RT Journal Article T1 Perturbations in electromagnetic dark energy A1 López Maroto, Antonio A1 Beltrán Jiménez, José A1 Koivisto, Tomi S. A1 Fonseca Mota, David AB It has been recently proposed that the presence of a temporal electromagnetic field on cosmological scales could explain the phase of accelerated expansion that the universe is currently undergoing. The field contributes as a cosmological constant and therefore, the homogeneous cosmology produced by such a model is exactly the same as that of Lambda CDM. However, unlike a cosmological constant term, electromagnetic fields can acquire perturbations which in principle could affect CMB anisotropies and structures formation. In this work, we study the evolution of inhomogeneous scalar perturbations in this model. We show that provided the initial electromagnetic fluctuations generated during inflation are small, the model is perfectly compatible with both CMB and large scale structure observations at the same level of accuracy as Lambda CDM. PB IOP Publishing Ltd SN 1475-7516 YR 2009 FD 2009-10 LK https://hdl.handle.net/20.500.14352/44338 UL https://hdl.handle.net/20.500.14352/44338 LA eng NO © 2009 IOP Publishing Ltd and SISSA.This work has been supported by Ministerio de Ciencia e Innovación (Spain) project numbers FIS 2008-01323 and FPA 2008-00592, UCM-Santander PR34/07-15875. J.B. wishes to thank the Institute for Theoretical Physics of the University of Heidelberg for their hospitality. NO Ministerio de Ciencia e Innovación (Spain) NO UCM-Santander DS Docta Complutense RD 3 jul 2025