Two Approaches to the Baryon Asymmetry of the Universe
2023171 pages
Thesis: PhD - U. Wurzburg (main)
- Published: 2023
DOI:
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Abstract: (U. Wurzburg (main))
Explaining the baryon asymmetry of the Universe has been a long-standing problem of
particle physics, with the consensus being that new physics is required as the Standard
Model (SM) cannot resolve this issue. Beyond the Standard Model (BSM) scenarios would
need to incorporate new sources of CP violation and either introduce new departures from
thermal equilibrium or modify the existing electroweak phase transition. In this thesis,
we explore two approaches to baryogenesis, i.e. the generation of this asymmetry.
In the first approach, we study the two-particle irreducible (2PI) formalism as a means
to investigate non-equilibrium phenomena. After arriving at the renormalised equations
of motions (EOMs) to describe the dynamics of a phase transition, we discuss the techniques
required to obtain the various counterterms in an on-shell scheme. To this end, we
consider three truncations up to two-loop order of the 2PI effective action: the Hartree
approximation, the scalar sunset approximation and the fermionic sunset approximation.
We then reconsider the renormalisation procedure in an MS scheme to evaluate the 2PI
effective potential for the aforementioned truncations. In the Hartree and the scalar sunset
approximations, we obtain analytic expressions for the various counterterms and subsequently
calculate the effective potential by piecing together the finite contributions. For
the fermionic sunset approximation, we obtain similar equations for the counterterms in
terms of divergent parts of loop integrals. However, these integrals cannot be expressed
in an analytic form, making it impossible to evaluate the 2PI effective potential with
the fermionic contribution. Our main results are thus related to the renormalisation
programme in the 2PI formalism: (i) the procedure to obtain the renormalised EOMs,
now including fermions, which serve as the starting point for the transport equations for
electroweak baryogenesis and (ii) the method to obtain the 2PI effective potential in a
transparent manner.
In the second approach, we study baryogenesis via leptogenesis. Here, an asymmetry in
the lepton sector is generated, which is then converted into the baryon asymmetry via the
sphaleron process in the SM. We proceed to consider an extension of the SM along the lines
of a scotogenic framework. The newly introduced particles are charged odd under a Z2
symmetry, and masses for the SM neutrinos are generated radiatively. The Z2 symmetry
results in the lightest BSM particle being stable, allowing for a suitable dark matter (DM)
candidate. Furthermore, the newly introduced heavy Majorana fermionic singlets provide
the necessary sources of CP violation through their Yukawa interactions and their out-ofequilibrium
decays produce a lepton asymmetry. This model is constrained from a wide range of observables, such as consistency with neutrino oscillation data, limits on branching
ratios of charged lepton flavour violating decays, electroweak observables and obtaining
the observed DM relic density. We study leptogenesis in this model in light of the results
of a Markov chain Monte Carlo scan, implemented in consideration of the aforementioned
constraints. Successful leptogenesis in this model, to account for the baryon asymmetry,
then severely constrains the available parameter space.- Baryonenasymmetrie
- Renormierung
- Elementarteilchenphysik
- Neutrino
- Quantenfeldtheorie
- 2PI Formalism
- Baryogenesis
- Leptogenesis
- Physics beyond the Standard Model
- Scotogenic Model
References(173)
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