We study phase transitions in uniformly frustrated SU(N)-symmetric
(2+ϵ)-dimensional lattice models describing type-II superconductors
near the upper critical magnetic field Hc2(T). The low-temperature
renormalization-group approach is employed for calculating the beta-function
β(T,f) with f an arbitrary rational magnetic frustration. The
phase-boundary line Hc2(T) is the ultraviolet-stable fixed point found
from the equation β(T,f)=0, the corresponding critical exponents being
identical to those of the non-frustrated continuum system. The critical
properties of the SU(N)-symmetric complex Ginzburg-Landau (GL) model are then
examined in (4+ϵ) dimensions. The possibility of a continuous phase
transition into the mixed state in such a model is suggested.Comment: REVTeX, 12 pages, to appear in the Phys.Rev.