  Theories beyond the standard model include a number of new particles some of
which might be light and weakly coupled to ordinary matter. Such particles
affect equation of state of nuclear matter and can shift admissible masses of
neutron stars to higher values. The internal structure of neutron stars is
modified provided the ratio between coupling strength and mass squared of a
weakly interacting light boson is above $g^2/\mu^2 \sim 25 ~\mathrm{GeV}^{-2}$.
We provide limits on the couplings with the strange sector, which cannot be
achieved from laboratory experiments analysis. When the couplings to the first
family of quarks is considered the limits imposed by the neutron stars are not
more stringent than the existing laboratory ones. The observations on neutron
stars give evidence that equation of state of the $\beta$-equilibrated nuclear
matter is stiffer than expected from many-body theory of nuclei and nuclear
matter. A weakly interacting light vector boson coupled predominantly to the
second family of the quarks can produce the required stiffening.
