Use ``invenio.utils.persistentid.is_arxiv()`` instead in the validator to validate the arxiv id.

If the you need to normalize the arxiv id (e.g. remove "arXiv" prefix), you likely need to add a method to ``invenio.utils.persistentid``.

I can see you regexp is different that the ones in ``persistentid`` module, so perhaps check if it ``is_arxiv`` is ok.  If you find problems, you can add test cases to ``invenio.testsuite.test_utils_pid``.