If I type
\boldmath $\widetilde T$\unboldmath
I get where unfortunately the tilde above the T is a little flimsy for my taste. Is there a better way to do this? I found a paper that has something, that appears a little bolder, in it.
I'm afraid you hit on something that can't be easily solved. Here for comparison all possible solutions for making math stuff bold and then a handmade bold tilde T:
Using .8em in the raisebox will be about the same height as the other tildes but I personally liked it better this way. I'm not saying it's pretty and I'm not saying it's easy :/