Paul Balduf#paperOfTheDay is "Exact evolution equation for the effective potential" from 1993 by Christof Wetterich. This is the paper where the Wetterich equation is first introduced in its modern form.
In #quantumFieldTheory , there are "quantum fluctuations" which lead to the full theory being different from the Lagrangian or action one starts with. A famous example is light by light scattering in QED: The Lagrangian in quantum electrodynamics contains basically one type of allowed interaction, namely matter (such as electrons) emitting or absorbing one photon. This can take many different forms in practice, for example Bremsstrahlung (electron being accelerated and producing photon), or electrostatic repulsion (photons being exchanged between two electrons, accelerating them away from each other). QED does not allow for an elementary interaction between photons. But such interaction does in fact take place due to #quantum fluctuations with "virtual" intermediate electrons. A central task for theoretical #physics is to compute such effects.
The effective action contains all such quantum effects, that is, if one uses the effective action as a "classical" one (without adding further quantum corrections), one obtains the full quantum answer. Many different methods are known to compute the effective action, several of them based on the renormalization group. Compared to the previous work by Wilson, Wegner, and Polchinski, the Wetterich equation is somewhat more explicit in terms of interpretation, and it has the advantage of directly giving the quantum effective action and not some proxy quantity. It has by now become the cornerstone of functional renormalization group ( #FRG ) methods. https://www.sciencedirect.com/science/article/pii/037026939390726X?via%3Dihub
In #quantumFieldTheory , there are "quantum fluctuations" which lead to the full theory being different from the Lagrangian or action one starts with. A famous example is light by light scattering in QED: The Lagrangian in quantum electrodynamics contains basically one type of allowed interaction, namely matter (such as electrons) emitting or absorbing one photon. This can take many different forms in practice, for example Bremsstrahlung (electron being accelerated and producing photon), or electrostatic repulsion (photons being exchanged between two electrons, accelerating them away from each other). QED does not allow for an elementary interaction between photons. But such interaction does in fact take place due to #quantum fluctuations with "virtual" intermediate electrons. A central task for theoretical #physics is to compute such effects.
The effective action contains all such quantum effects, that is, if one uses the effective action as a "classical" one (without adding further quantum corrections), one obtains the full quantum answer. Many different methods are known to compute the effective action, several of them based on the renormalization group. Compared to the previous work by Wilson, Wegner, and Polchinski, the Wetterich equation is somewhat more explicit in terms of interpretation, and it has the advantage of directly giving the quantum effective action and not some proxy quantity. It has by now become the cornerstone of functional renormalization group ( #FRG ) methods. https://www.sciencedirect.com/science/article/pii/037026939390726X?via%3Dihub