Some of the Most Popular Dark Matter Candidates: Looking Into the Standard Model

Table of Links

Acknowledgements

1 Introduction to thesis

1.1 History and Evidence

1.2 Facts on dark matter

1.3 Candidates to dark matter

1.4 Dark matter detection

1.5 Outline of the thesis

2 Dark matter through ALP portal and 2.1 Introduction

2.2 Model

2.3 Existing constraints on ALP parameter space

2.4 Dark matter analysis

2.5 Summary

3 A two component dark matter model in a generic 𝑈(1)𝑋 extension of SM and 3.1 Introduction

3.2 Model

3.3 Theoretical and experimental constraints

3.4 Phenomenology of dark matter

3.5 Relic density dependence on 𝑈(1)𝑋 charge 𝑥𝐻

3.6 Summary

4 A pseudo-scalar dark matter case in 𝑈(1)𝑋 extension of SM and 4.1 Introduction

4.2 Model

4.3 Theoretical and experimental constraints

4.4 Dark Matter analysis

4.5 Summary

5 Summary

Appendices

A Standard model

B Friedmann equations

C Type I seasaw mechanism

D Feynman diagrams in two-component DM model

Bibliography

1.3 Candidates to dark matter

In this section, we briefly mention some of the popular DM candidates.

Looking into the Standard Model

Thermal dark matter

These are DM candidates, which were produced thermally in the early universe when it was in the plasma state. One can do such a study and calculate the DM relic density using the Boltzmann equation. A popular mechanism following thermal DM is the freeze-out mechanism [33]. It assumes that DM is in thermal equilibrium with the SM bath in the very early stages of the universe, but as the universe expands and the interaction rate becomes ineffective against the expansion rate, DM number density or relic density freezes out. It is found that if DM is in the GeV - TeV mass range and couples weakly to SM, it can easily satisfy the correct relic density. This is called the WIMP miracle, and such particles are named weakly interacting massive particles (WIMPs). A brief on the freeze-out mechanism is described here [32, 33],

Strongly interacting massive particles (SIMPs) is another interesting DM candidate that lies in the MeV mass range and interacts strongly with both particles [56, 57]. These thermal DM candidates are being searched in several experiments.

Non-thermal dark matter

These are the candidates that are not in thermal equilibrium with SM in the early universe. Many mechanisms can produce a non-thermal DM, e.g. Freeze-in [58], exponential production [59], misalignment mechanism [60], gravitational production, etc.

Freeze-in is a popular mechanism to produce DM non-thermally in the early universe. It starts with a negligible abundance of DM in the early universe, but it grows and freezes in via a tiny coupling with the bath particles from the hidden sector (dark sector). DM mass or coupling can be tuned to have the correct relic. Such DM candidates are called feebly interacting massive particles (FIMPs). A FIMP candidate is hard to detect in the lab due to its tiny coupling with bath particles [58].

In particular, MACHOs are astrophysical objects like isolated planets, brown dwarfs (failed stars), neutron stars, black holes, etc. These objects have been ruled out by a survey done by the MACHO collaboration and the EROS-2 group using the microlensing technique [64].