centra

<p>Speaker:</p><p>Marco Bruni  (Institute of Cosmology and gravitation - University of Portsmouth) </p><p> </p><p>Abstract: </p><p>In this talk I first discuss some general properties of Unified Dark Matter (UDM) models.<br /> Using as an example models with an affine equation of state (EoS) I show how in general<br /> UDM models need to be extremely close to the standard LCDM model in order to be viable.<br /> The main problem is that the effective speed of sound - governing the Jeans length of the<br /> perturbations - needs to be extremely small, otherwise perturbations become incompatible<br /> with CMB and matter power spectra. In the second part of the talk I show how this problem<br /> can be avoided by UDM models with a fast transition. I will then introduce a <br /> phenomenological toy model and show that -  for a wide range of parameter values - </p><p>UDM models with a fast transition can fit the CMB and matter power spectra.</p><p> </p><p>Place:</p><p>Sala de Vídeo-conferência, Centro de Congressos do IST, Pavilhão de Civil, Piso 01 (-1)</p><p><font>IST, Campus da Alameda</font></p>