27. - 30. September 2018
22. German Conference of Women in Physics
Where: Oldenburg

10. - 21. September 2018
24th “Saalburg” Summer School
Where: Saalburg 

10. - 12. September 2018
RTG autumn workshop
Where: Bremen

1. - 7. July 2018
15th Marcel Grossmann Meeting
Where: Rome 

27. June 2018
RTG Colloquium
Where: Bremen

16. May 2018
RTG Colloquium
Where: Oldenburg

03. - 04. May 2018
13. Kosmologietag
Where: Bielefeld

18. April 2018
RTG Colloquium
Where: Bielefeld

19. - 23. March 2018
DPG Spring Meeting Würzburg
Where: Würzburg

15. March 2018
Bremen-Oldenburg Relativity Seminar
Where: Oldenburg

22. February 2018
Bremen-Oldenburg Relativity Seminar
Where: Oldenburg

22. February 2018 
Bremen-Oldenburg Relativity Seminar
Where: Bremen

21. February 2018
Fellow at Work
Where: Delmenhorst

19. - 20. February 2018
RTG Workshop
Where: Bremen

6. February 2018 
RTG Colloquium
Where: Bremen

5. February 2018
Guided tour through the observatory Oldenburg
Where: Oldenburg

25. January 2018
Workshop - Spiele mit der Macht

17. January 2018
Fellow lecture
Where: Delmenhorst

11. January 2018
Bremen-Oldenburg Relativity Seminar
Where: Bremen

10. January 2018
PhD Colloquium
Where: Bremen

9. January 2018
Where: Bielefeld


11 - 13 October 2017
RTG Autumn Workshop
Where: Oldenburg

28 September - 01 October 2017
21st German Conference of Women in Physics
Where: Ilmenau

18 -19 May 2017
12. Kosmologietag
Where: Center for Interdisciplinary Research, ZiF at Bielefeld University

13. - 17. March 2017
DPG Spring Meeting
Where: Universty of Bremen, ZARM

6 - 7 March 2017
GRK Workshop Hannover
Where: Hannover

Bremen-Oldenburg Relativity Seminar

                         Sarah Kahlen
                   University of Oldenburg

"Constraints on neutrino cosmology from the cosmic microwave background"

      Wednesday, 18. October 2018, 1015, Room W2 3-349

The cosmic microwave background (CMB) radiation and its angular power
anisotropy spectrum are well explored in the theoretical and experimental
sense, e.g. by measurements of the Planck satellite. But apart from the
cosmic photon background, the cosmic neutrino background (CNB), which is
much more difficult to explore because of the weakly interacting behavior
of neutrinos, fills our Universe. In general, it is difficult to obtain
information about neutrino physics from measurement. However, experiments
among other things proved that neutrinos are massive, although they are
massless according to the standard model of particle physics. Furthermore,
the CNB impacts cosmology and e.g. influences the expansion rate of the
Universe, the Big Bang Nucleosynthesis and finally also the photon
background. In my talk I am going to present the basic ideas about
cosmological perturbation theory, which is capable of explaining how the
structures observed in our Universe nowadays have formed and evolved as
well as it is able to predict the angular power spectrum of the microwave
background with high accuracy. After the presentation of the formalism of
linear perturbation theory, I am applying the theory to neutrinos and derive
their so-called Boltzmann hierarchy, which exist for all the different
particle species of the Universe. In combination with Einstein's field
equations these hierarchies yield the temporal evolution of perturbations
in the corresponding particles. These temporal evolutions for all the
components of the Universe will briefly be dealt with in the talk. The
Boltzmann hierarchies of massive and massless neutrinos differ. They thus
influence the angular power spectrum of the CMB in different ways.
Non-instantaneous decoupling of neutrinos causes extra energy in the
neutrino sector as compared to the standard scenario. This extra energy
is degenerate with neutrino temperature and their phase-space distribution
function, wherefore the so-called number of relativistic neutrino species
N_eff has been introduced to parametrize the extra neutrino energy. The
degeneracy between neutrino temperature and N_eff has been analyzed in
my work regarding their influence on the CMB angular power spectrum for
massless and massive neutrinos. The influence of the neutrino phase-space
distribution function was another important aspect of the analysis.
Whereas the Fermi-Dirac distribution function is usually assumed to
describe how neutrinos are distributed in phase-space, we used a Gaussian
distribution function and showed that, with an appropriate normalization,
its influence on the CMB angular power spectrum is rather small, also for
massive neutrinos.


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