**Résumé*** :*

In a joint work with Marcelo R. Hilario and Augusto Teixeira, we investigate the long-term behavior of a random walker evolving on top of the simple symmetric exclusion process (SSEP) at equilibrium. At each jump, the random walker is subject to a drift that depends on whether it is sitting on top of a particle or a hole. The asymptotic behavior is expected to depend on the density ρ in [0, 1] of the underlying SSEP.

Our first result is a law of large numbers (LLN) for the random walker for all densities ρ except for at most two values ρ- and ρ+ in [0, 1], where the speed (as a function of the density) possibly jumps from, or to, 0.

Second, we prove that, for any density corresponding to a non-zero speed regime, the fluctuations are diffusive and a Central Limit Theorem holds.

For the special case in which the density is 1/2 and the jump distribution on an empty site and on an occupied site are symmetric to each other, we prove a LLN with zero limiting speed.

Our main results extend to environments given by a family of independent simple symmetric random walks in equilibrium.

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