We present an introduction to cosmic inflation in the context of Palatini gravity, which is an interesting alternative to the usual metric theory of gravity. In the latter case only the metric $$g_{\mu \nu }$$ g μ ν determines the geometry of space-time, whereas in the former case both the metric and the space-time connection $$\varGamma ^\lambda _{\mu \nu }$$ Γ μ ν λ are a priori independent variables—a choice which can lead to a theory of gravity different from the metric one. In scenarios where the field(s) responsible for cosmic inflation are coupled non-minimally to gravity or the gravitational sector is otherwise extended, assumptions of the underlying gravitational degrees of freedom can have a big impact on the observational consequences of inflation. We demonstrate this explicitly by reviewing several interesting and well-motivated scenarios including Higgs inflation, $$R^2$$ R 2 inflation, and $$\xi $$ ξ -attractor models. We also discuss some prospects for future research and argue why $$r=10^{-3}$$ r = 10 - 3 is a particularly important goal for future missions that search for signatures of primordial gravitational waves.

中文翻译：

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追踪引力的高能理论：帕拉蒂尼暴胀简介

我们在帕拉蒂尼引力的背景下介绍了宇宙膨胀，这是对通常的引力度量理论的有趣替代。在后一种情况下，只有度量 $$g_{\mu \nu }$$ g μ ν 决定了时空的几何形状，而在前一种情况下，度量和时空连接 $$\varGamma ^\lambda _{\mu \nu }$$ Γ μ ν λ 是先验的自变量——一种选择可以导致一种不同于度量理论的引力理论。在导致宇宙暴胀的场与引力非最小耦合或引力扇区以其他方式扩展的情况下，潜在引力自由度的假设会对暴胀的观测结果产生重大影响。我们通过回顾几个有趣且动机良好的场景，包括 Higgs 通货膨胀、$$R^2$$R 2 通货膨胀和 $$\xi $$ ξ -attractor 模型，明确地证明了这一点。我们还讨论了未来研究的一些前景，并论证了为什么 $$r=10^{-3}$$ r = 10 - 3 是未来寻找原始引力波特征的任务的一个特别重要的目标。