1,586 research outputs found
An SUSY GUT of flavour in 6d
We propose a 6d model with a SUSY gauge symmetry. After
compactification, it explains the origin of the Family Symmetry with CSD3
vacuum alignment, as well as 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
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
Grand Unified Theory of Flavour and Leptogenesis
We propose a Grand Unified Theory of Flavour, based on together with
a non-Abelian discrete group , under which the unified three quark and
lepton 16-plets are unified into a single triplet . The model involves a
further discrete group 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
, an atmospheric angle in the first octant and neutrinoless double
beta decay with meV. We discuss leptogenesis, which
fixes the second right-handed neutrino mass to be
GeV, in the natural range predicted by the model.Comment: 26 pages, 10 figure
Transport properties of a two impurity system: a theoretical approach
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
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 , extending previous work with the
same formalism in the infinite- case. The treatment provides a very accurate
calculation of the ground state energy and their related zero temperature
properties in the case in which 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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