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How to use the Standard Model effective field theory
We present a practical three-step procedure of using the Standard Model
effective field theory (SM EFT) to connect ultraviolet (UV) models of new
physics with weak scale precision observables. With this procedure, one can
interpret precision measurements as constraints on a given UV model. We give a
detailed explanation for calculating the effective action up to one-loop order
in a manifestly gauge covariant fashion. This covariant derivative expansion
method dramatically simplifies the process of matching a UV model with the SM
EFT, and also makes available a universal formalism that is easy to use for a
variety of UV models. A few general aspects of RG running effects and choosing
operator bases are discussed. Finally, we provide mapping results between the
bosonic sector of the SM EFT and a complete set of precision electroweak and
Higgs observables to which present and near future experiments are sensitive.
Many results and tools which should prove useful to those wishing to use the SM
EFT are detailed in several appendices.Comment: 99 pages, 11 figures. V2: Typos corrected, references added. Fixed a
link to Mathematica notebook for download. Substantial text changes for
clarification with no change in results. In particular, sections 2.5, 3, and
5 received clarifying edits. Additionally, results from part of appendix A
have been separated out to a new appendi
Operator bases, -matrices, and their partition functions
Relativistic quantum systems that admit scattering experiments are
quantitatively described by effective field theories, where -matrix
kinematics and symmetry considerations are encoded in the operator spectrum of
the EFT. In this paper we use the -matrix to derive the structure of the EFT
operator basis, providing complementary descriptions in (i) position space
utilizing the conformal algebra and cohomology and (ii) momentum space via an
algebraic formulation in terms of a ring of momenta with kinematics implemented
as an ideal. These frameworks systematically handle redundancies associated
with equations of motion (on-shell) and integration by parts (momentum
conservation).
We introduce a partition function, termed the Hilbert series, to enumerate
the operator basis--correspondingly, the -matrix--and derive a matrix
integral expression to compute the Hilbert series. The expression is general,
easily applied in any spacetime dimension, with arbitrary field content and
(linearly realized) symmetries.
In addition to counting, we discuss construction of the basis. Simple
algorithms follow from the algebraic formulation in momentum space. We
explicitly compute the basis for operators involving up to scalar fields.
This construction universally applies to fields with spin, since the operator
basis for scalars encodes the momentum dependence of -point amplitudes.
We discuss in detail the operator basis for non-linearly realized symmetries.
In the presence of massless particles, there is freedom to impose additional
structure on the -matrix in the form of soft limits. The most na\"ive
implementation for massless scalars leads to the operator basis for pions,
which we confirm using the standard CCWZ formulation for non-linear
realizations.Comment: 75 pages plus appendice
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