When studying Quantum Electrodynamics (QED) and Quantum Chromodynamics (QCD) on curved space-times, several new phenomena emerge due to the interplay between quantum field theory and gravitational effects. Here are a few notable examples:
Gravitational Redshift and Time Dilation: In curved space-times, such as near massive objects or in regions with strong gravitational fields, time and energy are influenced by gravity. This can lead to gravitational redshift, where the frequency of electromagnetic waves decreases as they climb out of a gravitational well. Additionally, time dilation occurs, meaning that clocks in regions of different gravitational potentials may tick at different rates.
Hawking Radiation: When applying quantum field theory in the vicinity of black holes, physicist Stephen Hawking predicted that black holes can emit thermal radiation, now known as Hawking radiation. This phenomenon arises due to the interaction between quantum fields and the gravitational field of the black hole, leading to the creation and subsequent emission of particle-antiparticle pairs near the black hole's event horizon.
Vacuum Fluctuations and Particle Creation: In curved space-times, even in the absence of any particles, the vacuum state is not empty but instead exhibits vacuum fluctuations. These fluctuations can give rise to the creation of particle-antiparticle pairs. In the presence of a strong gravitational field, such as near a black hole or during the early stages of the universe's expansion, these vacuum fluctuations can become significant and lead to the creation of particles.
Topological Effects and Anomalies: The curvature of space-time can induce topological effects in quantum field theories. For instance, the presence of nontrivial topological configurations in gauge fields can lead to anomalies, which are quantum violations of certain symmetries that are present classically. These anomalies can have important consequences in particle physics and can affect the behavior of quantum fields in curved space-times.
Gravitational Waves: The presence of gravitational waves, which are ripples in the curvature of space-time caused by accelerating masses, can interact with quantum fields. This interaction can lead to the scattering and modification of particles and their properties.
Studying QED and QCD on curved space-times allows us to explore the interplay between quantum field theory and gravity, leading to the emergence of these and other fascinating phenomena. These investigations contribute to our understanding of the quantum nature of matter and its interaction with gravitational fields.