Sentence:  Some of the most beautiful and thus appealing physical theories, including quantum electrodynamics and quantum gravity, have been dogged for decades by infinities that erupt when theorists try to prod their calculations into new <WSD>domains</WSD>. Getting rid of these nagging infinities has probably occupied far more effort than was spent in originating the theories. 
Meaning of the word marked with <WSD> tags:  A group of related items, topics, or subjects.