Non-Perturbative Models For The Quantum Gravitational Back-Reaction On Inflation

We consider a universe in which inflation commences because of a positive cosmological constant, the effect of which is progressively screened by the interaction between virtual gravitons that become trapped in the expansion of spacetime. Perturbative calculations have shown that screening becomes non-perturbatively large at late times. In this paper we consider effective field equations which can be evolved numerically to provide a non-perturbative description of the process. The induced stress tensor is that of an effective scalar field which is a non-local functional of the metric. We use the known perturbative result, constrained by general principles and guided by a physical description of the screening mechanism, to formulate a class of ansatze for this functional. A scheme is given for numerically evolving the field equations which result from a simple ansatz, from the beginning of inflation past the time when it ends. We find that inflation comes to a sudden end, producing a system whose equation of state rapidly approaches that of radiation. Explicit numerical results are presented.Comment: 50 pages, LaTeX 2 epsilon, 11 Postscript files, uses psfig.st

Reduction of couplings in the MSSM

We present an application of the reduction of couplings program in the minimal supersymmetric Standard Model (MSSM). We investigate if a functional relation between $\alpha_1$ and $\alpha_2$ gauge couplings can be realized which is Renormalization Group Invariant (RGI). Following the same procedure for the top and bottom Yukawa couplings we end up with a prediction of a narrow window for tan$\beta$, which is one of the basic parameters that determine the light Higgs mass.Comment: 10 pages, 3 figures, Contribution for the proceedings of the Corfu Summer Institute 201

One Loop Graviton Self-Energy In A Locally De Sitter Background

The graviton tadpole has recently been computed at two loops in a locally de Sitter background. We apply intermediate results of this work to exhibit the graviton self-energy at one loop. This quantity is interesting both to check the accuracy of the first calculation and to understand the relaxation effect it reveals. In the former context we show that the self-energy obeys the appropriate Ward identity. We also show that its flat space limit agrees with the flat space result obtained by Capper in what should be the same gauge.Comment: 35 pages, plain TeX, 4 Postscript files, uses psfig.sty, revised June 1996 for publication in Physical Review

A Newtonian Model for the Quantum Gravitational Back-Reaction on Inflation

Quantum gravitational back-reaction offers a simultaneous explanation for why the cosmological constant is so small and a natural model of inflation in which scalars play no role. In this talk I review previous work and present a simple model of the mechanism in which the induced stress tensor behaves like negative vacuum energy with a density proportional to $-\Lambda/{8\pi G} \cdot (G \Lambda)^2 \cdot H t$. The model also highlights the essential role of causality in back-reaction.Comment: 4 pages, LaTeX 2.6, no figures. Talk given at the International Meeting on Quantum Gravity and Spectral Geometry, Naples, Italy, July 2-7, 200

Science and Technology Parks in Two Lagging Regions of Spain: A Comparative Evaluation Using an Innovation Network Approach

Science and Technology Parks (STPs) have been widely used as innovation support and regional development instruments in most European countries. In Objective 1 regions of South Europe STPs projects were developed during the 90s through regional, national or EU structural funds as tools for promoting innovation and technology upgrade. Most existing studies cast doubt on the effectiveness of parks in achieving their goals, focussing on the traditional measures of the parks added-value (profitability and growth) to the tenant companies, the university-industry linkages developed. However, more recent developments of territorial innovation models stress the role of networks and interactions for knowledge creation and diffusion. While these approaches imply that the Parks – in their strict spatial nature – may become redundant in a networked space, they can also be used to identify additional performance assessment criteria focusing on the role of the park for the development of interactions, linkages and cooperation inside as well as outside its area. The quantity and quality of linkages inside and outside the STP area and its operation as an innovation cooperation promoter in the regional and broader space are used in this assessment. The present work assesses the performance of STPs in Objective 1 regions of South Europe. It develops an evaluation framework that integrates – together with the traditional linear performance criteria – the concepts of networking, interaction and cooperation and uses it to compare the performance of Parks in two regions in Greece (Thessaloniki and Crete) and two in Spain (Asturias and Andalusia). Our preliminary results from in depth analysis show that while there are different levels of success in terms of the traditional metrics/criteria, we observe in general low levels of interaction and cooperation developed inside the parks as well as with the broader region. The Parks do not seem to operate – at least so far – as places that facilitate intensive knowledge exchange inside and outside their area.

Dimensionally Regulated Graviton 1-Point Function in de Sitter

We use dimensional regularization to compute the 1PI 1-point function of quantum gravity at one loop order in a locally de Sitter background. As with other computations, the result is a finite constant at this order. It corresponds to a small positive renormalization of the cosmological constant.Comment: 25 pages, LaTeX 2epsilon, uses Axodraw for one figure, revised to add some reference

Boltzmann equation in de Sitter space

In a time dependent background like de Sitter space, Feynman-Dyson perturbation theory breaks down due to infra-red divergences. We investigate an interacting scalar field theory in Schwinger-Keldysh formalism. We derive a Boltzmann equation from a Schwinger-Dyson equation inside the cosmological horizon. Our solution shows that the particle production is compensated by the reduction of the on-shell states due to unitarity. Although the degrees of freedom inside the horizon leads to a small and diminishing screening effect of the cosmological constant, there is a growing screening effect from those outside the horizon.Comment: 33pages, 2figure