I've been down this path mathematically and my conclusion is that mass itself IS invariant.

Hold on Jeff. If that is your viewpoint then I think a mathematical proof is in order for you too. Can you prove that mass is invariant other than choosing a definition in which it's invariant

*by definition*. That's how everyone who presents such an argument does so. They either define the term

**mass** as the value of mass as measured in the rest frame of the object/particle or they attempt to define it as the value of the particles 4-momentum (letting c = 1 for simplicity). Which do you do?

Let's once and for all resolve the problems with such a definition. Jeff:

*Please* study the following page

http://home.comcast.net/~peter.m.brown/sr/invariant_mass.htmvery deeply so that you don't miss a trick. After you study that

*please* study the section called "Definition of Mass" in my article at

http://arxiv.org/abs/0709.0687After you've studied those then you'll have an excellent understanding of these issues. Also let it be know that there is a difference between mass and energy in relativity. In GR the relativistic mass of a particle is defined as the time component of the particle's 4-momentum while the energy of the particle is defined as the time component of the particle's momentum 1-form. These two expressions do not equal each other. They're not even proportional. This is a fact that is all too often missed by most students studying relativity. It's one of the most important reasons why you can't say that relativistic mass and energy are the same thing.