Вплив в’язкої речовини та випромінювання на часову еволюцію Всесвіту

• Дата: 2022
• Автори: Hakk, E.A., Nada, A., Tawfik, A.N., Yassin, H.
• Формат: Стаття
• Мова: English
• Опубліковано: Publishing house "Academperiodika" 2022
• Теми: classical general relativity; classical statistical mechanics; early Universe; класичний загальний релятивiзм; класична статистична механiка; раннiй Всесвiт
• Онлайн доступ: https://ujp.bitp.kiev.ua/index.php/ujp/article/view/2021002
• Назва журналу: Ukrainian Journal of Physics

We propose that the cosmic background is simply characterized by an equation of state of a relativistic fluid consisting of homogeneously and isotropically distributed single particle and single photon. Other components such as dark matter and dark energy (cosmological constant) are not taken into consideration. We assume that the expansion of the Universe is isotropic. Accordingly, the shear viscosity coefficient vanishes. We have derived expressions for the energy density and the bulk viscosity and found that both quantities largely increase with the inclusion of the photon. As for their temporal evolution, there is a rapid decrease in the early stages of the Universe. This seems to saturate at large co-moving time. We also found that the scale factor in non-viscous and viscous cosmic backgrounds is almost non-distinguishable in the early Universe. The latter suggest going beyond the standard cosmological model (SCM). The nonviscous cosmic background seems to have a scale factor larger than that of the viscous one. The result obtained for the temporal evolution of the Hubble parameter confirms the scale factor results. Namely, the distinguishability between non-viscous and viscous cosmic backgrounds is the largest in the early Universe.