Cosmic lockdown: How the environment can isolate quantum fields
A simplified cosmological model suggests that decoherence can suppress quantum tunneling, effectively locking fields into the vacuum state they have reached.
In a simplified cosmological model, researchers suggest that decoherence can suppress quantum tunneling, effectively locking quantum fields into the vacuum state they have reached. The vacuum, in cosmology, is not completely devoid of energy but rather a state where a field sits at a minimum of its energy. There can be local minima, called false vacua, while the true vacuum is the lowest possible minimum.
Quantum fields, fundamental physical objects that permeate the universe, behave similarly to classical fields, with excitations appearing as particles.
A new study published in the Journal of Cosmology and Astroparticle Physics explores the factors that determine which vacuum a field may end up in within an expanding universe. The study uses the Higgs field as an example, as its vacuum value contributes to giving mass to particles in the Standard Model and helps determine the structure of low-energy physics.
Some calculations based on the Standard Model suggest that the Higgs field may be trapped in a false vacuum, while a deeper, lower-energy state exists at very large field values.
In principle, a transition to the deeper minimum would alter the structure of matter and the forces governing it. This transition can occur through quantum tunneling, where the state of the system extends beyond the barrier between the vacua, leaving a small probability of appearing on the other side. The study's authors built a simplified model to understand how the environment affects the evolution of a field. They noted that perfect isolation is an idealization, as fields continuously interact with their surroundings.
Interactions with the environment produce decoherence, a phenomenon where a quantum system exists in a superposition of different possibilities, eventually behaving more like an ordinary classical system. The model represents the environment as other fields interacting with the main field. The field's "lightness" or "heaviness" relative to the Hubble scale—indicating its relationship with the rate at which the universe is expanding—plays a more significant role than previously thought in determining the initial choice of vacuum.
Heavy fields are more likely to move toward the true vacuum, while lighter fields may remain in a false vacuum if the expansion is too rapid for the field to keep up with the changes.
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