# Master thesis defence by Mikkel Jensen – University of Copenhagen

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# Master thesis defence by Mikkel Jensen

Title: Environmentally induced neutrino decoherence in IceCube

Abstract: Neutrino oscillations were discovered two decades ago and have since been able to describe neutrino data accurately. The increase in detector capabilities coming with advances in technology delivers oscillation parameter measurements with increasing precision, which requires analyses of potential sub-leading effects to ensure that the data is not misinterpreted.

Quantum decoherence of neutrinos has the potential to be such an effect, and is motivated by certain quantum gravity models. It acts as a damping effect on neutrino oscillation probabilities. In decoherence theory the neutrinos are coupled to the environment, in which they propagate. This coupling can be described by a parameter, $\Gamma$, that characterizes the frequency and magnitude of perturbations caused by "interactions" with the environment. The coupling could depend on the neutrino energy, and models where the energy dependence follows a power law with $\Gamma = \Gamma_0\big(\frac{E_\nu}{GeV}\big)^n$ are investigated in this thesis.

The existence decoherence can be detected or limited by using the IceCube detector located at the geographic South Pole. IceCube is one of the best detectors for probing decoherence effects, due to the many different distances neutrinos generated in the Earths atmosphere travel before detection. The potential to discover decoherence is calculated by using pseudodata, where IceCube has an expected sensitivity down to $\Gamma = 1.6$ \textit{feV} at $90\%$ confidence, when considering the energy independent decoherence case.