4,585 research outputs found
Horizontal symmetry in Higgs sector of GUT with U(1)_A symmetry
In a series of papers, we pointed out that an anomalous gauge
symmetry naturally solves various problems in grand unified theories (GUTs) and
that a horizontal gauge symmetry, or , 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 models, the
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
Gauge Coupling Unification in GUT with Anomalous U(1) Symmetry
We show that in the framework of grand unified theory (GUT) with anomalous
gauge symmetry, the success of the gauge coupling unification in the
minimal SU(5) GUT is naturally explained, even if the mass spectrum of
superheavy fields does not respect SU(5) symmetry. Because the unification
scale for most realizations of the theory becomes smaller than the usual GUT
scale, it suggests that the present level of experiments is close to that
sufficient to observe proton decay via dimension 6 operators, .Comment: 4 pages, RevTeX, to appear in Phys.Rev.Let
The anapole form factor of the nucleon
The anapole form factor of the nucleon is calculated in chiral perturbation
theory in leading order. To this order, the form factor originates from the
pion cloud, and is proportional to the non-derivative parity-violating
pion-nucleon coupling. The momentum dependence of the form factor - and in
particular, its radius - is completely determined by the pion mass.Comment: 9 pages, 2 eps figures included by epsf.sty, minor changes in note
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Effects of different geometries on the conductance, shot noise and tunnel magnetoresistance of double quantum dots
The spin-polarized transport through a coherent strongly coupled double
quantum dot (DQD) system is analyzed theoretically in the sequential and
cotunneling regimes. Using the real-time diagrammatic technique, we analyze the
current, differential conductance, shot noise and tunnel magnetoresistance
(TMR) as a function of both the bias and gate voltages for double quantum dots
coupled in series, in parallel as well as for T-shaped systems. For DQDs
coupled in series, we find a strong dependence of the TMR on the number of
electrons occupying the double dot, and super-Poissonian shot noise in the
Coulomb blockade regime. In addition, for asymmetric DQDs, we analyze transport
in the Pauli spin blockade regime and explain the existence of the leakage
current in terms of cotunneling and spin-flip cotunneling-assisted sequential
tunneling. For DQDs coupled in parallel, we show that the transport
characteristics in the weak coupling regime are qualitatively similar to those
of DQDs coupled in series. On the other hand, in the case of T-shaped quantum
dots we predict a large super-Poissonian shot noise and TMR enhanced above the
Julliere value due to increased occupation of the decoupled quantum dot. We
also discuss the possibility of determining the geometry of the double dot from
transport characteristics. Furthermore, where possible, we compare our results
with existing experimental data on nonmagnetic systems and find qualitative
agreement.Comment: 15 pages, 12 figures, accepted in Phys. Rev.
Double Chargino Production in scattering
We point out the production of the charginos and neutralinos in
electron-electron process in several supersymmetric models, in order to show
that the International Linear Collider can discover double charged charginos if
these particles really exist in nature.Comment: 9 pages, 9 figures, Talk given at CTP symposium on Supersymmetry at
LHC: Theoretical and Experimental Perspectives, The British University in
Egypt, Cairo, Egypt, 11-14 March 200
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