Post-graduate theses
Current Record: 25 of 291
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Identifier |
000451421 |
Title |
Dark matter bound state formation and thermal decoupling in the early universe |
Alternative Title |
Δημιουργία δέσμιων καταστάσεων και θερμική παραγωγή σκοτεινής ύλης στο πρώιμο σύμπαν |
Author
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Βασιλάκη, Χριστιάνα Σ.
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Thesis advisor
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Παυλίδου, Βασιλική
Πετράκη, Καλλιόπη
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Reviewer
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Κυρίτσης, Ηλίας
Νιάρχος, Βασίλειος
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Abstract |
In this thesis we focus on the thermal production of dark matter (DM) that couples to force mediators significantly lighter than itself. In this case, the interactions between DM particles are long-range. Long-range
interactions give rise to non-perturbative effects, including the existence of bound states. The formation and
subsequent decay of metastable DM bound states opens up an additional DM annihilation channel. This affects
the DM relic density, thereby altering the predicted DM mass and couplings that can account for the observed
abundance. Here, we consider DM consisting of a pair of Dirac fermions coupled to a massless dark photon.
Due to the long-range interaction, the dark particle-antiparticle pairs can form positronium-like bound states.
The computation of the DM density requires solving a system of coupled Boltzmann equations that track the
densities of the free particles and the bound species, and describe the interplay among DM annihilation, boundstate formation, bound-state decay and the inverse processes, in an expanding universe. However, metastable
bound states remain in a quasi-steady state that can be employed to reduce the coupled system of equations to
a single one with an effective DM depletion cross-section that encodes all these effects. The effective equation is
solved numerically and the validity of the steady-state approximation is investigated. The coupling required to
reproduce the observed DM density is determined as a function of the DM mass. It is found that for DM masses
larger than a few TeV, the DM density is significantly affected by bound-state formation and decay. Lastly, the
back-reaction of the resonant radiation produced during bound-state formation is examined. It is shown that
rather than ionising the bound states, the resonant dark photons redshift due to the expansion of the universe
and thermalise with the dark particles at much smaller timescales.
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Language |
English |
Subject |
Bound-state formation |
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Long-range intraction |
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Δέσμιες καταστάσεις |
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Σκοτεινό φωτόνιο |
Issue date |
2022-11-25 |
Collection
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School/Department--School of Sciences and Engineering--Department of Physics--Post-graduate theses
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Type of Work--Post-graduate theses
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Permanent Link |
https://elocus.lib.uoc.gr//dlib/0/7/0/metadata-dlib-1664881943-89784-7799.tkl
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Views |
497 |