1,581 research outputs found

    An S4×SU(5)S_4 \times SU(5) SUSY GUT of flavour in 6d

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    We propose a 6d model with a SUSY SU(5)SU(5) gauge symmetry. After compactification, it explains the origin of the S4S_4 Family Symmetry with CSD3 vacuum alignment, as well as SU(5)SU(5) breaking with doublet-triplet splitting. The model naturally accounts for all quark and lepton (including neutrino) masses and mixings, incorporating the highly predictive Littlest Seesaw structure. It spontaneously breaks CP symmetry, resulting in successful CP violation in the quark and lepton sectors, while solving the Strong CP problem. It also explains the Baryon Asymmetry of the Universe (BAU) through leptogenesis, with the leptogenesis phase directly linked to the Dirac and Majorana phases.Comment: 23 pages, 6 figures. v3: Version published in JHE

    Single-photon exchange interaction in a semiconductor microcavity

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    We consider the effective coupling of localized spins in a semiconductor quantum dot embedded in a microcavity. The lowest cavity mode and the quantum dot exciton are coupled and close in energy, forming a polariton. The fermions forming the exciton interact with localized spins via exchange. Exact diagonalization of a Hamiltonian in which photons, spins and excitons are treated quantum mechanically shows that {\it a single polariton} induces a sizable indirect exchange interaction between otherwise independent spins. The origin, symmetry properties and the intensity of that interaction depend both on the dot-cavity coupling and detuning. In the case of a (Cd,Mn)Te quantum dot, Mn-Mn ferromagnetic coupling mediated by a single photon survives above 1 K whereas the exciton mediated coupling survives at 15 K.Comment: 4 pages, 3 figure

    SO(10)×S4\mathbf{SO(10)}\times \mathbf{S_4} Grand Unified Theory of Flavour and Leptogenesis

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    We propose a Grand Unified Theory of Flavour, based on SO(10)SO(10) together with a non-Abelian discrete group S4S_4, under which the unified three quark and lepton 16-plets are unified into a single triplet 33'. The model involves a further discrete group Z4R×Z43 \mathbb{Z}_4^R\times \mathbb{Z}_4^3 which controls the Higgs and flavon symmetry breaking sectors. The CSD2 flavon vacuum alignment is discussed, along with the GUT breaking potential and the doublet-triplet splitting, and proton decay is shown to be under control. The Yukawa matrices are derived in detail, from renormalisable diagrams, and neutrino masses emerge from the type I seesaw mechanism. A full numerical fit is performed with 15 input parameters generating 19 presently constrained observables, taking into account supersymmetry threshold corrections. The model predicts a normal neutrino mass ordering with a CP oscillation phase of 260260^{\circ}, an atmospheric angle in the first octant and neutrinoless double beta decay with mββ=11m_{\beta \beta}= 11 meV. We discuss N2N_2 leptogenesis, which fixes the second right-handed neutrino mass to be M22×1011M_2\simeq 2\times 10^{11} GeV, in the natural range predicted by the model.Comment: 26 pages, 10 figure

    Transport properties of a two impurity system: a theoretical approach

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    A system of two interacting cobalt atoms, at varying distances, was studied in a recent scanning tunneling microscope experiment by Bork et. al.[Nature Phys. 7, 901 (2011)]. We propose a microscopic model that explains, for all experimentally analyzed interatomic distances, the physics observed in these experiments. Our proposal is based on the two-impurity Anderson model, with the inclusion of a two-path geometry for charge transport. This many-body system is treated in the finite-U slave boson mean-field approximation and the logarithmic-discretization embedded-cluster approximation. We physically characterize the different charge transport regimes of this system at various interatomic distances and show that, as in the experiments, the features observed in the transport properties depend on the presence of two impurities but also on the existence of two conducting channels for electron transport. We interpret the splitting observed in the conductance as the result of the hybridization of the two Kondo resonances associated with each impurity.Comment: 5 pages, 5 figure

    Selfconsistent hybridization expansions for static properties of the Anderson impurity model

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    By means of a projector-operator formalism we derive an approximation based on a self consistent hybridization expansion to study the ground state properties of the Anderson Impurity model. We applied the approximation to the general case of finite Coulomb repulsion UU, extending previous work with the same formalism in the infinite-UU case. The treatment provides a very accurate calculation of the ground state energy and their related zero temperature properties in the case in which UU is large enough, but still finite, as compared with the rest of energy scales involved in the model. The results for the valence of the impurity are compared with exact results that we obtain from equations derived using the Bethe ansatz and with a perturbative approach. The magnetization and magnetic susceptibility is also compared with Bethe ansatz results. In order to do this comparison, we also show how to regularize the Bethe ansatz integral equations necessary to calculate the impurity valence, for arbitrary values of the parameters.Comment: 8 pages, 5 figure
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