What does $\text{PK}=\text{pk}\oplus\text{H}(\text{opk})$ represent in this paper?
Reading section III A of the paper (caveat, I've not read the whole paper), it looks like the construction has been generalised so that $H$ maps to the abelian group where the public key operations take place. As such the $\oplus$ operation generalises to the abelian group operation. This notation is unwelcome, but I think in previous work the abelian group in question did combine with XOR.
In the RSA case it would appear that the operation is multiplication modulo $N$ and the hash function maps to $\mathbb Z/N\mathbb Z$.