Particle horizon

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

Early homogeneous universe with variable cosmological constant: kinematics tests

Abstract: A spatially homogeneous cosmological model with flat geometry filled with perfect fluid is studied in the presence of a variable cosmological "constant." Einstein's field equations are solved by using the "gamma-law" equation of state p = (γ-1)ρ, where the adiabatic parameter γ, varies with cosmic time. The functional form of γ, which is assumed to be the function of scale factor R as proposed by Carvalho, is used to describe the early evolution of universe with variable cosmological "constant." A unified description of early universe is given in which an inflationary phase is followed by radiation-dominated phase. It has been observed that the solutions are compatible with the result of recent observations. Exact expressions for the look-back time, proper distance, luminosity distance and angular diameter distance versus redshift are derived and their meaning are discussed in detail. The various physical aspects of the models are also discussed.

The cosmic spacetime: Is the universe much simpler than we thought?

Abstract: The polish priest Nicolaus Copernicus (1473—1543) started a revolution with his heliocentric cosmology that displaced the Earth from the center of the Universe. His remarkable shift in paradigm continues to this day, the cornerstone of a concept we now call the Cosmological Principle, in which the Universe is assumed to be homogeneous and isotropic, without a center or boundary. But few realize that even this high degree of symmetry is insufficient for cosmologists to build a practical model of the Universe from the equations of General Relativity.

Dynamical behaviors of FRW universe containing a positive/negative potential scalar field in loop quantum cosmology

Abstract: The dynamical behaviors of FRW Universe containing a posivive/negative potential scalar field in loop quantum cosmology scenario are discussed. The method of the phase-plane analysis is used to investigate the stability of the Universe. It is found that the stability properties in this situation are quite different from the classical cosmology case. For a positive potential scalar field coupled with a barotropic fluid, the cosmological autonomous system has five fixed points and one of them is stable if the adiabatic index \(\gamma \) satisfies \(0<\gamma <2\). This leads to the fact that the universe just have one bounce point instead of the singularity which lies in the quantum dominated area and it is caused by the quantum geometry effect. There are four fixed points if one considers a scalar field with a negative potential, but none of them is stable. Therefore, the universe has two kinds of bounce points, one is caused by the quantum geometry effect and the other is caused by the negative potential, the Universe may enter a classical re-collapse after the quantum bounce. This hints that the spatially flat FRW Universe containing a negative potential scalar field is cyclic.

Genesis: How the Universe Began According to Standard Model Particle Physics

Abstract: I show that the mutual consistency of the Bekenstein Bound, the Standard Model (SM) of particle physics, and general relativity implies that the universe began in a unique state. I solve the coupled EYM equations for this unique state, show how the horizon problem is solved, and how SM baryogenesis naturally results from the triangle anomoly. Since the SU(2) winding number state is thus non-zero, the universe is not in the QCD ground state, and this plausibly yields a (small) positive cosmological constant. Since the initial state is unique, it is necessarily homogeneous and isotropic, as required by the Bekenstein Bound. Wheeler-DeWitt quantization implies an $S^3$ cosmology must be very close to flat if the universe is to be classical today. I show that the spectrum of any classical gauge field (or interacting massless scalar field) in a FRW universe necessarily obeys the Wien displacement law and the corresponding quantized field the Planck distribution law with the reciprocal of the scale factor playing the role of temperature, even if the fields have zero temperature. Thus the CBR could even today be a pure SU(2) electroweak field at zero temperature coupled to the Higgs field, in spite of early universe inverse double Compton and thermal bremsstrahlung.Such a CBR would not couple to right-handed electrons, and this property can be detected with a Penning trap or even using the late 1960's CBR detector with appropriate filters. I argue that ultrahigh energy (UHE) Genesisf.tex Genesisf.tex cosmic ray protons would not produce pions by interacting with such a CBR, and thus the existence of such protons may constitute an observation of this CBR property.

The Emergent Universe scheme and tunneling

Abstract: We present an alternative scheme for an Emergent Universe scenario, developed previously in Phys. Rev. D 86, 083524 (2012), where the universe is initially in a static state supported by a scalar field located in a false vacuum. The universe begins to evolve when, by quantum tunneling, the scalar field decays into a state of true vacuum. The Emergent Universe models are interesting since they provide specific examples of non-singular inflationary universes.