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### Dark Physics of the Universe

I. Coordinator:

• Chao-Qiang Geng, National Tsing Hua Univeristy, chengwei@phys.ntu.edu.tw
•

II. Core Members:

• We-Fu Chang (NTHU)
Chian-Shu Chen (Tamkang U.)
Chuan-Hung Chen (NCKU), Xiao-Gang He (NTU)
Wo-Lung Lee (NTNU), Guo-Chin Liu (Tamkang U.)

III. Research Themes:

• Dark Matter, Dark Energy, Neutrino Physics, Gravitational Waves.

• Goals:
• •Initiating collaborations; •Publishing excellent results; •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.

• Background:
• Neutrino, Dark Matter and Dark Energy consist of about 0.5%, 27% and 68% of the energy density of the Universe, respectively. Although they are the main constituents (~96%) of the Universe, they are dark as we cannot see them directly though the normal ways based on electric and magnetics interactions. The goal of Dark Physics Research is to find the real natures and origins of these three dark parts of the Universe, which are the most fundamental and important problems in particle physics, astronomy and cosmology. Professor Frank Hsu (2009 Shaw Prize), the former president of NTHU, once said publicly that the study of dark physics, in particular, dark energy, would result in at least 10 Nobel Prizes in physics, representing the importance of these problems.

• Neutrinos
• Neutrinos were first proposed by Pauli in 1930 to understand the energy spectrum in the beta decay. However, we still do not know why neutrino masses are much smaller than other fermions and their mixing angles quite different from those in the quark sector. To answer these questions, new physics is clearly involved as neutrino masses are zero without any mixing in the standard model of particle physics. As a result, neutrino physics is a real window to new physics.
Needless to say, there are many ongoing and future experiments related to neutrinos.
•
• Dark Matter
• Dark Matter is hypothetical matter, found about 80 years ago, that does not interact with ordinary matter through the electromagnetic force, but whose presence can be inferred from gravitational effects. The existence of dark matter has been well established without a deviation from the known laws of gravitation and the theory of general relativity. Dark matter plays a central role in the structure formation and galaxy evolution, and has measurable effects on the anisotropy of the cosmic microwave background. The evidences of dark matter include: rotational speeds of galaxies; orbital velocities of galaxies in clusters; gravitational lensing of background objects by galaxy; and temperature distributions of hot gas in galaxies and clusters of galaxies. Now, the questions for Dark Matter are: Does it purely involve gravitational interaction? Is it a weakly interacting massive particle (WIMP)? Can it be observed directly by the experiments at the underground or LHC? Do the positron excesses of the cosmic ray measurements from the PAMELA, FERMI-LAT and AMS-2 indicate the existence of Dark Matter in the sky around us?
•
• Dark energy
• Dark energy has been proposed to understand the current accelerating expansion of the Universe. There are two main approaches to account for the current accelerated expansion of the Universe besides the simplest candidate of the ΛCDM model with the cosmological constant L. One is to introduce some unknown matter, which is called dark energy'' in the framework of general relativity. The other is to modify the gravity theory, such as f(R) gravity, in which the action is described by an arbitrary function f(R) of the scalar curvature R. However, if Dark Energy is originated from Λ, it will run into so called the fine-tuning problem, i.e. the naturalness of the extreme small value for Λ. In addition, why is the energy density of dark energy so close to that of dark matter? So far, there are too many Dark Energy models in the literature. It is important to find a method to distinguish among these models. In particular, we are interested in answering if the accelerating universe is due to the cosmological constant or modified matter or modified gravity.
•
• Gravitational Waves
• Gravitational Waves were first detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) experiment on September 14, 2015 due to a merging binary black hole. Recently, some of the core members have joined the Kamioka Gravitational Wave Detector (KAGRA) experiment in Toyama, Japan and worked on the related topics related to gravitational waves (GWs). If the construction progress of KAGRA is on schedule in 2019 and established in 2020, the detector sensitivity would be possible to be better than LIGO and VIRGO in the future. To be ready for the KAGRA experiment, we should build up a real research group and train our young researchers to study GWs.
•
• For the topics of Neutrino Physics and Dark Matter in the proposal, collaborations between WF Chang, CH Chen, CS Chen, CQ Geng and XG He are expected since they are the main people working on neutrino physics and dark matter in Taiwan. For Dark Energy, collaborations between KW Ng, WL Lee and GC Liu have already existed. For Gravitational Waves, CQ Geng, CS Chen and GC Liu currently are the official members of GAGRA, so that collaborations between them are also expected. In the references below, we list the most recent publications during the first phase of this TG. Clearly, real collaborations among all core members would be strengthened through various activities of this TG.
•
• Reference:
• 1. W.F. Chang and J.N. Ng, Renormalization Group Study of the Minimal Majoronic Dark Radiation and Dark Matter Model,'' JCAP 1607, 027 (2016).
• 2. W.F. Chang, S.C. Liou, C.F. Wong and F. Xu, Charged Lepton Flavor Violating Processes and Scalar Leptoquark Decay Branching Ratios in the Colored Zee-Babu Model,'' JHEP 1610, 106 (2016).
• 3. W.F. Chang and J.N. Ng, Neutrino masses and gauged U(1)l lepton number,'' JHEP 1810, 015 (2018).
• 4. C.H. Chen, C.W. Chiang and T. Nomura, Dark matter for excess of AMS-02 positrons and antiprotons,'' Phys. Lett. B747, 495 (2015).
• 5. C.H. Chen and T. Nomura, Searching for vector dark matter via Higgs portal at the LHC,'' Phys. Rev. D93, 074019 (2016).
• 6. C.H. Chen, C.W. Chiang and T. Nomura, Explaining the DAMPE e+e- excess using the Higgs triplet model with a vector dark matter,'' Phys. Rev. D97, 061302 (2018).
• 7. C.S. Chen and Y.H. Lin, On the evolution process of two-component dark matter in the Sun,'' JHEP 1804, 074 (2018).
• 8. C.S. Chen and Y.H. Lin, Reheating neutron stars with the annihilation of self-interacting dark matter,'' JHEP 1808, 069 (2018).
• 9. C.Q. Geng, C.C. Lee and J.L. Shen, Matter Power Spectra in Viable f(R) Gravity Models with Massive Neutrinos,'' Phys. Lett. B740, 285 (2015).
• 10. C.Q. Geng, D. Huang and C. Lai, Revisiting Multi-Component Dark Matter with New AMS-02 Data,'' Phys. Rev. D91, 095006 (2015).
• 11. 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).
• 12. C.Q. Geng, D. Huang and C. Lai, Comment on A three-loop radiative neutrino mass model with dark matter’ [Phys. Lett. B 741 (2015) 163],'' Phys. Lett. B745, 56 (2015).
• 13. 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).
• 14. C.Q. Geng, D. Huang and L.H. Tsai, CP violations in predictive neutrino mass structures,'' Eur. Phys. J. C75, 557 (2015).
• 15. C.Q. Geng, C.C. Lee, R. Myrzakulov, M. Sami and E.N. Saridakis, Observational constraints on varying neutrino-mass cosmology,'' JCAP 1601, 049 (2016).
• 16. C.Q. Geng and C.C. Lee, Deflation of the cosmological constant associated with inflation and dark energy,'' JCAP 1606, 039 (2016)
• 17. C.Q. Geng, C.C. Lee and K. Zhang, Running cosmological constant with observational tests,'' Phys. Lett. B760, 422 (2016).
• 18. C.Q. Geng, D. Huang, C.H. Lee and Q. Wang, Direct Detection of Exothermic Dark Matter with Light Mediator,'' JCAP 1608, 009 (2016).
• 19. C.Q. Geng and C.C. Lee, Matter density perturbation and power spectrum in running vacuum model,'' Mon. Not. Roy. Astron. Soc. 464, 2462 (2016). 3
• 20. C.Q. Geng and L.W. Luo, Teleparallel conformal invariant models induced by Kaluza–Klein reduction,'' Class. Quant. Grav. 34, 115012 (2017).
• 21. C.Q. Geng, C.C. Lee, M. Sami, E.N. Saridakis and A.A. Starobinsky, Observational constraints on successful model of quintessential Inflation,'' JCAP 1706, 011 (2017).
• 22. C.Q. Geng, C.C. Lee and L. Yin, Constraints on running vacuum model with H(z) and f σ8,'' JCAP 1708, 032 (2017).
• 23. C.Q. Geng and D. Huang, Large ν-ν Oscillations from High-Dimensional Lepton Number Violating Operator,'' JHEP 1703, 103 (2017).
• 24. C.Q. Geng, D. Huang and C.H. Lee, Exothermic Dark Matter with Light Mediator after LUX and PandaX-II in 2016,'' Phys. Dark Univ. 18, 38 (2017).
• 25. C.Q. Geng and H. Okada, Neutrino masses, dark matter and leptogenesis with U(1)B-L gauge symmetry,'' Phys. Dark Univ. 20, 13 (2018).
• 26. X.G. He, C.J. Lee, J. Tandean and Y.J. Zheng, Seesaw Models with Minimal Flavor Violation,'' Phys. Rev. D91, 076008 (2015).
• 27. G.N. Li and X.G. He, CP violation in neutrino mixing with \delta = -\pi/2 in A_4 Type-II seesaw model,'' Phys. Lett. B750, 620 (2015).
• 28. C.F. Chang, X.G. He and J. Tandean, Exploring Spin-3/2 Dark Matter with Effective Higgs Couplings,'' Phys. Rev. D96, 075026 (2017).
• 29. P.H. Gu and X.G. He, Electrophilic dark matter with dark photon: from DAMPE to direct detection,'' Phys. Lett. B778, 292 (2018).
• 30. S.L. Cheng, W. Lee and K.W. Ng, Numerical study of pseudoscalar inflation with an axion-gauge field coupling,'' Phys. Rev. D93, 063510 (2016).
• 31. H. Tu and K.W. Ng, Effects of Goldstone Bosons on Gamma-Ray Bursts,'' JCAP 1603, 037 (2016).
• 32. H. Tu and K.W. Ng, Supernovae and Weinberg’s Higgs portal dark radiation and dark matter,'' JHEP 1707, 108 (2017).
• 33. C.C. Chang, W. Lee and K.W. Ng, Spherical Collapse Models with Clustered Dark Energy,'' Phys. Dark Univ. 19, 12 (2018).
• 34. S.L. Cheng, W. Lee and K.W. Ng, Primordial black holes and associated gravitational waves in axion monodromy inflation,'' JCAP 1807, 001 (2018).
• 35. G.C. Liu, K. Ichiki, H. Tashiro and N. Sugiyama, Reconstruction of CMB Temperature Anisotropies with Primordial CMB Induced Polarization in Galaxy Clusters,'' Mon. Not. Roy. Astron. Soc. 460, L104 (2016).
•

IV. Activities:

• • Seminars, Joint Meetings, Courses and Schools
• 1 workshop on Dark Physics
• 1 Joint Meeting with Gravity
• 1 Joint Meeting with LHC physics
• 1 schools with specific topics on Gravitational Waves and Modified Gravitational Theories
• 3 special courses on dark energy, neutrino physics, dark matter and gravitational waves
•
• • International Workshop
• 6th International Workshop on `Dark Matter, Dark Energy and Matter-antimatter Asymmetry,’’around Nov. 2020 @ NCTS
•
• • Attendance of International Activities
• Supporting students/postdocs to attend international conferences
•
• • Visitors and International Collaborations

V. Expected Achievement:

• We wish to publish about 5~10 research articles per year in the most important journals in Particle Physics and Cosmology, such as JHEP, JCAP, PRD, PLB and EPJC. We expect that some of our results will also be presented in the international conferences. This proposal should provide an excellent research environment to train postdocs and graduate students. It would also enhance the visibility of NCTS/Taiwan in the world.