We have a seminar tomorrow! WHEN: 11 May 2017 11:00 WHERE: Philosophenweg 16 SR Alexey Golovnev, , NOTE UNUSUAL DATE AND TIME (Saint Petersburg State University) - "Teleparallel gravity, its extensions, and the issue of local Lorentz invariance " Abstract: In teleparallel theory, the gravitational interaction is described by the torsion tensor while the curvature is set to zero. It goes in terms of tetrads, and the spin connection is taken to vanish. The latter condition clearly violates the local Lorentz symmetry in the space of tetrads. However, for teleparallel equivalent of GR, this violation amounts to merely a surface term in its action. This is the classical formulation of teleparallel gravity. Nowadays, many experts prefer to use an arbitrary flat (purely inertial) spin connection. A local Lorentz rotation would change this spin connection, otherwise keeping the model invariant. Actually, it can be done even with more elegance: one can allow for variation with respect to the flat spin connection since it anyway affects only the surface term. The things differ for modified versions of teleparallel gravity, such as f(T) which is often used for cosmological model building. The local Lorentz violation goes beyond the surface terms, and leads to increased number of degrees of freedom. In this case the covariantisation by arbitrary flat spin connection works differently. The variation is not empty, however the field equations are redundant with those coming from tetrads. It seems that these issues are not well understood and appreciated even among experts, and there is some confusion in the literature. I will offer a pedagogical introduction to these topics, review some known results and discuss new ideas. The talk is based in part on arXiv:1701.06271 by me, Tomi Koivisto, and Marit Sandstad.

We have a seminar today! Eva K. Grebel (ARI Heidelberg) will tell us about "Dwarf Galaxies - Fossils of Galaxy Evolution" WHEN: 10 May 2017 17:00 WHERE: Philosophenweg 16 SR Abstract: Dwarf galaxies are the most common type of galaxy in the Universe and include the most dark-matter-dominated objects known. They offer intriguing insights into evolutionary processes at low halo masses and low metallicities. Cosmological models of hierarchical structure formation describe the build-up of massive galaxies via the continuing accretion of smaller subhalos. If we consider dwarf galaxies to be the survivors of a once much more numerous population of such building blocks, their old stellar populations are key to understanding very early star and galaxy formation processes. The Local Group and in particular the Milky Way's dwarf galaxy entourage offer us the unique possibility to compare in detail dwarf and Galactic populations. This is an important step towards quantifying the magnitude and time scales of dwarf contributions to the build-up of massive galaxies the Milky Way and allows us to test predictions of cosmological scenarios.

We have a seminar today! Santiago Casas will tell us about "Non-linearities in Modified Gravity: Forecasts and parameterizations" WHERE : Philosophenweg 16, SR , WHEN: 26 Apr 2017 17:00 h Abstract: In this talk I will show the impact that different prescriptions for non-linearities and different choices of parameterizations for Modified Gravity have on forecasts for Galaxy Clustering and Weak Lensing. Modified Gravity (MG) theories generally affect the Poisson equation and the gravitational slip in an observable way, that can be parameterized by two generic functions ($\eta$ and $\mu$) of time and space. Here, I will focus on forecasts for future surveys, like Euclid, SKA1, SKA2 and DESI. I will show that non-linearities and the inclusion of priors can reduce the strong correlations between parameters and that applying a decorrelation method can help identify the best constrained combinations of MG parameters measured with future experiments. Towards the end of the talk I will show the effect that different prescriptions for non-linearities have on the parameter constraints and show how this can be improved in the future.

Physics and music share many aspects. Today we made an experiment in our 1st ITP CosmoConcert. Our artists asked the audience to suggest any arXiv paper to transform it into music. The public, trying to make life difficult to our amazing group chose: "Gods as Topological Invariants", arXiv:1203.6902. If you wanna read the abstract of this "peculiar" paper see below, if you wanna LISTEN TO IT, SEE THE VIDEO! "We show that the number of gods in a universe must equal the Euler characteristics of its underlying manifold. By incorporating the classical cosmological argument for creation, this result builds a bridge between theology and physics and makes theism a testable hypothesis. Theological implications are profound since the theorem gives us new insights in the topological structure of heavens and hells. Recent astronomical observations can not reject theism, but data are slightly in favor of atheism."

ITP COSMO CONCERT.