  In a disk graph, every vertex corresponds to a disk in $\mathbb{R}^2$ and two
vertices are connected by an edge whenever the two corresponding disks
intersect. Disk graphs form an important class of geometric intersection
graphs, which generalizes both planar graphs and unit-disk graphs. We study a
fundamental optimization problem in algorithmic graph theory, Bipartization
(also known as Odd Cycle Transversal), on the class of disk graphs. The goal of
Bipartization is to delete a minimum number of vertices from the input graph
such that the resulting graph is bipartite. A folklore (polynomial-time)
$3$-approximation algorithm for Bipartization on disk graphs follows from the
classical framework of Goemans and Williamson [Combinatorica'98] for
cycle-hitting problems. For over two decades, this result has remained the best
known approximation for the problem (in fact, even for Bipartization on
unit-disk graphs). In this paper, we achieve the first improvement upon this
result, by giving a $(3-\alpha)$-approximation algorithm for Bipartization on
disk graphs, for some constant $\alpha>0$. Our algorithm directly generalizes
to the broader class of pseudo-disk graphs. Furthermore, our algorithm is
robust in the sense that it does not require a geometric realization of the
input graph to be given.
