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Abstract

In this paper we obtain parameterized subexponential-time algorithms for \kaggLG{} (\kagg{}) --- a problem in social choice theory --- and for \oscmLG{} (\oscm{}) -- a problem in graph drawing (see the introduction for definitions). These algorithms run in time \Oh^*}(2^{\Oh(\sqrt{k}\log k)}), where k is the parameter, and significantly improve the previous best algorithms with running times \Oh^{*}(1.403^k) and \Oh^{*}(1.4656^k), respectively. We also study natural ``above-guarantee'' versions of these problems and show them to be fixed parameter tractable. In fact, we show that the above-guarantee versions of these problems are equivalent to a weighted variant of {\sc p-Directed Feedback Arc Set}. Our results for the above-guarantee version of \kagg{} reveal an interesting contrast. We show that when the number of ``votes'' in the input to \kagg{} is {\em odd} the above guarantee version can still be solved in time O^{*}(2^{\Oh(\sqrt{k}\log k)}), while if it is {\em even then the problem cannot have a subexponential time algorithm unless the exponential time hypothesis fails (equivalently, unless FPT=M[1]).