Max Joseph Fahn (DIFA)

Gravitationally induced decoherence: from theoretical models to signatures in neutrino oscillations

The formalism of Open Quantum Systems with linearised gravity as environment serves as a tool to predict the effective evolution of quantised matter systems under the influence of gravity. It is of use to analyse features of specific quantum gravity candidate theories and to search for signs of quantum gravity effects for instance in neutrino oscillations. In the talk, a model consisting of a scalar matter field and linearised gravity as environment is considered. In order to formulate dynamics and to deal with the gauge freedom present in the environment, the entire system is expressed in terms of relational observables that allow a physical interpretation of temporal and spatial coordinates. After a Fock quantisation of the observables, the effective time evolution equation for the quantised scalar field under the influence of gravity, called master equation, is obtained by tracing out the gravitational environment using projection operator techniques. This master equation exhibits UV-divergent terms. To extract the physics of a single scalar particle, its projection onto the one-particle subspace is discussed and the individual terms are interpreted as Feynman diagrams. That yields the possibility to perform a QFT renormalisation and the resulting master equation is cast into a completely positive Lindblad form using specific approximations.  As an application, a quantum mechanical toy model for a neutrino propagating in an environment of gravitational waves is analysed, its form being motivated by the above field theoretical model. The obtained master equation is compared with master equations from phenomenological models for a similar setup to provide a possible resolution of the phenomenological parameters. The influence of gravity manifests here as a decoherence effect that damps the neutrino's oscillations, allowing to get new insights into the physical properties of the model.