Timeline for Modeling fluid decay in FRW spacetime (dust -> radiation)
Current License: CC BY-SA 4.0
7 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Aug 8, 2023 at 13:59 | comment | added | Sten | @tertius For example, equation 9 of arxiv.org/abs/2006.16182 | |
| Aug 8, 2023 at 13:50 | comment | added | Sten | @tertius Your calculation is right, except that it doesn't have to equal zero (that's only if the energy of the dust alone is conserved). If you're not sure how $a^{-3}\frac{\partial}{\partial t}\left(\rho a^3\right)$ comes out of that, try working backwards, expanding the derivative with the product rule. | |
| Aug 8, 2023 at 8:03 | comment | added | perchlorious | Do you happen to have a paper or reference for the first equation. Interested in reading how they use it. | |
| Aug 8, 2023 at 4:31 | comment | added | Sten | @tertius Are you perhaps missing the partial derivative term in the covariant derivative? | |
| Aug 8, 2023 at 4:13 | comment | added | perchlorious | Is that because locally we do not see expansion, and so it is not possible to separate changes to density from decay vs. kinematics? | |
| Aug 8, 2023 at 4:11 | comment | added | perchlorious | Thanks. This is exactly what I was looking for. One follow up: the first equation clearly accounts for changes to the dust density from both kinematical expansion as well as decay. The second equation, which I just wrote out, seems to only reproduce the kinematical changes, not decay changes. The $\mu=0$ component is $d\rho/dt = -3H\rho$, when $U_0 = 1$. Have I missed something? | |
| Aug 8, 2023 at 3:43 | history | answered | Sten | CC BY-SA 4.0 |