the possibility of closed timelike curves (CTCs). Thus, tracing backwards in time through the original inflationary state we may eventually encounter a region of CTCs---giving no first-cause. This region of CTCs may well be over by now (being bounded toward the future by a Cauchy horizon). We illustrate that such models---with CTCs---are not necessarily inconsistent by demonstrating self-consistent vacuums for Misner space and a multiply connected de Sitter space in which the renormalized energy-momentum tensor does not diverge as one approaches the Cauchy horizon and solves Einstein's equations. Some specific scenarios (out of many possible ones) for this type of model are described. For example, a metastable vacuum inflates producing an infinite number of (big-bang-type) bubble universes. In many of these, either by natural causes or by action of advanced civilizations, a number of bubbles of metastable vacuum are created at late times by high energy events. These bubbles will usually collapse and form black holes, but occasionally one will tunnel to create an expanding metastable vacuum (a baby universe) on the other side of the black hole's Einstein-Rosen bridge as proposed by Farhi, Guth, and Guven. One of the expanding metastable-vacuum baby universes produced in this way simply turns out to be the original inflating metastable vacuum we began with. We show that a Universe with CTCs can be stable against vacuum polarization. And it can be classically stable and self-consistent if and only if the potentials in this Universe are retarded---which gives a natural explanation of the arrow of time in our universe. Interestingly, the laws of physics may allow the Universe to be its own mother.

Probing the equation of state of the early universe with a space laser interferometer

Abstract: We propose a method to probe the equation of state of the early universe and its evolution, using the stochastic gravitational wave background from inflation. A small deviation from purely radiatio...

Calibrating the cosmic distance scale ladder: the role of the sound horizon scale and the local expansion rate as distance anchors

Abstract: We exploit cosmological-model independent measurements of the expansion history of the Universe to provide a cosmic distance ladder. These are supernovae type Ia used as standard candles (at redshift between 0.01 and 1.3) and baryon acoustic oscillations (at redshifts between 0.1 and 0.8) as standard rulers. We calibrate (anchor) the ladder in two ways: rst using the local H0 value as an anchor at z = 0 (eectively calibrating the standard candles) and secondly using the cosmic microwave background-inferred sound-horizon scale as an anchor (giving the standard ruler length) as an inverse distance ladder. Both methods are consistent, but the uncertainty in the expansion history H(z) is smaller if the sound horizon scale is used. We present inferred values for the sound horizon at radiation drag rd which do not rely on assumptions about the early expansion history nor on cosmic microwave background measurements but on the cosmic distance ladder and baryon acoustic oscillations measurements. We also present derived values of H0 from the inverse distance ladder and we show that they are in very good agreement with the derived value from the state-of-the art cosmic microwave background data for a CDM model.