* Astronomy

Scientists slow the speed of light

A team of Scottish scientists has made light travel slower than the speed of light.
They sent photons - individual particles of light - through a special mask. It changed the photons' shape - and slowed them to less than light speed.
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Title: How stable is the photon?
Authors: Julian Heeck

Yes, the photon. While a nonzero photon mass has been under experimental and theoretical study for years, the possible implication of a finite photon lifetime lacks discussion. The tight experimental upper bound of the photon mass restricts the kinematically allowed final states of photon decay to the lightest neutrino and/or particles beyond the Standard Model. We discuss the modifications of the well-measured cosmic microwave background spectrum of free streaming photons due to photon mass and lifetime and obtain model-independent constraints on both parameters---most importantly a lower direct bound of 3 yrs on the photon lifetime, should the photon mass be at its conservative upper limit.

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Title: Black-Hole Bombs and Photon-Mass Bounds
Authors: Paolo Pani, Vitor Cardoso, Leonardo Gualtieri, Emanuele Berti, Akihiro Ishibashi

Generic extensions of the standard model predict the existence of ultralight bosonic degrees of freedom. Several ongoing experiments are aimed at detecting these particles or constraining their mass range. Here we show that massive vector fields around rotating black holes can give rise to a strong superradiant instability which extracts angular momentum from the hole. The observation of supermassive spinning black holes imposes limits on this mechanism. We show that current supermassive black hole spin estimates provide the tightest upper limits on the mass of the photon (mv<4x10^{-20} eV according to our most conservative estimate), and that spin measurements for the largest known supermassive black holes could further lower this bound to mv<10^{-22} eV. Our analysis relies on a novel framework to study perturbations of rotating Kerr black holes in the slow-rotation regime, that we developed up to second order in rotation, and that can be extended to other spacetime metrics and other theories.

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Heavy photons are too light to be behind dark matter

Sadly, dark matter is not made of light. That may sound obvious, but many physicists were hoping that photons - particles of light - could help us to piece together the nature of the mysterious stuff thought to make up 85 per cent of the universe's matter.
Instead, readings from Vitor Cardoso of the Technical University of Lisbon in Portugal and colleagues seem to have quashed this idea.
Some theories had hinted that "heavy photons", hypothetical versions of the more familiar massless particles, might be dark matter. According to that idea, the heavy photon would have a small amount of mass and might carry an unknown fundamental force that allows it to interact only with ordinary photons - effectively hiding it from the visible world.
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