We study the long wavelength shear modes (Tkachenko waves) of triangular lattices of singly quantized vortices in neutron star interiors taking into account the mutual friction between the superfluid and the normal fluid and the shear viscosity of th
e normal fluid. The set of Tkachenko modes that propagate in the plane orthogonal to the spin vector are weakly damped if the coupling between the superfluid and normal fluid is small. In strong coupling, their oscillation frequencies are lower and are undamped for small and moderate shear viscosities. The periods of these modes are consistent with the observed ~100-1000 day variations in spin of PSR 1828-11.
We show that the magnetization in color-flavor locked superconductors can be so strong that homogeneous quark matter becomes metastable for a wide range of magnetic field values. This indicates that magnetic domains or other type of magnetic inhomoge
neities can be present in the quark cores of magnetars.
