Cosmology

Thus far, the non-linear regime of structure formation is only accessible through expensive numerical N-body simulations since the conventional ana-
lytic treatment of cosmic density fluctuations via the hydrodynamical equations runs into severe problems even in a mildly non-linear regime. I will give an overview of Kinetic Field Theory, a novel analytic approach to cosmic large-scale structure formation, which provides a density fluctuation power spectrum that agrees well with state of the art N-body simulations up to k = 10h Mpc−1. I will point out how Kinetic Field Theory avoids the difficulties of standard perturbation theory by construction and allows to proceed deeply into the non-linear regime of density fluctuations. I will give a summary of the most important results and recent developments for cosmic structure formation and briefly show applications of Kinetic Field Theory outside of cosmology, stressing the opportunities this method provides for the study of the physics behind structure formation. I will then focus my discussion on how the form of the interaction potential influences the formation of cosmic structures in the highly non-linear regime and the implications it bears on the NFW density profile of dark matter halos.

Scattering amplitudes of massive spin-2 particles generically grow with energy and lead to violations of perturbative unitarity. One way to partially soften such amplitudes is with the infinite towers of particles present in Kaluza-Klein theories. In this talk I will discuss in detail this mechanism of unitarization for general dimensional reductions of pure gravity and show that it leads to some interesting constraints on the eigenfunctions and eigenvalues of the scalar Laplacian on closed manifolds. A consequence of these constraints is that there exists an upper bound on the gaps between Kaluza-Klein excitations of the graviton, which applies also to Calabi-Yau compactifications of string theory.   

Maps of the mass density field can be used to predict peculiar velocities point-by-point. The comparison of these predictions to peculiar velocity data can be used to determine the cosmological parameter combination f sigma_8. I will briefly discuss the history of this field, present some of our recent results as well as other applications to calibrating the Hubble constant via SNe and gravitational waves, and discuss ongoing work to improving these measurements, through better modelling and, more importantly, acquiring more peculiar velocity data.