CONTENTS CONTENTS Axions in the Early Universe Francesco DEramo12

2025-05-01 0 0 2.93MB 10 页 10玖币

侵权投诉

CONTENTS CONTENTS

Axions in the Early Universe

Francesco D’Eramo1,2?

1Dipartimento di Fisica e Astronomia, Università degli Studi di Padova,

Via Marzolo 8, 35131 Padova, Italy

2Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Padova,

Via Marzolo 8, 35131 Padova, Italy

*francesco.deramo@pd.infn.it

October 1, 2022

14th International Conference on Identiﬁcation of Dark Matter

Vienna, Austria, 18-22 July 2022

doi:10.21468/SciPostPhysProc.?

Abstract

The Peccei-Quinn solution to the strong CP problem provides a motivated framework rich in

cosmological consequence. Thermal axion production is unavoidable if there is a thermal

bath at early times. Scattering and decay processes of bath particles can dump relativistic

axions in the primordial plasma, and they can leave observable signatures in cosmologi-

cal observables probing both the early and the late universe if produced with a signiﬁcant

abundance. We present recent and signiﬁcant improvements for the calculation of the axion

production rate for different scenarios and apply these results to predict the abundance of

produced axions. Finally, we provide updated cosmological bounds on the QCD axion mass.

Contents

1 Introduction 2

2 Cold Axions 2

3 Hot Axions 3

4 Thermal QCD Axions 4

5 Conclusions 7

References 8

arXiv:2210.03814v1 [hep-ph] 7 Oct 2022

2 COLD AXIONS

1 Introduction

The ﬁrm observational evidence for some form of dark matter, approximately ﬁve times more

abundant than ordinary matter, leaves no doubt about the need for physics beyond the standard

model. Motivated particle candidates are not postulated to exist ad hoc but they tackle more than

one problem. The candidate discussed here, naturally arising from the investigation of symmetries

whose violation is small and structured, is one of the best examples.

The experimentally observed invariance of strong interactions when we ﬂip the arrow of time

is rather surprising. The Peccei-Quinn (PQ) mechanism [1,2]is an elegant dynamical solution, and

all microscopic realizations share some common features. The standard model is extended via a

new global symmetry U(1)PQ that must satisfy two key requirements: spontaneously broken, and

anomalous under strong interactions. The PQ symmetry breaking scale is bound to be much higher

than the energies we can reach with experiments, and the only accessible low-energy residual is a

pseudo-Nambu-Goldstone boson (PNGB) arising from the spontaneous PQ breaking. This pseudo-

scalar ﬁeld is known as the QCD axion [3,4], and as a consequence of the color anomaly it couples

to gluons via the dimension 5 operator

LPQ ⊃αs

8π

µν e

GAµν . (1)

Here, we have the QCD ﬁne structure constant αs=g2

s/(4π), the gluon ﬁeld strength tensor Ga

µν,

and its dual e

Gaµν. This operator deﬁnes the axion decay constant fa. Interactions with other

standard model ﬁelds are model dependent. Given its PNGB nature, all couplings are suppressed

by the scale fa. QCD non-perturbative effects generate a potential once strong interactions conﬁne,

and this leads to an axion mass [5]

ma'5.7 µeV 1012 GeV

fa. (2)

A light and elusive particle could play a prominent role in the early universe. Famously, the

QCD axion is a viable dark matter candidate [6–8]as discussed in Sec. 2. The PQ framework

leads to other fascinating phenomena in the early universe with testable consequences today. A

hot axion population, discussed in Sec. 3, is a notable example. We focus on thermal production

in Sec. 4, and we give updated predictions for the KSVZ [9,10]and DFSZ [11,12]frameworks. We

also compare cosmological bounds on ﬂavor-violating axions with laboratory searches and present

an updated cosmological bound on the QCD axion mass. Conclusions are given in Sec. 5.

2 Cold Axions

The axion contribution to the observed dark matter relic density can be computed by analyzing the

ﬁeld evolution across the expansion history. At early times, at temperatures much higher than the

QCD conﬁnement scale, the ﬁnite-temperature axion potential is negligible and Hubble friction

prevents any motion. The ﬁeld starts evolving only when the primordial plasma temperature

reaches values around the proton mass and the non-perturbative axion potential switches on.

The resulting motion is described by damped harmonic oscillations around the minimum of the

potential, and the amplitude of such oscillations gets damped by the Hubble expansion as non-

relativistic dark matter. This is the misalignment production mechanism.

文档加载中……请稍候！
如果长时间未打开，您也可以点击刷新试试。

下载文档到电脑，查找使用更方便

10 玖币 0人已下载

立即下载

摘要：

CONTENTSCONTENTSAxionsintheEarlyUniverseFrancescoD'Eramo1,2?1DipartimentodiFisicaeAstronomia,UniversitàdegliStudidiPadova,ViaMarzolo8,35131Padova,Italy2IstitutoNazionalediFisicaNucleare(INFN),SezionediPadova,ViaMarzolo8,35131Padova,Italy*francesco.deramo@pd.infn.itOctober1,202214thInternationalConfe...

展开>> 收起<<

CONTENTS CONTENTS Axions in the Early Universe Francesco DEramo12.pdf

共10页,预览2页

还剩页未读，继续阅读

声明：本站为文档C2C交易模式，即用户上传的文档直接被用户下载，本站只是中间服务平台，本站所有文档下载所得的收益归上传人(含作者)所有。玖贝云文库仅提供信息存储空间，仅对用户上传内容的表现方式做保护处理，对上载内容本身不做任何修改或编辑。若文档所含内容侵犯了您的版权或隐私，请立即通知玖贝云文库，我们立即给予删除！

CONTENTS CONTENTS Axions in the Early Universe Francesco DEramo12

相关推荐

开通VIP享超值会员特权

作者详情

相关内容

热门标签

举报选择: