RESCEU-1822 KOBE-COSMO-22-16 Generation of neutrino dark matter baryon asymmetry and radiation after

2025-05-01 0 0 747.01KB 19 页 10玖币

侵权投诉

RESCEU-18/22

KOBE-COSMO-22-16

Generation of neutrino dark matter, baryon asymmetry, and radiation after

quintessential inﬂation

Kohei Fujikura,1, ∗Soichiro Hashiba,2, 3, †and Jun’ichi Yokoyama2, 3, 4, 5, ‡

1Department of Physics, Kobe University, Kobe 657-8501, Japan

2Research Center for the Early Universe (RESCEU),

Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan

3Department of Physics, Graduate School of Science,

The University of Tokyo, Tokyo 113-0033, Japan

4Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU),

WPI, UTIAS, The University of Tokyo,

5-1-5 Kashiwanoha, Kashiwa 277-8583, Japan

5Trans-Scale Quantum Science Institute,

The University of Tokyo, Tokyo 113-0033, Japan

(Dated: October 12, 2022)

Abstract

We construct a model explaining dark matter, baryon asymmetry and reheating in quintessential inﬂa-

tion model. Three generations of right-handed neutrinos having hierarchical masses, and the light scalar

ﬁeld leading to self-interaction of active neutrinos are introduced. The lightest sterile neutrino is a dark

matter candidate produced by a Dodelson-Widrow mechanism in the presence of a new light scalar ﬁeld,

while the heaviest and the next heaviest sterile neutrinos produced by gravitational particle production are

responsible for the generation of the baryon asymmetry. Reheating is realized by spinodal instabilities of

the Standard Model Higgs ﬁeld induced by the non-minimal coupling to the scalar curvature, which can

solve overproduction of gravitons and curvature perturbation created by the Higgs condensation.

∗fujikura@penguin.kobe-u.ac.jp

†sou16.hashiba@resceu.s.u-tokyo.ac.jp

‡yokoyama@resceu.s.u-tokyo.ac.jp

arXiv:2210.05214v1 [hep-ph] 11 Oct 2022

I. INTRODUCTION

It is widely believed that the very early stage of the universe experienced exponentially accel-

erated expansion so-called inﬂation. Inﬂation not only solves fundamental issues such as horizon

and ﬂatness problems but also provides seeds of density perturbation. (See e.g. [1] for a review of

inﬂation.) Among many possible variants of inﬂationary universe models, quintessential inﬂation [2]

is interesting in the sense that the origin of dark energy is attributed to the same scalar ﬁeld as

the inﬂation-driving ﬁeld dubbed as the inﬂaton. This, however, is not achieved without expenses,

as this class of models is associated with a kination or kinetic-energy-dominant regime [3,4] after

inﬂation without ﬁeld oscillation, so that the reheating process after inﬂation is more involved. Note

that such cosmic evolution is also realized in k-inﬂation [5] and a class of (generalized) G-inﬂation

[6,7].

Traditionally, reheating in inﬂation models followed by a kination regime has been considered by

postulating gravitational particle production [8,9] of a massless minimally coupled scalar ﬁeld which

is produced with the energy density of order of T4

Hat the transition from inﬂation to kination [10,11].

Here TH=Hinf /(2π)is the Hawking temperature of de Sitter space with the Hubble parameter

Hinf . In this transition, gravitons are also produced twice as much as the aforementioned scalar

ﬁeld, which acts as dark radiation in the later universe. Since its energy density relative to radiation

is severely constrained by observations of the cosmic microwave background (CMB) [12], we must

assume creation of many degrees of freedom of such massless minimally coupled ﬁeld whose energy

density dissipates in the same way as radiation throughout. Furthermore, since such a scalar ﬁeld

acquire a large value during inﬂation due to the accumulation of long-wave quantum ﬂuctuations

[13–15], particles coupled to this ﬁeld tends to acquire a large mass so that thermalization is not

guaranteed.

In such a situation, two of us [16] calculated gravitational production rate of massive bosons

and fermions at the transition from inﬂation to kination, and concluded that suﬃcient reheating

without graviton overproduction can be achieved if they have an appropriate mass and long enough

lifetime, because their relative energy density increases in time with respect to graviton as they

redshift in proportion to a−3(t)with a(t)being the cosmic scale factor. They have further applied

the scenario to generations of heavy right-handed Majorana neutrinos to explain origin of radiation,

baryon asymmetry, and dark matter in terms of neutrinos [17].

Unfortunately, there are two issues in the previous analysis. One is that it turned out that

in order to explain the full mass spectrum of light neutrinos as inferred by neutrino oscillation,

the decay rate of massive right-handed neutrino cannot be small enough to realize appropriate

reheating, as shown in Sec. III. The other is the role of the standard Higgs ﬁeld. As discussed

in [11], if it is minimally coupled to gravity, it suﬀers from a large quantum ﬂuctuation during

inﬂation [18] which will be accumulated to contribute to the energy density of order of 10−2H4

inf at

the end of inﬂation. Furthermore its quantum ﬂuctuation is so large that it acts as an unwanted

curvaton, which should be removed [11].

The simplest remedy to the latter problem is to introduce a suﬃciently large positive non-

minimal coupling to gravity, so that it has an eﬀective mass squared of 12ξH2

inf during inﬂation

where ξ > 0is the coupling constant to the Ricci scalar [19]. With this coupling, the Higgs ﬁeld

is conﬁned to the origin without suﬀering from long wave quantum ﬂuctuations. Furthermore, we

can automatically ﬁnd another source of reheating, namely, the spinodal instability of the Higgs

ﬁeld, as the Ricci scalar will take a negative value in the kination regime and the Higgs ﬁeld starts

to evolve deviating from the origin. Its subsequent oscillation can create particles of the standard

model to reheat the universe as studied in [19].

The purpose of the present paper is to construct a consistent scenario of cosmic evolution

generating the observed material ingredients properly in the quintessential inﬂation model again

making use of three right-handed neutrinos with hierarchical masses inspired by the split seesaw

model [20]. The heaviest and the next heaviest right-handed neutrinos realize leptogenesis and

explain neutrino oscillation experiments via conventional seesaw mechanism [21,22]. The non-

minimally coupled SM Higgs ﬁeld realizes reheating after inﬂation via spinodal instabilities [19],

while the lightest sterile neutrino and the new light scalar ﬁeld lead to a successful dark matter

production [23].

In our scenario, baryogenesis through leptogenesis is realized by the decay of the next heaviest

right-handed neutrino with mass M2produced by gravitational particle production. The heaviest

right-handed neutrino is assumed to be much heavier than the Hubble parameter during inﬂation

and only provides the source of CP violation. We will show the mass range of M2where the

observed amount of the baryon asymmetry is realized.

Finally, the lightest right-handed neutrino can constitute cold dark matter if it is nearly stable so

that its life-time is longer than the age of the universe. The simplest production mechanism of such

a light right-handed neutrino dark matter is through neutrino oscillations between the left-handed

and right-handed neutrinos known as Dodelson-Widrow mechanism [24], apart from gravitational

particle production introducing a non-minimal coupling as assumed in [17]. However, constrains

from X-ray observation [25–28] combined with constraints from phase space analysis [29–31] and

Lyman-αforest [32–35] excludes this simplest possibility. (See e.g. Refs. [36,37] for review of the

sterile neutrino dark matter.)

Successful production mechanisms of the right-handed neutrino dark matter such as a resonant

production [38] and production with new physics in addition to the right-handed neutrinos [39–46]

have been suggested. Among them, we focus on the possibility of the sterile neutrino dark matter

production with a secret active neutrino self-interaction originally proposed in Ref. [23]. In this

scenario, a new light complex singlet scalar ﬁeld which induces a self-interaction of active neutrino

is introduced. Production rate of the active neutrino in the early universe is enhanced by the

new interaction, and the resultant relic density of the lightest sterile neutrino can make up all of

the dark matter in the parameter space consistent with current constraints. We will calculate the

relic abundance of the lightest sterile neutrino dark matter by analytically solving the Boltzmann

equation under some reasonable approximations and show that keV-scale sterile neutrino can explain

relic dark matter density when a mass scale of the new light scalar ﬁeld is around MeV scale.

The rest of the paper is organized as follows. In Sec. II, we review basic features of right-handed

neutrinos. In Sec. III, we see that reheating of the universe by the decay of gravitationally produced

right-handed neutrino cannot be achieved, but the non-minimal coupling between the SM Higgs

and the scalar curvature can lead to the eﬃcient reheating. In Sec. IV, we explain baryogenesis

through leptogenesis by gravitationally produced sterile neutrino. Then, we analytically calculate

the relic density produced by the lightest right-handed neutrino with a secret self-interaction of the

left-handed neutrinn in Sec. V. Sec. VI is devoted to the conclusion.

II. HIERARCHICAL STERILE NEUTRINOS

In this section, we review general features of the right-handed neutrinos. We consider the

following Lagrangian density for the right-handed neutrino νRi (i= 1,2,3) with hierarchical masses

Mi(M1M2M3)

−LN=hαi ¯

Lα˜

HSMNi+1

2Mi¯νc

RiνRi + h.c. . (1)

In this expression, Lα= (νLα, eLα)T, HSM and hαi are the SM lepton doublet, the SM Higgs doublet

and the Yukawa coupling constants, respectively. The suﬃces α=e, µ, τ denote the generation

of the SM leptons and ψcdenotes the charge conjugation of the ψﬁeld. After the electroweak

symmetry breaking, the SM Higgs ﬁeld acquires the vacuum expectation value, hHSMi=vSM/√2

where vSM '246 GeV, leading to the Dirac mass terms. The mass matrix of neutrinos is then given

−Lmass =1

2(¯νL,¯νc

R)Mνc

νR+ h.c. , M=0mD

DDM,(2)

where (mD)αi ≡hαivSM/√2is the 3×3Dirac mass matrix, and DM≡diag(M1, M2, M3), respec-

tively. The matrix, M, can be diagonalized by the unitary matrix U:

U†MU∗= diag(mνα0, mNI),(α0= 1,2,3, I = 1,2,3).(3)

Assuming mDMi, at the leading order, the unitary matrix can be expressed as [47]

U=UPMNS θ

−θ†UPMNS 13×3, θ ≡mDD−1

M.(4)

In this expression, UPMNS is the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix [48] deﬁned

by the following relation:

U†

PMNSMνU∗

PMNS = diag(mν1, mν2, mν3), Mν≡ −mDD−1

MmT

D.(5)

For θαi 1, mass eigenstates να0and Nicalled active and sterile neutrinos are explicitly given by

νLα = (UPMNS)αα0να0+θαiNc

i, νc

Ri =−θ∗

αi(UPMNS)αα0να0+Nc

i.(6)

One can see from the above expression that the active neutrinos, να0, and the sterile neutrinos,

NI, almost correspond to a linear combination of νLα and νRi itself, respectively. Also, the mass

of the sterile neutrino Niis almost identical to the Majorana mass of the right-handed neutrino,

mNI'δIiMifor θαi 1, and hence, we do not distinguish them in what follows.

There are several constraints on active neutrino masses from observations of neutrino oscillations

such as the Super-Kamiokande [49], KamLAND [50] and the MINOS [51]. Absolute values of active

neutrino mass-squared diﬀerences are constrained as m2

sol ≡ |m2

ν2−mν1|2= 7.59 ×10−5eV2and

atm ≡ |m2

ν3−m2

ν1|= 2.32 ×10−3eV2. One cannot take hαi arbitrarily free since it is related

to active neutrino masses through the relation Eq. (5). To make the lightest sterile neutrino dark

matter, it will turn out in Sec. Vthat Yukawa coupling of the lightest sterile neutrino becomes

vanishingly small, Pα|˜

hα1|21where ˜

h≡U†

PMNSh. Resultant contributions to mν2,3from ˜

hα1

are negligible amount and are decoupled in the seesaw formula. Under this setup with assuming

normal mass hierarchy mν3> mν2> mν1, constraints on active neutrino masses are simpliﬁed as

mν3'0.05 eV and mν2'0.01 eV.(7)

The above condition will be used in Sec. III and Sec. IV.

III. REHEATING

In this section, we discuss reheating in our model. Before discussing the reheating mechanism

in detail, we would like to clarify our setup. We consider a spatially ﬂat Friedmann-Lemaítre-

Robertson-Walker (FLRW) background, ds2=−dt2+a2(t)dx2, where a(t)denotes the scale factor.

We consider following smooth transition from the de Sitter phase to the kination phase [16]:

a2(η) = 1

21−tanh η

∆η1

1 + H2

inf η2+1 + tanh η

∆η(1 + Hinf η).(8)

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：

RESCEU-18/22KOBE-COSMO-22-16Generationofneutrinodarkmatter,baryonasymmetry,andradiationafterquintessentialinationKoheiFujikura,1,SoichiroHashiba,2,3,yandJun'ichiYokoyama2,3,4,5,z1DepartmentofPhysics,KobeUniversity,Kobe657-8501,Japan2ResearchCenterfortheEarlyUniverse(RESCEU),GraduateSchoolofScience...

展开>> 收起<<

RESCEU-1822 KOBE-COSMO-22-16 Generation of neutrino dark matter baryon asymmetry and radiation after.pdf

共19页,预览4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！

RESCEU-1822 KOBE-COSMO-22-16 Generation of neutrino dark matter baryon asymmetry and radiation after

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: