Lagrangian formulation of N=2 theories with (b, c, β, γ)-systems and comparison with the Landau-Ginzburg approachIn this section we consider the realization of (2,2)-supersymmetric models in terms of free (b, c, β, γ)-systems recently introduced in [37], and generalize it to include interactions of the Landau-Ginzburg (LG) type. As stressed in the introduction, N=2 superconformal theories with c = 9 are of primary interest in connection with superstring compactifications on six-dimensional Calabi-Yau spaces. More generally, a (2,2)-superconformal theory with c = 3d corresponds to the critical point of an N=2 σ-model on a target space with complex dimension d and vanishing first Chern class. We will call these spaces Calabi-Yau d-folds.In the LG formulation of (2,2)-supersymmetric models, the superconformal theory is viewed as the infrared fixed point of a two-dimensional N=2 Wess-Zumino model with a polynomial superpotential W . In particular, when W is an analytic quasi-homogeneous function of the chiral superfields X i , one can recover the complete ADE classification of the N=2 minimal models from the ADE classification of quasi-homogeneous potentials with zero modality [5,[33][34][35][36]. Furthermore, the polynomials W 's can be identified with those used in the construction of Calabi-Yau d-folds. Indeed, it can be shown [5,35] that a superconformal model with c = 3d, corresponding to a LG potential W , is the same as that associated to a σ-model on the Calabi-Yau d-fold defined by the polynomial constraint W (X i ) = 0 in a suitable projective or weighted projective space 1 . In this section we show that it is possible to add a polynomial interaction V of the LG type to a collection of free first-order (b, c, β, γ)-systems in such a way that, if V is a quasi-homogeneous function, the theory possesses an N=2 superconformal symmetry already at the classical level. We also show that the interaction potential unambiguously fixes the weights of the pseudo-ghost fields. As in the standard LG case, also here we can recover the ADE classification of the N=2 minimal models from ADE classification of the interaction potential [35,36]; however in our case the theory is always manifestly superconformal invariant. Our formulation allows us to add all relevant perturbations (versal deformations of the potential) and to study the renormalization group flows in a very simple way. Whenever we use a quasi-homogeneous potential with modality different from zero, we can study marginal deformations and eventually Zamolodchikov's metric on the associated moduli space. Alternatively, we can consider topological models by "twisting" the generators of the superconfromal algebra and compute topological correlation functions. Our formulation provides valuable methods to evaluate these latter.We start this program by defining our model. We consider a collection of pseudoghost fields {b ℓ , c ℓ , β ℓ , γ ℓ ;b r ,c r ,β r ,γ r } where ℓ = 1, . . . , N L and r = 1, . . . , N R . β ℓ and γ ℓ form a bosonic first-order system with weights...