Dark Physics of the Universe

I. Coordinator:

Chao-Qiang Geng, Department of Physics, National Tsing Hua University
II. Core Members:

Kin-Wang Ng (Academia Sinica), Chuan-Hung Chen (NCKU), Wo-Lung Lee (NTNU), Guo-Chin Liu (Tamkang U.), Xiao-Gang He (NTU), Je-An Gu (NTU), We-Fu Chang (NTHU)
III. Major Directions:

Dark Matter, Dark Energy, Neutrino Physics
IV. Activities:

•Regular weekly meetings at NCTS with young postdocs and students
•Organizing seminars, short courses and workshops
•Inviting foreign visitors to participate TG activities
•Promoting research projects among domestic research groups
•Training young researchers, especially students and postdocs
•Establishing exchange programs with foreign research organizations
VI. Highlight of Results (2015-2016):

During 2015, TG2 has published more than 20 research papers. Some of the results are highlighted as follows:
(a) Dark Energy: 

Consistency demands that the standard model of the Universe is complemented by an early phase of rapid expansion dubbed inflation and late time cosmic acceleration. By introducing potentials steeper than the standard exponential, we construct models that can give rise to a successful inflationary phase, with signatures consistent with Planck 2015 results. Additionally, using nonminimal coupling of the scalar field with massive neutrino matter, we obtain the standard thermal history of the Universe, with late-time cosmic acceleration as the last stage of evolution. In both cases, inflation and late-time acceleration are connected by a tracker solution.
Reference: C.Q. Geng, M.W. Hossain, R. Myrzakulov, M. Sami and E.N. Saridakis,``Quintessential inflation with canonical and noncanonical scalar fields and Planck 2015 results,'' Phys. Rev. D92, 023522 (2015).
(b) Dark Matter

We study the possible positron/electron excesses within the multi-component leptonically decaying dark matter scenario by fitting the most recent AMS-02 data on the positron fraction and total e++e- flux. We show that both the two-component DM models are able to fit the two AMS-02 datasets.
Reference:C.Q. Geng, D. Huang and C. Lai, ``Revisiting Multi-Component Dark Matter with New AMS-02 Data,'' Phys. Rev. D91, 095006 (2015).
(c) Neutrino Physics

We study neutrino models in which Majorana neutrino masses are generated radiatively through loop diagrams. We find that the neutrino mass spectrum is a normal hierarchy and the rate of the neutrinoless double beta decay can be large as it is dominated by the short-distance tree contribution. In addition, by using the neutrino oscillation data and comparing with the global fitting result in the literature, we obtain a unique neutrino mass matrix and predict the Dirac and two Majorana CP phases.
Reference:C.Q. Geng, D. Huang and L.H. Tsai,``CP Violation in Predictive Neutrino Mass Structures,'' Eur. Phys. J. C75, 557 (2015); C.Q. Geng, D. Huang, L.H. Tsai and Q. Wang, ``Connecting Neutrino Masses and Dark Matter by High dimensional Lepton Number Violation Operator,'' JHEP 1508, 141 (2015).

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