Axion-photon coupling from non-anomalous PQ symmetry with charged light fermions acts as bandpass filter, making lab constraints dominant for most axion masses.
First results from the new PVLAS apparatus: a new limit on vacuum magnetic birefringence
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abstract
Several groups are carrying out experiments to observe and measure vacuum magnetic birefringence, predicted by Quantum Electrodynamics (QED). We have started running the new PVLAS apparatus installed in Ferrara, Italy, and have measured a noise floor value for the unitary field magnetic birefringence of vacuum $\Delta n_u^{\rm (vac)}= (4\pm 20) \times 10^{-23}$ T$^{-2}$ (the error represents a 1$\sigma$ deviation). This measurement is compatible with zero and hence represents a new limit on vacuum magnetic birefringence deriving from non linear electrodynamics. This result reduces to a factor 50 the gap to be overcome to measure for the first time the value of $\Delta n_u^{\rm (vac,QED)}$ predicted by QED: $\Delta n_u^{\rm (vac,QED)}= 4\times 10^{-24}$ ~T$^{-2}$. These birefringence measurements also yield improved model-independent bounds on the coupling constant of axion-like particles to two photons, for masses greater than 1 meV, along with a factor two improvement of the fractional charge limit on millicharged particles (fermions and scalars), including neutrinos.
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A mini-review of axion phenomenology showing how light bosons can account for dark matter, drive cosmic acceleration, or contribute to relativistic backgrounds in the early and late Universe.
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A Bandpass Axion Or: How I Learned To Stop Worrying About Stars And Love The Lab
Axion-photon coupling from non-anomalous PQ symmetry with charged light fermions acts as bandpass filter, making lab constraints dominant for most axion masses.
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Axions as Dark Matter, Dark Energy, and Dark Radiation
A mini-review of axion phenomenology showing how light bosons can account for dark matter, drive cosmic acceleration, or contribute to relativistic backgrounds in the early and late Universe.