Yes and no: the theory is not protected by copyright in its semantic content. It is a scientific statement and must be freely available to science. If the theory is designed creatively and individually in linguistic terms, it is at least protected in this linguistic form. If the theory is used word-for-word by a third party, the exception of quotation must be observed pursuant to Art. 25 CopA; otherwise, the presumption of a work exists (plagiarism).