Naturalness of Neutralino Dark Matter

We investigate the level of fine-tuning of neutralino Dark Matter below 200 GeV in the low-energy phenomenological minimal supersymmetric Standard Model taking into account the newest results from XENON100 and the Large Hadron Collider as well as all other experimental bounds from collider physics and the cosmological abundance. We find that current and future direct Dark Matter searches significantly rule out a large area of the untuned parameter space, but solutions survive which do not increase the level of fine-tuning. As expected, the level of tuning tends to increase for lower cross-sections, but regions of resonant neutralino annihilation still allow for a band at light masses, where the fine-tuning stays small even below the current experimental limits for direct detection cross-sections. For positive values of the supersymmetric Higgs mass parameter \mu large portions of the allowed parameter space are excluded, but there still exist untuned solutions at higher neutralino masses which will essentially be ruled out if XENON1t does not observe a signal.For negative \mu untuned solutions are not much constrained by current limits of direct searches and, if the neutralino mass was found outside the resonance regions, a negative \mu-term would be favored from a fine-tuning perspective. Light stau annihilation plays an important role to fulfill the relic density condition in certain neutralino mass regions. Finally we discuss, in addition to the amount of tuning for certain regions in the neutralino mass-direct detection cross-section plane, the parameter mapping distribution if the allowed model parameter space is chosen to be scanned homogeneously (randomized).Comment: v2: 29 pages, 16 figures. Published versio

LHC Tests of Light Neutralino Dark Matter without Light Sfermions

We address the question how light the lightest MSSM neutralino can be as dark matter candidate in a scenario where all supersymmetric scalar particles are heavy. The hypothesis that the neutralino accounts for the observed dark matter density sets strong requirements on the supersymmetric spectrum, thus providing an handle for collider tests. In particular for a lightest neutralino below 100 GeV the relic density constraint translates into an upper bound on the Higgsino mass parameter $\mu$ in case all supersymmetric scalar particles are heavy. One can define a simplified model that highlights only the necessary features of the spectrum and their observable consequences at the LHC. Reinterpreting recent searches at the LHC we derive limits on the mass of the lightest neutralino that, in many cases, prove to be more constraining than dark matter experiments themselves.Comment: 22 pages, 8 figure

Asymmetric Mediator in Scotogenic Model

The scotogenic model is the Standard Model (SM) with Z_2 symmetry and the addition of Z_2 odd right-handed Majorana neutrinos and SU(2)_L doublet scalar fields. We have extended the original scotogenic model by an additional Z_2 odd singlet scalar field that plays a role in dark matter. In our model, the asymmetries of the lepton and Z_2 odd doublet scalar are simultaneously produced through CP-violating right-handed neutrino decays. While the former is converted into baryon asymmetry through the sphaleron process, the latter is relaid to the DM density through the decay of SU(2)_L doublet scalar that is named "asymmetric mediator". In this way, we provide an extended scotogenic model that predicts the energy densities of baryon and dark matter being in the same order of magnitude, and also explains the low-energy neutrino masses and mixing angles.Comment: 17 pages, 1 table, 5 figure

Model Building by Coset Space Dimensional Reduction Scheme Using Twelve-Dimensional Coset Spaces

We investigate the twelve-dimensional gauge-Higgs unification models with an eight-dimensional coset space. For each model, we apply the coset space dimensional reduction procedure and examine the particle contents of the resulting four-dimensional theory. Then, some twelve-dimensional SO(18) gauge theories lead to models of the SO(10)\times U(1) grand unified theory in four dimensions, where fermions of the Standard Model appear in multiple generations along with scalars that may break the electroweak symmetry. The representations of the obtained scalars and fermions are summarized.Comment: 17 pages, 4 table

Light neutralino in the MSSM: An update with the latest LHC results

We discuss the scenario of light neutralino dark matter in the minimal supersymmetric standard model, which is motivated by the results of some of the direct detection experiments --- DAMA, CoGENT, and CRESST. We update our previous analysis with the latest results of the LHC. We show that new LHC constraints disfavour the parameter region that can reproduce the results of DAMA and CoGENT.Comment: 4 pages, 4 figures, to appear in the conference proceedings of TAUP 2011, Munich Germany, 5-9 September 201