Spontaneous Lorentz violation via QED with non-exact gauge invariance J.L. Chkareuli, Z. Kepuladze and G. Tatishvili Eur. Phys. J. C, 55 2 (2008) 309-316 Published online: 27 March 2008 DOI: 10.1140/epjc/s10052-008-0574-x