We investigate the effects of an external magnetic field in the gap structure of a color superconductor with three massless quark flavors. Using an effective theory with four-fermion interactions, inspired by one-gluon exchange, we show that the long-range component $\tilde{B}$ of the external magnetic field that penetrates the color-flavor locked phase modifies its gap structure, producing a new phase of lower symmetry. A main outcome of our study is that the $\tilde{B}$ field tends to strengthen the gaps formed by $\tilde{Q}$-charged and $\tilde{Q}$-neutral quarks that coupled among themselves through tree-level vertices. These gaps are enhanced by the field-dependent density of states of the $\tilde{Q}$-charged quarks on the Fermi surface. Our considerations are relevant for the study of highly magnetized compact stars.

• Received 21 March 2005

DOI:https://doi.org/10.1103/PhysRevLett.95.152002