Galactic periodicity and the oscillating G model

We consider the model involving the oscillation of the effective gravitational constant that has been put forward in an attempt to reconcile the observed periodicity in the galaxy number distribution with the standard cosmological models. This model involves a highly nonlinear dynamics which we analyze numerically. We carry out a detailed study of the bound that nucleosynthesis imposes on this model. The analysis shows that for any assumed value for $\Omega$ (the total energy density) one can fix the value of $\Omega_{\rm bar}$ (the baryonic energy density) in such a way as to accommodate the observational constraints coming from the $^4{\rm He}$ primordial abundance. In particular, if we impose the inflationary value $\Omega=1$ the resulting baryonic energy density turns out to be $\Omega_{\rm bar}\sim 0.021$. This result lies in the very narrow range $0.016 \leq \Omega_{\rm bar} \leq 0.026$ allowed by the observed values of the primordial abundances of the other light elements. The remaining fraction of $\Omega$ corresponds to dark matter represented by a scalar field.Comment: Latex file 29 pages with no figures. Please contact M.Salgado for figures. A more careful study of the model appears in gr-qc/960603

Finite Temperature and Density Effect on Symmetry Breaking by Wilson Loops

A finite temperature and density effect of Wilson loop elements on non-simply connected space is investigated in the model suggested by Hosotani. Using one-loop calculations it is shown that the value of an "order parameter" does not shift as the temperature grows. We find that finite density effect is of much importance for restoration of symmetry.Comment: 11pages, no figur

Scaling solutions in general non-minimal coupling theories

A class of generalized non-minimal coupling theories is investigated, in search of scaling attractors able to provide an accelerated expansion at the present time. Solutions are found in the strong coupling regime and when the coupling function and the potential verify a simple relation. In such cases, which include power law and exponential functions, the dynamics is independent of the exact form of the coupling and the potential. The constraint from the time variability of $G$, however, limits the fraction of energy in the scalar field to less than 4% of the total energy density, and excludes accelerated solutions at the present.Comment: 10 pages, 3 figures, accepted for publication in Phys. Rev.

Gravity-Driven Acceleration of the Cosmic Expansion

It is shown here that a dynamical Planck mass can drive the scale factor of the universe to accelerate. The negative pressure which drives the cosmic acceleration is identified with the unusual kinetic energy density of the Planck field. No potential nor cosmological constant is required. This suggests a purely gravity driven, kinetic inflation. Although the possibility is not ruled out, the burst of acceleration is often too weak to address the initial condition problems of cosmology. To illustrate the kinetic acceleration, three different cosmologies are presented. One such example, that of a bouncing universe, demonstrates the additional feature of being nonsingular. The acceleration is also considered in the conformally related Einstein frame in which the Planck mass is constant.Comment: 23 pages, LaTex, figures available upon request, (revisions include added references and comment on inflation) CITA-94-1

Symmetric vacuum scalar--tensor cosmology

The existence of point symmetries in the cosmological field equations of generalized vacuum scalar--tensor theories is considered within the context of the spatially homogeneous cosmologies. It is found that such symmetries only occur in the Brans--Dicke theory when the dilaton field self--interacts. Moreover, the interaction potential of the dilaton must take the form of a cosmological constant. For the spatially flat, isotropic model, it is shown how this point symmetry may be employed to generate a discrete scale factor duality in the Brans--Dicke action.Comment: 10 pages, latex, To appear in Class. Quantum Gra

The Next Generation Virgo Cluster Survey. VIII. The Spatial Distribution of Globular Clusters in the Virgo Cluster

We report on a large-scale study of the distribution of globular clusters (GCs) throughout the Virgo cluster, based on photometry from the Next Generation Virgo Cluster Survey, a large imaging survey covering Virgo's primary subclusters to their virial radii. Using the g', (g'-i') color-magnitude diagram of unresolved and marginally-resolved sources, we constructed 2-D maps of the GC distribution. We present the clearest evidence to date showing the difference in concentration between red and blue GCs over the extent of the cluster, where the red (metal-rich) GCs are largely located around the massive early-type galaxies, whilst the blue (metal-poor) GCs have a more extended spatial distribution, with significant populations present beyond 83' (215 kpc) along the major axes of M49 and M87. The GC distribution around M87 and M49 shows remarkable agreement with the shape, ellipticity and boxiness of the diffuse light surrounding both galaxies. We find evidence for spatial enhancements of GCs surrounding M87 that may be indicative of recent interactions or an ongoing merger history. We compare the GC map to the locations of Virgo galaxies and the intracluster X-ray gas, and find good agreement between these baryonic structures. The Virgo cluster contains a total population of 67300$\pm$14400 GCs, of which 35% are located in M87 and M49 alone. We compute a cluster-wide specific frequency S_N,CL=$2.8\pm0.7$, including Virgo's diffuse light. The GC-to-baryonic mass fraction is e_b=$5.7\pm1.1\times10^{-4}$and the GC-to-total cluster mass formation efficiency is e_t=$2.9\pm0.5\times10^{-5}$, values slightly lower than, but consistent with, those derived for individual galactic halos. Our results show that the production of the complex structures in the unrelaxed Virgo cluster core (including the diffuse intracluster light) is an ongoing process.(abridged)Comment: 23 pages, 17 figures. Accepted for publication in the Astrophysical Journal. Figure 1 has reduced resolution. Revised version with updated references, corrected typos -- no changes to result

Classical Euclidean wormhole solutions in Palatini f(R~)f(\tilde{R}) cosmology

We study the classical Euclidean wormholes in the context of extended theories of gravity. With no loss of generality, we use the dynamical equivalence between $f(\tilde{R})$ gravity and scalar-tensor theories to construct a point-like Lagrangian in the flat FRW space time. We first show the dynamical equivalence between Palatini $f(\tilde{R})$ gravity and the Brans-Dicke theory with self-interacting potential, and then show the dynamical equivalence between the Brans-Dicke theory with self-interacting potential and the minimally coupled O'Hanlon theory. We show the existence of new Euclidean wormhole solutions for this O'Hanlon theory and, for an special case, find out the corresponding form of $f(\tilde{R})$ having wormhole solution. For small values of the Ricci scalar, this $f(\tilde{R})$ is in agreement with the wormhole solution obtained for higher order gravity theory $\tilde{R}+\epsilon \tilde{R}^2,\epsilon<0$.Comment: 11 page

Weak-Field Gravity of Revolving Circular Cosmic Strings

A weak-field solution of Einstein's equations is constructed. It is generated by a circular cosmic string revolving in its plane about the centre of the circle. (The revolution is introduced to prevent the string from collapsing.) This solution exhibits a conical singularity, and the corresponding deficit angle is the same as for a straight string of the same linear energy density, irrespective of the angular velocity of the string.Comment: 13 pages, LaTe

Scalar-Tensor Cosmological Models

We analyze the qualitative behaviors of scalar-tensor cosmologies with an arbitrary monotonic $\omega(\Phi)$ function. In particular, we are interested on scalar-tensor theories distinguishable at early epochs from General Relativity (GR) but leading to predictions compatible with solar-system experiments. After extending the method developed by Lorentz-Petzold and Barrow, we establish the conditions required for convergence towards GR at $t\rightarrow\infty$. Then, we obtain all the asymptotic analytical solutions at early times which are possible in the framework of these theories. The subsequent qualitative evolution, from these asymptotic solutions until their later convergence towards GR, has been then analyzed by means of numerical computations. From this analysis, we have been able to establish a classification of the different qualitative behaviors of scalar-tensor cosmological models with an arbitrary monotonic $\omega(\Phi)$ function.Comment: uuencoded compressed postscript file containing 41 pages, with 9 figures, accepted for publication in Physical Review

Can induced gravity isotropize Bianchi I, V, or IX Universes?

We analyze if Bianchi I, V, and IX models in the Induced Gravity (IG) theory can evolve to a Friedmann--Roberson--Walker (FRW) expansion due to the non--minimal coupling of gravity and the scalar field. The analytical results that we found for the Brans-Dicke (BD) theory are now applied to the IG theory which has $\omega \ll 1$ ($\omega$ being the square ratio of the Higgs to Planck mass) in a cosmological era in which the IG--potential is not significant. We find that the isotropization mechanism crucially depends on the value of $\omega$. Its smallness also permits inflationary solutions. For the Bianch V model inflation due to the Higgs potential takes place afterwads, and subsequently the spontaneous symmetry breaking (SSB) ends with an effective FRW evolution. The ordinary tests of successful cosmology are well satisfied.Comment: 24 pages, 5 figures, to be published in Phys. Rev. D1