1 5 D ec 2 00 4 Large - n expansion for m - axial Lifshitz points ♥

The large-n expansion is developed for the study of critical behaviour of d-dimensional systems at m-axial Lifshitz points with an arbitrary number m of modulation axes. The leading non-trivial contributions of O(1/n) are derived for the two independent correlation exponents η L2 and η L4 , and the related anisotropy index θ. The series coefficients of these 1/n corrections are given for general values of m and d with 0 ≤ m ≤ d and 2 + m/2 < d < 4 + m/2 in the form of integrals. For special values of m and d such as (m, d) = (1, 4), they can be computed analytically, but in general their evaluation requires numerical means. The 1/n corrections are shown to reduce in the appropriate limits to those of known large-n expansions for the case of d-dimensional isotropic Lifshitz points and critical points, respectively, and to be in conformity with available dimensionality expansions about the upper and lower critical dimensions. Numerical results for the 1/n coefficients of η L2 , η L4 and θ are presented for the physically interesting case of a uniaxial Lifshitz point in three dimensions, as well as for some other choices of m and d. A universal coefficient associated with the energy-density pair correlation function is calculated to leading order in 1/n for general values of m and d.