We consider the spaces $${\text {L}}^p(X,\nu ;V)$$
L
p
(
X
,
ν
;
V
)
, where X is a separable Banach space, $$\mu $$
μ
is a centred non-degenerate Gaussian measure, $$\nu :=Ke^{-U}\mu $$
ν
:
=
K
e
-
U
μ
with normalizing factor K and V is a separable Hilbert space. In this paper we prove a vector-valued Poincaré inequality for functions $$F\in W^{1,p}(X,\nu ;V)$$
F
∈
W
1
,
p
(
X
,
ν
;
V
)
, which allows us to show that for every $$p\in (1,\infty )$$
p
∈
(
1
,
∞
)
and every $$k\in \mathbb {N}$$
k
∈
N
the norm in $$W^{k,p}(X,\nu )$$
W
k
,
p
(
X
,
ν
)
is equivalent to the graph norm of $$D_H^{k}$$
D
H
k
(the k-th Malliavin derivative) in $${\text {L}}^p(X,\nu )$$
L
p
(
X
,
ν
)
. To conclude, we show exponential decay estimates for the V-valued perturbed Ornstein-Uhlenbeck semigroup $$(T^V(t))_{t\ge 0}$$
(
T
V
(
t
)
)
t
≥
0
, defined in Section 2.6, as t goes to infinity. Useful tools are the study of the asymptotic behaviour of the scalar perturbed Ornstein-Uhlenbeck $$(T(t))_{t\ge 0}$$
(
T
(
t
)
)
t
≥
0
, and pointwise estimates for $$|D_HT(t)f|_H^p$$
|
D
H
T
(
t
)
f
|
H
p
by means of both $$T(t)|D_Hf|^p_H$$
T
(
t
)
|
D
H
f
|
H
p
and $$T(t)|f|^p$$
T
(
t
)
|
f
|
p
.