Relaxing the Cosmological Moduli Problem by Low-scale Inflation. (arXiv:1901.01240v1 [hep-ph])
<a href="http://arxiv.org/find/hep-ph/1/au:+Ho_S/0/1/0/all/0/1">Shu-Yu Ho</a>, <a href="http://arxiv.org/find/hep-ph/1/au:+Takahashi_F/0/1/0/all/0/1">Fuminobu Takahashi</a>, <a href="http://arxiv.org/find/hep-ph/1/au:+Yin_W/0/1/0/all/0/1">Wen Yin</a>
We show that the cosmological abundance of string axions is much smaller than
naive estimates if the Hubble scale of inflation, H_{inf}, is sufficiently low
(but can still be much higher than the axion masses) and if the inflation lasts
sufficiently long. The reason is that the initial misalignment angles of the
string axions follow the Bunch-Davies distribution peaked at the potential
minima. As a result, the cosmological moduli problem induced by the string
axions can be significantly relaxed by low-scale inflation, and astrophysical
and cosmological bounds are satisfied over a wide range of the mass without any
fine-tuning of the initial misalignment angles. Specifically, the axion with
its decay constant f_phi = 10^{16} GeV satisfies the bounds over 10^{-18} eV
lesssim m_phi lesssim 10 TeV for H_{inf} lesssim 10 keV- 10^6 GeV. We also
briefly discuss cases with multiple axions and the QCD axion.
We show that the cosmological abundance of string axions is much smaller than
naive estimates if the Hubble scale of inflation, H_{inf}, is sufficiently low
(but can still be much higher than the axion masses) and if the inflation lasts
sufficiently long. The reason is that the initial misalignment angles of the
string axions follow the Bunch-Davies distribution peaked at the potential
minima. As a result, the cosmological moduli problem induced by the string
axions can be significantly relaxed by low-scale inflation, and astrophysical
and cosmological bounds are satisfied over a wide range of the mass without any
fine-tuning of the initial misalignment angles. Specifically, the axion with
its decay constant f_phi = 10^{16} GeV satisfies the bounds over 10^{-18} eV
lesssim m_phi lesssim 10 TeV for H_{inf} lesssim 10 keV- 10^6 GeV. We also
briefly discuss cases with multiple axions and the QCD axion.
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