Ruiz Cembranos, José Alberto2023-06-202023-06-2020111742-658810.1088/1742-6596/315/1/012004https://hdl.handle.net/20.500.14352/44919© 2011 IOP Publishing Ltd. International Workshop on the Dark Side of the Universe (6º. 2010. Guanajuato, México). I am grateful to K. Olive, M. Peloso, and M. Voloshin for useful discussions. DOE grant DOE/DE-FG02-94ER40823, FPA 2005-02327 project (DGICYT, Spain), CAM/UCM 910309 project, and MICINN Consolider-Ingenio MULTIDARK CSD2009-00064.There is a non-trivial four-derivative extension of the gravitational spectrum that is free of ghosts and phenomenologically viable. It is the so called R^2-gravity since it is defined by the only addition of a term proportional to the square of the scalar curvature. Just the presence of this term does not improve the ultraviolet behaviour of Einstein gravity but introduces one additional scalar degree of freedom that can account for the dark matter of our Universe.engAtribución 3.0 Españahttps://creativecommons.org/licenses/by/3.0/es/journal articlehttp://dx.doi.org/10.1088/1742-6596/315/1/012004http://iopscience.iop.org/open access53Cosmological modelsGeneral-relativityField-theoryGravityConsequencesInflationGeometryRelicsFísica (Física)22 Física