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One-loop Effective Lagrangian for a Standard Model with a Heavy Charged Scalar Singlet

High Energy Physics - Phenomenology · Submitted 18 Oct 1993 · 82 references

Pith's verdict: A careful, auditable one-loop matching calculation for a toy singlet model; the methodology section is the part worth keeping, the phenomenology is thin.

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arXiv IDhep-ph/9310302 (version 1)
Pith IDMXMEBLPF, Pith's permanent record of this paper and its review
CitationArcadi Santamaria, Mikhail Bilenky. "One-loop Effective Lagrangian for a Standard Model with a Heavy Charged Scalar Singlet." arXiv:hep-ph/9310302 (1993). https://pith.science/paper/MXMEBLPF
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Referee report
The paper

The paper claims

The paper works out, end to end, how to replace a heavy charged scalar with a local effective Lagrangian and checks that the replacement reproduces the full theory at one loop.

The reading

The authors take the Standard Model, add a singly charged scalar singlet $h$ that couples only to the lepton doublet through an antisymmetric matrix $f$ in flavour space, and then ask what the theory looks like at energies far below the scalar's mass $m$. They integrate $h$ out at one loop and expand the result in $1/m^2$, keeping operators up to dimension six, so that all the heavy particle's effects are packaged in a local Lagrangian built from light fields alone. The point is not the model itself but the procedure: how to obtain such a Lagrangian, how to renormalize it, how to match its couplings to the full theory, and how to tell which of its operators can be bounded by experiment and which cannot. The reward is a concrete, fully calculable example in which every step of the effective-Lagrangian programme can be checked against an honest renormalizable calculation, including a side-by-side comparison of the flavour-changing decay $Z$ into two different charged leptons.

What carries the argument

Two devices carry the argument. The first is the functional determinant: writing the one-loop effective action as $S_{eff} = S_{SM} + S_h[h_0] + i,mathrm{Tr},log(O)$ with fluctuation operator $O = -D^2 - m^2 - beta phi^dagger phi$, and expanding $mathrm{Tr},log$ in $1/m^2$ using the constant-field trick of appendix A, which trades a general gauge configuration for a constant matrix $N_mu$ with $U = -N^2$ and then inverts the map back to the general case. This yields eq. (A.27), a compact basis of gauge-invariant traces that would be tedious to obtain diagram by diagram. The second device is propagator splitting, $1/(k^2 - m^2) = -1/m^2 + k^2/(m^2(k^2 - m^2))$: the first piece is exactly what the effective four-fermion vertex gives, and the second piece is exactly the counterterm the effective Lagrangian must supply. That identity is what makes matching systematic rather than a guess, and it is why the divergent parts of the higher-dimension operators are fixed by the effective theory's own loops while their finite parts can only come from the full theory.

Extended reading notes

Core claim

The paper's central claim is that the Lagrangian of eq. (4.20) — the Standard Model, plus the tree-level four-lepton operator $(1/m^2)(~ell f ell)(ell f^dagger ~ell)$ of eq. (3.11), plus the one-loop determinant contribution of eq. (3.15), plus the matching terms of eq. (4.21) — reproduces the full renormalizable theory for light external particles, at one loop and through order $1/m^2$. The construction is done in two complementary halves. Functional methods give, in closed gauge-invariant form, all operators generated by diagrams with only the heavy scalar in internal lines: the determinant of the fluctuation operator $-D^2 - m^2 - beta phi^dagger phi$ is expanded in $1/m^2$, yielding dimension-four pieces that are absorbed into redefinitions of the Standard Model mass, quartic coupling and $U(1)_Y$ coupling, and dimension-six pieces that survive. The remaining operators come from matching: the authors compute self-energies, penguin vertices, seagull diagrams and boxes in the full theory, subtract the corresponding effective-theory diagrams, and read off the local counterterms that make the two agree at low momentum. The payoff is a check on a real process: the full-theory amplitude for $Z to e_a e_b$ in eq. (C.4) and the effective-theory amplitude in eq. (C.2) coincide as $m gg M_Z$, and figure 7 shows the two branching ratios converging once the scalar is heavier than the $Z$.

Load-bearing premise

The operator basis is reconstructed from a small set of Green functions, and in one case — the term proportional to $p!!!/ p^2$ — the promotion of a derivative to a covariant derivative is ambiguous between three inequivalent forms, resolved only by computing extra diagrams with external gauge bosons and checking a three-gauge-boson amplitude at zero external momentum.

Editorial extensions

If this is right

  • Any process mediated by the heavy scalar at energies below its mass can be computed entirely within the effective theory, with the scalar's unknown mass and couplings entering only through the matching conditions of eqs. (5.1)–(5.5).
  • The effective couplings obey a renormalization-group equation controlled by an anomalous-dimension matrix; in the two-operator example of eqs. (5.9)–(5.10), the mixing of the four-lepton operator into the penguin operator is computable, but its boundary value is not.
  • Without knowledge of the full theory, a one-loop effective-Lagrangian calculation can relate an operator's coefficient at one scale to its value at another, but cannot predict its size; only experiment or a more complete theory supplies the missing boundary conditions.
  • After spontaneous symmetry breaking the model predicts lepton-flavour-violating processes — $Z to e_a e_b$, $mu to e gamma$, $mu^- to e^- e^- e^+$, $tau^- to e^+ mu^- e^-$ — with rates set by the antisymmetric coupling matrix $f$ and falling as $1/m^2$.
  • The naturalness problem reappears, in dimensional regularization, purely as a fine-tuning in the matching condition for the Higgs mass parameter, eq. (5.2), rather than as a quadratic divergence.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The paper is a template as much as a result: the same two-step recipe — determinant for heavy-only loops, propagator splitting for heavy-light loops — applies to any extension in which a complete gauge multiplet is integrated out, which is why the authors can claim gauge invariance of the effective theory without arguing for it separately.
  • The observation that a bound on one operator implies a bound on another only when the underlying theory is known is a caution against reading a single-operator analysis as a measurement of new-physics scale; in this model the ratio $c_2(m)/c_1(m) = 10 g'^2/(9(4pi)^2)$ is a fixed prediction, so a future precision measurement of both coefficients would over-determine the model and could exclude it.
  • The comparison in figure 7 suggests a practical diagnostic for any such effective theory: the size of the discrepancy between full and effective amplitudes at $m$ near $M_Z$ indicates where the $1/m^2$ expansion stops being trustworthy, and could be used to set the mass reach of a given experiment rather than assuming it.
  • Because the scalar couples only through an antisymmetric matrix, the leading flavour-violating effects are necessarily off-diagonal, so the same coefficient that drives $Z to tau e$ also drives $mu to e gamma$; the two are not independent handles on the new physics.
Original abstract

We study several problems related to the construction and the use of effective Lagrangians by considering an extension of the standard model that includes a heavy scalar singlet coupled to the leptonic doublet. Starting from the full renormalizable model, we build an effective field theory by integrating out the heavy scalar. A local effective Lagrangian (up to operators of dimension six) is obtained by expanding the one-loop effective action in inverse powers of the heavy mass. This is done by matching some Green functions calculated with both the full and the effective theories. Using this simple example we study the renormalization of effective Lagrangians in general and discuss how they can be used to bound new physics. We also discuss the effective Lagrangian after spontaneous symmetry breaking, and the use of the standard model classical equations of motion to rewrite it in different forms. The final effective Lagrangian in the physical basis is well suited to the study of the phenomenology of the model, which we comment on briefly. Finally, as an example of the use of our effective field theory, we consider the leptonic flavour-changing decay of the $Z$ boson in the effective theory and compare the results obtained with the full model calculation.

The compiled record

The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

Compiled by classifier-1.13-20260917 via OpenRouter, question bank abstract-p1-20260923, 2026-09-23: 1 request, 6,292 input tokens, $0.0003 reported.

What the abstract itself states, as probabilities: claims first 0.03 · states limitation 0.22 · human participants 0.01 · controlled comparison 0.14 · randomized assignment 0.01 · states quantitative result 0.06 · compares with prior results 0.69 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v1. Results and the main claim are underlined; .

We study several problems related to the construction and the use of effective Lagrangians by considering an extension of the standard model that includes a heavy scalar singlet coupled to the leptonic doublet. Starting from the full renormalizable model, we build an effective field theory by integrating out the heavy scalar. A local effective Lagrangian (up to operators of dimension six) is obtained by expanding the one-loop effective action in inverse powers of the heavy mass. This is done by matching some Green functions calculated with both the full and the effective theories. Using this simple example we study the renormalization of effective Lagrangians in general and discuss how they can be used to bound new physics. We also discuss the effective Lagrangian after spontaneous symmetry breaking, and the use of the standard model classical equations of motion to rewrite it in different forms. The final effective Lagrangian in the physical basis is well suited to the study of the phenomenology of the model, which we comment on briefly. Finally, as an example of the use of our effective field theory, we consider the leptonic flavour-changing decay of the $Z$ boson in the effective theory and compare the results obtained with the full model calculation.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
s0 We study several problems related to the construction and the use of effective Lagrangians by considering an extension of the standard model that includes a heavy scalar singlet coupled to the leptonic doublet. contribution 0.98 0.93 0.07 asserted 0.95
s1 Starting from the full renormalizable model, we build an effective field theory by integrating out the heavy scalar. method 0.98 0.95 0.05 asserted 1.00
s2 A local effective Lagrangian (up to operators of dimension six) is obtained by expanding the one-loop effective action in inverse powers of the heavy mass. method 0.88 0.94 0.15 asserted 1.00
s3 This is done by matching some Green functions calculated with both the full and the effective theories. method 1.00 0.90 0.03 asserted 1.00
s4 Using this simple example we study the renormalization of effective Lagrangians in general and discuss how they can be used to bound new physics. contribution 0.98 0.91 0.13 asserted 0.99
s5 We also discuss the effective Lagrangian after spontaneous symmetry breaking, and the use of the standard model classical equations of motion to rewrite it in different forms. contribution 0.75 0.86 0.05 asserted 0.86
s6 The final effective Lagrangian in the physical basis is well suited to the study of the phenomenology of the model, which we comment on briefly. interpretation 0.52 0.85 0.16 asserted 0.99
s7 Finally, as an example of the use of our effective field theory, we consider the leptonic flavour-changing decay of the $Z$ boson in the effective theory and compare the results obtained with the full model calculation. contribution 0.83 0.94 0.13 asserted 0.96

What kind of paper the classifier reports this is: theoretical result 0.96 · evidence from proof or derivation 1.00.

What was examined, and what was not

sources read
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  • figures and tables
  • references and citing sentences
  • relations to other papers
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Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures
Figure 1. Diagram a) is the tree-level diagram contributing to the effective Lagrangian. The solid lines represent lepton doublets and the thick dashed line represents the heavy scalar. Diagram b) represents the four-lepton interaction in the effective theory. The symbol ⊗ means a scalar current insertion
Figure 5. fig. 5.c, we get the amplitude (B.5), which can be obtained fro

Showing 2 of the paper's 5 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:hep-ph/9310302 by the authors.

References
How the literature uses it

32 arXiv papers cite this in 42 sentences

Each citing sentence is taken from the citing paper's LaTeX source and typed by Pith's classifier. A label appears at probability 0.8 or more (0.95 for support), a contest at 0.7 or more; the quoted words are the citing authors'. How each label was checked · JSON

Papers citing it · 23 sentences without a confident label

Uses its method or tool 3 papers
  • A convenient normalization of this expansion fixes the $c_k$ coefficients as [equation] As already commented, the $O_k$ are combinations of traces of dimension–2$k$ operators, so that, in general, they should have the form [equation] For the first values of $k$ ($=1,2,3$), we shall employ the following sets as bases: [equation] The method proposed in Ref. [ref] relies on the fact that Eqs.([ref]), ([ref]) and ([ref]) are valid for any field configuration.

    Gauge invariance, quantization and integration of heavy modes in a gauge Kaluza-Klein theory · Extra–dimensional physics versus fundamental description · 0.94

  • We now use a slightly adapted form of a trick explained in the Appendix of [ref] : We evaluate expression ([ref]) in the special configuration $∂_μX̂_ν= ∂_μŶ=0$, allowing us to drop all derivatives.

    Two-Higgs Doublet Model Matched to Nonlinear Effective Theory · One-loop matching of $h^n X_μνX^μν$ to all orders in $n$ · 0.98

  • We carry out the integration [For a detailed example of the integration procedure in the case of a singly-charged scalar see [ref] . ] by using the equations of motion for $E$ and expanding in powers of $1 / m_E$.

    Exotic properties of neutrinos using effective Lagrangians and specific models · Lepton Flavour Violating processes · 0.88

Compares with it 3 papers
Cites it as background 10 papers
  • This is due to the so called non-decoupling effects (see e.g., [ref] ), induced by loop corrections, that survive in the large mass limit of the BSM particles living in the theory assumed to be valid at high energies.

    Decoupling Limits in Effective Field Theories via Higher Dimensional Operators · Introduction · 0.85

  • This indeed is the opposite of conventional analyses where one starts with a UV theory, identifies certain degrees of freedom as heavy and after suitably integrating out obtains a subset of the effective Lagrangian, i.e., higher mass dimension operator basis, of a low energy theory [ref] .

    EFT Diagrammatica: UV Roots of the CP-conserving SMEFT · Unfolding effective operators into Lorentz invariant vertices · 0.90

  • There are only few available examples of complete or partial one-loop matching for the SM extended with a charged scalar singlet [ref] , a real scalar singlet [ref] , a real scalar triplet [ref] , a vector-like quark singlet [ref] , a light sterile neutrino and heavy fermions and a scalar singlet [ref] , and two scalar leptoquarks [ref] by either diagrammatic calculations or functional approaches [ref] .

    Radiative Decays of Charged Leptons in the Seesaw Effective Field Theory with One-loop Matching · Introduction · 0.88

Discussion

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