Critical Behavior at the Onset ofk→-Space Instability on theλLine

We calculate the critical behavior of systems having a multicritical point of a new type, hereafter called a Lifshitz point, which separates ordered phases with $\overrightarrow{\mathrm{k}}=0\mathrm{}$ and $\overrightarrow{\mathrm{k}}\ne 0$ along the $\lambda$ line. For anisotropic systems, the correlation function is described in terms of four critical exponents, whereas for isotropic systems two exponents suffice. Critical exponents are calculated using an $\epsilon$-type expansion.