Hydrogen 21 cm Constraints on the Photon's Spin Scale
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| Main Authors: | , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866913931703877632 |
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| author | Reilly, Aidan Russo, Alessandro Schuster, Philip Toro, Natalia |
| author_facet | Reilly, Aidan Russo, Alessandro Schuster, Philip Toro, Natalia |
| contents | We explore the fundamental but untested possibility that the photon is a continuous spin particle (CSP) with a small but non-zero spin Casimir $ρ$. When $ρ\neq 0$, the familiar polarization modes of the photon transform non-trivially under Lorentz boosts, leading to deviations from familiar QED. Surprisingly, these deviations are strongest at low energy, but smoothly vanish in the $ρ\rightarrow 0$ limit. In this letter, we compute corrections to the hydrogen 21cm transition rate, which is expected to be particularly sensitive given the small hyperfine energy splitting $ω$. We find deviations from QED $\propto ρ^2 α^2/ω^2$ at leading order, suggesting experimental constraints $ρ\lesssim 1$ meV. Building on this work, we expect that a range of other atomic, molecular, or condensed matter systems could be used to provide even more stringent tests of $ρ$ in electromagnetic interactions. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2505_15890 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Hydrogen 21 cm Constraints on the Photon's Spin Scale Reilly, Aidan Russo, Alessandro Schuster, Philip Toro, Natalia High Energy Physics - Phenomenology Atomic Physics We explore the fundamental but untested possibility that the photon is a continuous spin particle (CSP) with a small but non-zero spin Casimir $ρ$. When $ρ\neq 0$, the familiar polarization modes of the photon transform non-trivially under Lorentz boosts, leading to deviations from familiar QED. Surprisingly, these deviations are strongest at low energy, but smoothly vanish in the $ρ\rightarrow 0$ limit. In this letter, we compute corrections to the hydrogen 21cm transition rate, which is expected to be particularly sensitive given the small hyperfine energy splitting $ω$. We find deviations from QED $\propto ρ^2 α^2/ω^2$ at leading order, suggesting experimental constraints $ρ\lesssim 1$ meV. Building on this work, we expect that a range of other atomic, molecular, or condensed matter systems could be used to provide even more stringent tests of $ρ$ in electromagnetic interactions. |
| title | Hydrogen 21 cm Constraints on the Photon's Spin Scale |
| topic | High Energy Physics - Phenomenology Atomic Physics |
| url | https://arxiv.org/abs/2505.15890 |