弦论启发下的轴-狄拉顿动力学：解决哈勃张力与早期暗能量

111 浏览量更新于2024-09-04 收藏 327KB PDF 举报

本文主要探讨的是轴力-狄拉顿失稳与哈勃张力之间的关系，特别是在弦理论的背景下。弦理论是一种量子引力理论，其中轴子(axions)和狄拉顿(dilatons)是两种重要的模态场(moduli fields)，它们在理论中起着关键作用。狄拉顿是理论中的标量场，与引力强度有关，而轴子则涉及基本粒子的磁性质量。研究者们注意到，测量到的哈勃常数(Hubble constant)存在显著差异，这暗示可能存在暗能量(dark energy)、暗物质(dark matter)或者两者的新物理效应。暗能量是推动宇宙加速膨胀的关键因素，其状态方程(w)决定了其能量密度随时间如何变化。标准模型中的暗能量通常假设w接近-1，但观测上的哈勃张力(tension)问题表明可能需要一个更早时期具有不同行为的暗能量形式，即早期暗能量(Early Dark Energy, EDE)。作者们在论文《Physics Letters B》797(2019)134830中，提出了一种理论框架，通过考虑轴子与狄拉顿的相互作用来解释这一现象。他们证明了当哈勃常数低于轴子的质量阈值时，轴子-狄拉顿系统的稳定性被破坏，引发狄拉顿的快速滚动。在这个过程中，狄拉顿的能量贡献转化为早期暗能量，其状态方程w可以暂时偏离-1，导致膨胀环在早期宇宙中表现为w ≈ -6，这有助于缓解哈勃张力。这种动力学机制使得狄拉顿在宇宙早期扮演了双重角色：一方面，它通过轴子的作用保持自身的稳定；另一方面，它作为早期暗能量的来源，影响宇宙的扩张历史。然而，这种模型假设需要进一步的实验验证，特别是对早期宇宙的观测数据，以确定是否真的能解决哈勃张力问题。这篇研究在理论层面上探讨了弦论中的基本粒子如何通过相互作用影响宇宙学尺度的现象，为理解暗能量的本质提供了一个新颖的角度。未来的研究将需要综合理论计算和天文观测，以确认这种轴力-狄拉顿机制的有效性，并进一步揭示宇宙的奥秘。

Physics Letters B 797 (2019) 134830

Contents lists available at ScienceDirect

Physics Letters B

www.elsevier.com/locate/physletb

Axion-dilaton destabilization and the Hubble tension

Stephon Alexander

a,b

, Evan McDonough

a,b,∗

Brown Theoretical Physics Center, Brown University, Providence, RI 02912, USA

Department of Physics, Brown University, Providence, RI 02912, USA

a r t i c l e i n f o a b s t r a c t

Article history:

Received

28 May 2019

Received

in revised form 1 July 2019

Accepted

1 August 2019

Available

online 8 August 2019

Editor:

M. Trodden

The discrepancy in measurements of the Hubble constant indicates new physics in dark energy, dark

matter, or both. Drawing inspiration from string theory, where axions interact with the other moduli

ﬁelds, including the dilaton, here we demonstrate that the dynamics of an interacting dilaton and axion

naturally realizes the proposal of Early Dark Energy. In this setup, stabilization of the dilaton is in part

due to the axion, and in the early universe the dilaton contributes to dark energy. The combined axion-

dilaton

system is destabilized when the Hubble constant falls below the mass of the axion, triggering

a phase of fast-roll evolution of the dilaton wherein its equation of state is w = 1, and the early dark

energy redshifts away as a

−6

(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP

1. Introduction

With the reﬁned measurement of the distance to the Large

Magellanic Cloud [1], the discrepancy between the observed and

inferred values of the Hubble constant has raised in signiﬁcance

to 4.4σ . The data supporting this discrepancy comes from a wide

range of redshift, providing the greatest challenge yet to the CDM

model. This growing observational evidence motivates the search

for theoretical explanations.

contrast with past cosmological glitches, e.g. anomalies in

the Cosmic Microwave Background, there are still relatively few

working theoretical explanations [2–8]. However, some of the nec-

essary

ingredients of a solution are now known. As emphasized

in [9], to rectify the cosmological distance ladder with the inverse

distance ladder and the CMB requires a modiﬁcation of the sound

horizon r

, and thus any solution must include new dynamics in

the very early universe.

1,2

The scenario of ‘Early Dark Energy’ [2,11]implemented a modi-

ﬁcation

of r

via the decay of dark energy into a ﬂuid that redshifts

as fast or faster than radiation, i.e. with equation of state w ≥ 1/3.

This ﬂuid can arise via a scalar ﬁeld with potential that is a poly-

nomial

in the cosine of the ﬁeld, V = μ

(cos φ)

[2], with param-

eters

such that the decay happens shortly before recombination.

Corresponding author.

E-mail

addresses: stephon_alexander@brown.edu (S. Alexander),

evan_mcdonough@brown.edu (E. McDonough).

We thank Matias Zaldarriaga and Christina D. Kreisch for emphasizing this to

us.

See also e.g. [10].

As an alternative to such a potential, [7]demonstrated that

single-ﬁeld models with polynomial potentials can realize the early

dark energy dynamics. The best ﬁt model was found to be V =

(φ/m

)

, substantiated by a complete perturbation analysis, in

which the perturbed ﬁeld equations were solved directly.

this letter we build on these previous works by demonstrat-

ing

that the requisite dynamics can be realized via the interacting

dynamical system of a dilaton ﬁeld, referred to as such due to an

exponential potential V = V

−λφ/m

, and an axion ﬁeld with co-

sine

potential. At early stages the axion is held up its potential by

Hubble friction, and due to an interaction, the dilaton is also held

up its potential, and thus acts as dark energy. Eventually, when the

Hubble constant falls below the mass of the axion, the axion rolls

down its potential and begins to oscillate. At this point the dila-

ton

is destabilized and also rolls down its potential. For λ > 1, this

rolling can be fast-roll with the energy density in φ predominantly

in kinetic energy. The equation of state of φ in this phase is w = 1

and

the energy density redshifts as a(t)

−6

This

realizes early dark energy, wherein the onset of the decay

of dark energy is due to the small axion mass, which is itself in

agreement with general intuition from the string theory axiverse,

and the ﬂuid into which the early dark energy decays is simply the

kinetic energy of the early dark energy ﬁeld.

a ﬁnal note before we proceed, we remark that the motiva-

tion

for this setup comes from a promising approach to cosmology

in string theory. The existence of moduli ﬁelds is one of the few

model-independent predictions of string theory (or more generally,

extra-dimensional theories). The prevailing approach is to stabilize

and subsequently ignore all these ﬁelds, in order to focus on the

https://doi.org/10.1016/j.physletb.2019.134830

0370-2693/

SCOAP

下载后可阅读完整内容，剩余4页未读，立即下载

weixin_38670186

粉丝: 8
资源: 945

弦论启发下的轴-狄拉顿动力学：解决哈勃张力与早期暗能量

爱因斯坦－狄拉顿－高斯－引擎盖和爱因斯坦－魏尔引力的狄拉克场的准正规模

高温下线性电阻率：轴力-狄拉顿理论的全息探索

爱因斯坦-麦克斯韦-狄拉顿引力的全息复杂性

爱因斯坦-麦克斯韦-狄拉顿理论的渐近结构及其五维起源

缓慢旋转的爱因斯坦-麦克斯韦-狄拉顿黑洞及其热力学的某些方面

动态爱因斯坦-狄拉顿模型中全息复杂度的时间依赖性

带电零流体来源的爱因斯坦-麦克斯韦-狄拉顿理论中的自相似解和临界行为

全息QCD相图，具有爱因斯坦–麦克斯韦-狄拉顿动力学的临界点

爱因斯坦-狄拉顿-高斯-帽子黑洞的铁谱分析

全息复杂性：爱因斯坦-麦克斯韦-狄拉顿引力的新洞察

最新资源