Relaxing the TCC Bound on Inflationary Cosmology?

弦时空不确定性原理与修正的跨普朗克审查准则

Stringy Spacetime Uncertainty Principle and a Modified Trans-Planckian Censorship Criterion

本文研究弦时空不确定关系（STUR）对暴胀宇宙学的启示，通过要求涨落模式不受STUR非局域性影响，得出比跨普朗克审查准则弱2倍的暴胀e-foldings数与能标上限，该界限仍与典型单场暴胀模型相冲突。

Relaxing inflation models with non-minimal coupling: A general study

We investigate the predictions of inflation models with a non-minimal coupling to gravity for inflationary observables such as the spectral index and tensor-to-scalar ratio in a general setting. We argue that, depending on the relation between the Jordan frame potential and a function characterizing the non-minimal coupling, one can classify the model into three categories each of which gives distinctive predictions for the inflationary observables. We derive general predictions for each class and also investigate some explicit models to discuss how the general features arise. Our results woul…

Trans-Planckian censorship and other swampland bothers addressed in warm inflation

The implications of the recently proposed Trans-Planckian censorship conjecture (TCC) are analyzed in the context of warm inflation. It is found that for a single-stage accelerated expansion the constraints imposed by the censorship are roughly the same as for cold inflation. Next, we study how a two-stage inflationary expansion with an intermediate radiation-dominated era can alleviate the bounds imposed by the censorship. For a demonstrative toy model we found $r<10^{-23}$, but can be $r<10^{-5}$ for a weaker form of TCC for the later stages of expansion, while still satisfying the other swa…

Non-Standard Cosmological Models and the trans-Planckian Censorship Conjecture

The trans-Planckian censorship conjecture (TCC) puts an upper bound on the life-time of de Sitter spacetimes. It has immediate consequences for inflationary cosmology. In the standard paradigm, the universe has experienced a single stage of inflation and follows a thermal history. Then, the TCC puts an upper bound on the Hubble parameter during inflation $H_{\rm inf}$ around $0.1$ GeV. Consequently, it implies a severe fine-tuning in initial condition for inflation and non-detection of primordial gravitational waves. In this note, we study non-standard cosmological paradigms with non-thermal h…

Universal Upper Bound on the Inflationary Energy Scale from the Trans-Planckian Censorship Conjecture

We study the constraint on the inflationary energy scale from the recently proposed Trans-Planckian Censorship Conjecture (TCC). We find a universal upper bound on the inflationary Hubble expansion rate $H_\text{inf}$ which is solely determined by the reheating temperature $T_\text{rh}$: $H_\text{inf}/M_\text{Pl}\lesssim T_0/T_\text{rh}$, where $T_0$ is the photon temperature today. The upper limit can be saturated by a post-inflationary oscillatory stage with the critical equation-of-state parameter $w\approx-1/3$, or by an inflation model with multiple stages. In the lowest reheating tempera…

Mass bound for primordial black hole from trans-Planckian censorship conjecture

The recently proposed trans-Planckian censorship conjecture (TCC) imposes a strong constraint on the inflationary Hubble scale, of which the upper bound could be largely relaxed by considering a noninstantaneous reheating history. In this paper we will show that, if the primordial black holes (PBHs) are formed at reentry in the radiation-dominated era from the enhanced curvature perturbations at small scales, the TCC would impose a lower bound on the PBH mass $M_\mathrm{PBH}>γ(H_\mathrm{end}/10^9\,\mathrm{GeV})^2\,M_\odot$ regardless of the details for reheating history, where $γ$ is the colla…

Role of trans-Planckian modes in cosmology

Motivated by the old trans-Planckian (TP) problem of inflationary cosmology, it has been conjectured that any consistent effective field theory should keep TP modes `hidden' behind the Hubble horizon, so as to prevent them from turning classical and thereby affecting macroscopic observations. In this paper we present two arguments against the Hubble horizon being a scale of singular significance as has been put forward in the TP Censorship Conjecture (TCC). First, refinements of TCC are presented that allow for the TP modes to grow beyond the horizon while still keeping the de-Sitter conjectur…

Trans-Planckian Censorship and Inflation in Grand Unified Theories

The recently proposed trans-Planckian censorship conjecture (TCC) amounts to the claim that inflation models with an inflationary energy scale larger than Lambda_inf^max ~ 10^9 GeV belong to the swampland, i.e., cannot be embedded into a consistent theory of quantum gravity. In this paper, we point out that this constraint can be readily satisfied in D-term hybrid inflation (DHI), which is a well-motivated inflation scenario in the context of supersymmetric grand unification. In DHI, the amplitude of the primordial scalar power spectrum originates from a Fayet-Iliopoulos term of the order of t…

Stochastic growth of quantum fluctuations during slow-roll inflation

We compute the growth of the mean square of quantum fluctuations of test fields with small effective mass during a slowly changing, nearly de Sitter stage which took place in different inflationary models. We consider a minimally coupled scalar with a small mass, a modulus with an effective mass $ \propto H^2$ (with $H$ as the Hubble parameter) and a massless non-minimally coupled scalar in the test field approximation and compare the growth of their relative mean square with the one of gauge-invariant inflaton fluctuations. We find that in most of the single field inflationary models the mean…

Staggered Multi-Field Inflation

We investigate multi-field inflationary scenarios with fields that drop out of the model in a staggered fashion. This feature is natural in certain multi-field inflationary setups within string theory; for instance, it can manifest itself when fields are related to tachyons that condense, or inter-brane distances that become meaningless when branes annihilate. Considering a separable potential, and promoting the number of fields to a smooth time-dependent function, we derive the formalism to deal with these models at the background and perturbed level, providing general expressions for the sca…

Locally Supersymmetric Effective Field Theories of Inflation

Supergravity, a locally supersymmetric gauge theory, may provide to describe new physics beyond the Standard Model (BSM). In this sense, cosmological applications of supergravity can be the arena for probing outcomes of supergravity. It is also attractive that supergravity can appear as a low-energy effective theory of superstrings, a possible candidate of quantum gravity. Nevertheless, it is not trivial to build inflationary models in supergravity due to difficulties arising mainly from the extremely constrained form of supergravity scalar potentials, complicated structure of interaction term…

扩展度规仿射引力中的极点暴胀

Pole inflation from extended metric-affine gravity

本研究在扩展度规仿射F(R)引力框架下，利用非正则动能项的极点结构实现暴胀，分类模型并放宽无鬼条件，显著扩大可行模型集合，重现吸引子预测。