REVIEW
Making the small oblique parameters large
High Energy Physics - Phenomenology · Submitted 14 Sep 1993 · 8 references
Pith's verdict: A correct one-loop calculation with a real punchline — the S/T hierarchy is not general — but the unqualified J³ claim outruns the one-loop regime it's derived in.
T0 · AI review
Why Pith says this
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Referee report
The paper
The paper claims
For large scalar multiplets, the oblique parameters U and V can outgrow S and T, which are usually assumed to dominate electroweak precision physics.
The reading
What carries the argument
The engine is the one-loop vacuum-polarization function $F(M_1,M_2,P)$ for a scalar pair, together with the angular-momentum weights that appear in the couplings: the photon couples with strength proportional to $I+Y$, the $Z$ with $Ic_w^2 - Ys_w^2$, and the $W$ with $e/(c_w s_w)$ times $F(M_I,M_{I-1},P)$ weighted by $(J^2-I^2+J+I)$. Summing these weights over $I=-J$ to $J$ converts powers of $I$ into polynomials in $J$ of one degree higher, which is where the $J^3$ growth comes from: one factor of $J$ from the number of graphs in the loop, and two more from the squared isospin at the two SU(2) vertices. The behaviour of $T$ is controlled separately by the function $theta_+(M_1,M_2)$, whose expansion in powers of $(M_2-M_1)/(M_2+M_1)$ carries a compensating $1/J^n$, leaving only linear growth. The paper also verifies the decoupling theorem: as the common mass $M$ goes to infinity with splittings fixed, all six parameters fall off like $1/M$.
Extended reading notes
Core claim
The paper's claim is a reversal of the usual hierarchy among oblique parameters. For one complex scalar multiplet of weak isospin $J$ and hypercharge $Y$, with the squared masses of its components taken to be equally spaced, $M_I = M + I(M_2-M_1)/J$, and with the extreme masses $M_1$ and $M_2$ held fixed as $J$ increases, the parameter $U$ and the three newer parameters $V$, $W$ and $X$ grow with the cube of $J$, while $T$ grows only linearly and $S$ quadratically. The reason $T$ is the exception is that it depends quadratically rather than logarithmically on mass differences, so each power of the shrinking mass splitting $(M_2-M_1)/J$ costs a factor $1/J$. The paper closes with plots for $J=1,3,5$ showing that, at low $m_2$ with $m_1=150$ GeV, $U'$ and $V$ become the largest of the six, though a partial cancellation between the two pieces of $S$ keeps $S$ from growing as fast as its $J^2$ scaling alone would suggest.
Load-bearing premise
The scaling result rests on assuming that the squared masses of the multiplet's components are exactly equally spaced, $M_I = M + I(M_2-M_1)/J$, as produced by a single quartic coupling to one Higgs doublet with no mixing and no vacuum expectation value; if additional couplings or radiative corrections distorted that spacing, the sums over isospin that generate the $J^3$ growth would not go through as stated, and the paper does not examine how natural or stable that spectrum is at large $J$.
Editorial extensions
If this is right
- Fits to precision electroweak data should not assume that $S$ and $T$ are the only parameters that can be large; $V$ and $X$ enter the $Z$-pole and low-energy observables and must be included when new scalars sit near the $Z$ mass.
- A large scalar multiplet with masses of order $m_Z$ would show up most strongly through $U$ and $V$, which affect $m_W$ and the $W$ width, rather than through the $S$–$T$ plane alone.
- Decoupling survives: when the common multiplet mass is taken to infinity with the splittings held fixed, all six oblique parameters vanish like $1/M$, so the effect is confined to new physics near the electroweak scale.
- The growth with $J$ is generic to any scalar sector of large weak isospin, since it follows from the isospin weights at the two gauge vertices rather than from details of the potential.
Reading between the lines
- The $J^3$ result is really a statement about summing a tower with equally spaced masses; one could ask whether an analogous tower sum applies to higher-spin or fermionic multiplets, where the isospin weights differ.
- Because the fits quoted in the paper bound $V$ and $X$ at roughly $\pm 1$, the region where $U$ and $V$ dominate is likely already in tension with data unless cancellations occur; checking whether the partial $S'$–$S''$ cancellation the authors note for small $m_2$ extends to $V$ would sharpen this.
- If such multiplets exist, the leading experimental handle would be a shift in the $W$ mass or width rather than a $Z$-pole asymmetry, since $U$ and $W$ are the parameters that enter there.
Original abstract
We compute the oblique parameters, including the three new parameters $ V $, $ W $ and $ X $ introduced recently by the Montreal group, for the case of one scalar multiplet of arbitrary weak isospin $ J $ and weak hypercharge $ Y $. We show that, when the masses of the heaviest and lightest components of the multiplet remain constant, but $ J $ increases, the oblique parameter $ U $ and the three new oblique parameters increase like $ J^3 $, while $ T $ only increases like $ J $. For large multiplets with masses not much higher than $ m_Z $, the oblique parameters $ U $ and $ V $ may become much larger than $ T $ and $ S $.
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.
The abstract, sentence by sentence
We compute the oblique parameters, including the three new parameters $ V $, $ W $ and $ X $ introduced recently by the Montreal group, for the case of one scalar multiplet of arbitrary weak isospin $ J $ and weak hypercharge $ Y $. We show that, when the masses of the heaviest and lightest components of the multiplet remain constant, but $ J $ increases, the oblique parameter $ U $ and the three new oblique parameters increase like $ J^3 $, while $ T $ only increases like $ J $. For large multiplets with masses not much higher than $ m_Z $, the oblique parameters $ U $ and $ V $ may become much larger than $ T $ and $ S $.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We compute the oblique parameters, including the three new parameters $ V $, $ W $ and $ X $ introduced recently by the Montreal group, for the case of one scalar multiplet of arbitrary weak isospin $ J $ and weak hypercharge $ Y $. | contribution 0.98 | 0.94 | 0.04 | asserted 0.89 |
| s1 | We show that, when the masses of the heaviest and lightest components of the multiplet remain constant, but $ J $ increases, the oblique parameter $ U $ and the three new oblique parameters increase like $ J^3 $, while $ T $ only increases like $ J $. | result 1.00 | 0.94 | 0.62 | asserted 1.00 |
| s2 | For large multiplets with masses not much higher than $ m_Z $, the oblique parameters $ U $ and $ V $ may become much larger than $ T $ and $ S $. | result 0.82 | 0.86 | 0.59 | hedged possibility 1.00 |
What was examined, and what was not
- arXiv listing abstract v1
- full text
- figures and tables
- references and citing sentences
- relations to other papers
- P abstract
- S sections
- T body sentences
- C citations
- R cross-paper relations
Figures
Figures reproduced from arXiv:hep-ph/9309262 by the authors.
References
How the literature uses it
37 arXiv papers cite this in 55 sentences
Papers citing it · 31 sentences without a confident label
Contests it 1 paper
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Since there was a typo in the $U$ parameter in Ref. [ref] , we re-drive the expressions using the result in Ref. [ref] which computed the oblique parameters for generic scalar multiplets assuming their VEVs are negligibly small.
Towards deconstructing the simplest seesaw mechanism · Calculation of the oblique parameters $S$, $T$ and $U$ parameters · contest 0.87
Builds on it 1 paper
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Following the notations used in [ref] , [equation] where $s = sinθ_W$, and $c=√(1-s^2)$.
Precision Electroweak Constraints on Neutrinophilic Scalars · Contribution to Electroweak Oblique Parameters · 0.88
Uses its method or tool 8 papers
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Using the full expressions for the oblique parameters [ref] and neglecting the tree-level contribution from Eq. [ref] by making $v_Δ≪v$, we find the required values in the $λ_4$–$m_H$ plane that resolve the $m_W$ anomaly in Fig. [ref] (top).
W-boson mass in the triplet seesaw model · Introduction · 0.95
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We use the general expressions presented in [ref] .
Consistency of New CDF-II W Boson Mass with 123-Model · Bounds from the Electroweak Precision tests · 0.97
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At one loop level, we obtain the oblique parameters by choosing the weak isospin $J=1$ and hypercharge $Y=1$ in Ref. [ref] [equation] where the functions are defined as [equation] We find that the above functions are symmetric under the exchange of $x$ and $y$.
Electroweak precision tests for triplet scalars · $Y=1$ triplet scalar · 0.88
Compares with it 3 papers
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Thus, the contribution of a scalar multiplet $Φ_JY$ to $S$ can be written as [equation] Note that the expressions of $S_Φ_JY$ and $T_Φ_JY$ are consistent with those given in Ref. [ref] .
$W$-Boson Mass Anomaly from a General $SU(2)_{L}$ Scalar Multiplet · Calculation Details for the Scalar Multiplet Contributions to $T$ and $S$ · 0.99
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We reproduced the oblique parameters computed in [ref] and note that our results of $S$ and $T$ are consistent with a similar calculation in [ref] .
GUT origins of general electroweak multiplets and their oblique parameters · $Π_IJ(q^2)$ for the general scalar electroweak multiplets · 1.00
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Our result for $_S$ is consistent with the result in Ref. [ref] , first computed in [ref] .
The last Complex WIMPs standing · Electroweak precision observables · 0.99
Cites it as background 6 papers
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It is well known that the triplet can affect the values of the oblique parameters, in particular the $S$ and $T$ parameters [ref] .
Scalar phenomenology in type-II seesaw model · Introduction · 0.80
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The new triplet Higgs bosons contribute to the electroweak precision observables, namely, the S,T, U parameters [ref] .
Revisiting the high-scale validity of Type-II seesaw model with novel LHC signature · Theoretical and Experimental constraints · 0.86
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In this section we analyze the impact of constraints arising from electroweak precision measurements, especially the oblique parameters [ref] on our model.
Revisiting Generalized Two Higgs Doublet Model in the Light of Muon Anomaly and Lepton Flavor Violating Decays at HL-LHC · Electroweak constraints · 0.91
Discussion
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