Observational properties of very weakly coupled dark matter
Tommi Tenkanen
Queen Mary University of London
Talk based on arXiv: 1706.07442 and 1705.05567
Nordita 12/7/2017
E-mail: [email protected] Tommi Tenkanen Observational properties of very weakly coupled dark matter 12/7/2017 1 / 14 Evidence for Dark Matter
Great deal of evidence for the existence of dark matter: rotational velocity curves of galaxies, Bullet Cluster, acoustic peaks in the Cosmic Microwave Background (CMB) radiation spectrum...
Still the nature of dark matter is unknown
Tommi Tenkanen Observational properties of very weakly coupled dark matter 12/7/2017 2 / 14 What is Dark Matter?
What is the correct explanation for the invisible matter content observed in the universe? Does the dark matter particle exist? Or are there many dark matter particles?
Are they WIMP’s, FIMP’s, SIMP’s, GIMP’s, PIDM’s, WISP’s, ALP’s, Wimpzillas, sterile neutrinos, or primordial black holes? Or should gravity be modified?
How can we tell which model is the correct one (if any)?
Tommi Tenkanen Observational properties of very weakly coupled dark matter 12/7/2017 3 / 14 Search for Dark Matter
Many on-going experiments exist
But... what if dark matter interacts only feebly with the known particles, or not at all?
Tommi Tenkanen Observational properties of very weakly coupled dark matter 12/7/2017 4 / 14 Model for a Decoupled Hidden Sector
The scalar sector of the model is specified by the potential
1 λ λ V (Φ, s) = µ2Φ†Φ + λ (Φ†Φ)2 + µ2s2 + s s4 + sh Φ†Φs2 h h 2 s 4 2
Here Φ and s are, respectively, the usual Standard Model Higgs doublet and a real singlet scalar.
The coupling between Φ and s acts as a portal between the Standard Model and an unknown Hidden Sector (the so-called Higgs portal).
Tommi Tenkanen Observational properties of very weakly coupled dark matter 12/7/2017 5 / 14 Other options
We can also introduce a sterile neutrino ψ
LHidden = ψ¯(i∂/ − mψ)ψ + igsψγ¯ 5ψ
or promote s to be a complex doublet of a hidden SU(2) symmetry, and so on1
Either the scalar s, the fermion ψ, the vector Aµ, or many of them simultaneously, can play the role of dark matter
How was the observed DM abundance produced?
1 See e.g. Heikinheimo, TT, Tuominen (arXiv:1704.05359) Tommi Tenkanen Observational properties of very weakly coupled dark matter 12/7/2017 6 / 14 Dark Matter production mechanisms
There are basically two mechanisms for dark matter production: freeze-out and freeze-in
-4 -4
-6 -6
-8 -8 Γ Y Y
10 -10 10 -10 log log
-12 -12
-14 -14 Γ
-16 -16
0.0 0.5 1.0 1.5 2.0 2.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
log10 x log10 x
Tommi Tenkanen Observational properties of very weakly coupled dark matter 12/7/2017 7 / 14 The Freeze-Out
Dark matter is initially in thermal equilibrium with the SM particles. This requires a rather strong coupling, λsh ' 0.1.
May lead to a WIMP miracle: thermal relic with weak cross-section and a mass ms ∼ EW scale gives the right relic abundance.
Starts to be very constrained by experiments2
2 For a recent review, see e.g. G. Arcadi et al. (arXiv: 1703.07364) Tommi Tenkanen Observational properties of very weakly coupled dark matter 12/7/2017 8 / 14 Frozen-in Dark Matter
−7 Requires λsh . 10 , or otherwise the singlet sector thermalizes with the SM (this is sometimes called a FIMP scenario)
Cannot (usually) be tested by collider experiments but can be tested by cosmological and astrophysical observations
These include indirect detection signals, astrophysical imprints of self-interacting or non-thermal DM, imprints on CMB etc.
Tommi Tenkanen Observational properties of very weakly coupled dark matter 12/7/2017 9 / 14 Review of freeze-in scenarios
Out now! See arXiv: 1706.07442
Tommi Tenkanen Observational properties of very weakly coupled dark matter 12/7/2017 10 / 14 No particle DM?
What if DM does not consist of new particles but primordial black holes (PBHs)?
PBHs can easily form in the early Universe from sufficiently large density perturbations3
Especially the LIGO observation of O(10)M BH mergers is interesting for PBHs
3 See e.g. Carr et al. (arXiv: 1705.05567) and Carr, TT, Vaskonen (arXiv: 1706.03746) + refs. therein Tommi Tenkanen Observational properties of very weakly coupled dark matter 12/7/2017 11 / 14 Primordial black holes (arXiv: 1705.05567)
monochromatic lognormal,σ=2 0.0 0.0
Planck
K M -0.5 WD NS -0.5 WB FL EROS -1.0 -1.0
Eri II
Evaporation PBH PBH f -1.5 f -1.5 10 10 log log
-2.0 HSC -2.0
Seg I
-2.5 -2.5
-3.0 -3.0 -15 -10 -5 0 -15 -10 -5 0
log10(Mc /M⊙) log10(Mc /M⊙)
power law,γ=-1 power law,γ=1 0.0 0.0
-0.5 -0.5
-1.0 -1.0 PBH PBH f -1.5 f -1.5 10 10 log log -2.0 -2.0
-2.5 -2.5
-3.0 -3.0 -15 -10 -5 0 -15 -10 -5 0
log10(Mc /M⊙) log10(Mc /M⊙) Tommi Tenkanen Observational properties of very weakly coupled dark matter 12/7/2017 12 / 14 Primordial black holes (arXiv: 1705.05567)
lognormal lognormal, all constraints 6 6
5 5
4 4
σ 3 σ 3
log f 2 2 10 max 0
1 1 -0.5
0 0 -15 -10 -5 0 -15 -10 -5 0 -1.0
log10(Mc /M⊙) log10(Mc /M⊙) -1.5 power law,γ<0 power law,γ>0 6 6 -2.0
5 5 -2.5
4 4 -3.0
σ 3 σ 3
2 2
1 1
0 0 -15 -10 -5 0 -15 -10 -5 0
log10(Mc /M⊙) log10(Mc /M⊙)
Tommi Tenkanen Observational properties of very weakly coupled dark matter 12/7/2017 13 / 14 Conclusions
The nature of dark matter is still unknown
Weakly coupled hidden sectors contain many interesting features, which have NOT been studied extensively
Primordial black holes are a compelling alternative to particle DM and may constitute all DM
Cosmological and astrophysical observations provide a valuable resource on testing different dark matter models
Tommi Tenkanen Observational properties of very weakly coupled dark matter 12/7/2017 14 / 14