This series consists of talks in the areas of Cosmology, Gravitation and Particle Physics.
In this talk I will
discuss a cosmological model where primordial inflation is driven by a `solid',
defined as a system of three derivatively coupled scalar fields obeying certain
symmetries and spontaneously breaking a certain subgroup of these. The symmetry
breaking pattern differs drastically from that of standard inflationary models:
time translations are unbroken. This prevents our model from fitting into the
standard effective field theory description of adiabatic perturbations. Consequently,
The de Sitter S-matrix provides a gauge-invariant and
field redefinition-invariant window into de Sitter QFTs and may provide a
crucial entry in any dS/CFT dictionary. In this talk I will summarize recent
progress on developing the S-matrix for theories with gauge fields and
perturbative gravity. Nonrenormalization theorems, hints of supersymmetry, and
perturbative stability will be discussed.
There are indications of a lower bound on magnetic fields
in the intergalactic media. Since magnetic fields on such large scales are
difficult to generate in the late universe, this might point to inflationary
magnetogenesis as the origin of intergalactic magnetic fields. If the magnetic
fields are generated during inflation, they are naturally correlated with the
inflaton perturbations in a general class of models. This leads to a
consistency relation between the power spectrum of primordial magnetic fields
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,
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.
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
traditional problems.
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.