Phase transitions and gravitational waves in models of dark matter
Date
2023-10-02
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Abstract
Kaudsed tõendid näitavad, et enamus universumi ainest esineb tumeaine kujul. Kuigi tumeainet on tavalisest ainest mitu korda rohkem, ei ole eksootiliste tumeaine osakeste loomus veel kindlaks määratud. Nende tuvastamiseks on välja mõeldud mitu võimalust. Käesolevas väitekirjas käsitleme tumeaine kaudset uurimist gravitatsioonilainete kaudu. Need lained sarnanevad vees levivatele helilainetele selle vahega, et gravitatsioonilainete puhul häirivad lainet mitte vett vaid aegruumi ennast. Gravitatsioonilained, mida ennustab Einsteini üldrelatiivsusteooria, avastati 2015. aastal, mis andis uue võimaluse tumeaine uuringuteks. Väitekirjas uuritakse esimest järku faasisiirdeid, mis võisid toimuda varajase universumi mahajahtumisel. See on sarnane kuuma vee üleminekuga vedelast gaasilisse faasi keemisel. Faasisiirde ajal aurumullid tekivad, kasvavad ja põrkavad teiste mullidega, kuni viimaks on kogu vesi aurustunud. Sarnaselt põrkuvad kosmilisel faasisiirdel teineteisega uue faasi mullid, kuid need tekitavad üksteisega põrkudes aegruumi häiritusi – gravitatsioonilaineid – just nagu vesi keemisel muliseb. Väitekirja eesmärk on uurida erinevaid tumeaine mudeleid, milles selline faasisiire võis varajases universumis toimuda ja ennustada signaali, mida võib olla võimalik detekteerida tulevikus kosmoses asuvate gravitatsioonilainete detektoritega nagu LISA, DECIGO või BBO. Sellise signaali avastamine võiks aidata välja selgitada tumeaine olemust.
Indirect evidence shows that most of the matter content in the Universe consists of dark matter. Despite this significant proportion, we have not elucidated the nature of these exotic dark particles yet. Several possible ways exist in order to detect them. The method we consider in this thesis is the indirect probe of dark matter through the detection of gravitational waves. These waves are like the sound waves propagating water, except that, in the case of gravitational waves, this is spacetime itself that is disturbed instead of water. These gravitational waves, originally predicted by the theory of General Relativity, were first discovered in 2015, thus opening a new channel to investigate dark matter. The gravitational waves studied in this thesis originate from a first-order phase transition that could have occurred in the early Universe, as it cools down. This can be viewed as water going from liquid phase to gas phase when heating the fluid and reaching the boiling point. During this phase transition, bubbles of the new (gas) phase nucleate, grow and collide with each other, eventually converting all of water into vapour. Similarly, for cosmic phase transitions, bubbles of the new phase collide but these collisions disturb the spacetime metric and generate gravitational waves, just like boiling makes a rumbling sound. The goal of this thesis is to study different models of dark matter in which such a phase transition occurred in the early Universe and to predict a signal that could be detectable by future space-based gravitational-wave detectors, such as LISA, DECIGO or BBO. Detecting such a signal could elucidate the nature of dark matter.
Indirect evidence shows that most of the matter content in the Universe consists of dark matter. Despite this significant proportion, we have not elucidated the nature of these exotic dark particles yet. Several possible ways exist in order to detect them. The method we consider in this thesis is the indirect probe of dark matter through the detection of gravitational waves. These waves are like the sound waves propagating water, except that, in the case of gravitational waves, this is spacetime itself that is disturbed instead of water. These gravitational waves, originally predicted by the theory of General Relativity, were first discovered in 2015, thus opening a new channel to investigate dark matter. The gravitational waves studied in this thesis originate from a first-order phase transition that could have occurred in the early Universe, as it cools down. This can be viewed as water going from liquid phase to gas phase when heating the fluid and reaching the boiling point. During this phase transition, bubbles of the new (gas) phase nucleate, grow and collide with each other, eventually converting all of water into vapour. Similarly, for cosmic phase transitions, bubbles of the new phase collide but these collisions disturb the spacetime metric and generate gravitational waves, just like boiling makes a rumbling sound. The goal of this thesis is to study different models of dark matter in which such a phase transition occurred in the early Universe and to predict a signal that could be detectable by future space-based gravitational-wave detectors, such as LISA, DECIGO or BBO. Detecting such a signal could elucidate the nature of dark matter.
Description
Väitkirja elektrooniline versioon ei sisalda publikatsioone
Keywords
dark matter, gravitation waves, phase transformations