Magnetic Catalysis
Magnetic catalysis is a physics phenomenon, which is defined as an enhancement of dynamical symmetry breaking by an external magnetic field in quantum field theory, used for the description of quantum (quasi-)particles in particle physics, nuclear physics and condensed matter physics. The underlying phenomenon is a consequence of the strong tendency of a magnetic field to enhance binding of oppositely charged particles into bound states. The catalyzing effect comes from a partial restriction (dimensional reduction) of the motion of charged particles in the directions perpendicular to the direction of the magnetic field. Commonly, the magnetic catalysis is specifically associated with spontaneous breaking of flavor or chiral symmetry in quantum field theory, which is enhanced or triggered by the presence of an external magnetic field. General description The underlying mechanism behind magnetic catalysis is the dimensional reduction of low-energy charged spin-1/2 particles. As a ...
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Dynamical Symmetry Breaking
Spontaneous symmetry breaking is a spontaneous process of symmetry breaking, by which a physical system in a symmetric state spontaneously ends up in an asymmetric state. In particular, it can describe systems where the equations of motion or the Lagrangian obey symmetries, but the lowest-energy vacuum solutions do not exhibit that same symmetry. When the system goes to one of those vacuum solutions, the symmetry is broken for perturbations around that vacuum even though the entire Lagrangian retains that symmetry. Overview By definition, spontaneous symmetry breaking requires the existence of physical laws (e.g. quantum mechanics) which are invariant under a symmetry transformation (such as translation or rotation), so that any pair of outcomes differing only by that transformation have the same probability distribution. For example if measurements of an observable at any two different positions have the same probability distribution, the observable has translational symmetry. ...
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