I want to find some algebraic models relating string topology to Hochschild and cyclic homologies. If the space $X$ is simply-connected and we are working over rational numbers, we can use Sullivan model or Quillen model of $X$ to do the job. See [nLab](https://ncatlab.org/nlab/show/Sullivan+model+of+free+loop+space) page or this [paper](https://arxiv.org/abs/math/0406593).


My question is how about non-simply conncted spaces? We still have Sullivan model. But how to relate them to free loop spaces? Can we still use Hochschild and cyclic homologies to compute loop homology and string homology?


For example, the torus $T^{2}$. Its Sullivan model is just $\wedge (x,\,y)$ with zero differential where $|x|=|y|=1$, and it is isomorphic to the Chevalley-Eilenberg cochain algebra of 2 dimensional abelian Lie algebra. But I don't know how to use this to compute loop and string homologies. 


Any help would be very appreciated.



Algebraic models of non-simply connected spaces in string topology
In my paper with Zeinalian (<https://arxiv.org/abs/1612.04801>) we prove that the coHochschild complex of the dg coalgebra of singular chains on a path connected (possibly non-simply connected) space calculates the homology of the free loop space of $X$. 


In my paper with Saneblidze (<https://arxiv.org/abs/1712.02644>) we describe a smaller model which might be suitable for your calculations.


However, you must be careful: if you use dg algebra models - such as the Sullivan model - under quasi-isomorphisms you loose the information the fundamental group.


If you want to calculate something for a non-simply connected space $X$ you may use any connected dg *coalgebra* $C$ which is weakly equivalent to the dg coalgebra of singular chains on $X$ with Alexander-Whitney coproduct in the following sense: we say a map $f: C \to C'$ between two dg connected coalgebras is a weak equivalence (we also called $\Omega$-quasi-isomorphism) if the map of dg algebras $\Omega f: \Omega C \to \Omega C'$ obtained after applying the cobar functor is a quasi-isomorphism. Note that this notion is stronger than quasi-isomorphism of dg coalgebras. 


