We present a new class of two-field inflationary attractor models, known as {}, whose behaviour is strongly multi-field but whose predictions are remarkably close to those of single-field inflation. In these models, the field space metric and potential are such that the inflaton trajectory is along an angular' isometry direction whoseradius’ is constant but {}. As a result, the radial (isocurvature) perturbations away from the trajectory are exactly {} and they freeze on superhorizon scales. These models are the first exact realization of the `ultra-light isocurvature’ scenario, previously described in the literature, where a combined shift symmetry emerges between the curvature and isocurvature perturbations and results in primordial perturbation spectra that are entirely consistent with current observations. Due to the turning trajectory, the radial perturbation sources the tangential (curvature) perturbation and makes it grow linearly in time. As a result, only one degree of freedom ({} the one from isocurvature modes) is responsible for the primordial observables at the end of inflation, which yields the same phenomenology as in single-field inflation. In particular, isocurvature perturbations and local non-Gaussianity are highly suppressed here, even if the inflationary dynamics is truly multi-field. We comment on the generalization to models with more than two fields.

中文翻译：

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偏移对称的轨道膨胀：单场还是多场？

我们提出了一种新的两场通货膨胀吸引模型，称为{}，其行为具有很强的多场作用，但其预测与单场通货膨胀的预测非常接近。在这些模型中，场空间量度和势能使充气子轨迹沿着angular' isometry direction whoseradius'是常数，但{}。结果，远离轨迹的径向（等曲率）扰动正好{}，并且冻结在超水平尺度上。这些模型是先前在文献中描述的“超光等曲率”场景的第一个精确实现，其中曲率和等曲率摄动之间出现了组合的偏移对称性，并产生了与当前观测值完全一致的原始摄动谱。由于转动轨迹，径向扰动会产生切向（曲率）扰动，并使其随时间线性增长。结果，只有一个自由度（等曲率模式的一个自由度）负责通货膨胀结束时的原始可观测量，这产生了与单场通货膨胀相同的现象。尤其是，即使通货膨胀动力学确实是多场的，在这里也能抑制等曲率扰动和局部非高斯性。我们对具有两个以上字段的模型的泛化发表评论。