中微子后期衰变：生成希格斯ino暗物质的新途径

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本文探讨了在最小超对称标准模型（MSSM）框架下的暗物质（DM）性质，特别是关注希格斯ino类型的DM。MSSM通常扩展了粒子物理学标准模型，引入了额外的右手中微子超场。研究者Anibal D. Medina等人提出了一种独特的非热生成机制，利用中微子的后期衰变来产生适量的希格斯ino-like DM。关键概念包括： 1. **希格斯ino-like dark matter (Higgsino DM)**: 希格斯ino是超对称理论中的一个假想粒子，它与标准模型中的希格斯玻色子有相似的特性，是暗物质候选者之一。在MSSM中，Higgsino DM由于其特殊的量子属性，可能具有稳定的特性，成为暗物质的主要组成部分。 2. **Minimal Supersymmetric Standard Model (MSSM)**: MSSM是对标准模型的超对称扩展，引入了超对称粒子以解决标准模型的一些未解问题，如希格斯机制、电弱统一和暗物质问题。在这里，作者假设存在额外的右手中微子超场，这在MSSM的基础上增加了新的粒子成分。 3. **Right-handed neutrinos**: 右手（即奇数自旋）的中微子在模型中起着关键作用。它们的存在不仅影响到中微子的性质，还可能参与到暗物质的生成过程中。由于模型中Higgsino DM的大型湮灭截面，需要在极低的温度下（Td ≪ TF，大约是χ01的质量约μ/25的量级）进行衰变，这就意味着最轻的右手中微子的 Yukawa相互作用非常小，从而抑制了衰变过程。 4. **Non-thermal production mechanism**: 本文的核心贡献在于提出了一种非热产生机制，即通过中微子的后期衰变来生成足够的暗物质。由于衰变温度远低于标准的热冻结温度，这个过程避免了过早的湮灭，确保了DM的稳定数量。 5. **Decay and relic density**: 中微子后期衰变产生的暗物质密度必须与观测到的宇宙暗物质总量相匹配。通过对温度条件的精确控制，可以解释目前观测到的暗物质密度，这是构建此类理论模型的重要目标。总结，这篇文章在超对称粒子物理领域提供了一个新颖的视角，探索了如何通过非传统的途径生成暗物质，特别是在中微子衰变的机制上。这对于理解暗物质的本质以及超对称理论的可能应用具有重要意义。

Physics Letters B 770 (2017) 161–165

Contents lists available at ScienceDirect

Physics Letters B

www.elsevier.com/locate/physletb

Higgsino-like dark matter from sneutrino late decays

Anibal D. Medina

a,b,∗

ARC Centre of Excellence for Particle Physics at the Terascale, School of Physics, The University of Melbourne, Victoria 3010, Australia

Institut de Physique Théorique, Université Paris Saclay, CNRS, CEA, F-91191 Gif-sur-Yvette, France

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

Article history:

Received

3 February 2017

Received

in revised form 3 April 2017

Accepted

13 April 2017

Available

online 26 April 2017

Editor: J.

Hisano

We consider Higgsino-like dark matter (DM) in the Minimal Supersymmetric Standard Model (MSSM)

with additional right-handed neutrino chiral superﬁelds, and propose a new non-thermal way of

generating the right amount of relic DM via sneutrino late decays. Due to the large DM annihilation cross-

section,

decays must occur at lower temperatures than the freeze-out temperature T

 T

F ,

∼ μ/25,

implying a mostly right-handed lightest sneutrino with very small Yukawa interactions. In that context,

the right amount of Higgsino-like DM relic density can be accounted for if sneutrinos are produced via

thermal freeze-in in the early Universe.

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

1. Introduction

Supersymmetry (SUSY) elegantly solves the quadratic ultra-

violet

(UV) sensitivity of the Higgs mass via the introduction of

particles (superpartners) with opposite statistics to each Standard

Model (SM) particle. Stability of the proton naturally leads to the

introduction of R-parity under which all superpartners are odd

while the SM content is even. Thus sparticles can only be created

in pairs at colliders and the lightest supersymmetric particle (LSP)

is stable, providing an interesting dark matter (DM) candidate.

the minimal supersymmetric extension of the SM a natural

and well-studied DM candidate is the lightest neutralino

, a lin-

ear

combination of the wino

W , bino

B and Higgsinos

and

superpartners. Given its weak couplings and for masses of order

the EW scale, the lightest neutralino can provide the well-known

“WIMP miracle” in which the total amount of DM relic density

is naturally obtained. Despite its appealing properties, neutralino

DM in the MSSM is being pushed toward corners of parameter

space, in particular due to the lack of positive signals in direct

detection experiments that probe spin-independent (SI) [1,2] and

spin-dependent (SD) [3] scattering of DM particles off of nuclei

target. Furthermore, the absence of discovery of superpartners at

Large Hadron Collider (LHC) and the discovery of a SM-like Higgs

with a mass m

∼ 126 GeV, seem to point towards a SUSY spec-

Correspondence to: Institut de Physique Théorique, Université Paris Saclay,

CNRS, CEA, F-91191 Gif-sur-Yvette, France.

E-mail

address: anibal.medina@cea.fr.

trum where at least part of the sparticle content have masses in

the TeV range.

Despite

the increasing constraints on the sparticle masses and

composition, a neutralino saturating the DM relic density and of

almost pure Higgsino composition is able to evade current direct

detection bounds due to its suppress coupling to the Higgs and

Z-gauge boson [4], see in particular Fig. 3 of Ref. [4]. Moreover,

if the theory is to remain natural one expects the supersymmet-

ric

Higgs mass parameter μ ≈ O(100) GeV, making a neutralino

LSP with almost pure Higgsino composition m

≈ μ a good can-

didate

for DM. As shown in Ref. [5], for μ < 0 and in the case of

a Higgsino-like neutralino with Bino admixture, there is a destruc-

tive

interference in the diagrams that contribute to DM-nucleon

scattering between the SM-like Higgs and the non-standard Higgs

H such that the latest LUX constraints can be avoided. Studies

have shown that pure thermal Higgsino DM is under-abundant

for masses below 1TeV[6]. This tension served as motivation for

non-thermal ways of generating the right amount of Higgsino relic

density [7,8].

this work we propose an alternative non-thermal way of

generating the right amount of Higgsino DM via late decays of

sneutrinos. As has been well established by now, neutrinos are

massive. A convenient manner of obtaining neutrino masses is

through the addition of right-handed neutrinos to the SM con-

tent,

which by means of heavy Majorana masses leads to the type I

see-saw mechanism of neutrino mass generation. When this extra

content in the SM is supersymmetrized, we ﬁnd that for the light-

est

sneutrino masses m

 μ and small Yukawa couplings Y

the Higgsino-chargino sector, late decays of sneutrinos either di-

rectly

to the lightest neutralino

or cascading to it via decays to

http://dx.doi.org/10.1016/j.physletb.2017.04.054

0370-2693/

SCOAP

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