AMS-02与Fermi-LAT观测下的暗物质简化模型解析
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本文探讨了在AMS-02（阿尔法磁谱仪-02）和Fermi-LAT（费米伽马空间望远镜）提供的宇宙射线观测数据背景下，对简化暗物质模型的重新评估。作者假设暗物质粒子可能是费米子、标量或矢量类型，其中有一个只与标准模型夸克以及暗物质相互作用的 leptophobic（不与轻子相互作用的）spin-0媒介，这种媒介通过标量和/或伪标量双线性耦合进行交互。
AMS-02的数据被用来确定宇宙射线的传播和注入参数，尤其是通过分析其观测到的核通量。研究结果显示，AMS-02的观测结果与简化暗物质模型的理论预期在误差范围内是一致的。对于反质子数据，模型倾向于支持30至5太电子伏特（GeV）的质量范围，而对于费米子暗物质模型，有效的湮灭交叉截面需要在4×10^-27至4×10^-24平方厘米每秒（cm^3/s）之间；对于标量和矢量暗物质模型，这个范围略有不同，约为7×10^-27至4×10^-24 cm^3/s。
值得注意的是，大约在100 GeV的暗物质质量下，如果暗物质的有效湮灭截面低于2×10^-26 cm^3/s，那么它可以避开Fermi-LAT对来自矮星系的暗物质信号的严格限制。这表明，尽管存在这些观测约束，简化暗物质模型仍然能够解释部分宇宙射线数据，但精确的参数空间需要进一步的研究来确认。
这篇论文发表于《Journal of High Energy Physics》（JHEP），2018年1月，是Springer出版社的开放存取资源，展示了研究人员如何利用最新的实验数据来检验和优化暗物质模型，以期更好地理解宇宙中的暗物质成分及其与普通物质的相互作用。
JHEP01(2018)151
different quark or gluon final states in 2-body spectrum we use PPPC4DMID [28] to gener-
ate the differential yield which is weighted by the corresponding annihilation fraction, i.e.
hσ
ann
vi
¯qq
/hσ
ann
vi and hσ
ann
vi
gg
/hσ
ann
vi. The 4-body cosmic ray spectrum is given by the
spectrum of the mediator decay in its rest frame followed by a Lorentz boost [12, 29]. The
spectrum is then weighted by the product of annihilation fraction and decay branching ratio
of the mediator, i.e.
hσ
ann
vi
Med
hσ
ann
vi
Γ
Med→q ¯q
Γ
Med
and
hσ
ann
vi
Med
hσ
ann
vi
Γ
Med→gg
Γ
Med
, to give (dN
i
/dE)
4−body
[30].
The expressions of mediator decay widths and dark matter annihilation cross sections are
collected in appendix.
3 Indirect observables from AMS-02 and Fermi-LAT
In this section we describe the observables of antiproton flux and gamma ray measured by
AMS-02 and Fermi-LAT respectively.
3.1 Antiproton flux from AMS-02
The two key unknowns about cosmic rays in the Galaxy are their origin and propagation.
The propagation of cosmic rays can be described as the process of diffusion. The diffusion
process is written in the form of the transport equation below [31]
∂ψ
∂t
= Q(~r, p) +
~
∇ ·
D
xx
~
∇ψ −
~
V ψ
+
∂
∂p
p
2
D
pp
∂
∂p
1
p
2
ψ
−
∂
∂p
h
˙pψ −
p
3
~
∇ ·
~
V
ψ
i
−
ψ
τ
f
−
ψ
τ
r
, (3.1)
where ψ(~r, t, p) is the density of cosmic rays,
~
V is the convection velocity and τ
f
(τ
r
) is
the time scale for fragmentation (radioactive decay). ˙p is the momentum loss rate. The
convection terms in the above equation are induced by the Galactic wind. The diffusion in
momentum space governs the reacceleration process. In this case the diffusion coefficient in
momentum space, i.e. D
pp
, is related to the spatial coefficient D
xx
and the Alfven velocity
v
A
[32]:
D
pp
D
xx
=
4p
2
v
2
A
3δ(4 − δ
2
)(4 − δ)w
, (3.2)
with the level of the interstellar turbulence parameter w being 1. The spatial diffusion
coefficient is usually written in this form
D
xx
= βD
0
(R/R
0
)
δ
, (3.3)
with R and β being the rigidity and particle velocity divided by light speed respectively.
This transport equation is numerically solved based on given boundary conditions, that
is, the cosmic ray density ψ vanishes at the radius R
h
and the height z
0
of the cylindrical
diffusion halo.
In eq. (3.1), the source term can be written by the product of the spatial distribution
and the injection spectrum function for cosmic ray species i
Q
i
(~r, p) = f(r, z)q
i
(p). (3.4)
– 4 –
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