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In quantum field theory, a quartic interaction is a type of self-interaction in a scalar field. Other types of quartic interactions may be found under the topic of four-fermion interactions. A classical free scalar field φ {\displaystyle \varphi } satisfies the Klein–Gordon equation. If a scalar field is denoted φ {\displaystyle \varphi } , a quartic interaction is represented by adding a potential energy term φ 4 {\displaystyle \varphi ^{4}} to the Lagrangian density. The coupling constant λ {\displaystyle \lambda } is dimensionless in 4-dimensional spacetime.
This article uses the {\displaystyle } metric signature for Minkowski space.