On 11. October at 16:00 Nico Benincasa will defend his doctoral thesis „Phase transitions and gravitational waves in models of dark matter“ for obtaining the degree of Doctor of Philosophy (in Physics).
Senior researcher Kristjan Kannike, NICBP
Senior researcher Abdelhak Djouadi, University of Granada, Spain
Associate professor Margus Saal, University of Tartu
dr. Bogumila Swiezewska, University of Warsaw (Poland)
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.