I. Introduction and Executive Summary
Quantum field theory is the fundamental mathematical structure describing the world. Not sur-
prisingly, its power and generality leads to overwhelming mathematical challenges in its application
to the real world, i.e., in non-idealized situations. A primary source of complexity arises from the
fact that typical physical systems depend upon physics arising from hierarchically distinct length
scales. However, given the local nature of physical laws, we may disentangle these scales in a way
that reduce the computational complexity for any given prediction. This procedure involves finding
the proper action to capture the physics at a particular length scale. These actions are constrained
by the symmetry breaking pattern which fixes the number of unknown parameters that either need
to be fit from experiment or calculated using the knowledge of the short distance theory. Finding a
systematic expansion within which to design these actions is the art of effective field theory (EFT).
EFTs were first utilized in a modern sense in describing pion physics and later the weak inter-
actions, though much of the physical insight, including the use of the renormalization group, came
from the realm of critical phenomena. While the EFT approach may be said to have been champi-
oned by the HEP community, it is has been utilized to great success in many fields and sub-fields of
physics, as described in various contributions to these proceedings. Here we summarize the recent
process and future opportunities reviewed in detail in the whitepapers [1–8].
Dark matter detection relies on EFTs for both direct and indirect measurements in various
contexts, including systematizing the low energy interactions with nuclei and re-summing large logs
in cosmic annihilation processes [3]. In cosmology, EFTs have been utilized to great success to
study Large Scale Structure (LSS) and inflation [1]. In particular, EFT calculations have led to
state-of-the-art predictions for cosmological parameters from the LSS data that compete with those
from the cosmic microwave background. In models of inflation, EFT techniques have been used to
place novel bounds on non-Gaussianities.
The ubiquitous nature of EFTs has lead to inter-disciplinary cross pollination. Condensed
Matter Physics (CMT) is another natural setting for EFT methods, where they has been utilized to
shed light on various systems, including out of equilibrium phenomena, hydrodynamics, and (non)
Fermi liquids [7]. Recently there has been a strong inter-disciplinary movement leveraging EFTs to
understand new exotic states of matter called “fractons." EFTs have also played an important role
in the nascent field of gravitational wave astronomy, with the development of an EFT to predict
the signatures of binary inspirals [8]. Scattering amplitudes techniques can be used within this
EFT to streamline-higher order calculations, much like in the case of QCD, and using these ideas,
state-of-the-art calculations have been performed by people within the HEP community. Given the
relative newness of this field and the wealth of new data, EFTs will play an important role in future
theoretical efforts.
EFTs also continue to play a central role in accelerator physics. Soft-Collinear Effective Theory
(SCET) has greatly improved our understand of factorization in high energy scattering, which
is a necessary ingredient for any theoretical prediction in order to disentangle the physics of the
proton from the high energy scattering process of interest. Moreover, SCET is utilized to sum large
logarithms which lead to poorly-behaved perturbative series. Its value has lead SCET to become
its own sub-field, with dedicated yearly conferences.
At the LHC, a core component of the search for new physics involves treating the Standard Model
as an effective theory (SMEFT) and looking for signatures associated with its higher dimensional
operators. There has been considerable progress in constraining the values of the Wilson coefficients
which capture the unknown UV physics of interest and systematizing calculational procedures [5,6].
The SMEFT formalism will continue to be a staple of experimental analyses.
The examples above highlight the critical role of EFTs in the direct comparison of theory with
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