Quantum Field Teory (QFT)

Attempts to investigate quantum mechanical effects in special relativistic settings stimulated the birth of Quantum Field Theory (QFT), which promotes quantum fields as the fundamental entities describing physical processes. QFT underlies modern elementary particle physics and provides essential tools in several frameworks, including nuclear and atomic processes, condensed matter physics and astrophysics. QFT predictions are often supported by experiments, as in the case of quantum electrodynamics (QED), which currently represents the most accurately tested physical theory. More recently, the possibility to include the gravitational field within a QFT framework has been also considered: despite a complete quantum theory of gravity still remains elusive, the dynamics of quantum fields can be studied on classical curved backgrounds, resulting in new and interesting phenomena such as the Unruh effect and particle production from vacuum, which are currently object of several investigations.

Producing particles from vacuum 

QFT in flat Minkowski spacetime heavily relies on Poincaré invariance. However, the presence of a background gravitational field breaks Poincaré symmetry and allows particle to be directly produced from vacuum. In particular:

• a time-dependent gravitational field breaks time-translation symmetry, so that quantum fields may absorb energy from the background;

• a spatially inhomogeneous gravitational field breaks space-translation symmetry, implying that quantum fields are now allowed to absorb linear momentum from the background field.

Both phenomena are thus peculiar of QFT in curved spacetime and represent promising candidates to explain the origin of dark matter in early universe scenarios. At the same time, particle production from vacuum may generate entanglement in the final state of quantum field, thus providing additional insights into the quantum properties of our Universe.