  The properties of neutron stars are studied in a composite model of the
strong interaction. In the regime of low to medium baryonic densities a
covariant hadronic model is adopted which includes an exclusive channel for the
hyperon-hyperon interaction mediated by hidden strangeness mesons, which in
turn couple to other mesons through polynomial vertices. The new coupling
constants are subject to phenomenological constraints. The presence of free
quarks in the core of the star is considered by using the Nambu-Jona Lasinio
model supplemented with a vector interaction. The deconfinement process is
described by a continuous coexistence of phases. Several structure parameters
of neutron stars, such as mass-radius relation, moment of inertia, tidal
deformability, and the propagation of nonradial f and g-modes within the
relativistic Cowling approximation are studied. The predictions of the model
are in good agreement with recent observational data, in particular the maximum
inertial mass is greater than the observational lower limit of two solar
masses.
