Dobado González, AntonioLópez Maroto, Antonio2023-06-202023-06-201997-12-141. B. Nodland and J. P. Ralston, Phys. Rev. Lett. 78, 3043 (1997). 2. D. J. Eisenstein and E. F. Bunn, astro-ph/9704247; S. M. Carroll and G. B. Field, Phys. Rev. Lett. 79, 2394 (1997); J. P. Leahy, astro-ph/9704285; J. F. C. Wardle, R. A. Perley and M. H. Cohen, Phys. Rev. Lett. 79, 1801 (1997); T. J. Loredo, E. E. Flanagan and I. M. Wasserman, astro-ph/9706258. 3. B. Nodland and J. P. Ralston, Phys. Rev. Lett. 79, 1958 (1997); astro-ph/9706126; astro-ph/9708114. 4. D. V. Ahluwalia and T. Goldman, Mod. Phys. Lett. A8, 2623 (1993); R. W. Kuhne, ibid. A12, 2473 (1997). 5. F. W. Hehl, P. von der Heyde, G. D. Kerlick and J. M. Nester, Rev. Mod. Phys. 48, 393 (1976). 6. A. Dobado and A. L. Maroto, Phys. Rev. D54, 5185 (1996). 7. V. De Sabbata and M. Gasperini, Phys. Lett. A83, 115 (1981). 8. S. M. Carroll and G. B. Field, Phys. Rev. D50, 3867 (1994); R. T. Hammond, ibid. D52, 6918 (1995).0217-732310.1142/S0217732397003125https://hdl.handle.net/20.500.14352/58728© World Scientic Publishing Company. We are grateful to B. Nodland for his comments to the preliminary version of this letter and also to J. P. Ralston for his suggestions. This work has been supported in part by the Ministerio de Educaci_on y Ciencia (Spain) (CICYT AEN96-1634).In this letter we provide a simple explanation of the recent finding of anisotropy in electromagnetic (EM) propagation claimed by Nodland and Ralston. We consider, as a possible origin of such effect, the effective coupling between EM fields and some tiny background torsion field. The coupling is obtained after integrating out charged fermions, it is gauge-invariant and does not require the introduction of any new physics.engjournal articlehttp://link.springer.com/article/10.1007%2Fs100529800993?LI=truehttp://link.springer.comhttp://arxiv.org/abs/hep-ph/9710313open access53Space-TimeFísica (Física)22 Física