REVIEW
A Resolution of the Flavor Problem of Two Higgs Doublet Models with an Extra U(1)_H Symmetry for Higgs Flavor
High Energy Physics - Phenomenology · Submitted 20 Apr 2012 · 26 references
Pith's verdict: The core idea — gauging Higgs flavor to kill tree-level FCNC — is clean and correct; the abstract's leptophobic/leptophilic claim is a property of one tuned completion, not of the Type-II/IV U(1)_H as such.
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Referee report
The paper
The paper claims
The paper proposes replacing the ad hoc discrete symmetry that suppresses Higgs-mediated flavor changing neutral currents in two-Higgs-doublet models with a local U(1) gauge symmetry acting on Higgs flavor, and works out what anomaly cancel
The reading
What carries the argument
The load-bearing object is the gauged Higgs-flavor charge assignment: two doublets with $h_1 neq h_2$ under $U(1)_H$, which makes the would-be flavor-changing operator $H_1^dagger H_2$ gauge non-invariant and simultaneously makes the determinant of the neutral gauge-boson mass matrix non-zero, Eq. (2). That single assignment does three jobs at once: it reproduces the Glashow-Weinberg NFC criterion, it removes the massless pseudoscalar by giving it to $Z_H$, and it forbids the soft $Z_2$-breaking term. The second piece of machinery is the anomaly-cancellation bookkeeping, which converts the requirement that the $U(1)_H$ be consistent into concrete charge relations among the Standard Model fermions, the two doublets, and extra vector-like chiral fields, with $3 hat{Q}_R hat{Q}_L + hat{n}_R hat{n}_L = 0$ for the $U(1)_H^3$ condition and further pairs added to cancel the $U(1)_Y U(1)_H^2$ mixed anomaly.
Extended reading notes
Core claim
The central claim is that natural flavor conservation in a two-Higgs-doublet model can be implemented by an extra local $U(1)_H$ symmetry for Higgs flavor rather than by a softly broken $Z_2$. Give $H_1$ and $H_2$ different charges $h_1 neq h_2$; then $H_1^dagger H_2$ and its square are forbidden in the scalar potential, so the potential reduces to the special case $m_3^2 = lambda_5 = 0$, and the massless pseudoscalar that would normally appear is absorbed by the $Z_H$ boson through the Higgs kinetic terms. Because the symmetry is local, the model does not need soft breaking and does not inherit the domain-wall problem of a spontaneously broken discrete symmetry. The authors then impose anomaly cancellation on the $U(1)_H$ charges and read off what survives in each of the four standard Type-I to Type-IV Yukawa assignments: Type-II becomes leptophobic, Type-IV leptophilic, and Type-I retains a two-parameter freedom whose simple points are $U(1)_{B-L}$, $U(1)_R$ and $U(1)_Y$. They also note that the $Z$-$Z_H$ mass mixing is constrained by the $rho$ parameter, Eq. (3), which limits how large the mixing and how light the new boson can be.
Load-bearing premise
The argument assumes that the anomaly-cancellation conditions can be satisfied for each type with the charge assignments and extra vector-like fermions the authors describe, without spoiling the leptophobic or leptophilic structure; for Type II the paper states that the $U(1)_Y U(1)_H^2$ anomaly is non-zero with the minimal matter content and defers the additional pairs to earlier work.
Editorial extensions
If this is right
- Every model in this class predicts a new neutral gauge boson $Z_H$ with couplings fixed by the $U(1)_H$ charges, plus a scalar singlet sector if the symmetry is broken away from the electroweak scale.
- The Type-II realization gives a leptophobic $Z_H$, which relaxes the LEP and Drell-Yan bounds that would otherwise push $m_{Z_H}/g_H$ above roughly 6 TeV in a $B-L$ model.
- The Type-IV realization gives a leptophilic $Z_H$, so the strongest existing constraints come from lepton searches rather than from dijet resonance searches.
- Anomaly cancellation requires extra chiral fermions in the Type-II and Type-IV cases, and some of these, together with a singlet scalar $X$ that does not acquire a vacuum expectation value, are stable and can serve as cold dark matter.
- Because there is no physical pseudoscalar $A$ in the minimal version, the usual CP-odd Higgs search channels are replaced by searches for $Z_H$ and for exotic Higgs decays such as $h to Z_H Z_H$.
Reading between the lines
- The construction suggests a general organizing principle: any multi-doublet model whose flavor protection is a gauge symmetry rather than a discrete parity automatically inherits a vector boson whose mass and couplings are correlated with the flavor structure, so flavor and resonance searches become the same measurement.
- If the Type-II charge assignment really is forced to be leptophobic by anomaly cancellation, then the model's collider signature is dijet resonances and $H^pm W^mp Z_H$ production rather than dilepton bumps, which is a qualitatively different search strategy from the usual $Z'$ hunting.
- The absence of a physical pseudoscalar in the minimal version is a sharp spectral prediction that distinguishes these models from a generic two-Higgs-doublet spectrum, and it could be tested by looking for the second CP-even state without a CP-odd partner of comparable mass.
- The paper's remark that the same structure underlies its earlier leptophobic flavor-dependent models hints that the gauge-symmetry reading may unify a family of apparently separate flavor constructions.
Original abstract
We propose to implement the Natural Flavor Conservation criterion in the two Higgs doublet model (2HDM) to an extra U(1)_H gauge symmetry for Higgs flavor, assuming two Higgs doublets carry different U(1)_H charges. Then one can easily avoid the tree level FCNC from neutral Higgs mediations using local gauge symmetries, instead of softly broken ad hoc Z_2 symmetry, and the pseudoscalar boson could be eaten by extra Z_H boson. Imposing the anomaly cancellation, we find that the U(1)_H in the Type-II and Type-IV 2HDM's become leptophobic and leptophilic, respectively. For the Type-I case, U(1)_H depends on two parameters, and some simple cases include U(1)_H = U(1)_{B-L}, U(1)_R, or U(1)_Y. We sketch qualitative phenomenology of these models.
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 propose to implement the Natural Flavor Conservation criterion in the two Higgs doublet model (2HDM) to an extra U(1)_H gauge symmetry for Higgs flavor, assuming two Higgs doublets carry different U(1)_H charges. Then one can easily avoid the tree level FCNC from neutral Higgs mediations using local gauge symmetries, instead of softly broken ad hoc Z_2 symmetry, and the pseudoscalar boson could be eaten by extra Z_H boson. Imposing the anomaly cancellation, we find that the U(1)_H in the Type-II and Type-IV 2HDM's become leptophobic and leptophilic, respectively. For the Type-I case, U(1)_H depends on two parameters, and some simple cases include U(1)_H = U(1)_{B-L}, U(1)_R, or U(1)_Y. We sketch qualitative phenomenology of these models.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We propose to implement the Natural Flavor Conservation criterion in the two Higgs doublet model (2HDM) to an extra U(1)_H gauge symmetry for Higgs flavor, assuming two Higgs doublets carry different U(1)_H charges. | contribution 0.96 | 0.80 | 0.21 | asserted 0.78 |
| s1 | Then one can easily avoid the tree level FCNC from neutral Higgs mediations using local gauge symmetries, instead of softly broken ad hoc Z_2 symmetry, and the pseudoscalar boson could be eaten by extra Z_H boson. | result 0.59 | 0.55 | 0.30 | hedged possibility 0.89 |
| s2 | Imposing the anomaly cancellation, we find that the U(1)_H in the Type-II and Type-IV 2HDM's become leptophobic and leptophilic, respectively. | result 1.00 | 0.92 | 0.22 | asserted 1.00 |
| s3 | For the Type-I case, U(1)_H depends on two parameters, and some simple cases include U(1)_H = U(1)_{B-L}, U(1)_R, or U(1)_Y. | result 0.97 | 0.82 | 0.08 | asserted 0.97 |
| s4 | We sketch qualitative phenomenology of these models. | contribution 0.96 | 0.83 | 0.04 | asserted 0.69 |
What was examined, and what was not
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References
How later papers used it
45 later papers cite it
1 paper by the same authors is listed below: 1 built on it.
Builds on it 1 paper · 1 by the same authors
By the same authors
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Extended its previous work on the new 2HDMs with U(1)_H Higgs symmetry.
Higgs phenomenology in Type-I 2HDM with U(1)_H Higgs gauge symmetry (2013) (same authors) · 1.00 · paraphrased: the licence does not allow quoting
How the literature uses it
43 arXiv papers cite this in 90 sentences
Papers citing it · 71 sentences without a confident label
Builds on it 1 paper
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In this paper, we extend our previous work about the new 2HDMs with $U(1)_H$ Higgs symmetry [ref] .
Higgs phenomenology in Type-I 2HDM with U(1)_H Higgs gauge symmetry · Introduction · 1.00
Compares with it 1 paper
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This structure of anomaly cancellation is similar to right-handed fermion specific $U(1)$ case [ref] where the extra charged lepton play a role of right-handed charged lepton in our case.
Lepton specific two-Higgs-doublet model based on a $U(1)_X$ gauge symmetry with dark matter · Model setup · 0.83
Cites it as support 1 paper
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For example, in the Type-II 2HDM$_U(1)$, which is the main subject of this work, there is no solution for the anomaly-free conditions without extra chiral fermions, as discussed in Ref. [ref] .
Higgs and Dark Matter Physics in the Type-II Two-Higgs-Doublet Model inspired by E_6 GUT · Introduction · 0.96
Cites it as background 16 papers
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In Refs. [ref] and [ref] , the authors proposed gauged $U(1)'$ symmetry to the SM fermions instead of $Z_2$ symmetry.
Top FB asymmetry vs. (semi)leptonic B decays in multi-Higgs-doublet models · Models with extra Higgs and gauged flavor $U(1)'$ · 0.91
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[ref] , gauged $U(1)'$ symmetry is assigned to the SM fermions and newly introduced extra Higgs doublets instead of $Z_2$ symmetry.
B -> D^(*) tau nu and B -> tau nu in chiral U(1)' models with flavored multi Higgs doublets · Models with extra Higgs and gauged flavor $U(1)'$ · 0.85
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Another intriguing and well-founded option is $U(1)_H$, initially proposed to tackle the significant flavor-changing neutral current (FCNC) issue in the two Higgs doublet model (2HDM) [ref] .
Explaining ATOMKI, $(g-2)_\mu$, and MiniBooNE anomalies with light mediators in $U(1)_H$ extended model · Introduction · 0.82
What it cites · 21 sentences without a confident label
Uses data or values from 1 paper
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Combination of their branching ratios deviates from the SM prediction by $3.4 σ$ [ref] .
Evidence for an excess of B -> D(*) Tau Nu decays · Phenomenology · 0.92
Cites as background 3 papers
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The 2HDMs have been studied in various contexts (see, for example, Ref. [ref] for a recent review).
Theory and phenomenology of two-Higgs-doublet models · Introduction · 1.00
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The Yukawa sectors can be controlled by assigning suitable $Z_2$ parities to the SM fermions, and the models are often categorized into four types as shown in Table [ref] [ref] .
Models of Yukawa interaction in the two Higgs doublet model, and their collider phenomenology · Introduction · 0.84
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In each type of 2HDMs, phenomenology of those Higgs bosons has been widely discussed in Refs. [ref] .
Studies on Extended Higgs Sectors as a Probe of New Physics Beyond the Standard Model · Phenomenology · 0.99
Discussion
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