One of the greatest remaining puzzles in physics is what particle dark matter consists of. For this project, the theory of dark pions is considered, a Hidden Valley model that extends the Standard...Show moreOne of the greatest remaining puzzles in physics is what particle dark matter consists of. For this project, the theory of dark pions is considered, a Hidden Valley model that extends the Standard Model with new, dark particles and a new force, dark QCD. A sensitivity study is performed to determine how many dark pions are expected to be in acceptance of the LHCb detector for Run 2 conditions; the LHCb is well-suited to search for particles in the considered O(1) GeV mass and O(1) - O(100) ps lifetime range. Additionally, a framework has been developed to study the dependence of the sensitivity on a number of theoretical parameters of the dark QCD model, namely the probability to form a dark vector meson instead of a dark pion, the number of colours in dark QCD, the dark QCD scale, and the Higgs mass. It is found that O(100) dark pions are in LHCb acceptance for different track categories, and that the considered the- oretical parameters do not drastically change the number of expected particles (with some small caveats), staying within a difference of about 20%. This is acceptable given the expected experimental uncertainty, showing theory inde- pendent searches for dark pions are possible.Show less
This work explores axion-photon conversion in the TeV halo of the Geminga pulsar and in neutron star magnetospheres. Based on the observed synchrotron and inverse Compton scattering radiation, the...Show moreThis work explores axion-photon conversion in the TeV halo of the Geminga pulsar and in neutron star magnetospheres. Based on the observed synchrotron and inverse Compton scattering radiation, the magnetic field inside the Geminga pulsar TeV halo is constrained to be < 2 μG, similar to literature constraints. The photon-axion conversion probability is ≲ 10−8, requiring an extreme signal-to-noise ratio for detection. In contrast, significant flux transfer can take place in the strongly magnetised anisotropic plasmas of neutron star magnetospheres. Following up on recent literature, this work provides a three-dimensional calculation of axion-photon conversion in anistropic plasmas, including the Euler-Heisenberg photon-photon scattering contribution in the limit BNS ≪ Bc = 4.4 · 1013 G. This allows for resonant double lens conversion, through which axion-like particles of arbitrarily small mass can resonantly induce photons. For relativistic axions the resonance length scale can exceed other typical scales of change in the plasma, in which case the conversion region and probability is truncated. For very light, relativistic axions, non-resonant contributions are important. In the Goldreich-Julian model with relativistic plasma, double lens resonance can occur at observable radio frequencies in the 100 GHz−1 THz regime. NB: Erratum. The derivation in chapter 3 sets magnetic permeability mu=1. For double lens resonant conversion this is inconsistent. Upon including the correct expression for mu, the EH contribution to the resonance condition (Eq. 3.28) is slightly changed:14*eta*B^2 -> 22*eta*B^2. The error should, of course, also be incorporated in the whole derivation.Show less
The Standard model of particle physics is extremely successful in explaining accelerator data. However, it is incomplete and fails to resolve several phenomena known as beyond the Standard model ...Show moreThe Standard model of particle physics is extremely successful in explaining accelerator data. However, it is incomplete and fails to resolve several phenomena known as beyond the Standard model (BSM) problems. The BSM problems may be solved by introducing new particles. In addition to particle experiments, cosmological observation offers a way we can put limits on the parameters of these new particles. This work gives a detailed qualitative description of several such cosmological constraints. The observations used are described, and then ways in which new particles could impact such observations. Then, these constraints are applied to two case studies: the scalar portal and the neutrino portal. In both cases, a significant part of the parameter space unexplored by direct experimental studies can be excluded based on these cosmological arguments.Show less
