Add massive neutrino support and improve CSV/CLI output

- Add neutrino mass parameter to SpectrumConfig and CLI interface - Update PhaseSpace component to handle neutrino mass effects properly - Update CSV headers to show basic endpoint and all transition types - Add --csv-verbosity option to CLI with 'full' and 'concise' options - Fix comparison plots to properly show linear scale variations - Add comprehensive tests for neutrino mass functionality
2026-07-02 10:33:28 +03:00
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+# ESSM — Enhanced Spectrum Shape Method
+
+## Overview
+
+The Enhanced Spectrum Shape Method (ESSM) extends the standard SSM by treating the small relativistic vector nuclear matrix element (sNME) as a free parameter alongside g_A. This allows simultaneous fitting of both the spectral shape AND the experimental half-life.
+
+## Motivation
+
+The sNME is difficult to compute accurately in nuclear shell model because it involves contributions outside the valence shell. The CVC prediction gives a "canonical" value, but this assumes a perfect many-body theory — which finite valence spaces are not.
+
+## Algorithm
+
+1. Fix g_A at a trial value
+2. Vary sNME to simultaneously fit the experimental half-life
+3. Because the half-life depends quadratically on sNME, there are typically **two solutions** for each g_A:
+   - **sNME(c)**: closer to the CVC value (closeCVC)
+   - **sNME(f)**: further from the CVC value (farCVC)
+4. Compare both solutions' spectral shapes with the data
+
+## sNME Values for ⁹⁹Tc
+
+| Model | g_A^eff | sNME(c) [fm³] | sNME(f) [fm³] | CVC sNME [fm³] |
+|---|---|---|---|---|
+| jj45pnb | 1.0 | 0.0666 | −0.0687 | −0.1705 |
+| glekpn | 1.0 | 0.1140 | −0.0202 | −0.0080 |
+
+## Results from Song et al. (2025)
+
+- **Best fit**: glekpn with g_A^eff = 1.2, sNME(f) = −0.0698 fm³, χ²_ν = 1.066
+- **Conclusion**: Quenched g_A = 1.0–1.2 with farCVC sNME provides the best agreement with data
+
+## References
+
+- [[SSM — Spectrum Shape Method]]
+- [[Shape Factor C(W, g_A)]]
+- [[Song et al. (2025)]]
+- [[Kumar et al. (2021)]]
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+# Nuclear Shell Model for β Decay
+
+## Overview
+
+The Nuclear Shell Model (NSM) is the primary theoretical framework for computing nuclear matrix elements (NMEs) in β decay. For forbidden nonunique decays like ⁹⁹Tc, the NSM computes one-body transition densities (OBTDs) that weight the single-particle transitions contributing to the decay.
+
+## Key Codes
+
+| Code | Description | Valence Spaces |
+|---|---|---|
+| NUSHELLX | Standard NSM code | Multiple (pf, sdg, etc.) |
+| KSHELL | High-performance NSM | Custom valence spaces |
+
+## Valence Spaces for ⁹⁹Tc
+
+### glekpn (Mach interaction)
+- **Protons**: 0f₇/₂, 0f₅/₂, 2p₃/₂, 2p₁/₂, 1g₉/₂
+- **Neutrons**: 0g₉/₂, 0g₇/₂, 1d₅/₂, 1d₃/₂, 2s₁/₂
+
+### jj45pnb (Brown-Lisetskiy interaction)
+- **Protons**: 0f₅/₂, 2p₃/₂, 2p₁/₂, 1g₉/₂
+- **Neutrons**: 0g₇/₂, 1d₅/₂, 1d₃/₂, 2s₁/₂, 0h₁₁/₂
+
+## OBTDs for ⁹⁹Tc
+
+| Transition | OBTD (glekpn) | OBTD (jj45pnb) |
+|---|---|---|
+| 1g₇/₂ → 1g₉/₂ | 0.00994 | 0.01107 |
+| 2d₅/₂ → 1g₉/₂ | 0.47752 | −0.43985 |
+
+**Key insight**: The dominant transition is 2d₅/₂ → 1g₉/₂ with OBTD ≈ 0.478. The jj45pnb model gives opposite sign for this transition.
+
+## sNME and CVC
+
+The small relativistic vector NME (sNME) is related to the large vector NME via the CVC hypothesis:
+
+```
+sNME = (R/√10) · [W₀ − (m_n − m_p) + E_C] · l-NME
+```
+
+where E_C is the Coulomb displacement energy. For ⁹⁹Tc, [W₀ − (m_n − m_p)] = −0.487 MeV (small Q-value makes this critical).
+
+## References
+
+- [[Shape Factor C(W, g_A)]]
+- [[SSM — Spectrum Shape Method]]
+- [[Ramalho & Suhonen (2024)]]
+- [[Song et al. (2025)]]
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+# Shape Factor C(W, g_A)
+
+## Overview
+
+The g_A-dependent nuclear shape factor C(W, g_A) is the key nuclear structure quantity that encodes the energy-dependent modification of the β decay spectrum due to forbidden nonunique transitions. For ⁹⁹Tc (second-forbidden nonunique, 9/2₁⁺ → 5/2₁⁺, Q ≈ 296 keV), the shape factor decomposes as:
+
+```
+C(W; g_A) = g_V² · C_V(W) + g_A² · C_A(W) + g_V · g_A · C_VA(W)
+```
+
+with g_V = 1.0 fixed by CVC.
+
+## Components
+
+| Component | Description | Sign for ⁹⁹Tc | Magnitude |
+|---|---|---|---|
+| C_V(W) | Vector contribution | + | 2.240 × 10⁻⁹ (integrated) |
+| C_A(W) | Axial-vector contribution | + | 2.130 × 10⁻⁹ (integrated) |
+| C_VA(W) | Vector-axial interference | − | −4.361 × 10⁻⁹ (integrated) |
+
+**Key insight**: C_VA is negative and twice as large as C_V or C_A. The total integrated shape factor is two orders of magnitude smaller due to destructive interference.
+
+## g_A Dependence
+
+The spectral shape is most sensitive to g_A in the **0–100 keV range** (low-energy region). Figure 9 from Paulsen et al. (2024) shows:
+
+- **Small g_A (0.5–1.0)**: Bell-shaped spectrum with low-energy enhancement
+- **Large g_A (1.4–2.0)**: Flattened spectrum with low-energy suppression
+- **Crossover point**: All spectra intersect around 100 keV
+
+## Table Data Sources
+
+| Source | Method | Coverage | Availability |
+|---|---|---|---|
+| Kostensalo & Suhonen (2017) PRC 96, 024317 | MQPM | 26 forbidden decays | Supplementary material (not public) |
+| Ramalho & Suhonen (2024) | NSM (NUSHELLX) | ⁹⁹Tc-specific | Supplementary material (not public) |
+| Song et al. (2025) arXiv:2506.17544 | ESSM + NSM/MQPM | ⁹⁹Tc | Integrated values only |
+
+## Implementation
+
+The ShapeFactorGA component should:
+1. Load C_V(W), C_A(W), C_VA(W) tables from CSV files
+2. Interpolate using cubic spline (scipy.interpolate.CubicSpline)
+3. Compute C(W; g_A) = C_V + g_A²·C_A + g_A·C_VA
+4. Return the shape factor for the full spectrum calculation
+
+## References
+
+- [[SSM — Spectrum Shape Method]]
+- [[Nuclear Shell Model]]
+- [[CVC Hypothesis]]
+- [[Paulsen et al. (2024)]]
+- [[Song et al. (2025)]]
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+# SSM — Spectrum Shape Method
+
+## Overview
+
+The Spectrum Shape Method (SSM) is a technique for determining the effective axial-vector coupling constant g_A by comparing theoretically computed β spectral shapes with experimental measurements. It is applicable to forbidden nonunique β decays, where the spectral shape depends nontrivially on g_A through the shape factor C(W; g_A).
+
+## Algorithm
+
+1. **Compute shape factor components** C_V(W), C_A(W), C_VA(W) from nuclear model
+2. **Build theoretical spectrum** for trial g_A values: N(W; g_A) = PhaseSpace × Fermi × ... × C(W; g_A)
+3. **Compare with experimental spectrum** using χ² minimization
+4. **Extract g_A** from the minimum χ² position
+5. **Estimate uncertainty** from χ² = χ²_min + 1
+
+## Key Requirements
+
+- **Forbidden nonunique transition**: The spectral shape must depend on g_A
+- **High-precision measurement**: Low energy threshold (< 10 keV), good energy resolution (< 1 keV)
+- **Accurate nuclear model**: Nuclear shell model (NSM) or MQPM with appropriate valence space
+
+## g_A Values from Literature
+
+| Source | g_A^eff | Method | Notes |
+|---|---|---|---|
+| Paulsen et al. (2024) | 1.526(92) | CVC-fixed sNME | Enhanced value |
+| Song et al. (2025) | 1.0–1.2 | ESSM (farCVC) | Quenched value |
+| Suhonen review | ~0.9 | Half-life comparison | Quenched value |
+
+## Uncertainty Budget
+
+| Component | Uncertainty on g_A | Relative |
+|---|---|---|
+| Fit method (statistics) | 0.0745 | 4.9% |
+| Coulomb displacement energy | 0.0425 | 2.8% |
+| Nuclear model | 0.0294 | 1.9% |
+| Lepton current treatment | 0.0127 | 0.8% |
+| Fit range | 0.0061 | 0.4% |
+| Endpoint energy | 0.0038 | 0.2% |
+| Radiative corrections | 0.0033 | 0.2% |
+| Atomic exchange | 0.0029 | 0.2% |
+| **Combined** | **0.0919** | **6.0%** |
+
+## References
+
+- [[Shape Factor C(W, g_A)]]
+- [[ESSM — Enhanced Spectrum Shape Method]]
+- [[Paulsen et al. (2024)]]
+- [[Song et al. (2025)]]