REVIEW 4 major objections 5 minor 136 references
Resonant TeV-scale electromagnetic leptogenesis can reproduce the observed baryon asymmetry of the Universe, within the electroweak crossover window, using only gauge-invariant neutrino-dipole operators and coherent heavy-neutrino evolution
Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →
T0 review · deepseek-v4-flash
2026-08-03 02:35 UTC pith:MGSY5DPA
load-bearing objection The formal machinery is real and the author is honest about approximations, but the abstract's headline numbers don't match the body's equations, and the central quantitative claim is unverified. the 4 major comments →
Resonant electromagnetic leptogenesis with coherent heavy-neutrino evolution
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The central claim is that, in the quasi-degenerate limit, the dipole-induced self-energy CP asymmetry regulated by Dyson-resummed widths becomes resonantly enhanced, and the resulting CP-odd source combined with coherent flavor evolution among the heavy neutrinos produces a large lepton asymmetry in the electroweak window T≈130–160 GeV. Solving the density-matrix QKEs with three resolved flavor charges and a finite-rate sphaleron equation, the paper obtains for the benchmark effective electromagnetic neutrino mass m~_1^EM = 3.97×10⁻² eV a positive near-resonant maximum Y_B^FO = +5.50×10⁻⁵ at ΔM = 1.29×10⁻¹¹ GeV with the decay-only pole prescription, and +8.44×10⁻⁵ at ΔM = 1.83×10⁻¹¹ GeV with
What carries the argument
The central objects are the gauge-invariant dimension-six neutrino-dipole operators O_NB and O_NW in the νSMEFT, generated in a Z2-symmetric UV completion with soft breaking, matched at 10 TeV and RG-evolved to 150 GeV. After electroweak symmetry breaking these induce effective dipole couplings μ^V_{αi} to γ, Z, and W, which mediate two-body decays, inverse decays, and ΔL=0 scatterings. The argument is carried by two mechanisms: (i) the Dyson-resummed self-energy CP asymmetry, regulated by the total width in a Breit–Wigner fashion, which becomes resonantly enhanced for quasi-degenerate heavy neutrinos; and (ii) density-matrix quantum kinetic equations derived from the Schwinger–Keldysh/Kadan
Load-bearing premise
The numerical result relies on starting the evolution at T_EW = 160 GeV with imposed initial conditions (thermal or zero heavy-neutrino abundance, zero lepton charges) and treating the Higgs VEV as constant at 246 GeV, so any pre-existing asymmetry or heavy-neutrino abundance generated in the symmetric phase above 160 GeV is neglected.
What would settle it
Extend the density-matrix QKEs to T > 160 GeV with a temperature-dependent Higgs VEV and include the symmetric-phase 1↔3 and crossed 2↔2 reactions; if the resulting Y_B^FO at sphaleron freeze-out no longer crosses the observed Y_B^obs at any ΔM near 1e-5 GeV, the central claim that the electroweak-window contribution alone can reproduce the baryon asymmetry would be falsified.
If this is right
- If the central claim is correct, TeV-scale dipole-dominated leptogenesis can reproduce the observed baryon-to-entropy ratio within the Standard-Model electroweak crossover, without relying on renormalizable neutrino Yukawa couplings.
- In the oscillation-motivated region (m~_1^EM in the 0.01–0.05 eV range), the undiluted yield exceeds the observed asymmetry, so a late-time entropy dilution factor is a natural ingredient to reconcile these parameter points.
- The ΔL=0 scatterings are numerically subdominant (∼10⁻⁵ relative to decays/inverse decays) in the benchmark, so they mainly rescale the efficiency; the dominant washout is from inverse decays.
- The closed UV-to-observable pipeline means that the baryon asymmetry is a prediction of the EFT inputs, enabling direct correlation with low-energy dipole observables such as μ→eγ, the electron EDM, and (g−2)_μ.
- The resonant regime requires the mass splitting to be comparable to the width that regulates the self-energy pole, which selects a narrow band of heavy-neutrino spectra for successful leptogenesis.
Where Pith is reading between the lines
- A direct extension of the paper would be to compute the baryon asymmetry with a fully temperature-dependent Higgs VEV and matched symmetric-phase processes above T=160 GeV; such a calculation would test whether the electroweak-window-only treatment is self-consistent.
- The same dipole operators that generate the baryon asymmetry also induce charged-lepton flavor violation and electric dipole moments at low energies, so the scenario can be probed or excluded by MEG II, JILA, and (g−2)_μ measurements—an implication the paper notes but does not fully quantify.
- The result suggests that resonant leptogenesis can operate in parameter space where the seesaw contribution to light-neutrino masses is negligible, decoupling the baryogenesis scale from the neutrino-mass scale and opening broader model-building possibilities.
- A scan over both the mass splitting ΔM and the effective dipole strength m~_1^EM, rather than fixing ΔM, could reveal regions where the observed asymmetry is reproduced without extra dilution; the paper's fixed-ΔM scan already indicates such regions exist.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper develops a UV-complete EFT description of TeV-scale electromagnetic leptogenesis. A softly Z2-broken model generates the νSMEFT dipole operators O_NB and O_NW; one-loop matching and RG running produce broken-phase dipole couplings to γ, Z, and W. The authors derive density-matrix QKEs from CTP/Kadanoff–Baym equations, with decays, inverse decays, and ΔL=0 scatterings included from the same self-energy structures, and solve them in the electroweak crossover window T≃130–160 GeV. The central claim is that, for quasi-degenerate heavy neutrinos, the resonantly enhanced CP source can produce a frozen-out baryon asymmetry of order or above the observed value, with the headline numerical results stated in the abstract: Y_B^FO=+5.50×10^-5 at ΔM=1.29×10^-11 GeV, crossings at 1.68×10^-5 and 2.34×10^-5 GeV, and a scattering-induced shift to +8.44×10^-5 at ΔM=1.83×10^-11 GeV.
Significance. If the numerical results are correct, the paper would demonstrate a complete and explicit EFT pipeline from a renormalizable UV model to a resonant leptogenesis mechanism, a substantial step beyond treatments that treat dipole couplings as free parameters. The formal derivation is extensive: one-loop matching, RG anomalous dimensions, Dyson-resummed self-energy CP asymmetries, and the reduction from Kadanoff–Baym to density-matrix QKEs are all presented in detail, and the paper explicitly includes the ΔL=0 scattering channels and checks their smallness. These are genuine strengths. However, the central quantitative output is not reproducible from the body as written, because the abstract reports a ΔM scan that the numerical section does not describe, and no implementation is provided. The paper also honestly acknowledges that only the electroweak-window contribution is computed, with imposed initial conditions and v(T)=246 GeV.
major comments (4)
- [Abstract vs §IX] The abstract's headline numbers cannot be obtained from the body. §IX A–B fix ΔM=5.0×10^-12 GeV (Eq. 654) and state that the scan is over ~m^EM_1 at fixed ΔM; Fig. 12 plots |Y_B^FO| versus ~m^EM_1, not a signed ΔM scan. The abstract quotes Y_B^FO=+5.50×10^-5 at ΔM=1.29×10^-11 GeV and crossings at 1.68×10^-5 and 2.34×10^-5 GeV. Unless a separate ΔM scan is documented, these numbers are not derivable from the presented equations and inputs. This is the core quantitative claim of the paper.
- [§IX F vs abstract] The abstract states that changing from decay-only to decay-plus-scattering shifts the maximum from 5.50×10^-5 to 8.44×10^-5 (~50%) and moves the resonant ΔM from 1.29×10^-11 to 1.83×10^-11 GeV (~40%). But §IX F reports S1/D1≃1.5×10^-5 and concludes that scatterings only rescale the efficiency at the 10^-5 level. A relative scattering rate of 10^-5 cannot produce a 50% shift in Y_B^FO or a 40% shift in the resonant ΔM. Either the abstract's numbers come from a different, undocumented set of inputs, or the body's own estimate is inconsistent with the abstract.
- [§IX C, §X C] The calculation covers only T∈[130,160] GeV, starts from Y_N(z_EW)=Y_N^eq or 0 and Y_Δα(z_EW)=0, and approximates v(T) by 246 GeV throughout. §X C explicitly defers temperature-dependent Higgs background and symmetric-phase reactions to future work. Therefore Y_B^FO is the electroweak-window contribution of one particular history, not a full prediction. If the symmetric phase generates a pre-existing asymmetry or a heavy-neutrino abundance, or if the evolving VEV changes decay kinematics, the final yield changes. The qualitative conclusion that 'EMLG can reproduce the observed BAU' should be stated with this caveat as a central limitation.
- [§IX C/Fig. 12, Eq. (665)] The conclusion (IV) states that Y_B^FO can reproduce Y_B^obs over a broad range of ~m^EM_1, but Fig. 12 and the text show that in the oscillation-motivated region the undiluted yield exceeds Y_B^obs by orders of magnitude. Matching to Y_B^obs then requires a late entropy dilution factor D in Eq. (665), which is an additional free parameter not predicted by the model. The paper therefore demonstrates that the mechanism can overproduce the BAU for some parameters, not that it predicts the observed value without tuning the scan inputs.
minor comments (5)
- [§IX B vs abstract benchmark] The abstract's benchmark ~m^EM_1=3.97×10^-2 eV is not used in the numerical section; §IX B uses ~m^EM_1=10^-3 eV for the evolution plots and notes that this point gives negative Y_B^FO. The benchmark underlying the abstract's numbers should be identified and its evolution, if different, shown.
- [§IX E text] The sentence 'the corresponding curves therefore exhibit an approximately linear [cf. Sec. IX E]' is self-contradictory: the subsection then derives a quadratic ~(mtilde)^2 scaling. Please correct.
- [Table IV and §VIII J] The susceptibility matrix and sphaleron factor are given at selected temperatures, but the numerical implementation uses v(T)=v(0) for all T in the window. This is stated, but a sentence indicating the expected size of the resulting systematic error (e.g., from v(160 GeV) vs v(246 GeV)) would be useful.
- [Eq. (643)] Y_N^eq is written with g⋆s in the denominator; earlier in §VIII H the entropy density s is used. Please define g⋆s consistently and state its value used in the numerics (the text uses g⋆=106.75 in Eq. 649 without specifying whether this is the relativistic degrees of freedom for entropy).
- [Data availability] The paper states 'Data availability' but does not provide code or the numerical data points of Fig. 12. Given that the abstract reports specific maxima and crossings, a public implementation or at least a table of the signed ΔM-scan results would greatly improve verifiability.
Circularity Check
No significant circularity: the EFT pipeline is self-contained; abstract/body numerical inconsistencies are a verification issue, not a circular reduction.
full rationale
The core derivation is not circular. The paper constructs a UV completion, matches it to the νSMEFT dipole operators, runs the Wilson coefficients with one-loop RGEs, computes CP asymmetries from explicit loop diagrams with Dyson-resummed widths, derives density-matrix QKEs from Kadanoff-Baym equations, and solves them over the electroweak window. The observed BAU enters only as a comparison line in Fig. 12 and as a benchmark against which overproduction is noted; the body explicitly presents a scan over \tilde m^EM_1 and states that successful points require either a particular range of this input or late-time dilution. That is parameter-space exploration, not fitting a parameter to the target and then renaming it a prediction. The abstract's quantitative claims (ΔM = 1.29×10^-11 GeV, crossings at 1.68×10^-5 and 2.34×10^-5 GeV, a ~50% scattering shift) are not reproduced by the body's stated implementation, which fixes ΔM = 5×10^-12 GeV and finds scatterings at the 10^-5 level; this is an internal-consistency/reproducibility problem, not a circular dependency. The explicit limitations (evolution only over T ≃ 130-160 GeV, v(T) approximated by 246 GeV, unmodeled dilution, deferred symmetric-phase matching) are caveats about the validity domain, not self-referential inputs. Citations such as Ref. [22] for the Z2-symmetric UV completion are external model assumptions, not a load-bearing self-citation chain, and no uniqueness theorem or ansatz is smuggled in via self-citation. No exhibited reduction of an output to an input by construction is present, so the circularity score is 0.
Axiom & Free-Parameter Ledger
free parameters (9)
- Effective electromagnetic neutrino mass \tilde m^EM_1 =
Benchmark 3.97×10^-2 eV (abstract); scanned over 10^-6–1 eV (body)
- Heavy-neutrino mass splitting ΔM =
5×10^-12 GeV in the body's fixed scan; abstract 'crossing' values 1.68×10^-5 and 2.34×10^-5 GeV
- UV Yukawa couplings y_H =
(1.0, 1.0 e^{-0.7i})^T × 10^-3
- UV Yukawa couplings y_Σ =
(10.0, 8.0 e^{-0.3i}, 6.0 e^{-1.1i})^T × 10^-4
- Dimensionful scalar coupling μ_s =
10.0 e^{-0.4i} GeV
- Soft-Z2-breaking scale μ_soft =
10.0 GeV
- Late entropy dilution factor D =
Unspecified, > 1
- Debye regulator coefficient κ_D =
1/3
- Benchmark scales M_eq, M_1 =
M_eq = 10 TeV, M_1 = 1 TeV
axioms (9)
- standard math Closed-time-path / Kadanoff-Baym formalism with leading-gradient Wigner expansion reduces to the stated density-matrix QKEs
- domain assumption Dyson resummation of the quasi-degenerate heavy-neutrino propagator with the vacuum width Γ_m as Breit-Wigner regulator
- domain assumption Quasiparticle + Kadanoff-Baym ansatz and kinetic-equilibrium momentum-averaging ansatz f_N - f_N^eq = f_N^eq (Y_N - Y_N^eq)/Y_N^eq
- domain assumption Internal lepton and gauge-boson lines are in equilibrium with Maxwell-Boltzmann statistics
- ad hoc to paper v(T) ≈ v(0) = 246 GeV throughout the electroweak window
- ad hoc to paper Initial conditions at T_EW = 160 GeV: Y_N = Y_N^eq or 0, Y_Δα = 0
- domain assumption Pole vs Landau-damping spectral split of the gauge propagator removes double counting, with no RIS subtraction needed
- ad hoc to paper The symmetric phase (T > 160 GeV) contributes negligibly to the final asymmetry
- domain assumption |ΔL|=2 washout from the Weinberg operator is negligible at T ≃ 130-160 GeV
invented entities (4)
-
Right-handed Majorana neutrinos N_1, N_2 at M ≈ 1 TeV
no independent evidence
-
Vector-like charged lepton E at 10 TeV
no independent evidence
-
Extra Higgs doublets Σ and D at 10 TeV
no independent evidence
-
Charged scalar Φ+ at 10 TeV
no independent evidence
read the original abstract
We study TeV-scale electromagnetic leptogenesis generated by the gauge-invariant neutrino-dipole operators $O_{NB}$ and $O_{NW}$. The benchmark Wilson coefficients are specified at the renormalization scale $\kappa_N=M_1=1\,\mathrm{TeV}$ and related to their values at $\kappa_{\rm match}=3\,\mathrm{TeV}$ through the coupled one-loop $\nu$SMEFT evolution. The collision network contains the symmetric-phase $1\leftrightarrow3$ and crossed $2\leftrightarrow2$ processes generated by the linear field-strength vertices and the VEV-induced two-body $\gamma$, $Z$, and $W$ channels through the electroweak crossover. We use a factorized leading-moment, momentum-averaged Markovian treatment for two $2\times2$ heavy-flavor density matrices, one for each helicity. Pole-resummed two-state effective couplings enter the lepton and antilepton collision tensors, while the off-diagonal density matrices describe coherent evolution and collision damping. Three resolved flavor charges are coupled to a finite-rate sphaleron equation, yielding the frozen baryon yield $Y_B^{\rm FO}$. For the benchmark $\tilde m^{\rm EM}_1=3.97\times10^{-2}\,\mathrm{eV}$, the decay-only pole prescription, in which only decay contributions enter the absorptive pole matrix, gives the locally optimized positive near-resonant maximum $Y_B^{\rm FO}=+5.50\times10^{-5}$ at $\Delta M=1.29\times10^{-11}\,\mathrm{GeV}$. Adding the thermally averaged crossed-scattering moment to the pole matrix defines the decay-plus-scattering prescription and shifts the maximum to $Y_B^{\rm FO}=+8.44\times10^{-5}$ at $\Delta M=1.83\times10^{-11}\,\mathrm{GeV}$. The corresponding signed mass-splitting curves cross the observed value $Y_B^{\rm obs}$ at $\Delta M=1.68\times10^{-5}\,\mathrm{GeV}$ and $2.34\times10^{-5}\,\mathrm{GeV}$.
Figures
Reference graph
Works this paper leans on
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[1]
Cutkosky rules Collecting the couplings into Eq
V ertex contribution (a) a. Cutkosky rules Collecting the couplings into Eq. (276), we write I (a) vert(V;U) =A V U µ,αimJ (a) vert(V;U),(D1) whereA V U µ,αim is a complex constant independent of kine- matics, andJ (a) vert(V;U) is given by J (a) vert(V;U) := i Z d4q1 (2π)4 N (a) vert(q1;k, q) (q2 3 −M 2m + iϵ)(q2 1 + iϵ)(q2 2 −m 2 U + iϵ). (D2) With this...
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[2]
mass term
V ertex contribution (b) The discontinuityJ (b) vert is given by puttingq 1 andq 2 on shell and carrying out the phase-space integral: DiscJ (b) vert(V;U) = Disc Z d4q1 (2π)4 T(b)|cut (q2 3 −M 2m + iϵ)(q2 1 + iϵ)(q2 2 −m 2 U + iϵ) = 4iM 8 i rV rU (1−r V )(1−r U ) × Z d4q1 (2π)4 (1−t 1)−2(r V +r U )(1 +t 1) − M 2 i 2 (D0 −D 1t1) ×(−2πi) 2δ(q 2 1)Θ(E1)δ(q 2...
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[3]
(F14) Similarly, theZexchange amplitude is MZ = 2eµZ αi sinθ W cosθ W 1 t−m 2 Z × ¯uα(p′)σµνqνPRui(p) × ¯uf (k′)γµ gf LPL +g f RPR uf (k) .(F15)
T ree-level amplitudes Thet-channel photon exchange amplitude is Mγ = 2eQf µγ αi t ¯uα(p′)σµνqνPRui(p) ¯uf (k′)γµuf (k) . (F14) Similarly, theZexchange amplitude is MZ = 2eµZ αi sinθ W cosθ W 1 t−m 2 Z × ¯uα(p′)σµνqνPRui(p) × ¯uf (k′)γµ gf LPL +g f RPR uf (k) .(F15)
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[4]
The Dirac-fermion self-energy is obtained by noting that the fermion–gauge-boson vertex is igγ µT a (a= 1,2,3)
Two-point function of a Dirac fermion Next, in order to determine the fermion field renormal- ization constantZ 2 for a Dirac fermionf, we compute the two-point function. The Dirac-fermion self-energy is obtained by noting that the fermion–gauge-boson vertex is igγ µT a (a= 1,2,3). We find iΣf = X a Z dnk (2π)n ×(igγ µT aPL) i(/k+m f ) k2 −m 2 f (igγ νT a...
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[5]
The gauge-boson propagator is−iδ abgµν/k2, the FP- ghost propagator is iδ ab/k2, and the gauge–ghost–anti- ghost three-point vertex factor is−gf abcqµ
Two-point function of an FP ghost Next, in order to determine the ghost-field renormal- ization constant ˜Z3, we compute the two-point function of the Faddeev–Popov ghost. The gauge-boson propagator is−iδ abgµν/k2, the FP- ghost propagator is iδ ab/k2, and the gauge–ghost–anti- ghost three-point vertex factor is−gf abcqµ. Therefore, the ghost two-point fu...
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[6]
Three-point function of an FP ghost In order to determine the renormalization constant ˜Z1 for the gauge-ghost vertex, we compute the gauge–ghost– anti-ghost three-point functionΓ ¯ccW. As can be seen from the counterterm structure (˜Z1 −1) ×g∂ µ¯caf abcW b µcc, the divergent part of this vertex func- tion must be proportional to ¯ε−1 f abcqµ, whereq µ is...
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NC differential cross sections Using the results above yields dσγ dt = e2Q2 f |µγ αi|2 4π∆2 ˜K(s, t) −t ,(F74) dσZ dt = e2 8π∆2 gf L 2 + gf R 2 sin2 θW cos2 θW |µZ αi|2 −t ˜K(s, t) (t−m 2 Z)2 (F75) dσγZ dt =− e2Qf gf L +g f R 4π∆2 Re(µγ αiµZ∗ αi ) sinθ W cosθ W ˜K(s, t) t−m 2 Z (F76) 88
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¯LβLα self-energy from aB+Lloop TheB-L-Lvertex factor is ig ′γµYL
¯LαLα self-energy a. ¯LβLα self-energy from aB+Lloop TheB-L-Lvertex factor is ig ′γµYL. From the fourth row of Table III, the hypercharge of the left-handed lep- ton doublet (ν, e)L isY L =−1/2. Unlike the Dirac- fermion loop contribution in Table II, which is summed over all fermion species, the present two-point function with external legs ¯Lβ andL α ha...
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(C112), the result is ΣLL,W (q) = g2 16π2 ¯ε−1 3 4 /qPL .(C147) The SU(2) L counterterm Lagrangian is given in Eq
¯LβLα self-energy from aW I +Lloop Since the vertex factor is igγ µT aPL, we obtain iΣLL,W (q) = 3 2 g2 Z dnk (2π)n /kPL (k2 −m 2 ℓ )(k−q) 2 .(C146) Since this is identical to Eq. (C112), the result is ΣLL,W (q) = g2 16π2 ¯ε−1 3 4 /qPL .(C147) The SU(2) L counterterm Lagrangian is given in Eq. (C102). Thus the UV divergence ofΣ LL,W (q) must be canceled b...
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[10]
˜H † ˜Hself-energy from aB+ ˜Hloop TheB- ˜H- ˜Hvertex factor is ig ′(kµ +q µ)Y ˜H
˜H † ˜Hself-energy a. ˜H † ˜Hself-energy from aB+ ˜Hloop TheB- ˜H- ˜Hvertex factor is ig ′(kµ +q µ)Y ˜H . From the last row of Table III, the hypercharge of the Higgs doubletHisY H = +1/2. Therefore, for ˜H= iτ 2H ∗ we haveY ˜H =−1/2. Here iτ 2 is an SU(2) L matrix and hence commutes with U(1) Y . The one-loop integral is then iΣHH,B (q) =− 1 4 g′2 Z dnk ...
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[11]
(C153) Applying the same Feynman-parameter formula as in Sec
˜H † ˜Hself-energy from aW I + ˜Hloop Since the scalar vertex factor is ig(k µ +q µ)T a (noP L appears for a scalar), we obtain iΣHH,W (q) =− 3 4 g2 Z dnk (2π)n k2 + 2k·q+q 2 (k−q) 2(k2 −m 2 H ) . (C153) Applying the same Feynman-parameter formula as in Sec. C 8 a, we obtain ΣHH,W (q) =− g2 16π2 ¯ε−1 3 2 q2 + 3 4 m2 H .(C154) The counterterm contribution ...
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[12]
(C158) Herey t is the SM top Yukawa coupling
˜H † ˜Hself-energy from at R +Q 3 loop In the electroweak-symmetric phase, the Yukawa in- teraction of the right-handed top quarkt R, the third- generation quark doubletQ 3 = (tL bL)⊺, and the Higgs doubletH= (ϕ + ϕ0)⊺ is −Lt =y t ¯Q3 ˜HP Rt+y t¯tPL ˜H †Q3, ˜H= iσ 2H ∗, (C157) i.e., −Lt =y t ¯tPRϕ0∗ −¯bPRϕ− PRt+y t¯tPL ϕ0PLt−ϕ +PLb . (C158) Herey t is the...
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Consequently, the RG evolu- tion overµ∈[µ ref , µmatch] closes within the couplings of this EFT
Couplings to be evolved together withC N Band CN W In this work, we integrate out the heavy new parti- clesE,Σ, D,Φ + at the matching scaleµ match and work in an EFT in which the low-energy degrees of freedom are those ofνSMEFT supplemented by the dimension-six operatorsO N BandO N W. Consequently, the RG evolu- tion overµ∈[µ ref , µmatch] closes within t...
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=δ (q0 1)2 −E 2 1 = 1 2E1 δ(q 0 1 −E 1) +δ(q 0 1 +E 1) . (D12) Therefore, δ(q 2 1)Θ(E1) = 1 2E1 δ(q 0 1 −E 1).(D13) Using this to integrate overq 0 1, we obtain Icut := Z d4q1 (2π)4 (2π)2δ(q 2 1)δ(q 2 2 −m 2 U )Θ(E1)Θ(E2)F(t 1) = Z d3q1 (2π)2 1 2E1 δ(q 2 2 −m 2 U )Θ(E2)F(t 1),(D14) wheret 1 := cosθ 1 := ˆq· ˆq1, andF(t 1) denotes the remain- ing cut integ...
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[15]
The main difference is already visible in the one-loop part (corresponding to Γ 2 = 0)
2PI effective action for fermions The construction of the 2PI effective action for fermionic fields proceeds along very similar lines as for bosons, with the crucial difference that one has to ac- count for the anti-commuting (Grassmann) nature of fermion fields. The main difference is already visible in the one-loop part (corresponding to Γ 2 = 0). For v...
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F eynman rules and kinematics For an outgoing gauge-boson momentumq, the dipole vertex and its conjugate vertex forV=γ, Zare (V V )ρ αi(q) = 2µV αiσρλqλPR, ( ˜V V )ρ αi(q) = 2µV∗ αi σρλqλPL, (V=γ, Z).(F2) The gauge interactions offare −L ⊃eQf Aµ ¯f γµf + e sinθ W cosθ W Zµ ¯f γµ gf LPL +g f RPR f,(F3) withQ f the electric charge in proton units, and gf L ...
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Mandelstam variables and inner products Define q :=k ′ −k=p−p ′, t :=q 2 <0, s := (p+k) 2.(F5) Using the massless approximationk 2 =k ′2 =p ′2 = 0 andp 2 =M 2 i , s= (p+k) 2 =p 2 + 2p·k+k 2 =M 2 i + 2p·k, t= (p−p ′)2 =p 2 −2p·p ′ +p ′2 =M 2 i −2p·p ′, u= (p−k ′)2 =p 2 −2p·k ′ +k ′2 =M 2 i −2p·k ′. (F6) Hence, p·k= s−M 2 i 2 .(F7) Squaring momentum conserv...
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Then qµJ (γ) µ = ¯uf (k′) q·(k ′ +k) 2mf + i qµσµνqν 2mf uf (k).(F17) The first term vanishes becauseq·(k ′ +k) =k ′2 −k 2 = m2 f −m 2 f = 0
Simplifyingσ µν qν using current conservation For a Dirac fermion of massm f , the Gordon identity gives ¯uf (k′)γµuf (k) = ¯uf (k′) (k′ +k) µ 2mf + iσµνqν 2mf uf (k) =: J (γ) µ , (F16) withq=k ′ −k. Then qµJ (γ) µ = ¯uf (k′) q·(k ′ +k) 2mf + i qµσµνqν 2mf uf (k).(F17) The first term vanishes becauseq·(k ′ +k) =k ′2 −k 2 = m2 f −m 2 f = 0. The second term...
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Spin-averaged squared amplitude:γ,Z, andγZ We define the kinematic polynomial K(s, t):= 4 (p·k)(p ′ ·k ′) + (p·k ′)(p′ ·k) = 2s2 + 2st+t 2 −2M 2 i s−M 2 i t,(F26) and ˜K(s, t):=K(s, t) +M 4 i −t 2 = 2s2 + 2st−2M 2 i s−M 2 i t+M 4 i .(F27) a. Photon exchange We start from the identity (F20) and recall that the photon current of the light fermionf, J (γ) µ ...
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(F65) 87 Usingp 1 ·p 2 = (s−m 2 1 −m 2 2)/2, we find F= 1 2 p λ(s, m2 1, m2 2),(F66) whereλis K¨ all´ en function λ(s, m2 1, m2
Differential cross sectiondσ/dt For 2→2 scattering 1(p1) + 2(p2)→3(p 3) + 4(p4),(F62) the Lorentz-invariant differential cross section is dσ= 1 4F |M|2 dΦ2,(F63) with Møller invariant flux [84] F := p (p1 ·p 2)2 −m 2 1m2 2,(F64) and two-body phase space dΦ2 = d3p3 (2π)32E3 d3p4 (2π)32E4 (2π)4δ4(p1 +p 2 −p 3 −p 4). (F65) 87 Usingp 1 ·p 2 = (s−m 2 1 −m 2 2)...
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[21]
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