We have weekly seminars dedicated to Cosmology and Astroparticle Physics (we also have other regular weekly meetings to discuss the latest results in our field). Former presentations are available from the past cosmology seminars pages. Please write to the contact below to join the mailing list.
Time: Wednesdays 14:15-15:15, during term time.
Place: room A315 (3rd floor of the Physicum building)
Format: 50′ + 10′ for questions
Contact: Sofie Marie Koksbang
- 25.01.2019 (A315 14:15-15:115) Abhishek Atreya (CAPSS, Bose Institute)
On Dark Matter Self Interactions, Viscosity and Cosmic Expansion
Abstract: In this talk we focus on the self interacting dark matter (SIDM) paradigm which can provide us with a consistent explanation of certain astrophyiscal observations that are in conflict with the cold dark matter (CDM) paradigm. We will make use of the constraints on SIDM cross-sections from astrophysical observations, to estimate the mean free path of the dark matter particles. Assuming thermalization within this volume we estimate the shear viscosity (ζ) and bulk iscosity (η) of SIDM, within kinetic theory formalism. The dissipation due to viscosity affects the solution of Einstein’s equation through energy conservation. In a simplified model, we calculate this change and try to argue that σ/m constraints on SIDM provide us with sufficient viscosity to contribute significantly to the observed cosmic cceleration at present epoch. We next calculate H(z) and q(z) within the simplified model, and perform χ2 analysis, using the the cosmic chronometer data, to estimate the best fit model parameters . The best fit values also explain type IA supernova data quite well.
- 20.02.2019 Shinsuke Kawai (Sungkyunkwan U.)
Dynamical systems in Gauss-Bonnet gravity
Abstract: In this talk I will describe some concepts of dynamical systems applied to semi-realistic models of higher curvature (Gauss-Bonnet) cosmology, including linear stability theory, bifurcation theory and coordinate-invariant characterization of chaos.
- 13.03.2019 Cyril Pitrou (IAP)
Precision big bang nucleosynthesis with improved Helium-4 predictions
Abstract : Primordial nucleosynthesis or Big-Bang Nucleosynthesis (BBN) happens during the first 300 seconds of our Universe. It is one of the three evidences for the big-bang model, together with the cosmological expansion and the Cosmic Microwave Background (CMB). Now that the number of neutrino families and the baryonic densities have been fixed by laboratory measurements or CMB observations, it has become a parameter free model. Hence, it is widely used to exclude or constrain extension of the standard cosmological model. Since the most recent measurements of primordial deuterium and Helium-4 abundances reach the percent level in precision, it is necessary to obtain a similar precision in theoretical predictions. I will first review the basic physics of primordial cosmology and BBN and then review the various effects which need to be taken into account at that epoch in order to obtain such precision.
- 03.04.2019 William Kinney (University at Buffalo & Stockholm University)
Swamp Creatures of the Inflationary Landscape
Abstract: Cosmological inflation provides an elegant framework for explaining initial conditions for a flat, homogeneous universe with Gaussian, nearly scale-invariant perturbations. Embedding inflation within a UV-complete theory has presented challenges, including eternal inflation and the possibility of a multiverse within the landscape of String Theory. I will discuss current ideas and issues in inflationary model building, including eternal inflation and recently proposed “swampland” conjectures for consistency with string-based UV completions.
- 17.04.2019 Thomas Collett (ICG, Portsmouth)