Takehiro Nabeshima

Can WIMP dark matter overcome the nightmare scenario

Even if new physics beyond the Standard Model (SM) indeed exists, the energy scale of new physics might be beyond the reach at the Large Hadron Collider (LHC) and the LHC could find only the Higgs boson but nothing else. This is the so-called “nightmare scenario”. On the other hand, the existence of the dark matter has been established from various observations. One of the promising candidates for thermal relic dark matter is a stable and electric charge-neutral Weakly Interacting Massive Particle (WIMP) with the mass below the TeV scale. In the nightmare scenario, we introduce a WIMP dark matter singlet under the SM gauge group, which only couples to the Higgs doublet at the lowest order, and investigate a possibility that such WIMP dark matter can be a clue to overcome the nightmare scenario via various phenomenological tests such as the dark matter relic abundance, the direct detection experiments for the dark matter particle, and the production of the dark matter particle at the LHC.

Neutrino masses from loop-induced Dirac Yukawa couplings

Abstract We consider a possibility to naturally explain tiny neutrino masses without the lepton number violation. We study a simple model with S U ( 2 ) L singlet charged scalars ( s 1 ± , s 2 ± ) as well as singlet right-handed neutrino ( ν R ). Yukawa interactions for Dirac neutrinos, which are forbidden at the tree level by a softly-broken Z 2 symmetry, are induced at the one-loop level via the soft-breaking term in the scalar potential. Consequently neutrinos obtain small Dirac masses after the electroweak symmetry breaking. It is found that constrains from neutrino oscillation measurements and lepton flavor violation search results (especially for μ → e γ ) can be satisfied. We study the decay pattern of the singlet charged scalars, which could be tested at the LHC and the ILC. We discuss possible extensions also, e.g. to introduce dark matter candidate.

Testing Higgs portal dark matter via

Abstract We investigate the possibility of detecting dark matter at TeV scale linear colliders in the scenario where the dark matter is a massive particle weakly interacting only with the Higgs boson h in the low energy effective theory (the Higgs portal dark matter scenario). The dark matter in this scenario would be difficult to be tested at the CERN Large Hadron Collider when the decay of the Higgs boson into a dark matter pair is kinematically forbidden. We study whether even in such a case the dark matter D can be explored or not via the Z boson fusion process at the International Linear Collider and also at a multi-TeV lepton collider. It is found that for the collision energy s > 1 TeV with the integrated luminosity 1 ab − 1 , the signal ( e ± e − → e ± e − h ⁎ → e ± e − D D ) can be seen after appropriate kinematical cuts. In particular, when the dark matter is a fermion, which is supposed to be singlet under the standard gauge symmetries, the signal with the mass up to about 100 GeV can be tested for the Higgs boson mass to be 120 GeV.

Z

We discuss the scenario with gauge singlet fermions (right-handed neutrinos) accessible at the energy of the Large Hadron Collider. The singlet fermions generate tiny neutrino masses via the seesaw mechanism and also have sizable couplings to the standard-model particles. We demonstrate that these two facts, which are naively not satisfied simultaneously, are reconciled in the five-dimensional framework in various fashions, which make the seesaw mechanism observable. The collider signal of tri-lepton final states with transverse missing energy is investigated for two explicit examples of the observable seesaw, taking account of three types of neutrino mass spectrum and the constraint from lepton flavor violation.

fusion at a linear collider

We discuss phenomenology of the radiative seesaw model in which spontaneous breaking of the U(1)

Seesaw Neutrino Signals at the Large Hadron Collider

_{B-L}

Radiative type-I seesaw model with dark matter via U(1)

gauge symmetry at the TeV scale gives the common origin for masses of neutrinos and dark matter (Kanemura et al., 2012). In this model, the stability of dark matter is realized by the global U(1)

_{B-L}

_{DM}

gauge symmetry breaking at future linear colliders

symmetry which arises by the B

Extra dimensions and Seesaw Neutrinos at the International Linear Collider

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