The previous proposal (by two of us) of chain inflation with the QCD axion is shown to fail. The proposal involved a series of fast tunneling events, yet here it is shown that tunneling is too slow. We calculate the bubble nucleation rates for phase transitions in the thick wall limit, approximating the barrier by a triangle. A similar problem arises in realization of chain inflation in the string landscape that uses series of minima along the monodromy staircase around the conifold point. The basic problem is that the minima of the potential are too far apart to allow rapid enough tunneling in these two models. We entertain the possibility of overcoming this problem by modifying the gravity sector to a Brans-Dicke theory. However, one would need extremely small values for the Brans-Dicke parameter. Many successful alternatives exist, including other "axions" (with mass scales not set by QCD) or potentials with comparable heights and widths that do not suffer from the problem of slow tunneling and provide successful candidates for chain inflation.
We study the effects of particle production on the evolution of the inflaton field in an axion monodromy model with the goal of discovering in which situations the resulting dynamics will be consistent with the {\it swampland constraints}. In the presence of a modulated potential the evolving background field (solution of the inflaton homogeneous in space) induces the production of long wavelength inflaton fluctuation modes. However, this either has a negligible effect on the inflaton dynamics (if the field spacing between local minima of the modulated potential is large), or else it traps the…
打破离散移位对称性（axion monodromy）的轴子最近发挥了核心作用，无论是在讨论通货膨胀和“松弛”的方法的层次结构问题。我们提出了一个非常简约的方式来约束这样的模型的弱引力猜想畴壁：虽然电侧的猜想总是满意的，如果余弦振荡的轴子潜力是足够小的，磁侧施加一个截止，$Λ^3 \sim m f M_{pl}$，独立于这些“摆动”的高度。我们比较了我们的方法与最近的相关建议，由Ibanez，Albero，Uranga和Valenzuela。我们还讨论了非平凡的问题的版本，如果有的话，域壁的弱引力猜想应该举行。特别是，我们证明了不同维度的膜包裹在不同圈上的弦紧化会导致一个与圈的体积、相应形式的范数和紧致空间的体积相关的“几何弱引力猜想”。强加这种“几何几何图形”的，例如~在更广泛接受的粒子弱引力猜想的基础上，至少为畴壁的（电和磁）猜想提供了一些支持。
Spectral Distortions from Axion Monodromy Inflation
Universidad Autónoma de Chiapas（奇亚帕斯自治大学）；Universidad de El Salvador（萨尔瓦多大学）；Consejo Nacional de Ciencia y Tecnología（国家科学技术委员会）；Instituto de Física, Universidad Nacional Autónoma de México（墨西哥国立自治大学物理研究所）
We consider a general class of axion models, including the QCD and string axion, in which the PQ symmetry is broken before or during inflation. Assuming the axion is the dominant component of the dark matter, we discuss axion star formation in virialized dark minihalos around primordial black holes through gravitational Bose-Einstein condensation. We determine the conditions for minihalos to kinetically produce axion stars before galaxy formation. Today, we expect up to $\sim 10^{17}$ ($\sim 10^9$) axion stars in a radius of 100 parsecs around the Sun for the case of the QCD (string) axion.
In string theory inspired models of axion-like fields, sub-leading non-perturbative effects, if sufficiently large, can introduce steep cliffs and gentle plateaus onto the underlying scalar potential. During inflation, the motion of a spectator axion $σ$ on this potential becomes temporarily fast, leading to localized amplification of one helicity state of gauge fields. In this model, the tensor and scalar correlators sourced by the vector fields exhibit localized peak(s) in momentum space corresponding to the modes that exit the horizon while the roll of $σ$ is fast. Thanks to the gravitation…
We present a scenario that ameliorates the tuning problems present in models of primordial black hole dark matter from inflation. Our setup employs the advantages of gravitational collapse in a long epoch of early matter domination with reheating temperature $\lesssim 10^{6}~\text{GeV}$. Furthermore, we make use of a string-inspired class of models where the inflaton is identified with a non-compact axion field. In this framework, the presence of multiple local minima in the inflaton potential can be traced back to an approximate discrete shift symmetry. This scenario allows the formation of p…
Very-High-Frequency Gravitational Waves from Multi-Monodromy Inflation
University of Parma（帕尔马大学）；INFN Gruppo Collegato di Parma（意大利国家核物理研究所帕尔马协作组）；Northwestern University（西北大学）；University of California Davis（加州大学戴维斯分校）；Deutsches Elektronen-Synchrotron DESY（德国电子同步加速器）
We revisit two-field hybrid inflation as an effective field theory for low-scale inflation with sub-Planckian scalar field ranges. We focus on a prototype model by Stewart because it allows for a red spectral tilt, which still fits the current data. We describe the constraints on this model imposed by current CMB measurements. We then explore the stability of this model to quantum corrections. We find that for relevant, marginal, and at least a finite set of irrelevant operators, some additional mechanism is required to render the model stable to corrections from both quantum field theory and …
A totally asymptotically free QCD axion model, where all couplings flow to zero in the infinite energy limit, was recently formulated. A very interesting feature of this fundamental theory is the ability to predict some low-energy observables, like the masses of the extra fermions and scalars. Here we find and investigate a region of the parameter space where the Peccei-Quinn (PQ) symmetry is broken quantum mechanically through the Coleman-Weinberg mechanism. This results in an even more predictive framework: the axion sector features only two independent parameters (the PQ symmetry breaking s…
Technically Natural Baryogenesis with the QCD Axion
University of California Santa Cruz（加州大学圣克鲁兹分校）；University of Washington（华盛顿大学）；International Centre for Theoretical Physics（国际理论物理中心）；Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Trieste（意大利国家核物理研究所的里雅斯特分部）；University of California, Berkeley（加州大学伯克利分校）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）
