Beltrán Jiménez, JoséCruz Dombriz, Álvaro de laDunsby, Peter K. S.Sáez Gómez, Diego2023-06-192023-06-192014-05-211475-751610.1088/1475-7516/2014/05/031https://hdl.handle.net/20.500.14352/33779© 2015 IOP Publishing. We would like to thank M. Seikel for useful comments to start this investigation. We are also indebted to C. Clarkson and J. P. Uzan for useful discussions. J.B.J. is supported by the Wallonia-Brussels Federation grant ARC No. 11/15-040. A.d.l.C.D. acknowledges financial support from MINECO (Spain) project FPA2011-27853-C02-01. A.d.l.C.D. thanks the financial support in 2013 from a Marie Curie - Beatriu de Pinós contract BP-B00195 Generalitat de Catalunya and a ACGC fellowship University of Cape Town. J.B.J. and A.d.l.C.D. thank projects FIS2011-23000 and Consolider-Ingenio MULTIDARK CSD2009-00064 for financial support. P.K.S.D. thanks the NRF for financial support. D. S.-G. acknowledges the support from the University of the Basque Country, Project Consolider CPAN Bo. CSD2007- 0042, the URC financial support from the University of Cape Town (South Africa) and MINECO (Spain) project FIS2010-15640. J.B.J. wishes to thank the Department of Mathematics and Applied Mathematics and ACGC, University of Cape Town for their warm hospitality.One possible explanation for the present observed acceleration of the Universe is the breakdown of homogeneity and isotropy due to the formation of non-linear structures. How inhomogeneities affect the averaged cosmological expansion rate and lead to late-time acceleration is generally considered to be due to some backreaction mechanism. In the recent literature most averaging calculations have focused their attention on General Relativity together with pressure-free matter. In this communication we focus our attention on more general scenarios, including imperfect fluids as well as alternative theories of gravity, and apply an averaging procedure to them in order to determine possible backreaction effects. For illustrative purposes, we present our results for dark energy models, quintessence and Brans-Dicke theories. We also provide a discussion about the limitations of frame choices in the averaging procedure.engjournal articlehttp://dx.doi.org/10.1088/1475-7516/2014/05/031http://iopscience.iop.org/open access53Hubble-Space-TelescopeDark EnergyCosmic AccelerationGeneral-RelativityGravity TheoriesCovariant PerturbationsInhomogeneous FluidsAverage PropertiesMachs PrincipleQuantum-GravityFísica (Física)22 Física