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.

 

Tuesday Jul 24, 2012
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We will discuss the estimated densities of dark matter in the
central regions of galaxies and discuss their inconsistency with
the predictions of cold dark matter only simulations. We will focus on
the satellites of the Milky Way to highlight this issue and then
explore dark matter with significant self-interactions as a
viable alternative. Milky Way satellites also place stringent
constraints on WIMP dark matter models in a completely different way
through Fermi-LAT observations and we will summarize those results.

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Tuesday May 29, 2012
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TBA

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Tuesday May 22, 2012
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How did inflation actually happen? Precision measurements of statistical properties of primordial fluctuations generated during inflation offer a direct probe of the physics of inflation. When we calculate statistical properties of primordial fluctuations generated during inflation, we usually assume that the initial state of quantum fluctuations is in a preferred vacuum state called Bunch-Davies vacuum. While there is some motivation for choosing such a state, this is an assumption, and thus needs to be tested by observations.

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Tuesday May 15, 2012
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In this talk I provide a model where the late time acceleration of the universe emerges from a BCS-like condensation of sterile neutrinos. This scenario can be naturally accommodated by general relativity covariantly coupled to sterile neutrinos, where the neutrinos act like an "aether" field.  We show that when active neutrinos couple to the neutrino condensate, they oscillate at a rate proportional to the dark energy density.  As a result, the oscillation of neutrinos and dark energy are tied in with the same mechanism.

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Tuesday May 08, 2012
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With the emergence of the dark sector in cosmology,  a variety of modified theories of gravity have come to the fore. I will discuss a framework which can be used to test gravity on large scales and the observational programmes that might lead to the tightest constraints.

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Thursday May 03, 2012
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I will discuss string cosmology and the dynamics of multiple scalar fields in potentials that can become negative, and their features as (Early) Dark Energy models. The point of departure is the ``String Axiverse'', a scenario that motivates the existence of cosmologically light axion fields as a generic consequence of string theory. These fields can constitute part of the Dark Matter, suppressing structure formation in a manner similar to massive neutrinos. Future observations will constrain their existence to percent level accuracy.

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Tuesday May 01, 2012
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We review the notion of a quantum state of the universe and its role in fundamental cosmology. Then we discuss recent work which points towards a profound connection, at the level of the quantum state, between (asymptotic) Euclidean AdS spaces and Lorentzian de Sitter spaces. This gives a new framework in which (a mild generalization of) AdS/CFT can be applied to inflationary cosmology.

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Monday Apr 30, 2012
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I will describe the tight connection between cosmic baryon number and cosmic magnetic fields, and also some recent work on chiral magnetic effects in cosmology.

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Tuesday Apr 24, 2012
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The curvaton scenario provides a simple explanation for the generation of the cosmological perturbations, however most works have focused on cases with rather trivial curvaton energy potentials, e.g. quadratic ones. In this talk I will present the rich phenomenology of curvatons by showing that non-quadratic curvatons exhibit new behaviors, leading to interesting signals in the resulting density perturbations. A string theory realization of the curvaton scenario will also be discussed, where D-branes located in a warped throat region of the internal space play the role of curvatons.

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Tuesday Apr 17, 2012
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In this talk I will present evidence that accounting for the presence of hierarchies in string compactifications naturally leads to a UV sensitivity of dark matter in contrast to what is usually assumed. In particular, we will see that the existence of cosmological moduli may lead to a non-thermal history for the early universe and modifications in the primordial production of dark matter.

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