In the first part of the talk, a model consisting of a scalar matter field coupled to linearised gravity as an environment is presented. To formulate the dynamics and address the gauge freedom, the full system is expressed in terms of relational observables associated with classical reference frames. After a Fock quantisation of these observables, the effective time evolution equation for the quantised scalar field, called master equation, is obtained by tracing out the gravitational environment using projection operator techniques. To extract the physics of a single scalar particle, the master equation is projected onto the one-particle subspace, and a connection to Feynman diagrams is established. This enables a QFT renormalisation of appearing UV-divergent terms. The resulting master equation is written in a completely positive, analytically solvable Lindblad form under suitable approximations. 

As an application, a quantum-mechanical toy model for a neutrino propagating in an environment of gravitational waves is analysed, motivated by the above field-theoretical model. This provides a possible microscopic resolution of decoherence parameters used in phenomenological models. The influence of gravity manifests in this case as a decoherence effect that damps the neutrino's oscillations, providing new insights into the physical properties of the model.

In the final part of the talk, decoherence effects induced by black hole horizons are discussed, both for underlying classical and quantum horizon geometries. Recent studies show that for classical horizon geometries, a spatial superposition held static in the metric experiences a constant decoherence rate due to the presence of the horizon. This behaviour changes if the existence of a minimal length in spacetime is assumed. Implementing such a minimal length at an effective level as a minimal quantum of area for the horizon, the decoherence saturates at values that are negligibly small for a minimal area on the order of the Planck length squared.

In the first part of the talk, a model consisting of a scalar matter field coupled to linearised gravity as an environment is presented. To formulate the dynamics and address the gauge freedom, the full system is expressed in terms of relational observables associated with classical reference frames. After a Fock quantisation of these observables, the effective time evolution equation for the quantised scalar field, called master equation, is obtained by tracing out the gravitational environment using projection operator techniques. To extract the physics of a single scalar particle, the master equation is projected onto the one-particle subspace, and a connection to Feynman diagrams is established. This enables a QFT renormalisation of appearing UV-divergent terms. The resulting master equation is written in a completely positive, analytically solvable Lindblad form under suitable approximations. 

As an application, a quantum-mechanical toy model for a neutrino propagating in an environment of gravitational waves is analysed, motivated by the above field-theoretical model. This provides a possible microscopic resolution of decoherence parameters used in phenomenological models. The influence of gravity manifests in this case as a decoherence effect that damps the neutrino's oscillations, providing new insights into the physical properties of the model.

In the final part of the talk, decoherence effects induced by black hole horizons are discussed, both for underlying classical and quantum horizon geometries. Recent studies show that for classical horizon geometries, a spatial superposition held static in the metric experiences a constant decoherence rate due to the presence of the horizon. This behaviour changes if the existence of a minimal length in spacetime is assumed. Implementing such a minimal length at an effective level as a minimal quantum of area for the horizon, the decoherence saturates at values that are negligibly small for a minimal area on the order of the Planck length squared.