An Extended Scalar Sector: Charged Higgs and Dark Matter
Doctoral thesis, Peer reviewed
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Despite the great success of the Standard Model in describing many aspects of the experiments, there are compelling reasons that it needs to be improved. One of the major mysteries physics has been exploring is the composition of matter in the Universe. The density of the luminous matter Ωlum is thought to be about 4% of the total energy density Ωtot of the Universe. Dark Matter makes up ∼ 26% of the energy density of the Universe which is inferred by its gravitational effects and bending of light from luminous matter as well as the geometry of the Universe. Over the last few years the paradigm of DM has shifted towards the subatomic Weakly Interacting Massive Particles (WIMPs). Thus, the existence of DM is one of the most important pieces of evidence for physics Beyond the Standard Model (BSM). The observation of DM will presumably indicate that there is a new particle. The discovery of the Higgs particle paves the way beyond the SM for exploring the existence of new particles and the component of dark matter. There are several attempts to extend the SM and include the new physics. The Two-Higgs-Doublet Model (2HDM) is one of those. This model offers a new spectrum of scalar particles. These particles can accommodate additional CP violation in the neutral sector of the Higgs potential. These particles can be produced at accelerators. If they are produced, they will decay to SM particles via a chain of decay modes. Their signals can be discerned against the SM background, by means of a set of feasible techniques. From this point of view, one good avenue in search for physics beyond the SM is to search for new charged particles. In the context of the 2HDM, the charged Higgs bosons can be produced in association with quarks, neutral Higgs bosons and the W bosons. The production rate of the charged Higgs bosons along with the neutral Higgs bosons is too low to give rise to visible signals over the SM background. But the other channels hold promises. In particular, the event analysis of the charged Higgs boson produced in association with theW boson leads to a number of surviving signal events after passing a set of filters. There are also extensions to the SM that accommodate a DM candidate. Let us consider the 2HDM extension of the SM model. The 2HDM could be equipped with an extra doublet which is inert in the sense that it has zero vacuum expectation value and does not couple to fermions. Therefore the resulting model is refereed to as CPviolating Inert Doublet Model (or IDM2). The lightest neutral member of the model, by help of an ad hoc Z2 symmetry, is stabilized to contribute to the missing mass of the Universe. The IDM2 is viable in two different mass domains of the DM candidate, namely low and high mass regions. The model can naturally reproduce the observed DM abundance due to effectiveDMself-annihilation in the early Universe in the low-mass region which is within reach of the LHC experiments at CERN. These experiments might illuminate our understanding of the nature of the DM. Besides, parameter points in the low mass region pass the constraints from the latest experiments in search for DM both in direct and indirect ones. Due to the nature of the imposed symmetry, the members of the inert doublet will be produced in pairs. In a suitable part of the parameter space the masses of the particles could be very close and therefore the decay is inhibited by phase space, and they can fly away from the interaction point before they decay to SM particles or escape the detector. In this case, the charged members of the inert doublet will lead to so-called displaced vertices and decay to charged leptons or jets and the DM candidate somewhat away from the interaction point. In case of the single production of the charged scalar, the experimental signature would be the observation of a track from the interaction point up to the decay vertex. In the decay vertex there will be a kink corresponding to the decay and a track of the charged lepton, if the charged scalar decays leptonically, or two jets, if the charged scalar decays hadronically. The kinematic properties of the jets depend on the mass of the charged scalar and the mass splitting of the charged and dark matter particles. If the mass splitting is below a couple of GeV, the displaced vertex could be realized. For mass splitting above a few GeV, one might be able to identify the hadronic decay of the charged scalar. A production channel for the charged scalar can also contain an extra hard jet. This extra jet can help in triggering the charged scalar. Therefor, the decay of the charged scalar may give unique signals that might enable physicists to detect them.
Består avPaper I: L. Basso, A. Lipniacka, F. Mahmoudi, S. Moretti, P. Osland, G. M. Pruna, M. Purmohammadi, Probing the charged Higgs boson at the LHC in the CP-violating type-II 2HDM, JHEP 1211, 011 (2012). The article is available here: http://hdl.handle.net/1956/7652
Paper II: B. Grzadkowski, O. M. Ogreid, P. Osland, A. Pukhov, M. Purmohammadi, Exploring the CP-Violating Inert-Doublet Model, JHEP 1106, 003 (2011). The article is available here: http://hdl.handle.net/1956/7660
Paper III: P. Osland, A. Pukhov, G. M. Pruna, M. Purmohammadi, Phenomenology of charged scalars in the CP-Violating Inert-Doublet Model, JHEP 1304, 040 (2013). Full-text is not available in BORA. The published version is available at: http://dx.doi.org/10.1007/jhep04(2013)040