Conserved Currents, Consistency Relations and Operator Product Expansions in the Conformally Invariant O(N) Vector Model

We discuss conserved currents and operator product expansions (OPE's) in the context of a $O(N)$ invariant conformal field theory. Using OPE's we find explicit expressions for the first few terms in suitable short-distance limits for various four-point functions involving the fundamental $N$-component scalar field $\phi^{\alpha}(x)$, $\alpha=1,2,..,N$. We propose an alternative evaluation of these four-point functions based on graphical expansions. Requiring consistency of the algebraic and graphical treatments of the four-point functions we obtain the values of the dynamical parameters in either a free theory of $N$ massless fields or a non-trivial conformally invariant $O(N)$ vector model in $2<d<4$, up to next-to-leading order in a $1/N$ expansion. Our approach suggests an interesting duality property of the critical $O(N)$ invariant theory. Also, solving our consistency relations we obtain the next-to-leading order in $1/N$ correction for $C_{T}$ which corresponds to the normalisation of the energy momentum tensor two-point function.Comment: 45 pages Latex + 2 uuencoded PostScript figures, DAMTP 94/1

Finite-Size Effects and Operator Product Expansions in a CFT for d>2

The large momentum expansion for the inverse propagator of the auxiliary field $\lambda(x)$ in the conformally invariant O(N) vector model is calculated to leading order in 1/N, in a strip-like geometry with one finite dimension of length $L$ for $2<d<4$. Its leading terms are identified as contributions from $\lambda(x)$ itself and the energy momentum tensor, in agreement with a previous calculation based on conformal operator product expansions. It is found that a non-trivial cancellation takes place by virtue of the gap equation. The leading coefficient of the energy momentum tensor contribution is shown to be related to the free energy density.Comment: 10 pages LaTeX 2 eps figures, minor changes in text. Revised version to be published in Phys.Lett. B. email: [email protected] [email protected]

Renormalization Group Flow and Thermodynamics of Conformal Field Theories

We discuss the free-energy density of bosonic and fermionic theories possessing strongly coupled critical points in D=3. We construct a stationary renormalization group trajectory which interpolates between the free massless theory of N scalars and a class of interacting theories including both bosons and fermions. At a special point of this trajectory the free-energy density is 5/4 times the free-energy density of the O(N) vector model at its nontrivial critical point. Our method could in principle be useful in the study of other theories with strongly coupled fixed points, such as {\cal N}=4 SYM in D=4.Comment: 13 pages, RevTeX, 1 figure, version to appear in JHE

On the Free-Energy of Three-Dimensional CFTs and Polylogarithms

We study the O(N) vector model and the U(N) Gross-Neveu model with fixed total fermion number, in three dimensions. Using non-trivial polylogarithmic identities, we calculate the large-N renormalized free-energy density of these models, at their conformal points in a ``slab'' geometry with one finite dimension of length L. We comment on the possible implications of our results.Comment: Latex, 13 pages, 2 eps figures; v2 typos corrected; v3 Expanded discussion of the results, added reference