Spectra and symmetric spectra in general model categories

(This is an updated version; following an idea of Voevodsky, we have strengthened our results so all of them apply to one form of motivic homotopy theory). We give two general constructions for the passage from unstable to stable homotopy that apply to the known example of topological spaces, but also to new situations, such as motivic homotopy theory of schemes. One is based on the standard notion of spectra originated by Boardman. Its input is a well-behaved model category C and an endofunctor G, generalizing the suspension. Its output is a model category on which G is a Quillen equivalence. Under strong hypotheses the weak equivalences in this model structure are the appropriate analogue of stable homotopy isomorphisms. The second construction is based on symmetric spectra, and is of value only when C has some monoidal structure that G preserves. In this case, ordinary spectra generally will not have monoidal structure, but symmetric spectra will. Our abstract approach makes constructing the stable model category of symmetric spectra straightforward. We study properties of these stabilizations; most importantly, we show that the two different stabilizations are Quillen equivalent under some hypotheses (that also hold in the motivic example).Comment: 45 page