arXiv subjects

Simon May

Publications and source records attributed to Simon May.

22 records · Page 2Linked to original sources

arXiv2021

minimal-lagrangians: Generating and studying dark matter model Lagrangians with just the particle content

minimal-lagrangians is a Python program which allows one to specify the field content of an extension of the Standard Model of particle physics and, using this information, to generate the most general renormalizable Lagrangian that describes such a model. As the program was originally created for the study of minimal dark matter models with radiative neutrino masses, it can handle additional scalar or Weyl fermion fields which are $\mathrm{SU}(3)_{\mathrm{C}}$ singlets, $\mathrm{SU}(2)_{\mathrm{L}}$ singlets, doublets or triplets, and can have arbitrary $\mathrm{U}(1)_{\mathrm{Y}}$ hypercharge. It is also possible to enforce an arbitrary number of global $\mathrm{U}(1)$ symmetries (with $\mathbb{Z}_2$ as a special case) so that the new fields can additionally carry such global charges. In addition to human-readable and $\mathrm{\LaTeX}$ output, the program can generate SARAH model files containing the computed Lagrangian, as well as information about the fields after electroweak symmetry breaking (EWSB), such as vacuum expectation values (VEVs) and mixing matrices. This capability allows further detailed investigation of the model in question, with minimal-lagrangians as the first component in a tool chain for rapid phenomenological studies of "minimal" dark matter models requiring little effort and no unnecessary input from the user.

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arXiv2020

Minimal dark matter models with radiative neutrino masses: From Lagrangians to observables

In this master's thesis, the minimal dark matter models with radiative neutrino masses introduced in arXiv:1308.3655 are examined both in general and, using the model T1-3-B ($α= 0$) as a representative, in more detail. In the process, it is both shown how such models are built and a numerical analysis tool chain is established, automating as many steps as possible from the very beginning (deriving the Lagrangian from a given field content) to the very end (calculating observables such as the dark matter relic density, the direct detection cross section and the neutrino masses and mixing matrices). As an important result in laying out the mathematical groundwork, a convention for representations of SU(2) is established which, in this form, is not found in previous works. Another major result is the development of the program minimal-lagrangians, whose capabilities are described in the thesis. It is of great use both for the construction of Lagrangians for new models as well their verification or quick surveys. minimal-lagrangians can be applied to any model within the class it is designed to handle, extending its utility far beyond a one-time result that is only obtained for a single model. Finally, the first steps in the analysis of the model T1-3-B ($α= 0$) are taken. It is shown that the model can reproduce both the singlet-doublet fermion dark matter model and the inert triplet model in the appropriate limits. Moreover, the neutrino mass matrix is found and it is demonstrated that the model can accommodate current constraints on the neutrino masses. Lastly, the behavior of the dark matter relic density as it depends on the parameter responsible for the generation of neutrino masses is investigated. Further in-depth study of the model T1-3-B ($α= 0$) was performed in a separate publication (arXiv:1812.11133).

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arXiv2019

Singlet-doublet/triplet dark matter and neutrino masses

In these proceedings, we present a study of a combined singlet--doublet fermion and triplet scalar model for dark matter (DM). Together, these models form a simple extension of the Standard Model (SM) that can account for DM and explain the existence of neutrino masses, which are generated radiatively. However, this also implies the existence of lepton flavour violating (LFV) processes. In addition, this particular model allows for gauge coupling unification. The new fields are odd under a new $\mathbb{Z}_2$ symmetry to stabilise the DM candidate. We analyse the DM, neutrino mass and LFV aspects, exploring the viable parameter space of the model. This is done using a numerical random scan imposing successively the neutrino mass and mixing, relic density, Higgs mass, direct detection, collider and LFV constraints. We find that DM in this model is fermionic for masses below about 1 TeV and scalar above. We observe a high degree of complementarity between direct detection and LFV experiments, which should soon allow to fully probe the fermionic DM sector and at least partially the scalar DM sector.

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arXiv2019

Singlet-doublet fermion and triplet scalar dark matter with radiative neutrino masses

We present a detailed study of a combined singlet-doublet fermion and triplet scalar model for dark matter. These models have only been studied separately in the past. Together, they form a simple extension of the Standard Model that can account for dark matter and explain the existence of neutrino masses, which are generated radiatively. This holds even if singlet-doublet fermions and triplet scalars never contribute simultaneously to the dark matter abundance. However, this also implies the existence of lepton flavour violating processes. In addition, this particular model allows for gauge coupling unification. The new fields are odd under a new $\mathbb{Z}_2$ symmetry to stabilise the dark matter candidate. We analyse the dark matter, neutrino mass and lepton flavour violation aspects both separately and in conjunction, exploring the viable parameter space of the model. This is done using a numerical random scan imposing successively the neutrino mass and mixing, relic density, Higgs mass, direct detection, collider and lepton flavour violation constraints. We find that dark matter in this model is fermionic for masses below about 1 TeV and scalar above. The narrow mass regions found previously for the two separate models are enlarged by their coupling. While coannihilations of the weak isospin partners are sizeable, this is not the case for fermions and scalars despite their often similar masses due to the relatively small coupling of the two sectors, imposed by the small neutrino masses. We observe a high degree of complementarity between direct detection and lepton flavour violation experiments, which should soon allow to fully probe the fermionic dark matter sector and at least partially the scalar dark matter sector.

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