# 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.

## Some Conceptual Problems in General Relativity and Cosmology

Tuesday Jun 03, 2014
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This talk will try to highlight some basic problems connected with conclusions uncritically drawn from well known works. These include: 1. The Schwarzschild solution 2. The formation of black holes by gravitational collapse 3. The no hair theorem 4. The principle of equivalence in the very early universe.

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## Black holes and Boyle's Law --- the thermodynamics of Einstein's greatest mistake

Tuesday May 20, 2014
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The thermodynamics of black holes will be reviewed and recent developments incorporating pressure into the first law described. The asymptotically AdS Kerr metric has a van der Waals type critical point with a line of first order phase transitions terminating at a critical point with mean field exponents. The phase structure and stability of black holes in higher dimensions will also be described.

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## Random models of inflation

Tuesday May 13, 2014
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Rather than writing down specific functional forms, one can generate inflation models via stochastic processes in order to explore generic properties of inflation models. I describe our explorations of the phenomenology of randomly-generated multi-field inflation models, both for canonical fields and for a braneworld-motivated scenario. Implications of some recent observational results, including BICEP2, will be discussed.

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## The Case for an Alternative Cosmology

Tuesday May 06, 2014
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This talk will describe the Quasi-Steady State Cosmology proposed in 1993 by Fred Hoyle, Geoffrey Burbidge and Jayant Narlikar. Starting with the motivation for this exercise, a formal field theoretic framework inspired by Mach’s principle is shown to lead to this model. The model is a generalization of the classical steady state model in the sense that it is driven by a scalar field which causes creation in explosive form. Such ‘minicreation events’ lead to a universe with a long term de Sitter expansion superposed with oscillations of shorter time scales.

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## Galileon Maps: Inequivalent Coset Constructions for Spacetime Symmetries

Tuesday Apr 29, 2014
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Non-linear realizations of spacetime symmetries can be obtained by a generalization of the coset construction valid for internal ones. The physical equivalence of different representations for spacetime symmetries is not obvious, since their relation involves not only a redefinition of the fields but also a field-dependent change of coordinates. A simple and relevant spacetime symmetry is obtained by the contraction of the 4D conformal group that leads to the Galileon group.

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## Large-scale homogeneity vs. small-scale inhomogeneity: testing ΛCDM with large scale structure

Tuesday Apr 22, 2014
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The most fundamental assumption of the standard cosmological model (LambdaCDM) is that the Universe is homogeneous on large scales. This is not true on small scales, and some studies suggest that galaxies follow a fractal distribution up to very large scales (~200 h-1 Mpc or more), whereas ΛCDM predicts homogeneity at ~100 h-1 Mpc. We have tested this using the WiggleZ Dark Energy Survey, a UV-selected spectroscopic survey of ~200,000 luminous blue galaxies up to z=1, with the Anglo-Australian Telescope.

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## Groups and Clusters of Galaxies: Where Cosmology and Astrophysics Collide

Tuesday Apr 15, 2014
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Groups and clusters of galaxies are the most massive gravitationally bound objects in the Universe. They are also the most recent cosmic objects to form. In the currently accepted models of cosmic structure formation, the number density distribution of the most massive of these systems, and how this has been changing with time, depend sensitively to the parameters describing the large-scale geometry and the expansion history of the universe. However, to exploit galaxy clusters as cosmological probes, we must be able to relate their observable properties to their total mass.

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## Is the Milky Way Ringing?

Tuesday Apr 08, 2014
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Recent observations from three different astronomical surveys have revealed evidence for asymmetries about the Galactic midplane in the kinematics of solar neighborhood stars. These asymmetries appear, in part, as compression-rarefaction modes in the bulk motions of stars perpendicular to the midplane. I will discuss the hypothesis that these motions were caused by the recent passage of a satellite galaxy or dark matter subhalo through the Galactic disk.

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## The not-so-homogeneous universe

Tuesday Apr 01, 2014
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The assumption of spatial homogeneity lies at the heart of the concordance cosmological model. But as I will discuss, truly solid empirical evidence for global (statistical) homogeneity is lacking, and tricky theoretical issues abound. I review a few recent advances in understanding the role inhomogeneity plays in cosmology, including some unexpected effects on light propagation, the death (and rebirth) of backreaction, and impending observational annoyances related to the lumpy local Universe.

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## Cosmic initial conditions and the CMB

Tuesday Mar 25, 2014
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One new frontier in cosmology is the frequency spectrum of the CMB. Future instruments may be precise enough to measure deviations from the nearly-perfect blackbody, measuring a chemical potential and thus probing energy injection at extremely high redshift. I will discuss ($\mu$ and $y$-type) CMB spectral distortions from the dissipation of entropy (isocurvature)-sourced acoustic modes. I will then discuss how a high-energy phase transition could also source such distortions.

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## RECENT PUBLIC LECTURE

### The Most Wanted Particle

Speaker: Jon Butterworth