# 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.

## Maximum entropy, the universal dark matter density profile... and its destruction

Tuesday Oct 16, 2012
Speaker(s):

I review some recent developments in attempting to reconcile
the observed galaxy population with numerical models of structure formation in
the 'LCDM' concordance cosmology. Focussing on behaviour of dwarf galaxies, I
describe the infamous 'cusp-core' dichotomy -- a long-standing challenge to the
LCDM picture on small scales -- and use toy models to show how it is resolved
in recent numerical simulations (Pontzen & Governato 2012). I then discuss
the current observational status of this picture (Teyssier, Pontzen & Read

Collection/Series:
Scientific Areas:

## Voids in the SDSS: from demography to cosmology

Tuesday Oct 09, 2012
Speaker(s):

Cosmic voids are potentially a rich source of information
for both astrophysics and cosmology. To enable such science, we produce the
most comprehensive void catalog to date using the Sloan Digital Sky Survey Data
Release 7 main sample out to redshift z = 0.2 and the Luminous Red Galaxy
sample out to z = 0.44. Using a modified version of the parameter-free void
finder ZOBOV, we fully take into account the presence of survey boundary and
masks. We discuss basic catalog statistics such as number counts and redshift

Collection/Series:
Scientific Areas:

## Scalars with Higher Derivatives in Supergravity and Cosmology

Tuesday Oct 09, 2012
Speaker(s):

There are many situations in cosmology that
motivate the study of scalar fields with higher-derivative actions. The best-known
such situations are probably k-inflation (with DBI-inflation being a special
case) and models based on galileon theories, but even eternal inflation and
cyclic universes provide good reasons to study such theories. After an extended
discussion of the motivations, I will show how scalar field theories with
higher derivatives can be constructed in (minimal, 4-dimensional) supergravity,

Collection/Series:
Scientific Areas:

## Homogeneous and Isotropic Universe from Nonlinear Massive Gravity

Tuesday Oct 02, 2012

The question of finite range gravity, or equivalently,
whether graviton can have a non-zero mass, has been one of the major challenges
in classical field theory for the last 70 years.

Collection/Series:
Scientific Areas:

## Supermassive black holes in non-spherical galactic nuclei and enhanced rates of star capture events

Tuesday Sep 25, 2012
Speaker(s):

We consider the stellar-dynamical processes which lead to
the capture or tidal disruption of stars by a supermassive black hole, review
the standard theory of two-body relaxation and loss-cone repopulation in
spherical galactic nuclei, and extend it to the axisymmetric and triaxial
nuclear star clusters.

Collection/Series:
Scientific Areas:

## New developments in massive gravity

Tuesday Sep 18, 2012

The idea that the graviton may be massive has seen a
resurgence of interest due to recent progress which has overcome its

I will review this recent progress, which has

led to a consistent ghost-free effective field theory of
a massive graviton, with a stable hierarchy between the graviton mass and the
cutoff, and how this theory has the potential to resolve the naturalness
problem of the cosmological constant.

Collection/Series:
Scientific Areas:

## Spectral distortions of the CMB and what we might learn about early universe physics

Tuesday Sep 11, 2012
Speaker(s):

The spectrum of the cosmic microwave background (CMB) is known to be extremely close to a perfect blackbody. However, even within standard cosmology several processes occurring in the early Universe lead to distortions of the CMB at a level that might become observable in the future. This could open an exciting new window to early Universe physics.

Collection/Series:
Scientific Areas:

## Inflation from Magnetic Drift

Tuesday Sep 04, 2012
Speaker(s):

I will describe a new, generic mechanism for realizing a
period of slowly-rolling inflation through the use of an analog of 'magnetic
drift.' I will demonstrate how the mechanism works through two particular
worked examples: Chromo-Natural Inflation, which exists as a purely 4D
effective theory, and a version that can appear naturally in string theory.

Collection/Series:
Scientific Areas:

## Exoplanet observation by microlensing and wave optics features

Tuesday Aug 14, 2012

I will introduce the theory and experimental technique of extra-solar planet observation by the gravitational microlensing and give a report on recent results. Then I will discuss the wave optics features in the gravitational microlensing, the analogy of this effect in the astronomical scales to the Young's double slit experiment. Finally I will discuss about the possibility of observation of diffraction patterns in the microlensing experiment.

Collection/Series:

## A Flow of Dark Matter Debris: Exploring New Possibilities for Substructure

Tuesday Aug 07, 2012
Speaker(s):

Tidal stripping of dark matter from subhalos falling into the Milky Way produces narrow, cold tidal streams as well as more spatially extended debris flows'' in the form of shells, sheets, and plumes.Here we focus on the debris flow in the Via Lactea II simulation, and show that this incompletely phase-mixed material exhibits distinctive high velocity behavior. Unlike tidal streams, which may not necessarily intersect the Earth's location, debris flow is spatially uniform at 8 kpc and thus guaranteed to be present in the dark matter flux incident on direct detection experiments.

Collection/Series:

## LECTURES ON-DEMAND

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

Speaker: Roger Melko