Dark Matter Phenomenology at Colliders

Dark Matter candidates are required in physics beyond the Standard Model. The preferable models should not only explain the observed phenomena, but also be testable by experiments including direct detection, indirect detection, and collider searches. In this thesis, we focus on simplified Dark Matter models, and try to combine the experiments at colliders with non–collider data to scrutinize such models. On the theoretical side, the models considered in this thesis are the simplified Dark Matter models containing spinor or scalar Dark Matter particles and a massive vector mediator, which couples to both Dark Matter and Standard Model particles including quarks and leptons. On the experimental side, recent collider analyses related to the simplified Dark Matter models are mainly from ATLAS and CMS collaborations at LHC. Nevertheless, we also apply some old LEP data at e+e- collider to probe the parameter region where the LHC data are insensitive. The analyses used in this thesis cover collider signatures with mono–jet + missing energy, di–jet + missing energy, di–jet resonance, 4–jet, di–lepton + missing energy, and multi–lepton final states. However, the published analyses are not always well designed for the selected models related to Dark Matter. Therefore, we further study the optimization for the signal–to–background ratio and the selection efficiency for Dark Matter models, in order to improve the results from published analyses through both the cut based methods and the Machine Learning based algorithms

Self-pollination by sliding pollen in Caulokaempferia coenobialis (Zingiberaceae)

Caulokaempferia coenobialis (Zingiberaceae) forms dense populations on steep cliffs in shady, humid monsoon forests in south China. It produces few consecutively opening bright yellow flowers that are 3 cm long and oriented parallel to the ground. Upon anther dehiscence at about 0600 hours, each pollen sac releases a drop of pollen onto the horizontally oriented style, and the two drops then merge to form an oily film that slowly flows toward the stigma, carrying out self-pollination between about 1500 and 0730 hours the next day. The distance covered by the pollen film is ca. 3 mm. There is no significant difference in fruit set between experimentally cross- and self-pollinated flowers or between naturally pollinated and bagged flowers. The low pollen/ovule ratio of 664 probably relates to the pollen grains being held together by pollen-connecting threads. The latter ensure that pollen grains always arrive as multiples, and this is the first report of such threads in the Zingiberaceae. During 35 h of observation at several locations and during three flowering periods, only three individual bees, five flies, and two butterflies visited single flowers. It remained unclear whether they affected pollination because no return visits were observed. The automatic selfing by pollen that reaches the stigma ca. 9 h after the onset of anthesis apparently constitutes a case of delayed selfing, providing reproductive reassurance in situations of low pollinator visitation