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Dynamics and Phenomenology of Scalar Field Dark Matter Through Dynamics and Phenomenology of Scalar Field Dark Matter through the Higgs Portal D Catarina Martins Cosme Programa Doutoral em Física Departamento de Física e Astronomia 2018 Orientador Orfeu Bertolami, Professor Catedrático, Faculdade de Ciências da Universidade do Porto Coorientador João G. Rosa, Investigador FCT, Universidade de Aveiro This thesis is dedicated to my parents, Quintino and Luísa, and my sister, Inês for all their love and care; and to my grandmother Nanda (1933-2012): I wish you were here to celebrate this with me. Para ser grande, sê inteiro: nada Teu exagera ou exclui. Sê todo em cada coisa. Põe quanto és No mínimo que fazes. Assim em cada lago a lua toda Brilha, porque alta vive. Fernando Pessoa, in Odes de Ricardo Reis Acknowledgements First of all, my most sincere thanks to my supervisors: João Rosa and Orfeu Bertolami. I feel so fortunate for having enrolled a PhD in Physics under their guidance, and there are no words to express my gratitude to them for their support and infinite patience for my questions. Thank you for teaching me how to be a theoretical physicist, and for always motivating me to go further. For financial support, I thank Fundação para a Ciência e Tecnologia for the research grants PD/BI/106012/2014 and PD/BD/114453/2016 and Centro de Física do Porto for other expenses, under the project UID/FIS/04650/2013. I am grateful for the opportunity to work with great collaborators: Tommi Tenka- nen, Nicolás Bernal and Ville Vaskonen. Thank you for the interesting and stimulating discussions we had together, from which I learned a lot. All this work would not be possible without very good professors. I would like to thank all my PhD professors, in particular, Nuno Castro. I must thank all my colleagues and administrative staff at the Department of Physics of the University of Porto, and my office mates: Artur Amorim, Cláudio Gomes, Daniel Passos, Emilio Trevisani, Gonçalo Ventura, Lauren Greenspan, Pedro Leal and, especially, Robert Carcassés, Paula Quitério, Niaz Ali Khan and André Guerra, who became my personal friends. Thank you for the great moments we have shared together. A word of gratitude to Gr@V members of the University of Aveiro for their hospi- tality during my weekly visits to Aveiro. Thank you for making me feel welcome and for sharing interesting discussions with me. A big thank you to all my friends but, especially, Ana, Ivo, Vasco, and Zé. I feel fortunate for having such amazing friends with whom I can share not only laughter and good moments, but also my worries and sorrows. Thank you for always being there for me. Last but not least, a special word of gratitude to my parents, Quintino and Luísa, and to my sister, Inês, for supporting my choices, for hearing my grumbling when I was not satisfied with my work but, primarily, for their care and love. Thank you for reminding me everyday that life has many obstacles but, if we fight hard, we can overcome them. After all, what really matters is not giving up on our dreams. i Abstract In this thesis, we discuss the dynamics and phenomenology of an oscillating scalar field coupled to the Higgs boson and which may account for the dark matter in the Universe. First, we study the case where the field has negligible self-interactions. We argue that the initial field amplitude should generically be of the order of the Hubble parameter during inflation, as a result of its quasi-de Sitter fluctuations. This implies that such a field may account for the present dark matter abundance for masses in the range 10−6 −10−4 eV, if the tensor-to-scalar ratio is within the range of planned Cosmic Microwave Background experiments. We show that such mass values can naturally be obtained through either Planck-suppressed non-renormalizable interactions with the Higgs boson or, alternatively, through renormalizable interactions within the Randall- Sundrum scenario. Then, we consider the case where the field’s potential has a quartic coupling accounting for the dark scalar self-interactions. The model assumes an underlying scale invariance such that the scalar field only acquires mass after the electroweak phase transition, behaving as dark radiation before the latter takes place. While for a positive coupling to the Higgs field the dark scalar is stable, for a negative coupling it acquires a vacuum expectation value after the electroweak phase transition and may decay into photon pairs, albeit with a mean lifetime much larger than the age of the Universe. We explore possible astrophysical and laboratory signatures of such a dark matter candidate in both cases and we find that dark matter within this scenario will be generically difficult to detect in the near future, except for the promising case of a 7 keV dark scalar decaying into photons, which may naturally explain the observed galactic and extra-galactic 3.5 keV X-ray line. Finally, we study the case where an oscillating scalar field coupled to the Higgs field drives a non-thermal electroweak symmetry breaking. We show that this possibility may be achieved with a late inflaton decay and, consequently, an early-matter era. We find that the dark matter candidate within this scenario is heavier than the ones considered above, making it more likely to be detected in the laboratory. ii Resumo Nesta tese, discutimos a dinâmica e fenomenologia de um campo escalar a oscilar acoplado ao bosão de Higgs e que pode constituir toda a matéria escura no Universo. Primeiramente, estudamos o caso em que o campo tem auto-interacções desprezá- veis. A sua amplitude inicial é da ordem do parâmetro de Hubble durante a inflação, devido às suas flutuações quasi-de Sitter, o que implica que o campo pode explicar a abundância observável de matéria escura para massas na ordem dos 10−6 −10−4 eV, se o rácio tensor-escalar não for muito suprimido. Além disso, mostramos que, embora estas massas sejam pequenas, podem ser naturalmente obtidas através de interacções não-renormalizáveis com o bosão de Higgs que sejam suprimidas pela escala de Planck ou através de interacções renormalizáveis no contexto do cenário de Randall-Sundrum. Em seguida, consideramos o caso em que o potencial do campo de matéria escura tem uma interacção quártica, representando as auto-interacções do campo. O mo- delo assume uma invariância de escala subjacente tal que o campo apenas adquire massa após a transição electrofraca, comportando-se como radiação escura antes de a transição ocorrer. Enquanto que para um acoplamento positivo ao Higgs o campo de matéria escura é estável, para um acoplamento negativo o campo de matéria escura adquire um valor esperado no vácuo após a transição electrofraca e pode decair em pares de fotões, sendo o tempo de vida médio deste processo superior à idade do Universo. Assim, exploramos possíveis assinaturas astrofísicas e no laboratório que possam advir deste candidato a matéria escura, e constatamos que, embora a sua detecção num futuro próximo seja muito difícil, há um caso promissor: o decaimento do nosso candidato, com uma massa de 7 keV, em fotões, o que poderia explicar a linha de 3.5 keV, na gama dos raios-X, observada na nossa galáxia e em sistemas fora dela. Finalmente, estudamos o caso em que o campo escalar a oscilar acoplado ao bosão de Higgs controla uma transição de fase electrofraca não térmica. Mostramos que esta possibilidade pode ser concretizada se o inflatão decair tardiamente, o que conduz a uma era de matéria logo após a inflação. Neste cenário, o candidato de matéria escura é mais pesado que os candidatos acima mencionados, o que o torna mais provável de ser detectado em laboratório. iii List of included papers This thesis is based on the following publications [1–4]: • Scalar field dark matter and the Higgs field, Orfeu Bertolami, Catarina Cosme and João G. Rosa Phys. Lett. B 759 (2016) 1-8 • Scalar field dark matter with spontaneous symmetry breaking and the 3.5 keV line, Catarina Cosme, João G. Rosa and Orfeu Bertolami Phys. Lett. B 781 (2018) 639-644 • Scale-invariant scalar field dark matter through the Higgs portal Catarina Cosme, João G. Rosa and Orfeu Bertolami JHEP 05 (2018) 129 • Can Dark Matter drive electroweak symmetry breaking? Catarina Cosme, João G. Rosa and Orfeu Bertolami submitted to JHEP In addition, during the course of my PhD studies, I have co-authored the following articles, which have not been included in the present thesis [5,6]: • Phenomenology of Self-Interacting Dark Matter in a Matter-Dominated Universe, Nicolás Bernal, Catarina Cosme and Tommi Tenkanen submitted to EPJ C • Scalar singlet dark matter in non-standard cosmologies, Nicolás Bernal, Catarina Cosme, Tommi Tenkanen and Ville Vaskonen submitted to EPJ C iv Contents List of Figures x 1 Introduction 1 1.1 Motivation . .1 1.2 The Standard Model of Particle Physics . .3 1.2.1 A historical overview . .3 1.2.2 The Standard Model as a gauge group SU(3)C × SU(2)L × U(1)Y 4 1.2.3 The Higgs mechanism . .5 1.2.4 Electroweak vacuum stability . .8 1.3 Standard Cosmology . 10 1.3.1 Geometry of the Universe . 10 1.3.2 ΛCDM model . 12 1.3.3 Cosmic Inflation . 13 1.3.4 Brief thermal history of the Universe . 19 1.4 Dark matter . 21 1.4.1 Observational motivation for dark matter . 22 1.4.2 What is dark matter made of? . 24 1.4.2.1 Freeze-out mechanism and WIMPs . 25 1.4.2.2 Freeze-in mechanism and FIMPs .
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