Open Universe Research Articles

Open inflationary universes in a brane world cosmology

In this paper, we study a type of one-field model for open inflationary universe models in the context of brane world models. In the scenario of a one-bubble universe model, we determine and characterize the existence of the Coleman--De Lucia instanton, together with the period of inflation after tunneling has occurred. Our results are compared to those found in the Einstein theory of relativistic models.

On the asymptotic character of electromagnetic waves in a Friedmann?Robertson?Walker universe

Asymptotic properties of electromagnetic waves are studied within the context of Friedmann–Robertson–Walker (FRW) cosmology. Electromagnetic fields are considered as small perturbations on the background spacetime and Maxwell’s equations are solved for all three cases of flat, closed and open FRW universes. The asymptotic character of these solutions is investigated and their relevance to the problem of cosmological tails of electromagnetic waves is discussed.

Do rotations beyond the cosmological horizon affect the local inertial frame?

If perturbations beyond the horizon have the velocities prescribed everywhere then the dragging of inertial frames near the origin is suppressed by an exponential factor. However if perturbations are prescribed in terms of their angular momenta there is no such suppression. We resolve this paradox and in doing so give new explicit results on the dragging of inertial frames in closed, flat and open universe with and without a cosmological constant.

Toroidal perturbations of Friedmann-Robertson-Walker universes

Explicit expressions are found for the axisymmetric metric perturbations of the closed, flat and open FRW universes caused by toroidal motions of the cosmic fluid. The perturbations are decomposed in vector spherical harmonics on 2-spheres, but the radial dependence is left general. Solutions for general odd-parity $l$-pole perturbations are given for either angular velocities or angular momenta prescribed. In particular, in case of closed universes the solutions require a special treatment of the Legendre equation.

GHOSTS IN A MIRROR

We look at some dynamic geometries produced by scalar fields with both the "right" and the "wrong" signs of the kinetic energy. We start with anisotropic homogeneous universes with closed, open and flat spatial sections. A non-singular solution to the Einstein field equations representing an open anisotropic universe with the ghost field is found. This universe starts collapsing from t→-∞ and then expands to t→∞ without encountering singularities on its way. We further generalize these solutions to those describing inhomogeneous evolution of the ghost fields. Some interesting solutions with the plane symmetry are discussed. These have a property that the same line element solves the Einstein field equations in two mirror regions |t|≥z and |t|≤z, but in one region the solution has the right and in the other, the wrong sign of the kinetic energy. We argue, however, that a physical observer cannot reach the mirror region in a finite proper time. Self-similar collapse/expansion of these fields are also briefly discussed.

Fusion and the cosmos

In the following investigation we pay special attention to the role of selforganization in fusion plasma physics and in the cosmos. We present a new approach to the expansion of the universe. Formally the technique developed relies on our experience from treating hot fusion plasmas. We account for the possibility that the universe, as it seems, could have a finite life-time (even if it is counted in billions of years), and combine this assumption with the experimental observation that the velocity of separation of distant galaxies is proportional to the distance between the galaxies (the Hubble law). By analysis of a NL PDE (nonlinear partial differential equation) we succed in proving that the crucial value of an exponent has a simple linear relationship with the Hubble constant. It is recognized that the scale-length that we use as a measure of the expansion is equivalent to the Einstein radius of curvature. The final results suggest that the Hubble law should be extended by a factor, which could have an explosive tendency of growth in time (open universe), or a decaying character (closed universe). The possibility of reversed expansion or an oscillating universe “cosmic pendulum” is also discussed.

String bit models of two-dimensional quantum gravity coupled with matter

We extend the formalism of Hamiltonian string bit models of quantum gravity type in two spacetime dimensions to include couplings to particles. We find that the single-particle closed and open universe models, respectively, behave like empty open and closed universes, and that a system of two distinguishable particles in a closed universe behaves like an empty closed universe. We then construct a metamodel that contains all such models, and find that its transition amplitude is exactly the same as the sl(2) gravity model.

Black hole versus cosmological horizon entropy

The generalized second law of thermodynamics states that entropy always increases when all event horizons are attributed with an entropy proportional to their area. We test the generalized second law by investigating the change in entropy when dust, radiation and black holes cross a cosmological event horizon. We generalize for flat, open and closed Friedmann–Robertson–Walker universes by using numerical calculations to determine the cosmological horizon evolution. In most cases, the loss of entropy from within the cosmological horizon is more than balanced by an increase in cosmological event horizon entropy, maintaining the validity of the generalized second law of thermodynamics. However, an intriguing set of open universe models shows an apparent entropy decrease when black holes disappear over the cosmological event horizon. We anticipate that this apparent violation of the generalized second law will disappear when solutions are available for black holes embedded in arbitrary backgrounds.

Open static Chaplygin universe

We apply the qualitative theory of dynamical systems to the study of the Chaplygin gas cosmological model. In difference to earlier works devoted to this model we give up sign restrictions on the choice of the sign of the energy density and on the parameters characterising initial conditions for a cosmological evolution. It appears that exists a static open universe filled with the Chaplygin gas. Besides exist universes where the acoustic waves have a velocity exceeding that of light in the vacuum.

On the Total Energy of Open Friedmann‐Robertson‐Walker Universes

The idea that the universe has zero total energy when one includes the contribution from the gravitational field is reconsidered. A Hamiltonian is proposed as an energy for the exact equations of FRW cosmology: it is then shown that this energy is constant. Thus, open and critically open FRW universes have the energy of their asymptotic state at infinite dilution, which is Minkowski space with zero energy. It is then shown that de Sitter space, the inflationary attractor, also has zero energy, and the argument is generalized to Bianchi models converging to this attractor.

CONICAL SINGULAR SOLUTIONS IN (2+1)-DIMENSIONAL GRAVITY EMPLOYING THE ADM CANONICAL FORMALISM

Topological solutions in the (2+1)-dimensional Einstein theory of gravity are studied within the ADM canonical formalism. It is found that a conical singularity appears in the closed expanding de Sitter universe solution as a topological defect in the case of the Einstein theory with a cosmological constant. Quantum effects on the conical singularity are studied using the de Broglie-Bohm interpretation. Finite quantum tunneling effects are obtained for the closed de Sitter universe, while no quantum effects are obtained for an open universe.

Extended open inflationary universes

In this paper we study a type of one-field model for open inflationary universe models in the context of the Jordan-Brans-Dicke theory. In the scenario of a one-bubble universe model we determine and characterize the existence of the Coleman-De Lucia instanton, together with the period of inflation after tunnelling has occurred. Our results are analogous to those found in the Einstein General Relativity models.

Post-Marxism: An Intellectual History

Introduction: Marxism's 'Disenchanted' 1. Marxism in a 'post-' world 2. An intellectual malady? The Laclau-Mouffe affair (I) 3. Without apologies: the Lacau-Mouffe affair (II) 4. Marxism is not a 'science of history': testing the boundaries of Marxism 5. Post-Marxism before post-Marxism: (I) Luxembourg to the Frankfurt School 6. Post-Marxism before post-Marxism: (II) hybridising Marxism 7. Constructing incredulity: (I) postmodernism 8. Constructing incredulity: (II) feminism 9. An open universe? Postmodern science and the Marxist dialectic 10. 'Not show biz': pluralist politics and the emancipation of critique

Functional approach to (2 + 1)-dimensional gravity coupled to particles

The quantum gravity problem of \U0001d4a9 point particles interacting with the gravitational field in 2 + 1 dimensions is approached by working out the phase-space functional integral. The maximally slicing gauge is adopted for a non-compact open universe with the topology of the plane. The momenta conjugate to the gravitational field are related to a class of meromorphic quadratic differentials. The boundary term for the non-compact space is worked out in detail. In the extraction of the physical degrees of freedom functional determinants related to the puncture formulation of string theory occur and cancel out in the final reduction. Finally, the ordering problem in the definition of the functional integral is discussed.

MISSING MASS AND THE ACCELERATION OF THE UNIVERSE: IS QUINTESSENCE THE ONLY EXPLANATION?

Detailed observations of the temperature fluctuations in the microwave background radiation indicate that we live in an open universe. From the size of these fluctuations, it is concluded that the geometry of the universe is quite close to Euclidean. In terms Friedmann models, this implies a mass density within 10% of the critical density required for a flat universe. Observed mass can only account for 30% of this mass density. Recently, an outstanding observation revealed that cosmos is accelerating. This motivated some astronomers to explain the missing 70% as some exotic dark energy called quintessence. In this essay, we present an alternative explanation to these cosmological issues in terms of the Friedmann Thermodynamics. This model has the capability of making definite predictions about the geometry of the universe, the missing mass problem, and the acceleration of the universe in-line with the recent findings. For future observations, we also predict where this model will start differing from the quintessence models.

AN OPEN SINGULARITY-FREE COSMOLOGICAL MODEL WITH INFLATION

In the light of recent observations which point to an open universe (Ω0 < 1), we construct an open singularity-free cosmological model by reconsidering a model originally constructed for a closed universe. Our model starts from a nonsingular state called prematter, governed by an inflationary equation of state P = (γp - 1)ρ where γp (≃ 10-3) is a small positive parameter representing the initial vacuum dominance of the universe. Unlike the closed models universe cannot be initially static hence, starts with an initial expansion rate represented by the initial value of the Hubble constant H(0). Therefore, our model is a two-parameter universe model (γp,H(0)). Comparing the predictions of this model for the present properties of the universe with the recent observational results, we argue that the model constructed in this work could be used as a realistic universe model.

Brane world cosmologies and statistical properties of gravitational lenses

Brane world cosmologies seem to provide an alternative explanation for the present accelerated stage of the Universe with no need to invoke either a cosmological constant or an exotic quintessence component. In this paper we investigate statistical properties of gravitational lenses for some particular scenarios based on this large scale modification of gravity. We show that a large class of such models are compatible with the current lensing data for values of the matter density parameter ${\ensuremath{\Omega}}_{\mathrm{m}}<~0.94(1\ensuremath{\sigma}).$ If one fixes ${\ensuremath{\Omega}}_{\mathrm{m}}$ to be $\ensuremath{\simeq}0.3,$ as suggested by most of the dynamical estimates of the quantity of matter in the Universe, the predicted number of lensed quasars requires a slightly open universe with a crossover distance between the 4- and 5-dimensional gravities of the order of ${1.76H}_{o}^{\ensuremath{-}1}.$

Galaxy Number Counts in the Subaru Deep Field: Multiband Analysis in a Hierarchical Galaxy Formation Model

Number counts of galaxies are reanalyzed using a semianalytic model (SAM) of galaxy formation based on the hierarchical clustering scenario. Faint galaxies in the Subaru Deep Field (SDF; near-infrared J and K') and the Hubble Deep Field (HDF; ultraviolet/optical U, B, V, and I) are compared with our model galaxies. We have determined the astrophysical parameters in the SAM that reproduce observations of nearby galaxies and used them to predict the number counts and redshifts of faint galaxies for three cosmological models, the standard cold dark matter (CDM) universe, a low-density flat universe with nonzero cosmological constant, and a low-density open universe with zero cosmological constant. The novelty of our SAM analysis is the inclusion of selection effects arising from the cosmological dimming of surface brightness of high-redshift galaxies, and from the absorption of visible light by internal dust and intergalactic H I clouds. As was found in our previous work, in which the ultraviolet/optical HDF galaxies were compared with our model galaxies, we find that our SAM reproduces counts of near-infrared SDF galaxies in a low-density universe either with or without a cosmological constant, and that the standard CDM universe is not preferred, as suggested by other recent studies. Moreover, we find that simple prescriptions for (1) the timescale of star formation being proportional to the dynamical timescale of the formation of galactic disks, (2) the size of galactic disks being rotationally supported with the same specific angular momentum as that of surrounding dark halo, and (3) the dust optical depth being proportional to the metallicity of cold gas, cannot completely explain all of the observed data. Improved prescriptions incorporating mild redshift-dependence for those are suggested from our SAM analysis.

A theoretical study of the mass–temperature relation for clusters of galaxies

I derive the mass–temperature relation and its time evolution for clusters of galaxies in different cosmologies by means of two different models. The first one is a modification and improvement of a model by Del Popolo & Gambera, namely based upon a modification of the top-hat model in order to take account of angular momentum acquisition by protostructures and of an external pressure term in the virial theorem. The second one is based on the merging-halo formalism of Lacey & Cole, accounting for the fact that massive clusters accrete matter quasi-continuously, and is an improvement of a model proposed by Voit, again to take account of angular momentum acquisition by protostructures. The final result is that, in both models, the M–T relation shows a break at T∼ 3–4 keV. The behaviour of the M–T relation is as usual, M∝T3/2, at the high-mass end, and M∝Tγ, with a value of depending on the chosen cosmology. Larger values of γ are related to open cosmologies, while Λ-cold dark matter (ΛCDM) cosmologies give results of the slope intermediate between the flat case and the open case. The evolution of the M–T relation, for a given Mvir, is more modest both in flat and open universes in comparison with previous estimates found in the literature, even more modest than what found by Voit. Moreover, the time evolution is more rapid in models with L= 0 than in models in which the angular momentum acquisition by protostructures is taken into account (L≠ 0). The effect of a non-zero cosmological constant is that of slightly increasing the evolution of the M–T relation with respect to open models with L≠ 0. The evolution is more rapid for larger values (in absolute value) of the spectral index, n. The mass–temperature relation, obtained using the quoted models, is also compared with the data by Finoguenov, Reiprich & Böeringer. The comparison shows that these data are able to rule out very low-Ω0 models (<0.3), particularly in the open case, and that a better fit is obtained by ΛCDM models and by CDM models with Ω0 > 0.3.

Separation of variables and exact solution of the Klein–Gordon and Dirac equations in an open universe

We solve the Klein–Gordon and Dirac equations in an open cosmological universe with a partially horn topology in the presence of a time dependent magnetic field. Since the exact solution cannot be obtained explicitly for arbitrary time dependence of the field, we discuss the asymptotic behavior of the solutions with the help of the relativistic Hamilton–Jacobi equation.