  Within an effective field theory method to general relativity, we calculate
the fifth-order post--Newtonian (5 PN) Hamiltonian dynamics also for the tail
terms, extending earlier work on the potential contributions, working in
harmonic coordinates. Here we calculate independently all (local) 5 PN
contributions to the tail terms using the in--in formalism, on which we give a
detailed account. The five expansion terms of the Hamiltonian in the effective
one body (EOB) approach, $q_{82}, q_{63}, q_{44}, \bar{d_5}$ and $a_6$, can all
be determined from the local contributions to periastron advance $K^{\rm
loc,h}(\hat{E},j)$, without further assumptions on the structure of the
symmetric mass ratio, $\nu$, of the expansion coefficients of the scattering
angle $\chi_k$. The $O(\nu^2)$ contributions to the 5 PN EOB parameters have
been unknown in part before. We perform comparisons of our analytic results
with the literature and also present numerical results on some observables.
