1. Teng, Y.-P., Lee, W., & Ng, K.-W., PHYSICAL REVIEW D 104, 083519 (2021)
  2. Cheng, S-L. , Lee, W. and Ng, K-W., PHYSICAL REVIEW D 99, 063524 (2019)
  3. We investigate the clustering effect of dark energy (DE) in the formation of galaxy clusters using the spherical collapse model. Assuming a fully clustered DE component, the spherical overdense region is treated as an isolated system which conserves the energy separately for both matter and DE inside the spherical region. Then, by introducing a parameter r to characterize the degree of DE clustering, which is defined by the nonlinear density contrast ratio of matter to DE at turnaround in the recollapsing process, i.e. r ≡ δNL /δNL , we are able to uniquely determine the spherical collapsing process and hence de,ta m,ta obtain the virialized overdensity ∆vir through a proper virialization scheme. Estimation of the virialized overdensities from current observation on galaxy clusters suggests that 0.5 < r < 0.8 at 1σ level for the clustered DE with w < −0.9. Also, we compare our method to the linear perturbation theory that deals with the growth of DE perturbation at early times. While both results are consistent with each other, our method is practically simple and it shows that the collapse process is rather independent of initial DE perturbation and its evolution at early times.
  4. In the axion monodromy inflation, the inflation is driven by the axion with super- Planckian field values in a monomial potential with superimposed sinusoidal modulations. The coupling of the axion to massless gauge fields can induce copious particle production during inflation, resulting in large non-Gaussian curvature perturbation that leads to the formation of primordial black holes. In this paper, we explore the parameter space in the axion monodromy inflation model that favors the formation of primordial black holes with masses ranging from 108 grams to 20 solar masses. We also study the associated gravitational waves and their detection in pulsar timing arrays and interferometry experiments.
  5. Trapped inflation has been proposed to provide a successful inflation with a steep potential. We discuss the formation of primordial black holes in the trapped inflationary scenario. We show that primordial black holes are naturally produced during inflation with a steep trapping potential. In particular, we have given a recipe for an inflaton potential with which particle production can induce large non-Gaussian curvature perturbation that leads to the formation of high stellar-mass primordial black holes. These primordial black holes could be dark matter observed by the LIGO detectors through a binary black-hole merger. At the end, we have given an attempt to realize the required inflaton potential in the axion monodromy inflation, and discussed the gravitational waves sourced by the particle production.
  6. A numerical study of a pseudoscalar inflation having an axion-photon-like coupling is performed by solving numerically the coupled differential equations of motion for inflaton and photon mode functions from the onset of inflation to the end of reheating. The backreaction due to particle production is also included self-consistently. We find that this particular inflation model realizes the idea of a warm inflation in which a steady thermal bath is established by the particle production. In most cases, this thermal bath exceeds the amount of radiation released in the reheating process. In the strong coupling regime, the transition from the inflationary to the radiation-dominated phase does not involve either a preheating nor reheating process. In addition, energy density peaks produced near the end of inflation may lead to the formation of primordial black holes.
  7. We discuss the generation of primordial magnetic fields during inflation in dilaton-axion electromagnetism, in which the dilaton and axion dynamics are introduced in terms of two time dependent functions of the cosmic scale factor, I(a)F2/4 and J(a)FF ̃/4, respectively, where F is the electromagnetic field strength and F ̃ is its dual. We study the form of J(a) that can generate a large seed magnetic field. Although the J(a) function is model dependent, the axion-photon coupling may open up a new window for a successful inflationary magnetogenesis.
  8. We apply the teleparallelism condition to the Poincar ́e gauge theory (PGT) of gravity. The resultant teleparallelized cosmology is completely equivalent to the Friedmann cos- mology derived from Einstein’s general theory of relativity. The torsion is shown to play the role of the cosmological constant driving the cosmic acceleration. We then extend such theory to include the effect of spin and explore the possibility of accounting for the current accelerating universe by a spinning dark energy.
  9. Contrary to the conventional wisdom, we find that it is possible to generate coherent magnetic seed fields over a scale of 10 Mpc efficiently via spinodal instability during the primordial inflation, provided that a fast-roll stage is involved before the inflaton entering into the slow-roll phase. How- ever, the primordial magnetic field produced in such a mechanism is far too powerful to consistently fit in the energy constraint required by the scalar field driving the cosmic inflation.
  10. Contrary to the conventional wisdom, we find that it is plausible to generate primordial magnetic seed fields via spinodal instability efficiently during cosmic inflation provided that a fast-roll stage is involved before the inflaton entering into the slow-roll phase. Moreover, the primordial magnetic field produced in such a mechanism can be used to constrain the low quadrupole moment of Cosmic Microwave Background.
  11. We develop a Lagrangian approach based on the influence functional method so as to derive self- consistently the Langevin equation for the inflaton field in the presence of trapping points along the inflaton trajectory. The Langevin equation exhibits the backreaction and the fluctuation-dissipation relation of the trapping. The fluctuation is induced by a multiplicative colored noise that can be identified as the particle number density fluctuations; and the dissipation is a new effect that may play a role in the trapping with a strong coupling. In the weak coupling regime, we calculate the power spectrum of the noise-driven inflaton fluctuations for a single trapping point and studied its variation with the trapping location. We also consider a case with closely spaced trapping points and find that the resulting power spectrum is blue.

名稱 開始日期 結束日期 委託單位 編號 參與身份別
早期宇宙反饋作用之探索 2019/08/01 2020/07/31 科技部(原國科會) MOST 108-2112-M-003-001 - 主持人
不均勻宇宙之膨脹與暗能量 2008/08/01 2011/07/31 國科會 NSC 97-2112-M-003-004-MY3 總主持人
非平衡宇宙微擾之研究（3／3） 2007/08/01 2008/07/31 國科會 NSC 96-2112-M-003-001 總主持人
非平衡宇宙微擾之研究（2／3） 2006/08/01 2007/07/31 國科會 NSC 95-2112-M-003-002 總主持人
非平衡宇宙微擾之研究（1／3） 2005/08/01 2006/07/31 國科會 NSC 94-2112-M-003-015 總主持人
暴脹宇宙之相關性檢測 2004/11/01 2005/07/31 國科會 NSC 93-2112-M-003-019 總主持人