Breaking rotational symmetry in two-flavor color superconductors

The color superconductivity under flavor asymmetric conditions relevant to compact star phenomenology is studied within the Nambu–Jona-Lasinio model. We focus on the effect of the deformation of the Fermi surfaces on the pairing properties and the energy budget of the superconducting state. We find that at finite flavor asymmetries the color superconducting BCS state is unstable towards spontaneous quadrupole deformation of the Fermi surfaces of the d and u quarks into ellipsoidal form. The ground state of the phase with deformed Fermi surfaces corresponds to a superposition of prolate and oblate deformed Fermi ellipsoids of d and u quarks.