What is the reference frame of an accelerated observer?

The general construction of extended refrence frames for noninertial observers in flat space is studied. It is shown that, if the observer moves inertially before and after an arbitrary acceleration and rotation, the region where reference frames can coincide with an inertial system is bounded for final velocities exceeding 0.6 c.Comment: 5 pages, 2 figures, published in Phys. Lett. A 215, 1 (1996

Spontaneous emission of polaritons from a Bose-Einstein condensate

We study the spontaneous emission of a partially excited Bose-Einstein condensate composed of two-level atoms. The formation of polaritons induced by the ground-state part of the condensate leads to an avoided crossing in the photon spectrum. This avoided crossing acts similarly to a photonic band gap and modifies the spontaneous emission rate.Comment: 4 pages, 2 figures, revte