RT Journal Article T1 Covariant gauge-invariant perturbations in multifluid f (R) gravity A1 Abebe, Amare A1 Abdelwahab, Mohamed A1 Cruz Dombriz, Álvaro de la A1 Dunsby, Peter K. S. AB We study the evolution of scalar cosmological perturbations in the 1 + 3 covariant gauge-invariant formalism for generic f(R) theories of gravity. Extending previous works, we give a complete set of equations describing the evolution of matter and curvature fluctuations for a multi-fluid cosmological medium. We then specialize to a radiation-dust fluid described by barotropic equations of state and solve the perturbation equations around a background solution of R^n gravity. In particular, we study exact solutions for scales much smaller and much larger than the Hubble radius and show that n > 2/3 in order to have a growth rate compatible with the Mészáros effect. PB Institute of Physics SN 0264-9381 YR 2012 FD 2012-07-07 LK https://hdl.handle.net/20.500.14352/44480 UL https://hdl.handle.net/20.500.14352/44480 LA eng NO © 2012 IOP Publishing Ltd. The authors thank the National Research Foundation (NRF, SouthAfrica) for financial support. AdlCD also acknowledges financial support from MICINN (Spain) project numbers FPA 2008-00592, FIS 2011-23000 and Consolider-Ingenio MULTIDARK CSD2009-00064. NO National Research Foundation (NRF, SouthAfrica) NO Ministerio de Ciencia e Innovación (MICINN), España NO Ministerio de Economía y Competitividad (MINECO), España DS Docta Complutense RD 7 jul 2025