This series consists of talks in the areas of Cosmology, Gravitation and Particle Physics.
Chameleon gravity is
a scalar-tensor theory that mimics general relativity in the Solar System. The
scalar degree of freedom is hidden in high-density environments because the
effective mass of the chameleon scalar depends on the trace of the
stress-energy tensor. In the early Universe, when the trace of the
stress-energy tensor is nearly zero, the chameleon is very light and Hubble
friction prevents it from reaching its potential minimum. Whenever a
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
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
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,
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.
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.
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.
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.
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.