  The critical behavior of the three-dimensional $N$-vector chiral model is
studied for arbitrary $N$. The known six-loop renormalization-group (RG)
expansions are resummed using the Borel transformation combined with the
conformal mapping and Pad\'e approximant techniques. Analyzing the fixed point
location and the structure of RG flows, it is found that two marginal values of
$N$ exist which separate domains of continuous chiral phase transitions $N >
N_{c1}$ and $N < N_{c2}$ from the region $N_{c1} > N > N_{c2}$ where such
transitions are first-order. Our calculations yield $N_{c1} = 6.4(4)$ and
$N_{c2} = 5.7(3)$. For $N > N_{c1}$ the structure of RG flows is identical to
that given by the $\epsilon$ and 1/N expansions with the chiral fixed point
being a stable node. For $N < N_{c2}$ the chiral fixed point turns out to be a
focus having no generic relation to the stable fixed point seen at small
$\epsilon$ and large $N$. In this domain, containing the physical values $N =
2$ and $N = 3$, phase trajectories approach the fixed point in a spiral-like
manner giving rise to unusual crossover regimes which may imitate varying
(scattered) critical exponents seen in numerous physical and computer
experiments.
