The High Energy/Cosmology Friday Seminar is a non-formal, interactive meeting
The presentations need not be advanced nor even on one's own subject of research, and students are encouraged to give talks. The only demand is: be interesting!
February 6
Keijo Kajantie:The big black hole in the center of the Milky Way
Abstract: I review the properties of and evidence for the 4 million
solar mass black hole in the center of the Milky Way.
February 27
Andrea Ferrantelli:Scattering of massive W bosons into gravitinos and tree unitarity in broken supergravity
Abstract: The WW scattering into gravitino and gaugino is investigated in the broken phase, by using both gauge and mass eigenstates. Differently from what is obtained for unbroken gauge symmetry, we find in the scattering amplitudes new structures, which can lead to violation of unitarity above a certain scale. This happens because, in the annihilation diagram, the longitudinal degrees of freedom in the propagator of the gauge bosons disappear from the amplitude, by virtue of the SUGRA vertex. We show that the longitudinal polarizations of the on-shell W become strongly interacting in the high energy limit, and that the inclusion of diagrams with off-shell scalars of the MSSM does not cancel the divergences.
March 20
Matts Roos:Dark matter: The evidence from astronomy, astrophysics and cosmology
Abstract: Dark matter has been introduced to explain many independent gravitational
effects at different astronomical scales, even at cosmological scales. This review
describes more than ten such effects. It is intended for an audience with little or no
knowledge of astrophysics or cosmology.
April 24
Patta Yogendran: A string theorists approach to inflation
Abstract: In this talk - I will try to present one fairly complete model
for inflation that has been constructed in string theory.
The aim of the talk will be to focus on the perspective
that string theory brings to the problem.
I will attempt to make the talk accessible to non-specialists.
More precisely, I will review the papers -
0808.2811, 0706.0360, 0705.3837, hep-th/0607050,
and if possible hep-th/0703088.
All these papers are summarised in the two reviews
0901.0265 and 0710.2951.
May 27 (Wednesday!)
Syksy Rasanen: Distance and expansion rate: testing the FRW metric
Abstract: I will show how the average expansion rate is related to measurements
of distance in statistically homogeneous and isotropic universes with
non-linear structures. I will compare this with the
Friedmann-Robertson-Walker result. These relations make it possible to
observationally test the FRW metric directly, independent of dark
energy or modified gravity, and to test the backreaction conjecture
without having a prediction for the average expansion rate.
May 29
Christian Byrnes:Large non-Gaussianity from slow-roll inflation
Abstract: Non-Gaussianity of the primordial curvature perturbation is a powerful and
topical way of distinguishing between the many competing models of inflation.
While the simplest models of inflation predict a tiny level of
non-Gaussianity, there are also many models which predict an observable level
of non-Gaussianity such as the curvaton scenario, modulated reheating etc.
In this talk I show that it is possible to generate a large level of (local)
non-Gaussianity (f_NL~100) during multiple-field inflation, without breaking
the slow-roll conditions. I present the conditions required to generate a
large non-Gausssianity and quantify the fine tuning of the initial conditions
required to achieve this. Finally these conditions are applied to hybrid
inflation.
June 8 (Monday! At 10:15!)
Pascal Vaudrevange:Constraining the topology of the universe after WMAP5
Abstract: We present an update to constraints on the topology of the universe by looking
for matching pairs of circles in the fluctuations of the cosmic microwave
background radiation as measured in the WMAP5 data release.