REVIEW
Yukawa and Tri-scalar Processes in Electroweak Baryogenesis
High Energy Physics - Phenomenology · Submitted 8 Mar 2006 · 37 references
Pith's verdict: New decay/inverse-decay Yukawa rates and the breakdown of the fast-ΓY approximation are real, but the 20–100% Y_B claims rest on an unclosed transport system and an untested supergauge assumption.
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Referee report
The paper
The paper claims
Decays, not scatterings, dominate the Yukawa transport rate that feeds MSSM electroweak baryogenesis.
The reading
What carries the argument
The central object is the Closed Time Path (CTP) Schwinger-Dyson formulation of quantum transport, applied to three-body source terms through the rate functions $I_B$ (tri-scalar decays) and $I_F$ (Yukawa decays). These integrals encode thermally averaged decay, emission, and absorption rates with all mass-threshold and Bose/Fermi distribution structure, and they are what determine whether the $O(\alpha_s^0)$ channels are kinematically open; they enter the transport equations through $\Gamma_Y$ and $\bar{\Gamma}_Y$ in Eqs. (40a)-(40b). The reduction to a closed set of equations uses the chemical-potential equalities enforced by fast gauge and gaugino interactions, including the supergauge equilibrium condition $\mu_H = \mu_{\widetilde H}$ of Eq. (37), which lets Higgs and Higgsino densities be combined into the reduced set $(T,Q,H,h)$.
Extended reading notes
Core claim
On this paper's own terms, the central discovery is a hierarchy reversal in the transport equations: the coefficient $\Gamma_Y$ that couples Higgs-supermultiplet densities to third-generation quark-supermultiplet densities receives its leading contributions from two-body decay and inverse-decay channels---for example $t_R + \tilde t_L \leftrightarrow H_u^0$ and the analogous superpartner processes---at order $\alpha_s^0$, not from the $O(\alpha_s)$ scattering processes such as $t_R + g \to t_L + H_u^0$ on which earlier treatments focused. The paper derives the rate functions $I_B$ and $I_F$ for tri-scalar and Yukawa three-body sources, builds $\Gamma_Y$ and $\bar{\Gamma}_Y$ from them, and shows that for MSSM parameters consistent with a strong first-order phase transition and precision electroweak data the decay contributions are typically several times larger than the scattering contribution. It also derives the new coefficient $\tilde{\Gamma}_Y$ and shows $|\bar{\Gamma}_Y/\Gamma_Y| < 1/2$, the paper's correction to an earlier equality. Because the relaxation rates $\Gamma_H$ and $\Gamma_M$ computed in the same CTP framework are as large as or larger than $\Gamma_Y$ inside the bubble wall, the $1/\Gamma_Y$ expansion fails; numerically, the finite-$\Gamma_Y$ correction to $Y_B$ is 20% in the resonant case and up to 100% in the nonresonant case.
Load-bearing premise
The load-bearing premise is that gaugino-mediated interactions are fast enough during the phase transition to keep the Higgs scalars and their Higgsino partners in chemical equilibrium with a single chemical potential ($\mu_H = \mu_{\widetilde H}$); the paper explicitly defers a test of this assumption, and if it fails, the reduced transport equations and all numerical baryon-asymmetry results derived from them are not correct.
Editorial extensions
If this is right
- At MSSM parameter points where the relevant three-body decay channels are kinematically open, previous $O(\alpha_s)$ scattering estimates understate $\Gamma_Y$; when $\Gamma_Y$ is in the realistic few-GeV range, including the decay contributions changes $Y_B$ at the 10\u201320% level.
- The fast-$\Gamma_Y$ approximation should not be used: the $1/\Gamma_Y$ expansion misses $O(1)$ corrections to the Higgs density $H$, and therefore to $Q$ and $T$, so the transport equations must be solved numerically with finite $\Gamma_Y$.
- The earlier assumption $|\bar{\Gamma}_Y| = |\Gamma_Y|$ is not correct; for the MSSM parameters considered here $|\bar{\Gamma}_Y/\Gamma_Y| < 1/2$, making the $h/k_h$ term in the transport equations weaker than assumed.
- In large-$\tan\beta$ scenarios the new coefficient $\tilde{\Gamma}_Y$ and the bottom-quark supermultiplet densities are not suppressed, and the general formulas given in the paper let future calculations include them.
Reading between the lines
- The same $I_B$ and $I_F$ building blocks should transfer to extensions such as the NMSSM or $U(1)^\prime$ models, where a light stop is not needed for the phase transition; in those settings the tri-scalar $A$-dependent part of $\Gamma_Y$ may be relatively more important than in the MSSM benchmark studied here.
- A spectrum measurement has direct transport consequences: if future colliders place the relevant superpartner masses far from the threshold where the largest mass is just above the sum of the other two, the $O(\alpha_s^0)$ decay contribution is Boltzmann-suppressed and the fast-$\Gamma_Y$ approximation becomes more reliable; measuring the spectrum would therefore test which regime governs baryogen
- Because finite $\Gamma_Y$ raises $Y_B$ relative to the $\Gamma_Y \to \infty$ limit, the paper's results imply that slightly less CP violation is needed in the Higgs sector to match the observed baryon asymmetry, modestly easing the tension with electron and neutron EDM limits while preserving the conclusion that sleptons must be heavier than about 1 TeV.
Original abstract
We derive the contributions to the quantum transport equations for electroweak baryogenesis due to decays and inverse decays induced by tri-scalar and Yukawa interactions. In the Minimal Supersymmetric Standard Model (MSSM), these contributions give rise to couplings between Higgs and fermion supermultiplet densities, thereby communicating the effects of CP-violation in the Higgs sector to the baryon sector. We show that the decay and inverse decay-induced contributions that arise at zeroth order in the strong coupling, \alpha_s, can be substantially larger than the O(\alpha_s) terms that are generated by scattering processes and that are usually assumed to dominate. We revisit the often-used approximation of fast Yukawa-induced processes and show that for realistic parameter choices it is not justified. We solve the resulting quantum transport equations numerically with special attention on the impact of Yukawa rates and study the dependence of the baryon-to-entropy ratio Y_B on MSSM parameters.
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 derive the contributions to the quantum transport equations for electroweak baryogenesis due to decays and inverse decays induced by tri-scalar and Yukawa interactions. In the Minimal Supersymmetric Standard Model (MSSM), these contributions give rise to couplings between Higgs and fermion supermultiplet densities, thereby communicating the effects of CP-violation in the Higgs sector to the baryon sector. We show that the decay and inverse decay-induced contributions that arise at zeroth order in the strong coupling, \alpha_s, can be substantially larger than the O(\alpha_s) terms that are generated by scattering processes and that are usually assumed to dominate. We revisit the often-used approximation of fast Yukawa-induced processes and show that for realistic parameter choices it is not justified. We solve the resulting quantum transport equations numerically with special attention on the impact of Yukawa rates and study the dependence of the baryon-to-entropy ratio Y_B on MSSM parameters.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We derive the contributions to the quantum transport equations for electroweak baryogenesis due to decays and inverse decays induced by tri-scalar and Yukawa interactions. | contribution 0.99 | 0.96 | 0.09 | asserted 0.99 |
| s1 | In the Minimal Supersymmetric Standard Model (MSSM), these contributions give rise to couplings between Higgs and fermion supermultiplet densities, thereby communicating the effects of CP-violation in the Higgs sector to the baryon sector. | interpretation 0.61 | 0.69 | 0.12 | asserted 1.00 |
| s2 | We show that the decay and inverse decay-induced contributions that arise at zeroth order in the strong coupling, \alpha_s, can be substantially larger than the O(\alpha_s) terms that are generated by scattering processes and that are usually assumed to dominate. | result 1.00 | 0.93 | 0.63 | asserted 0.98 |
| s3 | We revisit the often-used approximation of fast Yukawa-induced processes and show that for realistic parameter choices it is not justified. | result 0.70 | 0.90 | 0.12 | asserted 1.00 |
| s4 | We solve the resulting quantum transport equations numerically with special attention on the impact of Yukawa rates and study the dependence of the baryon-to-entropy ratio Y_B on MSSM parameters. | method 0.64 | 0.97 | 0.13 | asserted 0.97 |
What was examined, and what was not
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Figures
Showing 6 of the paper's 8 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:hep-ph/0603058 by the authors.
References
How the literature uses it
27 arXiv papers cite this in 64 sentences
Papers citing it · 36 sentences without a confident label
Contests it 1 paper
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In addition, the Boltzmann equations of Refs. [ref] follow from Eqs. ([ref],b,[ref]); they too are no longer valid for $τ_yb,τ_yτ ≲τ_diff$.
Lepton-mediated electroweak baryogenesis · Setting up the Boltzmann equations · contest 0.83
Builds on it 2 papers
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The plot is based on our recent computation [ref] of the function $F_μ$ in Eq. ([ref]) that builds on our earlier treatment of the quantum transport during a supersymmetric electroweak phase transition [ref] .
Neutrons and the New Standard Model · EDMs and the Origin of Matter · 0.95
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Electroweak baryogenesis utilizing these sources in the MSSM has been extensively analyzed in recent studies (e.g. [ref] ), and we build on these analyses in our study of the accidental SUSY scenario.
Accidental Supersymmetric Dark Matter and Baryogenesis · Introduction · 0.96
Uses its method or tool 10 papers
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To obtain $Y_B$ as a function of the MSSM parameters, we rely on the work of Ref. [ref] , which include the parameter dependence of both the CPV source terms in the quantum Boltzmann equations as well as that of the CP-conserving, particle number-changing interactions.
MSSM Baryogenesis and Electric Dipole Moments: An Update on the Phenomenology · MSSM Baryogenesis and EDMs · 0.84
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With the above considerations, we calculate the baryon asymmetry following the techniques and assumptions detailed in Refs. [ref] .
Accidental Supersymmetric Dark Matter and Baryogenesis · The Baryon Asymmetry · 1.00
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We refer the reader to Ref. [ref] for the general form of $ℐ_F$, which is the form used in our numerical analysis.
Lepton-mediated electroweak baryogenesis · Determination of bottom/tau Yukawa rates · 0.86
Uses its data or values 1 paper
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The Yukawa-loop self energy function $I_F$ is taken from Ref. [ref] ,
Electroweak Baryogenesis with Vector-like Leptons and Scalar Singlets · Transport Equation Formulae · 0.89
Compares with it 2 papers
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In particular, we find that the EWB resonance found in previous treatments [ref] does persist somewhat in our more exact formalism.
Flavored Quantum Boltzmann Equations · Introduction · 0.93
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Modern summaries [ref] present a slightly different convention, writing \(Γ_ws= 6 κα_w^5T^4\), while [ref] , even though quoting [ref] , they use the numerical value $Γ_ws= 6.3×10^-6 T$.
Electroweak Baryogenesis with BARYONET: a self-contained review of the WKB approach · Reconciliation with the literature for Gamma_ws · 0.84
Cites it as support 1 paper
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Previous studies have shown that the solutions to the Boltzmann equations are insensitive to sub-$𝒪(1)$ variations in the interaction coefficients [ref] .
CP violation Beyond the MSSM: Baryogenesis and Electric Dipole Moments · Baryon Asymmetry Computation · 0.98
Cites it as background 7 papers
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Should one allow for additional source terms, such as non-resonant sources (see e.g. [ref] ) or sources associated with left-right stops, sbottoms or staus (see e.g. [ref] ), all of our conclusions would be weakened.
Closing in on Supersymmetric Electroweak Baryogenesis with Dark Matter Searches and the Large Hadron Collider · EWB and Bino-like Dark Matter · 0.81
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As discussed in Refs. [ref] , these scales include a decoherence time, $τ_d$, associated with the departure from adiabatic dynamics; a plasma time, $τ_p$, associated with mixing between degenerate states in the plasma; and an intrinsic quasiparticle evolution time, $τ_int$, associated with the time evolution of a state of a given energy.
Supergauge interactions and electroweak baryogenesis · Three-body rates: general formalism · 0.81
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The various issues of calculating the baryon asymmetry of the universe (BAU) in a given particle physics model are a subject of active research (see, for example, [ref] ).
Beyond MSSM Baryogenesis · Introduction · 1.00
Discussion
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