Study of models of the sine-Gordon type in flat and curved spacetime D. Bazeia, L. Losano, R. Menezes and Roldão da Rocha Eur. Phys. J. C, 73 7 (2013) 2499 Published online: 24 July 2013 DOI: 10.1140/epjc/s10052-013-2499-2