REVIEW
Baryon Asymmetry of the Universe in the Minimal Standard Model
High Energy Physics - Phenomenology · Submitted 17 May 1993 · 11 references
Pith's verdict: A genuinely new kinematic window for MSM baryogenesis, but the central number is quoted at the optimistic end of an uncomputed range — press on f(ρ).
T0 · AI review
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Referee report
The paper
The paper claims
The authors argue that ordinary Standard Model quark scattering off the walls of expanding electroweak bubbles can generate the observed baryon asymmetry of the universe, with no new particles required.
The reading
What carries the argument
The argument is carried by the one-dimensional equation of motion for quark quasiparticles in the wall rest frame, a $2$-by-$2$ block system in flavor space whose diagonal entries are the thermal dispersion relation $1 + (1 + 2v_w) + 2v_w$ — more precisely $1 + (1+2v_w) + 2v_w$ — and whose off-diagonal entries are the spatially varying Higgs-induced mass matrix. The thermal self-energies $1 + (1+2v_w) + 2v_w$ are taken from one-loop high-temperature propagators and are matrices in flavor space, which is what makes the physical eigenstates position-dependent and the CP-violating phase spatially varying. The reflection coefficients computed from this equation are summed over flavors to give $1 + (1+2v_w) + 2v_w$, then weighted by the difference of Fermi distributions on the two sides of the moving wall to give the current $1 + (1+2v_w) + 2v_w$. The final conversion to $n_B/s$ uses the factor $1 + (1+2v_w) + 2v_w$, which is $1$ when $1 + (1+2v_w) + 2v_w$ is large and $1 + (1+2v_w) + 2v_w$ when it is small; this factor encodes how long a scattered quark sits in the baryon-violating phase before the wall overtakes it.
Extended reading notes
Core claim
The claim is that the standard dismissal of Standard Model baryogenesis — an estimate of order $10^{-21}$ because the relevant quark energies are taken to be of order $T$ and the three flavors cancel almost perfectly — misses the regime that matters. The authors observe that the reflection of quarks from the bubble wall is large only in a narrow window of momenta, roughly $p_t$ of order $10^{-1} T$, in which the strange quark is totally reflected while the down quark is partly reflected and partly transmitted. In that window the GIM cancellation between $d$ and $s$ is incomplete, and the residual asymmetry is set by the mass splitting $(m_s - m_d)/T$ times the KM invariant $J = s_{12}s_{13}s_{23}$ times the wall velocity, rather than by the product of six mass-squared differences over $T^{12}$. Solving the one-dimensional scattering problem numerically for representative masses and mixing angles, they find a reflection asymmetry concentrated in a peak of width about the strange mass, with a notch of width about $m_d$ where the down quark is also totally reflected and the cancellation is exact. Feeding that current through the sphaleron equilibration of the high-temperature phase gives a baryon-to-entropy ratio of the observed magnitude and, for positive $J$, the observed sign.
Load-bearing premise
The magnitude claim rests on the suppression factor $f( ho)$, with $ ho = 3D/Gamma/v^2$, being of order one; the authors concede that the diffusion length, sphaleron rate and wall velocity are uncertain enough that a suppression as large as $10^{-3}$ is possible, which would put the prediction three orders of magnitude below the observed asymmetry.
Editorial extensions
If this is right
- The baryon asymmetry becomes a constraint on the KM phase and on the top mass rather than a free cosmological parameter, with the prediction rising by more than a factor of four as $m_t$ goes from 150 to 210 GeV.
- The sign of the predicted asymmetry tracks the sign of $\sin\delta_{CP}$, so a positive KM phase yields a baryon excess and a negative one an antibaryon excess.
- Requiring that sphaleron transitions be switched off in the low-temperature phase places an upper limit on the Higgs mass, if non-perturbative thermal effects are small.
- A fourth generation with a comparable KM structure would replace the $d$–$s$ degeneracy with a $b$–$s$ degeneracy and enhance the asymmetry by roughly three orders of magnitude.
- Precision comparison between the predicted and observed asymmetry would test the picture of the electroweak phase transition, including wall velocity, wall thickness and quasiparticle scattering lengths.
Reading between the lines
- The whole mechanism presupposes a first-order electroweak transition; a definitive lattice determination that the transition is a smooth crossover for the physical Higgs mass would remove the bubble walls this argument needs, independently of any detail of the scattering calculation.
- The narrow-window logic — CP violation is maximized where one member of a nearly degenerate pair is totally reflected and the other is not — looks portable to any wall-scattering baryogenesis or leptogenesis scenario, and would be worth stating as a general selection rule for where to look.
- Because the predicted sign is tied to $\sin\delta_{CP}$, an improved determination of the KM phase from the kaon system would turn this from a consistency check into a genuine one-bit prediction.
- The factor $f(\rho)$ is the natural place for a dedicated transport calculation: a coupled diffusion-and-sphaleron treatment in the hot plasma would convert the present order-of-magnitude estimate into a number that can actually be compared with observation.
Original abstract
We calculate the baryon asymmetry of the Universe which would arise during a first order electroweak phase transition due to minimal standard model processes. It agrees in sign and magnitude with the observed baryonic excess, for resonable KM parameters and m$_t$ in the expected range, and plausible values of bubble velocity and other high temperature effects. A detailed version of this work (77pp) is being simultaneously submitted to the net. A shortened version of this recently appeared in Phys. Rev. Lett. {\bf 70}, 2833, 1993.
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 calculate the baryon asymmetry of the Universe which would arise during a first order electroweak phase transition due to minimal standard model processes. It agrees in sign and magnitude with the observed baryonic excess, for resonable KM parameters and m$_t$ in the expected range, and plausible values of bubble velocity and other high temperature effects. A detailed version of this work (77pp) is being simultaneously submitted to the net. A shortened version of this recently appeared in Phys. Rev. Lett. {\bf 70}, 2833, 1993.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We calculate the baryon asymmetry of the Universe which would arise during a first order electroweak phase transition due to minimal standard model processes. | contribution 1.00 | 0.95 | 0.13 | asserted 0.93 |
| s1 | It agrees in sign and magnitude with the observed baryonic excess, for resonable KM parameters and m$_t$ in the expected range, and plausible values of bubble velocity and other high temperature effects. | result 0.98 | 0.84 | 0.85 | asserted 0.91 |
| s2 | A detailed version of this work (77pp) is being simultaneously submitted to the net. | background 0.42 | 0.57 | 0.02 | asserted 0.97 |
| s3 | A shortened version of this recently appeared in Phys. Rev. Lett. {\bf 70}, 2833, 1993. | background 0.72 | 0.31 | 0.02 | asserted 0.99 |
What was examined, and what was not
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- P abstract
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References
How the literature uses it
45 arXiv papers cite this in 58 sentences
Papers citing it · 36 sentences without a confident label
Contests it 1 paper
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[ref] , but this turned out to be spoiled by quantum decoherence by finite temperature scattering [ref] .
TASI Lectures on Early Universe Cosmology: Inflation, Baryogenesis and Dark Matter · Electroweak baryogenesis · contest 0.89
Uses its method or tool 1 paper
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[ref] and confirmed that the CP-even phase produced by the total reflection is not suppressed in the thick-wall regime.
Electroweak-like Baryogenesis with New Chiral Matter · The zero-temperature contribution ((iii)-(A),(B)) · 0.81
Compares with it 1 paper
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In addition, we note that at $T_eff≳10$ GeV, all $c_i$'s are at most of order $10^-14$, consistent with the estimates of Shaposhnikov et al. [ref] .
Temperature Dependence of Standard Model CP Violation · Introduction · 0.91
Cites it as support 2 papers
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The strength of the CPV in the CKM matrix is, however, too small to explain baryogenesis [ref] .
Electric dipole moments and the search for new physics · Introduction · 0.98
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This is too small to explain baryogenesis [ref] .
Quark Chromo-Electric Dipole Moment Operator on the Lattice · Baryogenesis and the need for new sources of CP violation · 0.96
Cites it as background 15 papers
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Assuming a strong first order electroweak phase transition, Farrar and Shaposhnikov estimated the baryon asymmetry produced by a moving bubble wall on the thermal background, in which quarks and leptons obtain thermal masses and behave as quasiparticles [ref] .
Electroweak-like Baryogenesis with New Chiral Matter · Introduction · 0.88
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Electroweak baryogenesis (EWBG) is an elegant mechanism [ref] that generates the observed baryon asymmetry at the electroweak phase transition (EWPT).
Electroweak Baryogenesis From Dark CP Violation · Introduction · 0.99
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Cosmic phase transitions [ref] are macroscopic cosmic events so dramatic that they are capable of leaving imprint via non-adiabatic vacuum fluctuations and creation of particles [ref] , formation of defects [ref] , generation of magnetic field [ref] , generation of baryonic asymmetry [ref] , and the gravitational wave background [ref] , and yet their properties are determined by particle physics.
Cosmic phase transitions: their applications and experimental signatures · Introduction · 0.93
Discussion
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