We prove an exact formula for the variance of the divisor function over short intervals in $${\mathcal {A}}:= {\mathbb {F}}_q [T]$$
A
:
=
F
q
[
T
]
, where q is a prime power; and for correlations of the form $$d(A) d(A+B)$$
d
(
A
)
d
(
A
+
B
)
, where we average both A and B over certain intervals in $${\mathcal {A}}$$
A
. We also obtain an exact formula for correlations of the form $$d(KQ+N) d (N)$$
d
(
K
Q
+
N
)
d
(
N
)
, where Q is prime and K and N are averaged over certain intervals with $${{\,\textrm{deg}\,}}N \le {{\,\textrm{deg}\,}}Q -1 \le {{\,\textrm{deg}\,}}K$$
deg
N
≤
deg
Q
-
1
≤
deg
K
; and we demonstrate that $$d(KQ+N)$$
d
(
K
Q
+
N
)
and d(N) are uncorrelated. We generalize our results to $$\sigma _z$$
σ
z
defined by $$\sigma _z (A):= \sum _{E \mid A} |A |^z$$
σ
z
(
A
)
:
=
∑
E
∣
A
|
A
|
z
for all monics $$A \in {\mathcal {A}}$$
A
∈
A
. Our approach is to use the orthogonality relations of additive characters on $${\mathbb {F}}_q$$
F
q
to translate the problems to ones involving the ranks of Hankel matrices over $${\mathbb {F}}_q$$
F
q
. We prove several results regarding the rank and kernel structure of these matrices, thus demonstrating their number-theoretic properties. We also discuss extending our method to other divisor sums, such as those involving $$d_k$$
d
k
.