An extension of the cosmological standard model with a bounded Hubble expansion rate.pdf

An extension of the cosmological standard model with a bounded Hubble expansion rate J.L. Corte?s? and J. Indura?in? Departamento de F??sica Teo?rica, Universidad de Zaragoza, Zaragoza 50009, Spain The possibility to have an extension of the cosmological standard model with a Hubble expansion rate H constrained to a finite interval is considered. Two epochs of accelerated expansion arise nat- urally when the Hubble expansion rate approaches to the two limiting values. The new description of the history of the universe is confronted with cosmological data and with several theoretical ideas going beyond the standard cosmological model. INTRODUCTION According to General Relativity, if the universe is filled with the particles of the Standard Model of particle physics, gravity should lead to a slowing down of the expansion of the universe. However, in 1998 two inde- pendent evidences of present accelerated expansion were presented [1, 2] and later confirmed by different observa- tions [3, 4, 5]. On the other hand measurements of large scale structure [6] and CMB anisotropy [3] also indicate that the Universe evolved through a period of accelerated expansion early on (inflation). There is no compelling explanation for any of these cosmic accelerations, but many intriguing ideas are be- ing explored. In the case of inflation the origin of the accelerated expansion can be a modification of gravity at small scales [7] or a coupling of the expansion of the universe to the progress of phase transitions [8]. In the case of the present accelerated expansion these ideas can be classified in three main groups: new exotic sources of the gravitational field with large negative pressure [9] (Dark Energy), modifications of gravity at large scales [10] and rejection of the spatial homogeneity as a good approximation in the description of the present universe [11]. Different models (none of them compelling) for the source responsible of each of the two periods of accel- eration have be