/usr/lib/x86_64-linux-gnu/ThePEG/Onium3GDecayer.so.15 is in libthepeg15 1.8.0-1.1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/ThePEG/Onium3GDecayer.so.15.0.0
/usr/lib/x86_64-linux-gnu/ThePEG/Onium3GDecayer.so.15.0.0