Lorentz boost and non-Gaussianity in multifield DBI inflation
Lorentz boost and non-Gaussianity in multifield DBI inflation
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多场 DBI 膨胀中的洛伦兹提升和非高斯性
DOI：
10.1103/physrevd.80.023530
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发表时间：
2009
影响因子：
5
通讯作者：
Mizuno S
中科院分区：
文献类型：
--
作者：
Mizuno S
我们表明，多场狄拉克-玻恩-因菲尔德（DBI）膨胀模型中宇宙扰动的高阶作用是通过从膜的静止框架到膜移动的框架的洛伦兹提升获得的。我们确认，这种简单的方法在慢滚和小声速限制的前导阶上提供了与通常的 Arnowitt-Deser-Misner 形式所获得的相同的三阶和四阶作用。作为一个应用，我们计算了来自多场 DBI 暴胀模型中固有的四阶接触相互作用的原初曲率扰动的前阶连通四点函数。在三阶，相互作用哈密顿量纯粹是由膜的静止框架中的二阶作用的推动产生的。升压以相同的方式作用于绝热模态和熵模态，因此绝热模态和熵模态之间存在对称性。但在四阶，由于静止坐标系中固有的四阶作用以及拉格朗日量和相互作用哈密顿量之间的差异，这种对称性被打破。因此，与三点函数相反，四点函数中纯绝热分量和包含熵贡献的分量的动量依赖性是不同的。这表明三谱可以区分多场 DBI 膨胀模型和单场 DBI 膨胀模型。
We show that higher-order actions for cosmological perturbations in the multifield Dirac-Born-Infeld (DBI) inflation model are obtained by a Lorentz boost from the rest frame of the brane to the frame where the brane is moving. We confirm that this simple method provides the same third- and fourth-order actions at leading order in slow roll and in the small sound speed limit as those obtained by the usual Arnowitt-Deser-Misner formalism. As an application, we compute the leading order connected four-point function of the primordial curvature perturbation coming from the intrinsic fourth-order contact interaction in the multifield DBI-inflation model. At third order, the interaction Hamiltonian arises purely by the boost from the second-order action in the rest frame of the brane. The boost acts on the adiabatic and entropy modes in the same way, thus there exists a symmetry between the adiabatic and entropy modes. But at fourth order this symmetry is broken due to the intrinsic fourth-order action in the rest frame and the difference between the Lagrangian and the interaction Hamiltonian. Therefore, contrary to the three-point function, the momentum dependence of the purely adiabatic component and the components including the entropic contributions are different in the four-point function. This suggests that the trispectrum can distinguish the multifield DBI-inflation model from the single field DBI-inflation model.