# Cosmology & Gravitation

This series consists of talks in the areas of Cosmology, Gravitation and Particle Physics.

## Seminar Series Events/Videos

Currently there are no upcoming talks in this series.

Thursday Nov 17, 2005
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## Acceleration of highest energy cosmic rays

Tuesday Nov 01, 2005
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Highest energy cosmic rays reach {\it macroscopic} energies $> 10^{20}$ eV ($\sim 10$ joules; corresponding linear momentum in one proton is similar to a slapshot hockey puck's). Such protons can either be accelerated by nearby astrophysical sources or be by-products of decay of unknown superheavy fundamental particles. After reviewing phenomenology of cosmic rays, I will discuss a novel {\it non-stochastic} acceleration mechanism in jets of powerful active galactic nuclei. The mystery of ultra high energy cosmic rays is likely soon to be resolved by Pierre Auger observatory.

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## The entanglement interpretation of black hole entropy

Tuesday Oct 11, 2005
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We show that the entropy resulting from the counting of microstates of non extremal black holes using field theory duals of string theories can be interpreted as arising from entanglement. The conditions for making such an interpretation consistent are discussed. First, we interpret the entropy (and thermodynamics) of spacetimes with non degenerate, bifurcating Killing horizons as arising from entanglement. We use a path integral method to define the Hartle-Hawking vacuum state in such spacetimes and discuss explicitly its entangled nature and its relation to the geometry.

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## Unitarity in the Presence of Closed Timelike Curves

Tuesday Oct 04, 2005
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TBA

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## Thermalization after Inflation and Supersymmetery

Tuesday Sep 20, 2005
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tba

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## GISMs, Coulomb Branches, Tachgons?

Tuesday Jun 07, 2005
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## Relaxation and unitarity in eternal black hole

Friday May 20, 2005
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## Chameleon Scalar Fields: Detecting Dark Energy with Tests of Gravity

Thursday Mar 10, 2005
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Chameleon scalar fields are candidates for the dark energy, the mysterious component causing the observed acceleration of the universe. Their defining property is a mass which depends on the local matter density: they are massive on Earth, where the density is high, but essentially massless in the cosmos, where the density is much lower. All current constraints from tests of general relativity are satisfied. Nevertheless, chameleons lead to striking predictions for tests of gravity in the laboratory and in space.

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## SU(N) Yang-Mills Thermodynamics and its Cosmological Consequences

Wednesday Oct 06, 2004
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## Supersymmetric Black Rings and Supertubes

Thursday Sep 30, 2004
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## LECTURES ON-DEMAND

### Roger Melko: Perimeter Institute and University of Waterloo

Speaker: Roger Melko