This series consists of talks in the areas of Cosmology, Gravitation and Particle Physics.
Weak gravitational lensing is a highly valued tool for inferring the structure of the spacetime metric between an observer and a cosmologically distant “wallpaper,” most commonly either the CMB or faint background galaxies. The best-measured quantities are the second derivatives of the projected scalar potential(s), which are manifested as apparent shearing and magnification of the wallpaper. Given a collection of faint-galaxy images, what information can we extract about the shear and magnification that these images have undergone?
Photometric surveys are often larger and extend to fainter magnitudes than spectroscopic samples, and can therefore yield more precise cosmological measurements. However, photometric data are significantly contaminated by multiple sources of systematics, either intrinsic, observational, or instrumental. These systematics affect the properties of the raw images in complex ways, propagate into the final catalogues, and create spurious spatial correlations.
More than a decade after its discovery, cosmic acceleration still
poses a puzzle for modern cosmology and a plethora of models of dark energy
or modified gravity, able to reproduce the observed expansion history, have
been proposed as alternatives to the cosmological standard model. In recent
years it has become increasingly evident that probes of the expansion his-
tory are not sufficient to distinguish among the candidate models, and that
Given a large landscape of vacua that statistically favors large values of the neutrino mass sum, $m_\nu$, I will present the probability distribution over $m_\nu$ obtained by weighting this prior by the amount of galaxies that are produced. Using Boltzmann codes to compute the smoothed density contrast on Mpc scales, we find that large dark matter halos form abundantly for $m_\nu \gtrsim 10$\,eV. However, in this regime structure forms late and is dominated by cluster scales, as in a top-down scenario.
Visible matter consists mostly of hydrogen and helium, only a small fraction
of which is in stars. Until recently, the bulk of the gas in the local
universe was in fact not seen. In the largest structures, massive galaxy
clusters, the gas is seen via its x-ray emission, but in the much more
numerous groups and isolated galaxies, it has not been possible to detect
it. I will describe how, in the last year or so, the situation has changed,
with the detection of a cross-correlation between the thermal SZ effect and
The cosmic microwave background contains a wealth of
information about cosmology as well as high energy physics. It tells
us about the composition and geometry of the universe, the properties
of neutrinos, dark matter, and even about the conditions in our
universe long before the cosmic microwave background was emitted.
After a brief review of what we may hope to learn from studies of the
cosmic microwave background about the early universe, I will review
An exciting and largely unexplored frontier in observational and theoretical cosmology is to understand the properties of the universe between 400,000 years and one billion years after the big bang. Notably, the first galaxies formed in this time period, perhaps a few hundred million years after the big bang. These galaxies strongly influenced the gas in their surroundings as well as the formation of subsequent generations of galaxies. The early galaxies emitted ultraviolet light and ionized "bubbles" of hydrogen gas around them.
It is well known that S-matrix Analyticity, Lorentz invariance and Unitarity place strong constraints on whether Effective Field Theories can be UV completed. A large class of gravitational field theories such as Massive Gravity and DGP inspired braneworld models contain as limits Galileon theories which in the past have been argued to violate the conditions necessary for a UV completion.
The last years have seen a renewed interest in theories of massive gravity. They represent an infra-red modification of gravity where the gravitational force weakens at very large scales. Heuristically, they provide the playground to understand a possible modification of GR which could potentially provide a dynamical solution to the cosmological constant problem. In this talk I will discuss a number of theoretical aspects of massive gravity theories, focusing on the relevance of the so-called Vainstein mechanism, both at the classical and the quantum level.