Natural%20Phantom%20Dark%20Energy,%20Wiggling%20Hubble%20Parameter%20H(z)%20and%20Direct%20H(z)%20Data

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Natural Phantom Dark Energy, Wiggling Hubble
Parameter H(z)and Direct H(z) Data

• ???(KASI)
• Principle reference Zhang,Hongsheng and Zhu,
  Zong-Hong, JCAP03(2008)007

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Outline

• A quick glance at DE models
• New features of H(z) data
• NP DE model
• Summary

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Acceleration

• Really accelerating?
• 1. Problem of the standard candles
• 2. Nebulae and interstellar matters
• Alternative gravity theory
• 1. f(R) gravity
• 2. Braneworld gravity
• Exotic matters (or called dark energy)
• 1. Cosmological constant (w-1)
• 2. Dynamical ones
• a. Quintessence (wgt-1)
• b. Phantom (wlt-1)
• c. Quintom (crossing w-1)
• D. The EoS of the total fluid (not only
  the dark energy) crosses
• w-1, which is the topic of my
  report.

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Wiggles on H(z)

• The deficiency of luminosity distances
• Hence, direct H(z) data can break the
  degeneration.
• (J. Simon, L. Verde and R. Jimenez, Phys. Rev. D
  71, 123001 (2005))

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Wiggles on H(z) parameterizations

• We can directly parameterize the H(z) data with
  oscillation behavior, for examples,
• (H. Wei and S. N. Zhang, Phys. Lett. B 644, 7
  (2007))

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Pseudo Nambu-Goldstone Boson (PNGB)
The H(z) data in table I implies the EOS of total
fluid in the universe crosses -1, not only the
dark energy sector. PNGB is an important idea in
particle physics. It emerges whenever a global
symmetry is spontaneously broken. There are two
key scales of PNGB generation. One is the scale
at which the global symmetry breaks, denoted by
f, and the other is the scale at which the soft
explicit symmetry breaks, denoted by C. The
property of oscillation appears naturally in the
present natural dark energy model.
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Construction
We work in a frame of standard general
relativity and spatially flat FRW universe
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Fitting result
The fitting result of the parameters and
p. (a) The 68.3 confidence contour plot by using
the direct H(z) data. (b) The 68.3 confidence
contour plot by using the SNLS data.
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Some discussions

• Comparing the two figures, it is evident
  that the resolution of supernavae data is less
  inefficiency than direct H(z) data to the
  oscillating behaviour of H(z).
• The 68.3 confidence contour of H(z) data
  is disconnect. The physical explanation is that
  the data set of direct H(z) is too small, that
  is, the data do not distinctly illuminate how
  many wiggles inhabit on H(z). New wiggles may
  hide in the gaps of the data set, which leads
  that a much bigger p lies in the same confidence
  region as a smaller p.

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Deceleration parameter
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Quantum stability

• A severe problem of any phantom field is
  quantum stability. In practice, we do not require
  that the phantom is fundamentally stable, but
  quasi-stable, which means, its lifetime is larger
  than the age of the universe.
• We consider both the ordinary coupling and
  derivative coupling, and we find that We find it
  is a viable model if we treat it as an effective
  theory truncated by an upperbound.

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Summary

• To summarize, this research illuminates that
  direct H(z) data is much more efficient than the
  supernovae for the fine structures of Hubble
  diagram.
• We first put forward a model based on the
  previous studies on the PNGB. In this model the
  total fluid in the universe may evolve as phantom
  in some stages, which contents the direct H(z)
  data. We fit our model by using H(z) data and
  supernovae data, respectively. The results are
  quite different, as we expected.
• We investigate the stability of the present
  model. Our treatise is to treat the phantom model
  as an effective model truncated at some energy
  scale. We find that the couplings between
  phantom and graviton are viable for the special
  potential of the present model.

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• Thanks