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arXiv 1702.05924hep-phastro-ph.COhep-th
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关于轴宇宙中的暗辐射问题

On the dark radiation problem in the axiverse

Dmitry Gorbunov, Anna Tokareva

摘要:

弦理论一般预言我们生活在一个所谓的轴宇宙中:宇宙中有大约100种轻的轴子,它们与标准模型粒子脱钩。然而,轴子可以耦合到暴胀子,导致它们在暴胀后产生。然后,这些轴子留在膨胀的宇宙中,贡献了暗辐射分量,这与目前的宇宙学数据严重相关。我们把一个一般的约束的轴子生产率,并将其应用到几个变种的合理的膨胀轴子耦合。这个极限仅仅限制了超轻轴子的数量和膨胀子与轴子耦合的相对强度。它在大、小场暴胀模型中都是有效的,与轴子的能量尺度和质量无关。因此,这个极限与宇宙过闭合和轴子等曲率波动的极限是互补的。特别是,如果暴胀子在再加热时普遍耦合到所有的场,则禁止一百个轴子。在引力扇区负责宇宙再加热的情况下(这在所有具有修正引力的暴胀模型中是一个自然的选择),轴子的产生可以是有效的。我们发现,在Starobinsky $R^2$ -暴胀中,即使是一个单一的轴子(例如标准的QCD-轴子)与普朗克数据的张力,使模型与轴宇宙不一致。一般的结论是,低再加热温度和低再加热机制的暴胀可能与轻标量的存在处于紧张状态。

英文摘要:

String scenarios generically predict that we live in a so called axiverse: the Universe with about a hundred of light axion species which are decoupled from the Standard Model particles. However, the axions can couple to the inflaton which leads to their production after inflation. Then, these axions remain in the expanding Universe contributing to the dark radiation component, which is severely bounded from present cosmological data. We place a general constraint on the axion production rate and apply it to several variants of reasonable inflaton-to-axion couplings. The limit merely constrains the number of ultralight axions and the relative strength of inflaton-to-axion coupling. It is valid in both large and small field inflationary models irrespectively of the axion energy scales and masses. Thus, the limit is complementary to those associated with the Universe overclosure and axion isocurvature fluctuations. In particular, a hundred of axions is forbidden if inflaton universally couples to all the fields at reheating. In the case of gravitational sector being responsible for the reheating of the Universe (which is a natural option in all inflationary models with modified gravity), the axion production can be efficient. We find that in the Starobinsky $R^2$-inflation even a single axion (e.g. the standard QCD-axion) is in tension with the Planck data, making the model inconsistent with the axiverse. The general conclusion is that an inflation with inefficient reheating mechanism and low reheating temperature may be in tension with the presence of light scalars.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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