REVIEW
Baryogenesis from mixed particle decays
High Energy Physics - Phenomenology · Submitted 26 Nov 1996 · 20 references
Pith's verdict: A clean, self-contained extension of the Liu–Segrè mixing formalism to arbitrary mass splittings, with the peak at splitting ~ width derived rather than assumed; the leptogenesis application is honest about its initial-state caveat.
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Referee report
The paper
The paper claims
The paper derives the integrated CP asymmetry from mixing of two heavy scalars at arbitrary mass splitting and shows it peaks when the squared mass difference is of order the squared decay widths, with an application to sneutrino leptogénes
The reading
What carries the argument
The mechanism is the wave-function contribution: a loop of light particles mixes the decaying heavy state with a second heavy state before it decays. The load-bearing object is the non-Hermitian effective squared-mass matrix $H^2=M^2-iGamma^2$, whose imaginary part $Gamma^2$ comes from absorptive loops. It is diagonalized by a non-unitary matrix $V$, so the propagation eigenstates are not orthonormal; the mismatch between production and propagation bases generates the asymmetry. The integrated result is controlled by $F_1$ in Eq. (21), which encodes the competition between the mass splitting and the widths and produces the peak at $M_2^2-M_1^2simGamma^2$.
Extended reading notes
Core claim
The central claim is that the mixing, or wave-function, CP asymmetry in the decay of a heavy scalar is governed by Eq. (20) with the function $F_1$ of Eq. (21), and that for arbitrary mass splittings this function has a maximum at $M_2^2-M_1^2simeq Gamma_1^2+Gamma_2^2$ when $|Gamma_{12}^2|$ is small compared with $|Gamma_{22}^2-Gamma_{11}^2|$, with peak value $F_1simeq M_1/[Gamma_1^2(Gamma_1^2+Gamma_2^2)]$. In the large-splitting limit $F_1$ reduces to the earlier result, while for the sneutrino leptogenesis application the summed asymmetry is given by Eq. (29). The authors emphasize that the result depends on the initial state: they take the produced state to be a mass eigenstate, $M_{12}^2=0$, and warn that ignoring mixing at production gives incorrect asymmetries.
Load-bearing premise
The leptogenesis application assumes that the heavy scalar is produced as an eigenstate of the renormalized mass matrix, $M_{12}^2=0$, and the paper itself warns that a different production basis changes the asymmetry without supplying a general production prescription.
Editorial extensions
If this is right
- Near-degenerate heavy scalars with a mass splitting of order their widths can generate a wave-function CP asymmetry much larger than the large-splitting estimate, so leptogenesis may require smaller Yukawa couplings or CP phases.
- The enhancement is resonant in the mass splitting, peaking at $M_2^2-M_1^2simeq Gamma_1^2+Gamma_2^2$ when the off-diagonal width is small, which makes the degeneracy pattern of heavy states a relevant input for baryogenesis.
- In the large-splitting limit the new expression reduces to the earlier result, and in the authors' example the wave contribution approaches twice the vertex contribution.
- For the equal-width case, the propagation eigenstates become degenerate at $|M_2^2-M_1^2|=2|Gamma_{12}^2|$, where the asymmetry vanishes.
Reading between the lines
- The same non-Hermitian effective-mass mechanism should apply to any unstable mixed scalar, not only sneutrinos; the resonant peak is a general feature of unstable mixing when width and mass splittings are comparable.
- Because the asymmetry depends on the production basis, a full quantum-kinetic treatment of sneutrino production is needed before the peak can be used as a quantitative leptogenesis prediction; this is the main gap between the derivation and an observable.
- If the enhancement survives, it loosens the usual tension between leptogenesis and low-scale supersymmetry or lepton-flavour constraints by allowing smaller couplings, but it also makes the baryon asymmetry sensitive to the detailed spectrum of the two lightest heavy sneutrinos.
- The paper's comparison with the vertex contribution assumes the same Yukawa combination; with three families and independent phases, the third heavy state can still dominate, so a realistic estimate needs the full three-flavour interference.
Original abstract
We consider the $CP$ violating asymmetries produced in the decay of heavy particles, studying the effects of heavy particle mixing for arbitrary mass splittings. A considerable enhancement of the asymmetries is achieved when the masses of the mixed states are comparable, and the enhancement is maximal for mass splittings of the order of the widths of the decaying particles. We apply the results to the particular case of heavy scalar neutrino decays relevant for leptogenesis scenarios.
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 consider the $CP$ violating asymmetries produced in the decay of heavy particles, studying the effects of heavy particle mixing for arbitrary mass splittings. A considerable enhancement of the asymmetries is achieved when the masses of the mixed states are comparable, and the enhancement is maximal for mass splittings of the order of the widths of the decaying particles. We apply the results to the particular case of heavy scalar neutrino decays relevant for leptogenesis scenarios.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We consider the $CP$ violating asymmetries produced in the decay of heavy particles, studying the effects of heavy particle mixing for arbitrary mass splittings. | contribution 0.99 | 0.85 | 0.07 | unclear 0.60 |
| s1 | A considerable enhancement of the asymmetries is achieved when the masses of the mixed states are comparable, and the enhancement is maximal for mass splittings of the order of the widths of the decaying particles. | result 1.00 | 0.85 | 0.75 | asserted 1.00 |
| s2 | We apply the results to the particular case of heavy scalar neutrino decays relevant for leptogenesis scenarios. | contribution 0.94 | 0.85 | 0.07 | asserted 0.95 |
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/9611425 by the authors.
References
How the literature uses it
32 arXiv papers cite this in 47 sentences
Papers citing it · 30 sentences without a confident label
Uses its method or tool 2 papers
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This method was used in [ref] to calculate the CP asymmetry in the decay of heavy particles with arbitrary mass splittings that mix, which elucidated various issues.
CP violation in mixing and oscillations for leptogenesis with quasi-degenerate neutrinos · Introduction · 0.84
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The first part of our discussion will follow closely [ref] , where leptogenesis from mixed particle decays was considered.
Probing Resonant Leptogenesis at the LHC · Oscillation derivation · 0.94
Compares with it 1 paper
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This is different from flavored-scalar leptogenesis [ref] , where more delicate collider confirmation is needed.
Forbidden neutrinogenesis · Phenomenology · 0.97
Cites it as background 10 papers
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The mass scale of leptogenesis can be significantly lowered if two HNLs are nearly degenerate in mass, this phenomenon was dubbed resonant leptogenesis [ref] .
Uniting low-scale leptogeneses · Introduction · 0.80
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In this scenario, a lepton asymmetry is produced through out-of-equilibrium and $CP$-violating decays of the RHNs [ref] .
Hot Leptogenesis · Introduction · 0.91
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In its simplest realisation, the lepton asymmetry is generated via out-of-equilibrium decays of heavy Majorana neutrinos [ref] .
Three-Flavoured Non-Resonant Leptogenesis at Intermediate Scales · Introduction · 0.96
Discussion
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