بررسي رفتار ديناميكي و آينده‌ي مدل‌هاي گرانش تعميم يافته

چكيده انگليسي :

Studying the dynamical behavior and the future of modified gravitational theories Maryam Aghaei Abchouyeh m aghaei@ph iut ac ir Department of Physics Isfahan University of Technology Isfahan 84156 83111 IranSupervisor Prof Dr Behrouz Mirza b mirza@cc iut ac irAbstractThe dynamical behavior of some modified gravitational theories has been studied to check their con sistency with the current observational evidence about the different cosmological epochs In additionwe have studied the existence of Anyon Van der Waals black holes Anyons are particles with inter mediate statistics in 2 1 dimensional space time Our results show that only Anyon Van der Waalsblack holes with quasi bosonic statistics can exist because although the Anyon Van der Waals blackholes with quasi fermionic statistics are Einstein equations solution they don t have physical horizon f R T R T gravitational theory is a modified version of f T theory which allows a more com plete coupling between the geometry and matter part of the theory Studying the dynamical behaviorof this theory by using the autonomous dynamical system analysis shows that the cosmological epochsand their stability in this theory is consistent with our expectation Furthermore the late time behaviorof this gravitational theory will make an extension to the members of a class of future singularitiesof the universe by adding a new member to it The stability of the fixed points of Ho ava Lifshitzgravitational theory with both dark energy and cosmological constant to be the energy components ofthe universe we have shown that the dark energy epoch is a saddle fixed point while the cosmologicalconstant epoch is a stable one This means that the universe in which the cosmological constant isdominant is the last destination of the universe we have studied here In addition we have consideredthis gravitational theory by assuming more complicated equation of state for dark energy and the re sults show that only for certain intervals of the parameters the theory can describe the cosmologicalepochs stability properly One of the other gravitational theory is a universe which a boundary screenhas been considered for it As a result there will be two additional terms in the equations of motionwhich will make changes in the dynamical behavior of the universe The dynamical considerationof this theory puts boundaries on the values of C1 and C2 to make the cosmological epochs orderingconsistent with the observation We have also investigated the theory in the absence of dark energyand the results show that instead of dark energy the entropic force terms can describe the presentaccelerated expansion of the universe It is also interesting to see that considering both dark energyand entropic force to be the energy components of the universe will lead us to this output that de pending on the equation of state of dark energy the dark energy epoch will be a saddle point whilethe entropic force universe represents a stable fixed point In addition to these we have presentedsome features of primordial gravitational waves Their equations of motion and constraints have beenpresented for different epochs for in the Einstein Hilbert background gravity In this way the effect ofrelativistic degrees of freedom and second horizon crossing on them have been applied to the equa tions Primordial gravitational waves are great messengers of the very beginning of the universe andtheir detectability is quite important The solution of their equation of motion will give us a set ofinformation to check if they can be detectable in the near future The point is that their energy den sity and detectability depends on the background gravity Thus the results of the other sections willbe used in our future studies to determine the gravitational waves energy density and detectability indifferent modified gravitational theories Keywords Cosmology Autonomous dynamical systems Ho ava Lifshitz gravity Anyon Black Holes Primor dial gravitational Waves

آقائي ابچويه، مريم

بررسي رفتار ديناميكي و آينده‌ي مدل‌هاي گرانش تعميم يافته

كيهان‌شناسي , سيستم‌ديناميكي , پايداري , سياهچاله‌ي آنيوني , امواج گرانشي