C++11 8.5.3 describes initialization of references (including rvalue references).
It says:
Otherwise, a temporary of type “cv1 T1” is created and initialized from the initializer expression using the rules for a non-reference copy-initialization (8.5). The reference is then bound to the temporary.
So, a temporary of type int is bound to the rvalue reference, and thrown away immediately after the call returns.
Section 12.2 (Temporaries) gives examples very similar to yours.