  We study the XY-rotors model on small networks whose number of links scales
with the system size $N_{links}\sim N^{\gamma}$, where $1\le\gamma\le2$. We
first focus on regular one dimensional rings in the microcanonical ensemble.
For $\gamma<1.5$ the model behaves like short-range one and no phase transition
occurs. For $\gamma>1.5$, the system equilibrium properties are found to be
identical to the mean field, which displays a second order phase transition at
a critical energy density $\varepsilon=E/N, \varepsilon_{c}=0.75$. Moreover for
$\gamma_{c}\simeq1.5$ we find that a non trivial state emerges, characterized
by an infinite susceptibility. We then consider small world networks, using the
Watts-Strogatz mechanism on the regular networks parametrized by $\gamma$. We
first analyze the topology and find that the small world regime appears for
rewiring probabilities which scale as $p_{SW}\propto1/N^{\gamma}$. Then
considering the XY-rotors model on these networks, we find that a second order
phase transition occurs at a critical energy $\varepsilon_{c}$ which
logarithmically depends on the topological parameters $p$ and $\gamma$. We also
define a critical probability $p_{MF}$, corresponding to the probability beyond
which the mean field is quantitatively recovered, and we analyze its dependence
on $\gamma$.
