arXiv subjects

Kuo-Hsing Tsao

Publications and source records attributed to Kuo-Hsing Tsao.

3 recordsLinked to original sources

arXiv2018

FIMP Dark Matter Freeze-in Gauge Mediation and Hidden Sector

We explore the dark matter freeze-in mechanism within the gauge mediation framework, which involves a hidden Feebly Interacting Massive Particle (FIMP) coupling feebly with the messenger fields while the messengers are still in the thermal bath. The FIMP is the fermionic component of the pseudo-moduli in a generic metastable supersymmetry (SUSY) breaking model and resides in the hidden sector. The relic abundance and the mass of the FIMP are determined by the SUSY breaking scale and the feeble coupling. The gravitino, which is the canonical dark matter candidate in the gauge mediation framework, contributes to the dark matter relic abundance along with the freeze-in of the FIMP. The hidden sector thus becomes two- component with both the FIMP and gravitino lodging in the SUSY breaking hidden sector. We point out that the ratio between the FIMP and the gravitino is determined by how SUSY breaking is communicated to the messengers. In particular when the FIMP dominates the hidden sector, the gravitino becomes the minor contributor in the hidden sector. Meanwhile, the neutralino is assumed to be both the Weakly Interacting Massive Particle (WIMP) dark matter candidate in the freeze-out mechanism and the Lightest Observable SUSY Particle (LOSP). We further find out the neutralino has the sub-leading contribution to the current dark matter relic density in the parameter space of our freeze-in gauge mediation (FIGM) model. Our result links the SUSY breaking scale in the gauge mediation framework with the FIMP freeze-in production rate leading to a natural and predicting scenario for the studies of the dark matter in the hidden sector.

hep-ph↗

arXiv2017

Axial Vector $Z'$ and Anomaly Cancellation

Whilst the prospect of new $Z'$ gauge bosons with only axial couplings to the Standard Model (SM) fermions is widely discussed, examples of anomaly-free renormalisable models are lacking in the literature. We look to remedy this by constructing several motivated examples. Specifically, we consider axial vectors which couple universally to all SM fermions, as well as those which are generation-specific, leptophilic, and leptophobic. Anomaly cancellation typically requires the presence of new coloured and charged chiral fermions, and we argue that in a large class of models masses of these new states are expected to be comparable to that of the axial vector. Finally, an axial vector mediator could provide a portal between SM and hidden sector states, and we also consider the possibility that the axial vector couples to dark matter. If the dark matter relic density is set due to freeze-out via the axial vector, this strongly constrains the parameter space.

hep-ph↗

arXiv2010

Hidden Sector Dirac Dark Matter, Stueckelberg Z' Model and the CDMS and XENON Experiments

For the milli-charged Dirac dark matter in the Stueckelberg Z' model, we discuss the contributions from the vector couplings of the dark matter with the neutral gauge bosons to the spin-independent scattering cross section in the direct detections. We also compute the effective coupling between the fermionic dark matter particle and the standard model Higgs boson generated through a triangular loop of Z and/or Z' bosons which may contribute to the spin-independent scattering cross section at the quantum level. We show that the latter contribution is consistent with the most recent experimental limits from CDMS II and XENON100. In the case that the dark matter particle carries a milli-charge of order O(10^{-3}e), we found that it would lose all its kinetic energy by colliding with nucleons in the atmosphere before reaching the detector. Even though we use the Stueckelberg Z' model for illustration, the results we obtain are rather general and applicable to other Z-Z' portal-type hidden-sector models as well.

hep-ph↗