### effective field theory

**(EFT)**
(type of useful simplification of a field theory)

An **effective field theory** (**EFT**) is a simplification
of a theory of a physical field aimed at giving a
usable approximation within a particular regime (e.g., within a
specific spatial scale). EFT replaces some of the "hard parts" of
the formulas with simpler expressions more amenable to manipulation
and calculation. EFTs are used in basically any branch of physics
that includes difficult field equations, including general relativity,
quantum mechanics, statistical mechanics, and fluid dynamics.

The above EFT description is loose and would fit the role of
classical and non-relativistic physics's relation to more modern
physics. However, the term was coined and is generally used for
more modern approximation methods such as those developed to deal
with regimes not amenable to classical physics, e.g., using an
approximation of the difference between the classical and the "modern
physics" result. One difficult problem tackled by EFT is many-body
quantum field theory (QFT) and an example is the exotic matter presumed to be in the
center of neutron stars. **Chiral EFT** is the name of a method
used to tackle it.

(*physics,mathematics*)
**Further reading:**

http://en.wikipedia.org/wiki/Effective_field_theory

http://home.thep.lu.se/~bijnens/talks/odense08.pdf

http://www.people.fas.harvard.edu/~hgeorgi/review.pdf

https://arxiv.org/abs/1804.05863

https://arxiv.org/abs/hep-ph/9806303

Index