Let $G = G(K)$ be a Chevalley group over an algebraically closed field $K$ of characteristic $p > 0$. Consider the finite group $G(q) = G(\mathbb{F}\_q)$. (For example, if $G = \operatorname{SL}\_n(K)$ then $G(q) = \operatorname{SL}\_n(\mathbb{F}\_q)$).


It was proven by Steinberg that every irreducible $\mathbb{F}\_q[G(q)]$-module is absolutely irreducible, and correspond to $q$-restricted dominant weights (i.e. weights $\lambda$ such that $0 \leq \langle \lambda, \alpha \rangle < q$ for all simple roots $\alpha$).


Consider an indecomposable $\mathbb{F}\_q[G(q)]$-module $V$. Is $V \otimes\_{\mathbb{F}\_q} K$ an indecomposable $K[G(q)]$-module?


EDIT: In case this is not true, I also would be interested if what I am asking for is true under some mild restrictions on $q$ and/or $G$.



Are indecomposable representations of a finite group of Lie type absolutely indecomposable?
This is rarely the case for all $V$. $KG(q)$ would need to have finite representation type, so $G(q)$ would need to have a cyclic Sylow $p$-subgroup. Otherwise a counterexample can be found by taking an indecomposable module over some field extension of $\mathbb{F}\_q$, that is not defined over $\mathbb{F}\_q$ and regarding it as a module for $\mathbb{F}\_qG$.


Suppose $KG$ has infinite representation type, where $K$ is the algebraic closure of $\mathbb{F}\_q$.


Then for some $d$ there are infinitely many isomorphism classes of $d$-dimensional indecomposable $KG$-modules. Since there are only finitely many $d$-dimensional $\mathbb{F}\_qG$-modules up to isomorphism, there must be a $d$-dimensional $KG$-module $M$ that is not defined over $\mathbb{F}\_q$: i.e., such that there is no $\mathbb{F}\_qG$-module $N$ such that $M\cong N\otimes\_{\mathbb{F}\_q}K$.


The structure constants of $M$ only involve finitely many elements of $K$, and so $M$ is defined over some finite extension $k$ of $\mathbb{F}\_q$: i.e., $M\cong L\otimes\_kK$ for some $kG$-module $L$, where $L$ is indecomposable and can't be defined over $\mathbb{F}\_q$.


Let $L'$ be $L$ regarded as an $\mathbb{F}\_qG$-module (so $L'$ is $[k:\mathbb{F}\_q]d$-dimensional).


Then $L'\otimes\_{\mathbb{F}\_q}k$ is a direct sum of $[k:\mathbb{F}\_q]$ copies of $L$, so there can be no indecomposable direct summand $N$ of $L'$ with $N\otimes\_{\mathbb{F}\_q}k$ indecomposable. 


