Effective Field Theory in Particle Physics

Effective field theory (EFT) provides a systematic framework for describing the phenomena of particle physics at energies below a chosen cutoff scale. By integrating out heavy degrees of freedom, EFT isolates the relevant low-energy interactions in terms of local operators organised by increasing mass dimension. In the context of the Standard Model, the Standard Model Effective Field Theory (SMEFT) supplements the renormalisable Lagrangian with higher-dimension operators whose coefficients encode possible effects of new physics. Renormalisation group evolution then governs the energy-scale dependence of these coefficients, enabling high-precision predictions for processes ranging from Higgs boson production and electroweak observables to rare meson decays. Complementary EFTs address strong-interaction regimes, such as chiral perturbation theory for pions or heavy-quark effective theory for the dynamics of heavy hadrons. Together, these approaches bridge experimental measurements at colliders and low-energy facilities with the search for physics beyond the Standard Model, offering a unified language to interpret global data and guide the design of future experiments.

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Technical terms

Effective Field Theory (EFT): A framework that describes low-energy phenomena by systematically expanding around a chosen cutoff scale and integrating out heavy fields.

Standard Model Effective Field Theory (SMEFT): The extension of the Standard Model Lagrangian by higher-dimension operators encoding possible effects of physics beyond known particles.

Operator: A local combination of fields and derivatives in the Lagrangian whose dimension determines its suppression by powers of the cutoff scale.

Wilson coefficient: A numerical factor multiplying an operator in an EFT Lagrangian, encapsulating the strength of the corresponding interaction.

Renormalisation group evolution (RGE): The formalism describing how Wilson coefficients vary with energy scale due to quantum corrections.

Cutoff scale (Λ): The energy threshold above which the effective description breaks down and new degrees of freedom must be included explicitly.

References

1. HighPT: A tool for high-p T Drell-Yan tails beyond the standard model. Computer Physics Communications (2023).
2. Renormalization group evolution of the Standard Model dimension six operators III: gauge coupling dependence and phenomenology. Journal of High Energy Physics (2014).
3. Renormalization group evolution of the Standard Model dimension six operators II: Yukawa dependence. Journal of High Energy Physics (2014).