New candidates welcome! Possible winners with respect to the addition of new candidates

In voting contexts, some new candidates may show up in the course of the process. In this case, we may want to determine which of the initial candidates are possible winners, given that a fixed number k of new candidates will be added. We give a computational study of this problem, focusing on scoring rules, and we provide a formal comparison with related problems such as control via adding candidates or cloning. ► We study voting with a dynamic set of candidates. ► We study the possible winner problem upon candidate addition for scoring voting rules. ► We show that some rules allow efficient determination of possible winners, while some other give rise to algorithmically difficult problems.