Fraunhofer Chalmers Research Centre for Industrial Mathematics
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Particle/Antiparticle Nature of Light Dark Matter in Direct Detection
No full textIn the last century, astronomers have concluded that the luminous mass in the Universe impossibly can
be responsible for the huge gravitational pull observed in stellar and galactic systems. The explanation
for this discrepancy between luminous mass and gravitational eects is believed to be dark matter {
an unknown particle species that does not emit or absorb light at detectable wavelengths. Although
extensive eorts have been made to detect this mysterious particle, it remains undiscovered, and its
nature is one of the greatest unsolved questions in fundamental physics.
This thesis investigates the prospects of discriminating between Dirac and Majorana dark matter,
if dark matter is to be found in direct detection experiments. The Dirac or Majorana nature of a
particle corresponds to the existence or absence of a distinct antiparticle, which for the invisible, and
therefore probably neutral, dark matter particle is a property of major importance. The theoretical
framework is fermionic dark matter at the sub-GeV mass scale, interacting with electrons in direct
detection experiments with argon, xenon and germanium targets. The coupling constant parameter
space of photon mediated interactions is explored, and the regions where statistical rejection of a
Majorana hypothesis could be possible in the future are determined.
It is found that the discrimination signicance for rejecting a Majorana hypothesis, given simulated
Dirac-like experimental signals, reaches values of >4 standard deviations for a substantial part of the
coupling constant parameter space for germanium targets, whereas argon and xenon targets entail
stronger restrictions on the discrimination parameter space. The discrimination signicance is highly
dependent on the available detection energy region, and the dark matter mass