The integrated Sachs–Wolfe effect in unified dark matter scalar field cosmologies: ananalytical approach

Abstract

We perform an analytical study of the integrated Sachs–Wolfe (ISW) effect within theframework of unified dark matter models based on a scalar field which aim at a unifieddescription of dark energy and dark matter. Computing the temperature power spectrum ofthe cosmic microwave background anisotropies we are able to isolate those contributionsthat can potentially lead to strong deviations from the usual ISW effect occurring in aΛCDM universe. This helps to highlight the crucial role played by the sound speed in the unifieddark matter models. Our treatment is completely general in that all the results dependonly on the speed of sound of the dark component and thus it can be applied to a variety ofunified models, including those which are not described by a scalar field but rely on a singledark fluid.