422
C. Cosme
The idea of this work is to introduce a dark matter candidate which is never in
thermal equilibrium with the cosmic plasma. However, there are two main processes
that can lead to the evaporation of the condensate. One of them is the Higgs
annihilation into higher-momentum φ particles, which is prevented if [1, 2]
g 8 × 10
−4
g ∗
100
1/8
.
(15)
The other process is the production of φ particles from the coherent oscillations of
the background condensate in a quartic potential, which is not efficient if [1, 2]
λ φ < 6 × 10
−10
g ∗
100
1/5 r
0.01
−1/5
ξ
1/10 .
(16)
If the constraints of Eqs. (15) and (16) are satisfied, the dark scalar is never in
thermal equilibrium with the cosmic plasma, behaving like an oscillating condensate
of zero-momentum particles throughout its cosmic history. Equation (16) yields the
most stringent constraint on the model, limiting the viable dark matter mass to be
m φ 1 MeV [1, 2].
4 Phenomenology
In this section, we will discuss two possible ways of probing the proposed model.
For more examples and a complete and detailed discussion, see Refs. [1, 2].
4.1 Dark Matter Decay
Since the dark scalar and the Higgs field are coupled, they exhibit a small mass
mixing, =
g 2 φ 0 v
m 2
h
[1]. This means that the dark scalar can decay into the same
decay channels as the Higgs, provided that they are kinematically accessible. Due to
the mass restriction coming from Eq. (16), which translates into m φ 1 MeV, the
only kinematically accessible decay channel is the decay into photons. It is possible
to show that the decay width of the dark matter candidate into photons is suppressed
by a factor 2 with respect to the decay width of a virtual Higgs boson into photons,
yielding for the dark scalar’s lifetime [1, 2]:
τ φ 7 × 10
27
7 keV
m φ
5 x DM
0.5
2
s.
(17)
C. Cosme
The idea of this work is to introduce a dark matter candidate which is never in
thermal equilibrium with the cosmic plasma. However, there are two main processes
that can lead to the evaporation of the condensate. One of them is the Higgs
annihilation into higher-momentum φ particles, which is prevented if [1, 2]
g 8 × 10
−4
g ∗
100
1/8
.
(15)
The other process is the production of φ particles from the coherent oscillations of
the background condensate in a quartic potential, which is not efficient if [1, 2]
λ φ < 6 × 10
−10
g ∗
100
1/5 r
0.01
−1/5
ξ
1/10 .
(16)
If the constraints of Eqs. (15) and (16) are satisfied, the dark scalar is never in
thermal equilibrium with the cosmic plasma, behaving like an oscillating condensate
of zero-momentum particles throughout its cosmic history. Equation (16) yields the
most stringent constraint on the model, limiting the viable dark matter mass to be
m φ 1 MeV [1, 2].
4 Phenomenology
In this section, we will discuss two possible ways of probing the proposed model.
For more examples and a complete and detailed discussion, see Refs. [1, 2].
4.1 Dark Matter Decay
Since the dark scalar and the Higgs field are coupled, they exhibit a small mass
mixing, =
g 2 φ 0 v
m 2
h
[1]. This means that the dark scalar can decay into the same
decay channels as the Higgs, provided that they are kinematically accessible. Due to
the mass restriction coming from Eq. (16), which translates into m φ 1 MeV, the
only kinematically accessible decay channel is the decay into photons. It is possible
to show that the decay width of the dark matter candidate into photons is suppressed
by a factor 2 with respect to the decay width of a virtual Higgs boson into photons,
yielding for the dark scalar’s lifetime [1, 2]:
τ φ 7 × 10
27
7 keV
m φ
5 x DM
0.5
2
s.
(17)