Spacetime wave packets
Spacetime wave packets are a form of spatially correlated light that seems to violate the normal physical rules applying to light beams. In particular, their group velocity in free space can differ from the normal speed of light in vacuum. and their behavior under refraction does not follow the normal expectations given by Snell's law. Monochromatic Gaussian beam is shown to be transformed into spacetime wave packets under Lorentz transformation, thus any monochromatic Gaussian beam observed in a reference frame moving at relativistic velocity appears as spacetime wave packets. 
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group velocity
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free space
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speed of light in vacuum
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refraction
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Snell's law
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Spacetime wave packets
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