Theory Seminar DATE: 2012-01-10 11:00 - 12:00 PLACE: Kenkyu Honkan 1F, Meeting Room 3 TITLE: TeV-Scale Seesaw with Loop-Induced Dirac Mass Term and Dark Matter from U(1)_{B−L} Gauge Symmetry Breaking CONTACT: Masato Yamanaka, masato.yamanaka-AT-kek.jp SPEAKER: Dr. Takehiro Nabeshima  (Toyama University) LANGUAGE: English URL: http://research.kek.jp/group/www-theory/schedule.html ABSTRACT: I show a TeV-scale seesaw model where Majorana neutrino masses, the dark matter mass, and stability of the dark matter can be all originated from the U(1)_{B−L} gauge symmetry. Dirac mass terms for neutrinos are forbidden at the tree level by U(1)_{B−L}, and they are induced at the one-loop level by spontaneous U(1)_{B−L} breaking. The right-handed neutrinos can be naturally at the TeV-scale or below because of the induced Dirac mass terms with loop suppression. Such right- handed neutrinos would be discovered at the CERN Large Hadron Collider (LHC). On the other hand, stability of the dark matter is guaranteed without introducing an additional Z_2 symmetry by a remaining global U(1) symmetry after the U(1)_{B−L} breaking. A Dirac fermion Psi_1 or a complex neutral scalar s^0_1 is the dark matter candidate in this model. Since the dark matter (Psi_1 or s^0_ 1 ) has its own B−L charge, the invisible decay of the U(1)_{B−L} gauge boson Z′ is enhanced. Experimental constraints on the model are considered, and the collider phenomenology at the LHC as well as future linear colliders is discussed briefly Back