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| Format: | Preprint |
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2025
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| Online Access: | https://arxiv.org/abs/2508.09400 |
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| _version_ | 1866911111949844480 |
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| author | Flores-Orea, Y. Toscano, J. J. |
| author_facet | Flores-Orea, Y. Toscano, J. J. |
| contents | CPT-odd effects on the neutrino charge radius are studied within the Standard Model Extension. We consider CPT violation from the electroweak Yang-Mills sector, characterized by Lorentz-violating coefficients $(k_1)_μ$ and $(k_2)_μ$, which have positive mass units. The $\barννγ$ vertex arises at tree level via exchange of two $Z$ bosons. Although suppressed by $\frac{1}{m_Z^4}$, this process is notable. The vertex function $Γ_μ$ includes three independent gauge structures satisfying the Ward identity $q^μΓ_μ= 0$, characteristic of neutral particles, and induces gauge-independent electromagnetic form factors. Besides charge and anapole, two novel form factors appear. The charge form factor $f_Q(q^2)$ contains an energy-dependent term causing $f_Q(0)\neq 0$, so electromagnetic properties are undefined for real photons with CPT violation. Instead, $f_Q$ and the charge radius are defined in the static limit: $q^0=0$ and $\mathbf{q}\to 0$. Here, $f_Q(0, \mathbf{0})=0$ and a correction to the SM neutrino charge radius is found: \[ \langle r^2_ν\rangle_{CPTV} = \frac{3c_{2W}}{2c_W^4} \left[\frac{k_2^2}{m_Z^2} + \frac{\mathbf{k}_2^2}{m_Z^2}\cos^2θ_γ\right] \frac{1}{m_Z^2}, \] with $θ_γ$ the angle between $\mathbf{q}$ and $\mathbf{k}_2$. Using recent bounds on $(k_i)_μ$ and reasonable assumptions, we obtain a small correction $\langle r^2_ν\rangle_{CPTV} \leq 0.83 \times 10^{-51}\ \mathrm{cm}^2$. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2508_09400 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Effects of CPT violation on the neutrino charge radius in the Standard Model Extension Flores-Orea, Y. Toscano, J. J. High Energy Physics - Phenomenology CPT-odd effects on the neutrino charge radius are studied within the Standard Model Extension. We consider CPT violation from the electroweak Yang-Mills sector, characterized by Lorentz-violating coefficients $(k_1)_μ$ and $(k_2)_μ$, which have positive mass units. The $\barννγ$ vertex arises at tree level via exchange of two $Z$ bosons. Although suppressed by $\frac{1}{m_Z^4}$, this process is notable. The vertex function $Γ_μ$ includes three independent gauge structures satisfying the Ward identity $q^μΓ_μ= 0$, characteristic of neutral particles, and induces gauge-independent electromagnetic form factors. Besides charge and anapole, two novel form factors appear. The charge form factor $f_Q(q^2)$ contains an energy-dependent term causing $f_Q(0)\neq 0$, so electromagnetic properties are undefined for real photons with CPT violation. Instead, $f_Q$ and the charge radius are defined in the static limit: $q^0=0$ and $\mathbf{q}\to 0$. Here, $f_Q(0, \mathbf{0})=0$ and a correction to the SM neutrino charge radius is found: \[ \langle r^2_ν\rangle_{CPTV} = \frac{3c_{2W}}{2c_W^4} \left[\frac{k_2^2}{m_Z^2} + \frac{\mathbf{k}_2^2}{m_Z^2}\cos^2θ_γ\right] \frac{1}{m_Z^2}, \] with $θ_γ$ the angle between $\mathbf{q}$ and $\mathbf{k}_2$. Using recent bounds on $(k_i)_μ$ and reasonable assumptions, we obtain a small correction $\langle r^2_ν\rangle_{CPTV} \leq 0.83 \times 10^{-51}\ \mathrm{cm}^2$. |
| title | Effects of CPT violation on the neutrino charge radius in the Standard Model Extension |
| topic | High Energy Physics - Phenomenology |
| url | https://arxiv.org/abs/2508.09400 |