Presentation av mastersarbete i fysik. Titeln på examensarbetet är "Dark Matter Phonon Couplings in Effective Theories".
The existence of Dark Matter is one of the greatest mysteries of contemporary physics, and a wide variety of possible explanations have been proposed since its discovery. In order to determine its true nature, it is crucial to directly measure its properties. This thesis explores the possibility that Dark Matter is composed of a hitherto undetected bosonic particle beyond the Standard Model, whose mass is too small to reliably allow detection by electronic excitation. Instead, the absorption of Dark Matter through the creation of one or more phonons in a crystal is investigated. Building on the formalism established by previous researchers, the method of determining the absorption rate of Dark Matter through its self-energy is rederived using the optical theorem. Next, the relativistic quantum field theory describing the simplest possible interaction of scalar Dark Matter with the fermions in the crystal is reduced to a non-relativistic effective field theory. Then, the non-relativistic Lagrangian is expressed in terms of the properties of the crystal lattice. Finally, the self-energy of the Dark Matter is calculated by extracting the phonon field from the lattice Lagrangian, and a general formula is derived which describes the total self-energy contribution from an arbitrary number of phonons. The formula is entirely expressed in terms of the Dark Matter momentum and the properties of the crystal, and extends previous works to the case of Dark Matter absorption through multiphonon excitations. Further research could apply this formalism to more realistic interaction Lagrangians, or use code to compute numerical values for the absorption rate in a given crystal.
Supervisor: Riccardo Catena (Chalmers)
Examiner: Johannes Hofmann (GU)
Opponent: Gustav Strandlycke (Chalmers)