近日，西班牙马德里自治大学的Ignacio Ruiz及其研究团队取得一项新进展。经过不懈努力，他们对宇宙学变色龙，弦理论和沼泽地原则进行研究。相关研究成果已于2024年11月14日在国际知名学术期刊《高能物理杂志》上发表。

该研究团队研究了一种可能在弦理论模空间渐近区域实现的、包含宇宙学加速暂态阶段的情景。由于重态的非零密度效应，一个非常陡峭的标量势被暂时稳定下来，从而导致加速，这相当于宇宙学中的变色龙机制（Chameleon mechanism）。随着宇宙的膨胀，重态的密度被稀释，其效应也随之减弱。大约经过一个e折（e-fold）后，其效应不再能够稳定势，加速阶段结束。

研究人员还研究了一种没有势的情景，其中通过轻态和重态塔的相互平衡效应实现了暂态加速。研究人员获得了暂态德西特（dS）寿命上限的解析表达式，结合沼泽地（Swampland）原则，这意味着在不进行超普朗克场变的情况下，不可能获得超过O(1)个e折的加速。他们还讨论了这些模型的一般有效场论（EFT）约束，并探索了将该情景具体嵌入弦理论的一些初步尝试。所有这些尝试都面临着重大的挑战。

附：英文原文

Title: Cosmological Chameleons, string theory and the swampland

Author: Casas, Gonzalo F., Montero, Miguel, Ruiz, Ignacio

Issue&Volume: 2024-11-14

Abstract: We study a scenario with a transient phase of cosmological acceleration that could potentially be realized in asymptotic corners of String Theory moduli space. A very steep scalar potential is temporarily stabilized by the effect of a nonzero density of heavy states, leading to acceleration, in what amounts to a cosmological version of the Chameleon mechanism. The density of heavy states is diluted by cosmological expansion, weakening their effect. After roughly one e-fold their effect can no longer stabilize the potential, and the accelerating phase ends. We also study a scenario where there is no potential and the transient acceleration is achieved by the counterbalancing effects of light and heavy towers of states. We obtain analytic expressions for the upper bounds on the transient dS lifetime, which when combined with Swampland principles imply that it is not possible to obtain more than O(1) e-folds without transplanckian field excursions. We also discuss the general EFT constraints on these models and explore a number of first attempts at concrete embeddings of the scenario in String Theory. These all turn out to face significant challenges.

DOI: 10.1007/JHEP11(2024)091

Source: https://link.springer.com/article/10.1007/JHEP11(2024)091