Horizontal symmetry in Higgs sector of GUT with U(1)_A symmetry

In a series of papers, we pointed out that an anomalous $U(1)_A$ gauge symmetry naturally solves various problems in grand unified theories (GUTs) and that a horizontal gauge symmetry, $SU(2)_H$ or $SU(3)_H$, not only realizes the unification of three generation quarks and leptons in fewer multiplets but also solves the supersymmetric flavor problem. In this paper, we examine the possibility that the Higgs sectors of the GUT symmetry and of the horizontal symmetry are unified, that is, there are some Higgs fields whose vacuum expectation values (VEVs) break both the GUT gauge symmetry and the horizontal symmetry at the same time. Although the scale of the VEVs become too large to suppress the flavor changing neutral current processes sufficiently, the unification is possible. In addition, for the $SU(3)_H$ models, the $SU(3)_H$ gauge anomaly is cancelled in the unified models without introducing additional fields in contrast with the previous models in which the Higgs sectors are not unified.Comment: 35 page

Probing the exchange field of a quantum-dot spin valve by a superconducting lead

Electrons in a quantum-dot spin valve, consisting of a single-level quantum dot coupled to two ferromagnetic leads with magnetizations pointing in arbitrary directions, experience an exchange field that is induced on the dot by the interplay of Coulomb interaction and quantum fluctuations. We show that a third, superconducting lead with large superconducting gap attached to the dot probes this exchange field very sensitively. In particular, we find striking signatures of the exchange field in the symmetric component of the supercurrent with respect to the bias voltage applied between the ferromagnets already for small values of the ferromagnets' spin polarization.Comment: published version, 10 pages, 7 figure

Sliding Singlet Mechanism Revisited

We show that the unification of the doublet Higgs in the standard model (SM) and the Higgs to break the grand unified theory (GUT) group stabilizes the sliding singlet mechanism which can solve the doublet-triplet (DT) splitting problem. And we generalize this attractive mechanism to apply it to many unified scenarios. In this paper, we try to build various concrete E_6 unified models by using the generalized sliding singlet mechanism.Comment: 13 page

Stability of Spinmotive Force in Perpendicularly Magnetized Nanowires under High Magnetic Fields

Spinmotive force induced by domain wall motion in perpendicularly magnetized nanowires is numerically demonstrated. We show that using nanowires with large magnetic anisotropy can lead to a high stability of spinmotive force under strong magnetic fields. We observe spinmotive force in the order of tens of microvolt in a multilayered Co/Ni nanowire and in the order of several hundred microvolt in a FePt nanowire; the latter is two orders of magnitude greater than that in permalloy nanowires reported previously. The narrow structure and low mobility of a domain wall under magnetic fields in perpendicularly magnetized nanowires permits downsizing of spinmotive force devices.Comment: submitted to Applied Physics Letter

Current-spin coupling for ferromagnetic domain walls in fine wires

The coupling between a current and a domain wall is examined. In the presence of a finite current and the absence of a potential which breaks the translational symmetry, there is a perfect transfer of angular momentum from the conduction electrons to the wall. As a result, the ground state is in uniform motion. This remains the case when relaxation is accounted for. This is described by, appropriately modified, Landau-Lifshitz-Gilbert equations.Comment: 4 pqges, no figure