For troubleshooting purposes, I'm wondering if someone who's seeing the problem where LR 5.5 quits right after showing the splash screen on a *MAC* can perform the following experiment:
1) Launch the Terminal app from /Applications/Utilities
2) Copy and paste the following command into the Terminal app, and hit enter (after pasting in the command):
sudo export HOME=~; /Applications/Adobe\ Photoshop\ Lightroom\ 5.app/Contents/MacOS/Adobe\ Photoshop\ Lightroom\ 5
3) In the Terminal app, you will be prompted for a password. Assuming that the logged in user has admin privileges, that user's password will work.
This experiment is intended to help figure out if it is some sort of permissions problem that's the underlying cause.
Thanks!