  Determining the presence of widely separated substellar-mass companion is
crucial to understand the dynamics of inner planets in extrasolar planetary
systems (e.g. to explain their high mean eccentricity as inner planets are
perturbed by the Kozai mechanism). We report the results of our
$\textit{Spitzer}$/Infrared Array Camera (IRAC) imaging search for widely
separated (10 to 25$^{\prime\prime}$) substellar-mass companions for 14
planet-host stars within 15 pc of the Sun. Using deep 3.6 and 4.5 $\mu$m
observations in subarray mode, we found one object in the field of 47 UMa with
[3.6]$-$[4.5] color similar to a T5 dwarf, which is, however, unlikely to share
common proper motion with 47 UMa. We also found three objects with
brown-dwarf-like [3.6]$-$[4.5] color limits in the fields of GJ 86, HD 160691,
and GJ 581, as well as another in the field of HD 69830 for which we have
excluded common proper motion. We provide model-based upper mass limits for
unseen objects around all stars in our sample, with typical sensitivity to 10
M$_{J}$ objects from a projected separation of 50 to 300 au from the parent
star. We also discuss our data analysis methods for point-spread-function
subtraction, image co-alignment, and artifact subtraction of IRAC subarray
images.
