arXiv subjects

R. Laflamme

Publications and source records attributed to R. Laflamme.

61 records · Page 4Linked to original sources

arXiv1995

Renormalization Group Calculation of the Galaxy-Galaxy Correlation Function

The observable Universe is described by a collection of equal mass galaxies linked into a common unit by their mutual gravitational interaction. The partition function of this system is cast in terms of Ising model spin variables and maps exactly onto a three-dimensional stochastic scalar classical field theory. The full machinery of the renormalization group and critical phenomena is brought to bear on this field theory allowing one to calculate the galaxy-galaxy correlation function, whose critical exponent is predicted to be between 1.530 to 1.862, compared to the phenomenological value of 1.6 to 1.8

gr-qc↗

arXiv1995

Ising Model formulation of Large Scale Dynamics: Universality in the Universe

The partition function of a system of galaxies in gravitational interaction can be cast in an Ising Model form, and this reformulated via a Hubbard--Stratonovich transformation into a three dimensional stochastic and classical scalar field theory, whose critical exponents are calculable and known. This allows one to {\it compute\/} the galaxy to galaxy correlation function, whose non--integer exponent is predicted to be between 1.530 and 1.862, to be compared with the phenomenological value of 1.6 to 1.8.

astro-ph↗

arXiv1994

Decoherence, Re-coherence, and the Black Hole Information Paradox

We analyze a system consisting of an oscillator coupled to a field. With the field traced out as an environment, the oscillator loses coherence on a very short {\it decoherence timescale}; but, on a much longer {\it relaxation timescale}, predictably evolves into a unique, pure (ground) state. This example of {\it re-coherence} has interesting implications both for the interpretation of quantum theory and for the loss of information during black hole evaporation. We examine these implications by investigating the intermediate and final states of the quantum field, treated as an open system coupled to an unobserved oscillator.

gr-qc↗

arXiv1993

Decoherence Functional and Inhomogeneities in the Early Universe

We investigate the quantum to classical transition of small inhomogeneous fluctuations in the early Universe using the decoherence functional of Gell-Mann and Hartle. We study two types of coarse graining; one due to coarse graining the value of the scalar field and the other due to summing over an environment. We compare the results with a previous study using an environment and the off-diagonal rule proposed by Zurek. We show that the two methods give different results.

gr-qc↗

arXiv1993

The Least Action Principle And The Spin Of Galaxies In The Local Group

Using Peebles' least action principle, we determine trajectories for the galaxies in the Local Group and the more massive galaxies in the Local Neighbourhood. We deduce the resulting angular momentum for the whole of the Local Group and study the tidal force acting on the Local Group and its galaxies. Although Andromeda and the Milky Way dominate the tidal force acting on each other during the present epoch, we show that there is a transition time at $z\approx 1$ before which the tidal force is dominated by galaxies outside the Local Group in each case. This shows that the Local Group can not be considered as an isolated system as far as the tidal forces are concerned. We integrate the tidal torques acting on the Milky Way and Andromeda and derive their spin angular momenta, obtaining results which are comparable with observation.

astro-ph↗

arXiv1993

The Origin of Time Asymmetry

It is argued that the observed Thermodynamic Arrow of Time must arise from the boundary conditions of the universe. We analyse the consequences of the no boundary proposal, the only reasonably complete set of boundary conditions that has been put forward. We study perturbations of a Friedmann model containing a massive scalar field but our results should be independent of the details of the matter content. We find that gravitational wave perturbations have an amplitude that remains in the linear regime at all times and is roughly time symmetric about the time of maximum expansion. Thus gravitational wave perturbations do not give rise to an Arrow of Time. However density perturbations behave very differently. They are small at one end of the universe's history, but grow larger and become non linear as the universe gets larger. Contrary to an earlier claim, the density perturbations do not get small again at the other end of the universe's history. They therefore give rise to a Thermodynamic Arrow of Time that points in a constant direction while the universe expands and contracts again. The Arrow of Time does not reverse at the point of maximum expansion. One has to appeal to the Weak Anthropic Principle to explain why we observe the Thermodynamic Arrow to agree with the Cosmological Arrow, the direction of time in which the universe is expanding.

gr-qc↗

arXiv1993

Black Strings and p-Branes are Unstable

We investigate the evolution of small perturbations around black strings and branes which are low energy solutions of string theory. For simplicity we focus attention on the zero charge case and show that there are unstable modes for a range of time frequency and wavelength in the extra $10-D$ dimensions. These perturbations can be stabililized if the extra dimensions are compactified to a scale smaller than the minimum wavelength for which instability occurs and thus will not affect large astrophysical black holes in four dimensions. We comment on the implications of this result for the Cosmic Censorship Hypothesis.

hep-th↗