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Yukawa sector in non-supersymmetric renormalizable SO(10)

High Energy Physics - Phenomenology · Submitted 11 Oct 2005 · 48 references

Pith's verdict: A clean 126+120 non-SUSY SO(10) construction: the neutrino-mass/θ_A correlation survives scrutiny, but the Vcb–θ_A relation misses by a factor of ~7 inside its own two-generation truncation.

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arXiv IDhep-ph/0510139 (version 2)
Pith IDHWYDMHUA, Pith's permanent record of this paper and its review
CitationAlejandra Melfo, Borut Bajc, Francesco Vissani, Goran Senjanovic. "Yukawa sector in non-supersymmetric renormalizable SO(10)." arXiv:hep-ph/0510139 (2005). https://pith.science/paper/HWYDMHUA
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The paper

The paper claims

In a non-supersymmetric SO(10) grand unified theory built from Higgs fields in the 126 and 120 representations, two-generation analytic relations tie the neutrino mass splitting, and the small quark mixing $V_{cb}$, to how far the measured

The reading

The paper asks whether ordinary, non-supersymmetric SO(10) grand unification can host a realistic and predictive account of fermion masses, given that the renormalizable see-saw mechanism forces a $126_H$ and that a second Higgs representation is needed to generate any mixing at all. The authors construct the two minimal Yukawa sectors, $126_H$ with $10_H$ and $126_H$ with $120_H$, and show that the first cannot work with a real $10_H$: the ratio that a real bidoublet forces comes out of order $m_t/m_b$, far from one. Complexifying the Higgs then invites a Peccei-Quinn symmetry, which supplies an axion dark matter candidate and solves the strong CP problem as a by-product. The centre of the paper is the $126_H+120_H$ case, where a two-by-two treatment of the second and third generations produces closed-form relations among the atmospheric mixing angle, the neutrino mass splitting, the bottom-to-tau mass ratio, and $V_{cb}$. The claim a sympathetic reader should take away is that in this model large leptonic mixing and small quark mixing are not independent accidents but two readings of the same angle.

What carries the argument

The load-bearing device is a two-by-two parametrisation of the mass matrices in the basis where the $126_H$ Dirac matrix is $M_1 propto diag(sin^2 theta, cos^2 theta)$, with the antisymmetric $120_H$ contribution entering as a single off-diagonal structure. Expanding the diagonalising matrices $L_f$ and $R_f$ to first order in the small parameters $epsilon_f$ turns each fermion sector into two equations, one fixing the third-generation mass scale and one fixing the ratio of second to third generation masses times $sin 2theta$. The mechanism that makes the model predictive is that the type I see-saw mass matrix $M_N^I propto 9c_1^2 M_1 - c_4^2 M_2 M_1^{-1} M_2$ and the type II contribution $M_N^{II} propto M_1$ both reduce to the same diagonal structure, so the angle already fixed by the charged fermions is the leptonic mixing angle, and the neutrino masses are read off directly from the same $sin^2 theta$ and $cos^2 theta$ entries.

Extended reading notes

Core claim

Working in the basis where the $126_H$ contribution $M_1$ is diagonal and proportional to $diag(0,1)$ after a rotation by $theta$, the authors write the charged-fermion mass matrix as $M_f = mu_f$ times a two-by-two matrix whose off-diagonal entries are $i(sin theta cos theta + epsilon_f)$, with $epsilon_f$ scaling as the second-generation mass over the third. Diagonalising to leading order in $epsilon_f$ gives $|mu_f| = m_{f3}$ and $sin 2theta |epsilon_f| = m_{f2}/m_{f3}$. Because both the type I and type II see-saw contributions come out proportional to $M_1$, the same angle $theta$ controls the neutrino sector, and it is identified with the atmospheric mixing angle $theta_A$ up to corrections of order $m_mu/m_tau$. Three relations follow: the fractional neutrino mass splitting equals $cos 2theta_A/(1 - sin^2 2theta_A/2)$ up to $O(epsilon)$, so neutrino degeneracy is measured by how close $theta_A$ is to maximal; $m_tau/m_b = 3 + 3 sin 2theta_A Re[epsilon_E - epsilon_D]$; and $|V_{cb}| = |Re xi - i cos 2theta_A Im xi|$ with $xi = cos 2theta_A (epsilon_D - epsilon_U)$. The last two pull in opposite directions from the first: fitting the small $V_{cb}$ wants $cos 2theta_A$ as large as possible, that is, $theta_A$ as far from $45^circ$ as the data allow.

Load-bearing premise

The relations carry quantitative weight only if dropping the first generation and the loop corrections is genuinely a small perturbation, an assumption the authors state and then explicitly say leaves the $V_{cb}$ prediction and the model itself unjudged.

Editorial extensions

If this is right

  • If the relation holds after running and after including the first generation, the atmospheric mixing angle stops being a free parameter and becomes a measurement of how degenerate the two heavier neutrinos are.
  • A value of $theta_A$ measurably away from $45^circ$ is what allows $V_{cb}$ to come out small, so the observed pattern of one large leptonic and one small quark mixing angle is explained rather than assumed.
  • The model's prediction $m_tau/m_b \approx 3$ at the unification scale sits against the Standard Model extrapolation of about 2, so the charged-lepton and down-quark sectors must receive corrections of order ten to twenty percent from phases, the large Dirac Yukawa coupling, or the full three-flavour fit.
  • Complexifying either $10_H$ or $120_H$ brings in a Peccei-Quinn symmetry whose breaking scale is tied to the right-handed neutrino mass scale, giving axion dark matter in a theory that otherwise has no stable neutral candidate.
  • The symmetry-breaking analysis restricts viable patterns to those with an intermediate Pati-Salam scale and $M_R$ above roughly $10^{13}$ GeV, which is what the see-saw needs to keep the heaviest neutrino heavy enough.

Reading between the lines

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

  • The relation between $theta_A$ and the neutrino mass splitting is stated for the two heavier states only; if it survived a three-generation fit, a near-maximal $theta_A$ would be in tension with the atmospheric mass splitting being the larger one, which is a sharper handle than the paper's own numerical remark that $m_2 > 30$ meV.
  • Because $V_{cb}$ and the neutrino degeneracy both depend on $cos 2theta_A$, a future precision measurement of $theta_A$ would over-determine the framework: the same number would have to reproduce both the quark mixing and the neutrino mass ratio, so the two tests are not independent checks but one check made twice.
  • The Peccei-Quinn symmetry is introduced to fix a fermion-mass problem, not a cosmological one, and its scale is pinned near the right-handed neutrino scale; this makes the axion mass a derived quantity in this class of models rather than a free parameter, which is a prediction that could be confronted with axion searches.
  • The paper's own escape hatch, that neglected first-generation effects and loops prevent a verdict on the $V_{cb}$ relation, is the natural place for a follow-up: a full three-generation numerical fit including two-loop Yukawa running would either confirm the correlation or retire it.
Original abstract

We discuss the ordinary, non-supersymmetric SO(10) as a theory of fermion masses and mixings. We construct two minimal versions of the Yukawa sector based on $\bar{126}_H $ and either $10_H$ or $120_H$. The latter case is of particular interest since it connects the absolute neutrino mass scale with the size of the atmospheric mixing angle $\theta_A$. It also relates the smallness of $V_{cb}$ with the largeness of $\theta_A$. These results are based on the analytic study of the second and third generations. Furthermore, we discuss the structure of the light Higgs and the role of the Peccei-Quinn symmetry for dark matter and the predictivity of the theory.

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, 4,873 input tokens, $0.0002 reported.

What the abstract itself states, as probabilities: claims first 0.03 · states limitation 0.57 · human participants 0.01 · controlled comparison 0.02 · randomized assignment 0.01 · states quantitative result 0.08 · compares with prior results 0.08 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v2. Results and the main claim are underlined; .

We discuss the ordinary, non-supersymmetric SO(10) as a theory of fermion masses and mixings. We construct two minimal versions of the Yukawa sector based on $\bar{126}_H $ and either $10_H$ or $120_H$. The latter case is of particular interest since it connects the absolute neutrino mass scale with the size of the atmospheric mixing angle $\theta_A$. It also relates the smallness of $V_{cb}$ with the largeness of $\theta_A$. These results are based on the analytic study of the second and third generations. Furthermore, we discuss the structure of the light Higgs and the role of the Peccei-Quinn symmetry for dark matter and the predictivity of the theory.

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 discuss the ordinary, non-supersymmetric SO(10) as a theory of fermion masses and mixings. background 0.54 0.63 0.05 asserted 0.91
s1 We construct two minimal versions of the Yukawa sector based on $\bar{126}_H $ and either $10_H$ or $120_H$. contribution 0.98 0.95 0.07 asserted 1.00
s2 The latter case is of particular interest since it connects the absolute neutrino mass scale with the size of the atmospheric mixing angle $\theta_A$. interpretation 0.48 0.77 0.28 asserted 0.97
s3 It also relates the smallness of $V_{cb}$ with the largeness of $\theta_A$. result 0.86 0.84 0.18 asserted 1.00
s4 These results are based on the analytic study of the second and third generations. method 0.84 0.86 0.06 asserted 1.00
s5 Furthermore, we discuss the structure of the light Higgs and the role of the Peccei-Quinn symmetry for dark matter and the predictivity of the theory. contribution 1.00 0.83 0.08 asserted 0.82

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

What was examined, and what was not

sources read
  • arXiv listing abstract v2
not examined
  • full text
  • figures and tables
  • references and citing sentences
  • relations to other papers
levels run
  • P abstract
not run
  • S sections
  • T body sentences
  • C citations
  • R cross-paper relations

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

References
How the literature uses it

55 arXiv papers cite this in 116 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 · 83 sentences without a confident label

Cites it as support 5 papers
Cites it as background 22 papers

Discussion

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