Showing papers by "Joel R. Primack published in 1991"
TL;DR: In this article, the authors explored the possibility of measuring the density parameter OMEGA-0 and the cosmological constant lambda-0 = LAMBDA/(3H0(2)) using dynamical tests in linear and non-linear theory.
Abstract: The possibility of measuring the density parameter OMEGA-0 and the cosmological constant lambda-0 = LAMBDA/(3H0(2)) using dynamical tests is explored in linear and non-linear theory. In linear theory we find that the rate of growth of the perturbations at the present epoch is approximated by f(z = 0) almost-equal-to-OMEGA-0(0.6) + 1/70 lambda-0(1 + 1/2 OMEGA-0). Therefore, dynamical tests such as infall around clusters and dipoles at the present epoch do not distinguish well between universes with and without a cosmological constant. At higher redshifts, the perturbations also depend mainly on the matter density at a particular epoch, f(z) almost-equal-to OMEGA-0.6(z), which has a strong dependence on lambda-0 at z almost-equal-to 0.5-2.0. Therefore, information on both parameters can be obtained by looking at clustering at different redshifts. In practice, however, the other observables also depend on the cosmology, and in some cases conspire to give a weak dependence on lambda-0. By using the non-linear spherical infall model for a family of Cold Dark Matter (CDM) power-spectra we also find that dynamics at z = 0 does not tell much about lambda-0. At higher redshifts there is unfortunately another conspiracy between conventional observables, which hides information about lambda-0. The final radius of a virialized cluster (relative to the turnaround radius) is approximated by R(f)/R(ta) almost-equal-to (1 - eta/2)/(2 - eta/2), where eta is the ratio of LAMBDA to the density at turn-around. Therefore a repulsive-LAMBDA gives a smaller final radius than a vanishing-LAMBDA.
720 citations
TL;DR: In this paper, the authors represent scientific groups that are opposed to the use of nuclear power in near space and feel that the best course for space-borne reactors is to ban them from Earth orbit and use them in deep space.
Abstract: Nuclear reactors have provided energy for satellites-with nearly disastrous results. Now the US government is proposing to build nuclear-powered boosters to launch Star Wars defenses. These authors represent scientific groups that are opposed to the use of nuclear power in near space. The authors feel that the best course for space-borne reactors is to ban them from Earth orbit and use them in deep space.
49 citations
TL;DR: In this article, models for the evolution of the disc of spiral galaxies that include the effects of viscosity but assume no continuous infall of gas on to the disc were studied, and it was confirmed that these models are able to reproduce the oberved radial distribution of gas and stars for a variety of model parameters and initial conditions.
Abstract: Models are studied for the evolution of the disc of spiral galaxies that include the effects of viscosity but assume no continuous infall of gas on to the disc. The time-scale for star formation is assumed to be of the same order as the time-scale for viscous redistribution of the mass and angular momentum in the disc. It is confirmed that these models are able to reproduce the oberved radial distribution of gas and stars for present day spirals for a variety of model parameters and initial conditions
20 citations
TL;DR: It is found that strings of relevance for structure formation can form in the absence of coupling to the inflaton or curvature through the process of quantum creation, but only if the strings are strongly type I, or if they are global strings.
Abstract: We examine mechanisms, several of which are proposed here, to generate structure formation, or to just add large-scale features, through either gauged or global cosmic strings or global texture, within the framework of inflation. We first explore the possibility that strings or texture form if there is no coupling between the topological theory and the inflaton or spacetime curvature, via (1) quantum creation, and (2) a sufficiently high reheat temperature. In addition, we examine the prospects for the inflaton field itself to generate strings or texture. Then, models with the string/texture field coupled to the curvature, and an equivalent model with coupling to the inflaton field, are considered in detail. The requirement that inflationary density fluctuations are not so large as to conflict with observations leads to a number of constraints on model parameters. We find that strings of relevance for structure formation can form in the absence of coupling to the inflaton or curvature through the process of quantum creation, but only if the strings are strongly type I, or if they are global strings. If formed after reheating, naturalness suggests that gauged cosmic strings correspond to a type-I superconductor. Similarly, gauged strings formed during inflation via conformal couplingmore » {xi}=1/6 to the spacetime curvature (in a model suggested by Yokoyama in order to evade the millisecond pulsar constraint on cosmic strings) are expected to be strongly type I.« less
19 citations
01 Jan 1991
TL;DR: In this article, the authors review the recent work of the Santa Cruz group on the generation of non-Zel'dovich (including non-Gaussian) fluctuations in chaotic inflation and distinguish between local and non-local nGf.
Abstract: I review the recent work of the Santa Cruz group on the generation of non-Zel’dovich (including non-Gaussian) fluctuations in chaotic inflation. With a single inflaton having the most general quartic polynomial potential, most of the space of the parameters of the potential corresponds to fluctuations with an approximately Zel’dovich spectrum. To the extent that significant deviations from the Zel’dovich spectrum arise, the spectrum characteristically has a dip at a particular scale; in this case the usual upper limit on the quartic coefficient is relaxed and the reheat temperature is correspondingly increased. In the context of the cold dark matter model, such a dip spectrum may help explain both increased large scale structure and earlier galaxy formation. If we consider a general inflaton potential, it is possible to invert the slow-roll equations of motion and find the potential corresponding to almost any desired fluctuation spectrum. In models with multiple inflatons such as double inflation, de Sitter fluctuations in the second inflaton generated during the inflationary period controlled by the first inflaton make it impossible to preset the value of the second inflaton, and thus to get structure in the fluctuation spectrum on a cosmologically interesting scale. Regarding non-Gaussian fluctuations (nGf), we distinguish between local and non-local nGf. With a single inflaton, the inflationary nGf are negligible if the fluctuation amplitude lies below the upper limit from nonobservation of cosmic background radiation fluctuations. Several nonstandard possibilities arise in the generation of non-local nGf such as cosmic strings and texture, with the corresponding scalar fields either free or coupled to the inflaton or to curvature. In particular, such cosmic strings typically correspond to a strongly Type I superconductor, a case that should be investigated further.
1 citations
01 Jan 1991
TL;DR: It is shown that a repulsive Λ gives a smaller final radius of a virialized cluster than a vanishing Λ, and the possibility of measuring the density parameter Ω0 and the cosmological constant λ0 from dynamical tests using linear and non-linear spherical models.
Abstract: We discuss the possibility of measuring the density parameter Ω0 and the cosmological constant λ0 = Λ/(3H 2 0) from dynamical tests using linear and non-linear spherical models. While information on both parameters can be obtained by looking at clustering at different redshifts, in practice the other observables also depend on the cosmology, and in some cases conspire to give a weak dependence on λ0. We also show that a repulsive Λ gives a smaller final radius of a virialized cluster than a vanishing Λ.