جهان شبه هولوگرافيك در فضازمان خميده

چكيده انگليسي :

Semi Holographic Universe in Curved Spacetime Hamidreza Mahani hr mahani@ph iut ac ir 3 12 2012 Department of Physics Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language PersianSupervisor Dr B Mirza b mirza@cc iut ac irAbstract The existence of dark energy is one of the most significant cosmological discoveries over the lastcentury Various models of dark energy have been proposed such as Holographic Dark Energy Inthis model of dark energy cosmologists try to estimate the entropy of whole world based on the areaof the universe But what is the surface of the universe In the context of black hole physics webelieve that the event horizon of a black hole is the proper surface since every physical quantity ofthe black hole especially the entropy shows itself properly on that surface And they strictly obeythe first law of the thermodynamics But in the general solution for holographic dark energy there areseveral evidences that show the apparent horizon should be a causal horizon and is associated withthe gravitational entropy and Hawking temperature Hence it seems that the apparent horizon is theright holography of the universe There are decisive evidences that our observable universe evolves adiabatically after inflation ina comoving volume that is there is no energy momentum flow between different patches of the ob servable universe so that the universe keeps homogeneous and isotropic after inflation That is thereason why we can use an FRW geometry to describe the evolution of the universe Based on thesepostulates cosmologists proposed a model evaluating cosmological components such as decelera tion parameter effective pressure of dark energy and dark matter and equation of state of these darkcomponents in the holographic dark energy model in the flat space time In this proposal we try togeneralize that model and calculate the quantities of the holographic dark energy model in the curvedspace time In our results it is obvious that the evolution of the model in the open space time is thesame as the flat space time But in closed space time results are different Consequently we canconclude that our universe can be flat or open in the holographic dark energy model We find that under this condition the dark energy must evolve non adiabatically But the totalmatter in a comoving volume should evolve adiabatically Hence a compensating component shouldexist which we called dark matter The final ratio of dark matter to dark energy only depends to deeand dme which is independent on the initial values of the densities of dark matter and dark energy This result is helpful to solve the coincidence problem In a numerical example we find that thedeceleration parameter can be well consistent with observations All of all By assuming that dark energy in the universe obeys the holographic principle based onthe first low of thermodynamic and by using the methods of dynamical system analysis we find thatthere exists a stable dark energy dark matter solution at late time in the curved space time which ishelpful to solve coincidence problem For reasonable parameters the deceleration parameter is wellconsistent with current observations Keywords Holographic Dark Energy Dark Matter Deceleration Parameter First Low of Thermodynamic Holo graphic Principle Coincidence Problem

ماهاني، حميدرضا

جهان شبه هولوگرافيك در فضازمان خميده

انرژي تاريك هولوگرافيك , ماده ي تاريك , شتاب كندشونده , قانون اول ترموديناميك , مسئله انطباق