Internal Seminars SS 15

 

Fri 19.02.2016 14:00 (MBP1 026)

Cosmology seminar:

Luca Amendola (Heidelberg)

Two new methods for testing gravity at cosmological scales

Abstract:
Testing gravity at large scales is one of the most interesting goals of current and planned surveys. In this talk I will present two new methods that complement and enrich the cosmologist toolbox. The first employs CMB B-mode polarization to test for modification of the gravitational wave propagation at early times. The second one uses the scatter in the supernovae magnitude due to lensing to infer the clustering and growth of matter along the line of sight.

 

Fri 05.02.2016 10:30 (MBP1 1st floor meeting room)

Cosmology seminar:

Maciej Bilicki (Leiden Observatory)

The largest all-sky galaxy catalogues and their cosmological applications

Abstract:
Various aspects of cosmology require comprehensive all-sky mapping of the cosmic web to considerable depths. In order to probe the whole extragalactic sky beyond 100 megaparsecs, one must draw on multiwavelength datasets and state-of-­the‐art photometric redshift techniques. I will summarise our dedicated programme that employs the largest photometric all-­sky surveys – 2MASS, WISE and SuperCOSMOS – to obtain accurate redshift estimates of millions of galaxies. Two catalogues have been constructed so far, and are being used for various cosmological applications. The first one – 2MASS Photometric Redshift catalogue (2MPZ) – was publicly released in 2013 and includes almost 1 million galaxies with a median depth over 300 Mpc. The second dataset, soon to be released, combines the WISE mid-­infrared survey with SuperCOSMOS optical data and reaches depths over 1 gigaparsec on unprecedented angular scales. These photometric redshift samples, with about 20 million sources in total, provide access to volumes large enough to study observationally the Copernican Principle of universal homogeneity and isotropy, as well as to probe various aspects of dark energy and dark matter through cross-­correlations with other data such as the cosmic microwave or gamma-ray backgrounds. Last but not least, they constitute a test-­bed for forthcoming wide-­angle multi-­million galaxy samples expected from such instruments as the SKA, Euclid or LSST.

 

Fri 22.01.2016 10:30 (MBP1 1st floor meeting room)

Cosmology seminar:

Stefano Orani (Basel)

Impact of other scalar fields on oscillons after hilltop inflation

Abstract:
During hilltop inflation, the inflaton rolls away from the maximum of its potential and towards the minimum where the universe reheats. The first stage of reheating, preheating, is non-perturbative and, in this model, spatially localized oscillating bubbles of the inflaton field, called oscillons, are formed. Furthermore, when other fields are present, they can be produced via a parametric resonance with the non-homogeneous inflaton field. In this talk, I will discuss lattice simulations of the evolution of oscillons, how they are affected by the resonance with another field and their effect on the expansion history of the universe.

 

Fr. 15.01.2016 15:00 (MBP1 026)

Presentation of the master thesis:

Marc Joosten (RWTH Aachen)

Fragmentation in top quark decays at the LHC

 

Thu 10.12.2015 14:30 (MBP1 026)

Cosmology seminar:

Mario Ballardini (Bologna)

Constraints on induced gravity dark energy models

Abstract:
We study the predictions for structure formation in an induced gravity dark energy model with a quartic potential. By developing a dedicated Einstein-Boltzmann code, we study self-consistently the dynamics of homogeneous cosmology and of linear perturbations without using any parametrization, accurately recovering the quasi-static analytic approximation in the matter dominated era. We use CMB anisotropies data and a compilation of BAO data to constrain the coupling γ to the Ricci curvature and the other cosmological parameters. By connecting the gravitational constant in the Einstein equation to the one measured in a Cavendish-like experiment, we find γ<0.0012 at 95 % confidence level with Planck 2013 and BAO data, and present the updated Planck 2015 constraint. Because of a degeneracy between γ and the Hubble constant H0, we show how larger values for γ are allowed, but not preferred at a significant statistical level, when local measurements of H0 are combined in the analysis with Planck data. We also extend the analysis and constraints to a simple monomial potential with a positive exponent.

 

Mi. 09.12.2015 14:00 (26 C 402)

Presentation of the master thesis:

Lars Poschwatta (RWTH Aachen)

Higgs Boson Production in Association with Two Jets via Gluon Fusion at the LHC

 

Mon 23.11.2015 14:30 (MBP1 026)

Cosmology seminar:

Elena Sellentin (Heidelberg)

Forecasting with accuracies similar to MCMC

Abstract:
Non-Gaussian posterior likelihoods appear frequently when many degenerate parameters shall be constrained by data. Their shape could so far only be determined accurately by time-consuming techniques, such as Monte Carlo Markov Chains. The talk presents the new method DALI that is able to recover the essential shapes of such non-Gaussian posteriors much faster. The method needs as input a parametric model and the maximum likelihood point. The talk presents first how an always positive-definite and normalizable likelihood approximation can then be constructed, and afterwards some applications to cosmology. Due to technical interest from the seminar organizers, the talk will also provide a short introduction to the publicly available DALI-code.

 

Fri 06.11.2015 13:30 (MBP1 026)

PhD Defense:

Jory Sonneveld (RWTH)

Simplified Models and the Interpretation of Supersymmetry Searches

 

Tue 20.10.2015 14:00 (MBP1 026)

PhD Defense:

Clemens Mellein (RWTH)

Production of heavy Higgs bosons and decay into top quarks at the LHC