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arXiv 1812.03340gr-qcastro-ph.COhep-th
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混合螺旋度暴胀及其对CMB的观测影响

Inflation with mixed helicities and its observational imprint on CMB

Lavinia Heisenberg, Héctor Ramírez, Shinji Tsujikawa

摘要:

在有效场论的框架内,突出的螺旋度-0和螺旋度-1场通过三维算子相互耦合,我们研究了由螺旋度-0模式驱动的暴胀动力学,具有给定的势能,以及宇宙学扰动的演变,影响两个螺旋度之间的混合项的存在。在这种情况下,螺旋度-1模式的时间分量是辅助场,并且可以根据螺旋度-0模式的时间导数进行积分,使得背景动态有效地减少到由与螺旋度-0和螺旋度-1模式之间的耦合相关联的参数$β$调制的单场膨胀中的背景动态。我们讨论了纵向标量扰动$ψ$和暴胀波动$δϕ$的演变,并明确表明,这两个,这对应于一个isocurvature模式的一个特定的组合,受到指数抑制的矢量质量可比的哈勃膨胀率在通货膨胀。此外,我们还发现,由$β$修正的有效单场描述也适用于暴胀过程中产生的曲率扰动的功率谱。我们计算了标准的暴胀观测量,如标量谱指数$n_s$和张量标量比$r$,并与普朗克2018年提供的最新观测数据进行了比较。我们的结果表明,螺旋度-0和螺旋度-1模式之间的耦合可以导致更小的张量标量比的值,特别是对于小场暴胀模型,所以我们的方案表现出更好的兼容性与当前的观测数据。

英文摘要:

In the framework of effective field theories with prominent helicity-0 and helicity-1 fields coupled to each other via a dimension-3 operator, we study the dynamics of inflation driven by the helicity-0 mode, with a given potential energy, as well as the evolution of cosmological perturbations, influenced by the presence of a mixing term between both helicities. In this scenario, the temporal component of the helicity-1 mode is an auxiliary field and can be integrated out in terms of the time derivative of the helicity-0 mode, so that the background dynamics effectively reduces to that in single-field inflation modulated by a parameter $β$ associated to the coupling between helicity-0 and helicity-1 modes. We discuss the evolution of a longitudinal scalar perturbation $ψ$ and an inflaton fluctuation $δϕ$, and explicitly show that a particular combination of these two, which corresponds to an isocurvature mode, is subject to exponential suppression by the vector mass comparable to the Hubble expansion rate during inflation. Furthermore, we find that the effective single-field description corrected by $β$ also holds for the power spectrum of curvature perturbations generated during inflation. We compute the standard inflationary observables such as the scalar spectral index $n_s$ and the tensor-to-scalar ratio $r$ and confront several inflaton potentials with the recent observational data provided by Planck 2018. Our results show that the coupling between helicity-0 and helicity-1 modes can lead to a smaller value of the tensor-to-scalar ratio especially for small-field inflationary models, so our scenario exhibits even better compatibility with the current observational data.

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