CAS simplifying non-zero expressions to 0

[parisse]

kickniko, I just read your first post where you wrote in bold the command simplify(6.0929985e-32*Cvar^2*Omega^8), a mix of floating point value and symbolic expression. It means you have replaced some constant(s) by a numeric value before the end of the computation, and that's the explanation of my previous post. By the way, if I set epsilon to 0 in my emulator, the simplify command above returns the expression unchanged.
If you need to work with mixed data (float and symbols) you should use a command that uses numerical algorithms and not symbolic algorithms, e.g. fsolve for numeric equation solving, or polynomial operations in list form (poly1[coeffs]), etc.. Trying to run simplify is a bad idea: simplify and related command can not work properly with approx data (the reason is that simplifying fractions is implemented via the Euclidean gcd algorithm). If you really think you need to run simplify, rewriting floating point numbers as an exact fraction might be a solution, but only if the computation does not require too much ressources and in the end you will probably get something big and not useful.
I have no idea how mathematica handles that, because I don't have a license of mathematica (I will certainly not spend the money for that myself) and even if I had one, there is probably a Xcas way that would be as appropriate as the mma way.
I can understand that you are frustated not to find the right way on the Prime if you are used to mathematica, but you can not expect that Xcas or the Prime CAS will work the same way. I can help you adapt, but I will not do that (remember it's on my free time) if your request is "it should be like in mma". If you don't want to adapt, then just stick with mma and goodbye!