Thermalized axion inflation
Thermalized axion inflation
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热化轴子膨胀
DOI：
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
A. Notari
中科院分区：
文献类型：
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作者：
R. Z. Ferreira;A. Notari
我们分析了暴胀模型的动力学与暴胀子耦合的规范场的形式<$F F <$/f，在轴子的情况下。已知这会导致不稳定性，伴随着规范场的指数放大，由参数λ = λ今/（2fH）控制，这会强烈影响宇宙学微扰的产生，甚至是背景。我们表明，涉及规范场的散射率可以变得大于膨胀率H，由于非常大的占有数，并在膨胀过程中产生温度为T的粒子的热浴。在热状态下，能量被转移到更小的尺度上，从根本上改变了这种情况的预测。因此，我们认为，以前的限制，减轻了。如果规范场具有标准模型相互作用，这自然会提供再加热，那么它们在微扰性约束和反反应发生之前就已经在2.9处热化了。在没有SM相互作用的情况下（即对于暗光子），我们发现，规范场和暴胀子扰动热化，如果ε 3.4;然而，观测需要ε 6，这是上面的微扰和反反应的界限，所以需要专门的研究。然而，热化之后，由于不稳定性和规范场热质量之间的竞争，系统应该会发生非平凡的演化。如果热质量和不稳定性平衡，我们预计平衡温度为Teq H/，其中是有效规范耦合。最后，我们估计的扰动谱，如果张量是热的，并发现张量标量比抑制H/（2 T），如果张量不热化。
We analyze the dynamics of inflationary models with a coupling of the inflaton ϕ to gauge fields of the form ϕ F F̃/f, as in the case of axions. It is known that this leads to an instability, with exponential amplification of gauge fields, controlled by the parameter ξ= ϕ̇/(2fH), which can strongly affect the generation of cosmological perturbations and even the background. We show that scattering rates involving gauge fields can become larger than the expansion rate H, due to the very large occupation numbers, and create a thermal bath of particles of temperature T during inflation. In the thermal regime, energy is transferred to smaller scales, radically modifying the predictions of this scenario. We thus argue that previous constraints on ξ are alleviated. If the gauge fields have Standard Model interactions, which naturally provides reheating, they thermalize already at ξ≳2.9, before perturbativity constraints and also before backreaction takes place. In absence of SM interactions (i.e. for a dark photon), we find that gauge fields and inflaton perturbations thermalize if ξ≳3.4; however, observations require ξ≳6, which is above the perturbativity and backreaction bounds and so a dedicated study is required. After thermalization, though, the system should evolve non-trivially due to the competition between the instability and the gauge field thermal mass. If the thermal mass and the instabilities equilibrate, we expect an equilibrium temperature of Teq ≃ ξ H/ḡ where ḡ is the effective gauge coupling. Finally, we estimate the spectrum of perturbations if ϕ is thermal and find that the tensor to scalar ratio is suppressed by H/(2T), if tensors do not thermalize.