Coupling matter in modified $Q$-gravity
  We present a novel theory of gravity by considering an extension of symmetric
teleparallel gravity. This is done by introducing, in the framework of the
metric-affine formalism, a new class of theories where the nonmetricity $Q$ is
nonminimally coupled to the matter Lagrangian. More specifically, we consider a
Lagrangian of the form $L \sim f_1(Q) + f_2(Q) L_M$, where $f_1$ and $f_2$ are
generic functions of $Q$, and $L_M$ is the matter Lagrangian. This nonminimal
coupling entails the nonconservation of the energy-momentum tensor, and
consequently the appearance of an extra force. The motivation is to verify
whether the subtle improvement of the geometrical formulation, when implemented
in the matter sector, would allow more universally consistent and viable
realisations of the nonminimal curvature-matter coupling theories. Furthermore,
we consider several cosmological applications by presenting the evolution
equations and imposing specific functional forms of the functions $f_1(Q)$ and
$f_2(Q)$, such as power-law and exponential dependencies of the nonminimal
couplings. Cosmological solutions are considered in two general classes of
models, and found to feature accelerating expansion at late times.
