Given  an integral  domain $R$,  the  Steinberg  group $St_n(R)$  is  the   group  given  by  generators  
$e_{pq}(\lambda) := \mathbf{1} + a_{pq}(\lambda)$,
 $p\neq q$, $1\leq p,q \leq n$

Subject  to the  relations  
$$\begin{align}
e_{ij}(\lambda) e_{ij}(\mu) &= e_{ij}(\lambda+\mu) \\
\left[ e_{ij}(\lambda),e_{jk}(\mu) \right] &= e_{ik}(\lambda \mu) && \mbox{for } i \neq k\\
\left[ e_{ij}(\lambda),e_{kl}(\mu) \right] &= \mathbf{1}          && \mbox{for } i \neq l, j \neq k\\
\end{align}$$

The Steinberg  group  is  the  universal  central extension  of the  special  linear  group over  $R$; $Sl_n(R)$. 

Is  there  a  description of the  Steinberg  group $St_n(Z)$, the  special linear  group over  the integers as a  lattice  in  some  lie  group,  and  some  covering  map  realizing  the   universal  central  extension  of $Sln(R)$ (  real  coefficients), which  restricts  to the integral universal  central  extension of  $Sln(Z)$ given by the  Steinberg  group ?