On the Crawford number attaining operators

We study the denseness of Crawford number attaining operators on Banach spaces. Mainly, we prove that if a Banach space has the Radon–Nikodým property, then the set of Crawford number attaining operators is dense in the space of bounded linear operators. We also see among others that the set of Crawford number attaining operators is dense in the space of all bounded linear operators while they do not coincide, by observing the case of compact operators when the Banach space has a 1-unconditional basis. Furthermore, we show a Bishop–Phelps–Bollobás type property for the Crawford number for certain Banach spaces, and we finally discuss some difficulties and possible problems on the topic.