Neutrinos and dark energy
2007121 pages
Supervisors:
Thesis: Master - A. Ringwald,
- J. Louis
- Hamburg U.
Report number:
- DESY-THESIS-2008-004
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Abstract:
From the observed late-time acceleration of cosmic expansion arises the quest for the nature of Dark Energy. As has been widely discussed, the cosmic neutrino background naturally qualifies for a connection \Vith the Dark Energy sector and as a result could play a key role for the origin of cosmic acceleration. In this thesis we explore various theoretical aspects and phenomenological consequences arising from non-standard neutrino interactions, which dynamically link the cosmic neutrino background and a slowly-evolving scalar field of the dark sector. In the considered scenario, known as Neutrino Dark Energy, the complex interplay between the neutrinos and the scalar field not only allows to explain cosmic acceleration, but intriguingly, as a distinct signature, also gives rise to dynamical, time-dependent neutrino masses. In a first analysis, we thoroughly investigate an astrophysical high energy neutrino process which is sensitive to neutrino masses. We work out, both semi-analytically and numerically, the generic clear-cut signatures arising from a possible time variation of neutrino masses which we compare to the corresponding results for constant neutrino masses. Finally, '"'e demonstrate that even for the lowest possible neutrino mass scale, it is feasible for the radio telescope LOFAR to reveal a variation of neutrino masses and therefore to probe the nature of Dark Energy within the next decade. A second independent analysis deals with the recently challenged stability of Neutrino Dark Energy against the strong growth of hydrodynamic perturbations, driven by the new scalar force felt between neutrinos. Within the framework of linear cosmological perturbation theory, we derive the equation of motion of the neutrino perturbations in a model-independent way. This equation allows to deduce an analytical stability condition which translates into a comfortable upper bound on the scalar-neutrino coupling which is determined by the ratio of the densities in cold dark matter and in neutrinos. We illustrate our findings by presenting numerical results for representative examples of stable as well as of unstable scenarios.- thesis
- dark energy
- neutrino: cosmic radiation
- cosmic background radiation
- field theory: scalar
- neutrino: mass
- mass: time dependence
- neutrino: mixing angle
- perturbation theory: linear
- stability
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