Snowmass Theory Frontier Effective Field Theory Topical Group Summary October 10 2022

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Snowmass Theory Frontier
Effective Field Theory Topical Group Summary
October 10, 2022
Matthew Baumgart, Fady Bishara, Tomas Brauner, Joachim Brod, Giovanni Cabass, Timothy
Cohen, Nathaniel Craig, Claudia de Rham, Patrick Draper, A. Liam Fitzpatrick, Martin
Gorbahn, Sean Hartnoll, Mikhail Ivanov, Pavel Kovtun, Sandipan Kundu, Matthew Lewandowski,
Hong Liu, Xiaochuan Lu, Mark Mezei, Mehrdad Mirbabayi, Ulserik Moldanazarova, Alberto
Nicolis, Riccardo Penco, Walter Goldberger, Matthew Reece, Nicholas L. Rodd, Ira Rothstein,
Shu-Heng Shao, Will Shepherd, Marko Simonovic, Mikhail Solon, Dam Thanh Son, Robert
Szafron, Andrew Tolley, Zhengkang Zhang, Shuang-Yong Zhou, Jure Zupan
pdraper@illinois.edu, izr@andrew.cmu.edu
Submitted to the Proceedings of the US Community Study
on the Future of Particle Physics (Snowmass 2021)
arXiv:2210.03199v1 [hep-ph] 6 Oct 2022
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
1
observation across a huge range of physical systems. Thinking critically about the self-consistency of
our EFT descriptions of nature has also played an essential role in establishing the “big" questions
that physics should seek to answer. The major naturalness puzzles – the electroweak hierarchy
problem, the strong CP problem, and the cosmological constant problem – are strongly suggestive
of new dynamics and principles, and they continue to drive creative new theoretical approaches and
experimental designs in tandem [4]. At the same time, more formal studies of EFT have resulted
in new methods to constrain consistent low energy theories [2,9], exploiting basic principles both of
QFT and of quantum gravity. These approaches have lead to testable predictions about the possible
forms new physics can take.
EFTs have become an essential tool in many areas of physics and are continually being developed.
Given that the scientific output of any experiment is bounded by the accuracy of the theoretical
predictions, it is not an understatement to say that EFTs play a vital role in any scientific program.
The HEP community has leaned heavily on this formalism and the need for further developments
in this field is driven by experimental exigencies. Meanwhile more formal EFT research continues
to provide new tools for attacking some of the deepest questions in the field.
II. Dark Matter
It is difficult to overstate the scientific importance of the dark matter problem. This is evidenced
by the tremendous amount of resources presently being focussed to find the solution. The list of
experiments, both large and small, dedicated to this problem is an increasing function of time. The
reason for the challenging nature of DM detection is not difficult to discern given its name. The
design of an appropriate experiment involves some speculation as to the dark matter abundance
and interaction rate, and this relies heavily on the theoretical input which quantifies the reach of
an experiment in the space of DM parameters.
EFT has played in increasingly important role in both direct and indirect dark matter detec-
tion [3]. In case of the former, for heavy DM candidates (MMW), the cross section for DM
to interact with nuclei can be described a heavy particle effective theory which is derivative of the
heavy-quark effective theory (HQET). In the heavy mass limit spin-independent WIMP-nucleon
scattering cross sections become universal for given WIMP electroweak quantum numbers. More-
over, the EFT analysis revealed that the generic amplitude involved cancellations which suppress
the cross section orders of magnitude below naive estimates. Furthermore, working within the EFT,
one is able to systematically include the effects of QCD corrections. When the mediator mass is
larger than the momentum exchanges one can then write down as set of operators where by the DM
has contact interactions with nucleons, leading to a reduced operator basis which can be scanned
by experiment.
The nature of the relevant EFT changes when considering indirect detection, as now the physics
involves a semi-inclusive annihilation process. If the DM is charged under SU(2)LU(1)Y(or
another force with light mediators), then it is subject to a long-range potential (when MDM mW)
which can boost its annihilation rate via a so-called “Sommerfeld enhancement". Moreover, when
calculating the gamma ray spectrum from annihilation, the hierarchy of scales leads to large (double)
logarithms that may necessitate resummation. Thus the EFT in this case is richer as it must be
able to systematically describe both the Coulombic infra-red singularities as well as the soft and
collinear singularities which arise due to gauge boson emission. Since the DM velocity is smaller for
the signal events then in the early universe freeze-out, Coulombic corrections are more enhanced in
the former case.
To resum the Coulombically enhanced terms, which form a power series in the ratio mDM /mW,
one may lean upon NRQCD (Non-Relativistic QCD), the EFT developed to describe quarkonia in
2
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SnowmassTheoryFrontierEectiveFieldTheoryTopicalGroupSummaryOctober10,2022MatthewBaumgart,FadyBishara,TomasBrauner,JoachimBrod,GiovanniCabass,TimothyCohen,NathanielCraig,ClaudiadeRham,PatrickDraper,A.LiamFitzpatrick,MartinGorbahn,SeanHartnoll,MikhailIvanov,PavelKovtun,SandipanKundu,MatthewLewandows...

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