Particle Physics Probes from Cosmology by Anthony Fradette B.Sc., McGill University, 2010 M.Sc ...

185 Pages·2017·4.5 MB·English

Particle Physics Probes from Cosmology
by
Anthony Fradette
B.Sc., McGill University, 2010
M.Sc., University of Victoria, 2012
A Dissertation Submitted in Partial Fulfillment of the
Requirements for the Degree of
DOCTOR OF PHILOSOPHY
in the Department of Physics and Astronomy
c Anthony Fradette, 2017
(cid:13)
University of Victoria
All rights reserved. This dissertation may not be reproduced in whole or in part, by
photocopying or other means, without the permission of the author.
ii
Particle Physics Probes from Cosmology
by
Anthony Fradette
B.Sc., McGill University, 2010
M.Sc., University of Victoria, 2012
Supervisory Committee
Dr. Maxim Pospelov, Supervisor
(Department of Physics and Astronomy)
Dr. Adam Ritz, Departmental Member
(Department of Physics and Astronomy)
Dr. Alexandre Brolo, Outside Member
(Department of Chemistry)
iii
ABSTRACT
In this dissertation, we explore the cosmological sensitivity of well-motivated ex-
tensions of the Standard Model (SM) of particles. We focus on two specific models,
the vector portal and the Higgs portal, that can connect the SM to a dark sector of
new hidden particles. We find that both portals have sensitivity in the ultra-weak
coupling regime, where the relic abundance is set by the freeze-in mechanism. Pro-
vided that the mediators of the portal interactions decay into the SM, we derive the
constraints on masses and couplings of such states from precision cosmology. As a
primary source of constraints, we use Big Bang Nucleosynthesis (BBN), the Cosmic
Microwave Background (CMB) and the diffuse X-ray background. For the Higgs por-
tal scalar, we improve the relic abundance calculation in the literature and provide an
estimate of thermal corrections to the freeze-in yield. We find that the cosmological
bounds are relatively insensitive to improvements in the abundance accuracy, and a
full finite-temperature calculation is not needed.
We also investigate the BBN constraints for hypothetical long-lived metastable
scalars particles S that can be produced at the Large Hadron Collider from decays
of the Higgs boson. We find that for viable branching ratios Br(h SS), the early
→
universe metastable abundance of S, regulated by its self-annihilation through the
Higgs portal, is so large that the lifetime of S is strongly constrained to τ < 0.1 s
S
to maintain the consistency of BBN predictions with observations. This provides a
useful upper bound on the lifetimes of S particles that a purposely-built detector,
such as the one suggested in the MATHUSLA proposal, seek to discover.
We also investigate the viability and detectability of freeze-in self-interacting
fermionic dark matter communicating with the SM via a vector portal. We focus
on the parameter where the χχ¯ AA is negligible, as required by a variety of
(cid:48) (cid:48)
→
indirect detection constraints. We find that planned upgrades to the direct detection
experiments will be able to probe the region of parameter space that can alleviate
smallscalestructureproblemsofdarkmatterviaself-interactionsforadarkfinestruc-
ture constant as small as α = 10 4. We forecast the sensitivity for Lux-ZEPLIN,
d −
XENONnT and PandaX-4T.
iv
Contents
Supervisory Committee ii
Abstract iii
Table of Contents iv
List of Tables viii
List of Figures ix
List of Abbreviations xii
Acknowledgements xiv
Dedication xv
1 Introduction 1
1.1 Thermal history of the universe . . . . . . . . . . . . . . . . . . . . . 3
1.1.1 Relic densities . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1.2 Big bang nucleosynthesis . . . . . . . . . . . . . . . . . . . . . 6
1.1.3 Cosmic microwave background . . . . . . . . . . . . . . . . . . 8
1.2 The dark sector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.2.1 Experimental motivation . . . . . . . . . . . . . . . . . . . . . 11
1.2.2 Dark Sector Portals . . . . . . . . . . . . . . . . . . . . . . . . 12
1.2.3 Dark Matter searches . . . . . . . . . . . . . . . . . . . . . . . 14
1.3 Cosmological probes of the dark sector . . . . . . . . . . . . . . . . . 15
1.3.1 Energy injection in BBN . . . . . . . . . . . . . . . . . . . . . 16
1.3.2 Energy injection in the CMB . . . . . . . . . . . . . . . . . . 17
1.4 Structure of the dissertation . . . . . . . . . . . . . . . . . . . . . . . 18
v
I Vector Portal 20
2 Very Dark Photons in Cosmology 21
2.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.3 Freeze-in abundance of VDP . . . . . . . . . . . . . . . . . . . . . . . 26
2.4 Impact on BBN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.5 Impact on the CMB . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2.6 Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
2.7 Supplementary: Resonant Production . . . . . . . . . . . . . . . . . . 40
2.7.1 Relativistic Case . . . . . . . . . . . . . . . . . . . . . . . . . 40
2.7.2 Nonrelativistic Corrections . . . . . . . . . . . . . . . . . . . . 42
2.8 Supplementary: Hadronic Production . . . . . . . . . . . . . . . . . . 44
2.9 Supplementary: BBN Analysis . . . . . . . . . . . . . . . . . . . . . . 45
3 Self-interacting dark matter from freeze-in 50
3.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
3.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
3.3 Model and Set-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.4 Production of the dark sector . . . . . . . . . . . . . . . . . . . . . . 53
3.4.1 Freeze-in regime . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.4.2 Dark thermalization and reannihilation . . . . . . . . . . . . . 57
3.5 Self-Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
3.6 Probes and Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . 61
3.6.1 Direct Detection . . . . . . . . . . . . . . . . . . . . . . . . . 62
3.6.2 Indirect Detection . . . . . . . . . . . . . . . . . . . . . . . . . 65
3.7 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
3.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
3.9 Supplementary: Analytical freeze-in yields . . . . . . . . . . . . . . . 68
3.10 Supplementary: Field rotations and couplings . . . . . . . . . . . . . 70
3.11 Supplementary: Dark sector energy flow . . . . . . . . . . . . . . . . 71
II Higgs Portal 73
4 Long-Lived Scalars at the LHC 74
vi
4.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
4.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
4.3 The minimal Higgs portal model . . . . . . . . . . . . . . . . . . . . . 76
4.3.1 Decay products . . . . . . . . . . . . . . . . . . . . . . . . . . 78
4.3.2 Cosmological metastable abundance . . . . . . . . . . . . . . . 80
4.4 Big Bang Nucleosynthesis . . . . . . . . . . . . . . . . . . . . . . . . 83
4.4.1 Neutron enrichment . . . . . . . . . . . . . . . . . . . . . . . . 84
4.4.2 Energy density requirements . . . . . . . . . . . . . . . . . . . 90
4.4.3 Late-time energy injection . . . . . . . . . . . . . . . . . . . . 93
4.5 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
4.6 Events at MATHUSLA . . . . . . . . . . . . . . . . . . . . . . . . . . 97
4.7 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
4.8 Supplementary: Muon injections in early BBN . . . . . . . . . . . . . 101
4.8.1 Neutron enrichment . . . . . . . . . . . . . . . . . . . . . . . . 101
4.8.2 Energyinjectionpartitionedbetweenphotonandneutrinobaths
(e.g. muon injection) . . . . . . . . . . . . . . . . . . . . . . . 102
5 Feeble Scalar Portal in Cosmology 104
5.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
5.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
5.3 The super-renormalizable Higgs portal model . . . . . . . . . . . . . . 106
5.3.1 S γγ decay rate . . . . . . . . . . . . . . . . . . . . . . . . 107
→
5.3.2 Finite-temperature effects . . . . . . . . . . . . . . . . . . . . 108
5.3.3 Higher order corrections to the thermal mixing angle . . . . . 109
5.4 Cosmological production via freeze-in . . . . . . . . . . . . . . . . . . 111
5.4.1 QCD production . . . . . . . . . . . . . . . . . . . . . . . . . 113
5.4.2 Infrared divergences . . . . . . . . . . . . . . . . . . . . . . . 116
5.4.3 Resonant S production . . . . . . . . . . . . . . . . . . . . . . 119
5.4.4 Thermalization of the S sector with the SM . . . . . . . . . . 120
5.4.5 Validity of the Maxwell-Boltzmann approximation . . . . . . . 121
5.5 Cosmological constraints . . . . . . . . . . . . . . . . . . . . . . . . . 123
5.5.1 Diffuse X-ray background . . . . . . . . . . . . . . . . . . . . 124
5.5.2 Cosmic Microwave Background . . . . . . . . . . . . . . . . . 125
5.5.3 Spectral distortions . . . . . . . . . . . . . . . . . . . . . . . . 126
5.5.4 N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
eff
vii
5.5.5 Big Bang Nucleosynthesis . . . . . . . . . . . . . . . . . . . . 130
5.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
5.7 Supplementary: Large energy limit of production cross sections . . . . 135
5.8 Supplementary: Strategytonumericalintegrationwithquantumstatis-
tics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
6 Conclusion 140
A Relativistic degrees of freedom 142
Bibliography 144
viii
List of Tables
Table 5.1 S freeze-in yield for each production channels. . . . . . . . . . . 114
ix
List of Figures
Figure 1.1 Schematic representation of the normalized particle density evo-
lution in freeze-out and freeze-in scenarios. . . . . . . . . . . . . 5
Figure 1.2 Schematic representation of the relic density relationship with
respect to the coupling strength with the bath. . . . . . . . . . 6
Figure 1.3 Network of main reactions in BBN. . . . . . . . . . . . . . . . . 7
Figure 1.4 Time-dependence of the light nuclei abundances relative to hy-
drogen during BBN. . . . . . . . . . . . . . . . . . . . . . . . . 8
Figure 1.5 Left: Temperature anisotropies in the CMB measured by the
Planck satellite. Right: Temperature power spectrum associated
with the Planck data. . . . . . . . . . . . . . . . . . . . . . . . 9
Figure 1.6 Illustration of the connection between the interactions for the
relic density, direct and indirect detection. . . . . . . . . . . . . 14
Figure 2.1 An overview of the constraints on the plane of vector mass versus
kinetic mixing, showing the regions excluded due to their impact
on BBN and the CMB anisotropies, in addition to various ter-
restrial limits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Figure 2.2 Illustration of the coalescence production of the dark photon V
via an off-shell photon. . . . . . . . . . . . . . . . . . . . . . . . 26
Figure 2.3 Total energy stored per baryons for α = 10 35 and Γ 1 = 1014s. 29
eff − −V
Figure 2.4 EffectsonBBNfromthedecayofrelicdarkphotonsasafunction
vector mass of m and kinetic mixing parameter κ. . . . . . . . 33
V
Figure 2.5 CMB constraints on the energy injection parameters ζ and Γ. . 36
Figure 2.6 Effective deposition efficiency for each decay channel with the
sum weighted by the branching ratios for Γ 1 = 1014s. . . . . . 37
−V
Figure 2.7 CMB constraints on the VDP parameter space. . . . . . . . . . 38
Figure 2.8 The dependence of the resonant temperatures T and T on
r,L r,T
frequency ω. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
x
Figure 2.9 The average number of particles and electromagnetic energy in-
jected per V decay with m > 2.5 GeV, from a Pythia simulation. 47
V
Figure 2.10Theadoptedeffectivebranchingratiosintothevariousfinalstates
that are relevant for BBN considerations. . . . . . . . . . . . . 48
Figure 3.1 Contribution of each production channels in the freeze-in relic
with a light mediator (m m ) as a function of dark matter
A(cid:48) Z
(cid:28)
m for αα = 10 26. . . . . . . . . . . . . . . . . . . . . . . . . 56
χ (cid:48) d −
Figure 3.2 Thermal evolution of the normalized number density Y = n/s
for m = 100 GeV with a strong reannihilation, negligible rean-
χ
nihilation and from freeze-in only. . . . . . . . . . . . . . . . . . 58
Figure 3.3 Valuesofαα neededforthecorrectrelicdensityinthefrozen-in
(cid:48) d
fermionic SIDM model with a dark photon mediator. . . . . . . 59
Figure 3.4 SIDM parameter space for α = 10 4 with current constraints
d −
and forecasted sensitivity of DD experiments. . . . . . . . . . . 61
Figure 3.5 Spin-independent cross section limits from current DD experi-
ments and projected sensitivity for future upgrades. . . . . . . . 64
Figure 3.6 Dark photon parameter space with current constraints and ki-
netic mixing range valid for a fermionic SIDM with α = 10 4. . 65
d −
Figure 4.1 Left: Branching ratios of the scalar S in our baseline decay
model. Right: Scalar S lifetime of our baseline model and the
spectator model for the mixing angle θ = 10 6. . . . . . . . . . 80
−
Figure 4.2 Left: Temperature evolution (x = m/T) of the Y intermediate
S
abundance for m = 5 MeV and 500 MeV for the three bench-
S
mark Higgs branching ratios. Right: Metastable abundance of S
prior to its decay normalized over the baryon density. . . . . . . 82
Figure 4.3 Left: X evolution for the SBBN and the injection of pions,
n
kaons, baryons and muons (neutrinos) for lifetimes of 0.05 s with
theinitialY abundancetunedtoyield∆Y = 0.01. Right: Limit
S p
of injected pairs for each channel as a function of the S lifetime. 86
Figure 4.4 Constraints on Y2 σv from SS annihilations into charged
S(cid:104) (cid:105)π+π−
pions from the BBN 4He abundance at Y = 0.26. . . . . . . . . 90
p