Schwinger effect in QCD and nuclear physics

Abstract

We provide a pedagogical review of the Schwinger effect, i.e., the non-perturbative production of particle and anti-particle pairs from the vacuum by strong fields, as well as related strong-field phenomena. Beginning with an overview of the Schwinger effect in quantum electrodynamics, we discuss its extensions to quantum chromodynamics and its applications in nuclear physics, including high-$Z$ nuclei, string breaking, relativistic heavy-ion collisions, and the chiral anomaly.

Figures (1)

• Figure 1: Schematic illustration of the quantum vacuum and its response to an external electric field ${\bm E}$. (a) In the absence of an electric field, the spontaneous creation and annihilation of virtual particle ($\bullet$) and anti-particle ($\bullet$) pairs occur randomly in the vacuum. (b) Once an electric field is applied, the virtual pairs tend to align along the field direction (provided they are electrically charged), leading to vacuum polarization. (c) When the field strength goes beyond the critical strength $|eE| \gtrsim m^2$, the vacuum decays: the field supplies sufficient energy to tear the virtual pairs apart, allowing them to materialize as real particles. The same picture applies equally to QCD, where the vacuum fluctuations of colorful quarks and gluons are polarized and eventually materialized by the presence of a color electric field.