I'm not creating a login account to read this report, but the analysis I can find leads me to conclude that they're definitely jazzing up their claim for the news.

They're talking about beams of light in their experiment, but individual photons in their conclusions. They discuss that they're not using "single frequency" light beams, in that they have used both a Gaussian and a Bessel setup. These are probability distributions, meaning the wave packets consist of many frequencies of photons, grouped about a mean. This is going to force us to discuss dispersion, and to understand that wave velocity has 2 components: phase velocity and group velocity.

A wave packet which experiences dispersion can have different group velocity and phase velocity... to the extremes that one can be in the opposite direction of the other. One can even be greater than c.

When they say they've changed the shape of the photons, they mean that they've passed the multi-frequency beam through a dispersive medium, causing the phase velocity and group velocity to change relative to one another. Then they measured that one of them was less than c.


The final clicher on the "not because photons have mass" argument is that the authors of the paper say this is a widely known effect which is observable when a large lens is focused over a short focal length, and can be reproduced in wave pools with mechanical waves.

That sounds like it's a property of any wave, and nothing particular to photons.