812 research outputs found
Non-integrability of Self-dual Yang-Mills-Higgs System
We examine integrability of self-dual Yang-Mills system in the Higgs phase,
with taking simpler cases of vortices and domain walls. We show that the vortex
equations and the domain-wall equations do not have Painleve property. This
fact suggests that these equations are not integrable.Comment: 15 pages, no figures, v2: references added, v3: typos corrected, the
final version to appear in NP
Solitons in Supersymmety Breaking Meta-Stable Vacua
In recently found supersymmetry-breaking meta-stable vacua of the
supersymmetric QCD, we examine possible exsitence of solitons. Homotopy groups
of the moduli space of the meta-stable vacua show that there is no nontrivial
soliton for SU(N_c) gauge group. When U(1)_B symmetry present in the theory is
gauged, we find non-BPS solitonic (vortex) strings whose existence and
properties are predicted from brane configurations. We obtain explicit
classical solutions which reproduce the predicitions. For SO(N_c) gauge group,
we find there are solitonic strings for N = N_f-N_c+4 = 2, and Z_2 strings for
the other N. The strings are meta-stable as they live in the meta-stable vacua.Comment: 30 pages, 14 figures, Comments on stability of non-BPS vortices are
added, Comments on sigma model solitons are added, An appendix is adde
QCD String as Vortex String in Seiberg-Dual Theory
We construct a classical vortex string solution in a Seiberg-dual theory of
N=1 supersymmetric SO(N_c) QCD which flows to a confining phase. We claim that
this vortex string is a QCD string, as previouly argued by M.Strassler. In
SO(N_c) QCD, it is known that stable QCD strings exist even in the presence of
dynamical quarks. We show that our vortex strings are stable in the
Seiberg-dual theory.Comment: 15 pages, 1 figur
1/2, 1/4 and 1/8 BPS Equations in SUSY Yang-Mills-Higgs Systems -- Field Theoretical Brane Configurations --
We systematically classify 1/2, 1/4 and 1/8 BPS equations in SUSY gauge
theories in d=6, 5, 4, 3 and 2 with eight supercharges, with gauge groups and
matter contents being arbitrary. Instantons (strings) and vortices (3-branes)
are only allowed 1/2 BPS solitons in d=6 with N=1 SUSY. We find two 1/4 BPS
equations and the unique 1/8 BPS equation in d=6 by considering configurations
made of these field theory branes. All known BPS equations are rederived while
several new 1/4 and 1/8 BPS equations are found in dimension less than six by
dimensional reductions.Comment: 41 pages, no figures, v2: 49 pages, no figures, typos corrected,
references added, the final version in NP
Scaling analysis of Kondo screening cloud in a mesoscopic ring with an embedded quantum dot
The Kondo effect is theoretically studied in a quantum dot embedded in a
mesoscopic ring. The ring is connected to two external leads, which enables the
transport measurement. Using the "poor man's" scaling method, we obtain
analytical expressions of the Kondo temperature T_K as a function of the
Aharonov-Bohm phase \phi by the magnetic flux penetrating the ring. In this
Kondo problem, there are two characteristic lengths. One is the screening
length of the charge fluctuation, L_c=\hbar v_F/ |\epsilon_0|, where v_F is the
Fermi velocity and \epsilon_0 is the energy level in the quantum dot. The other
is the screening length of spin fluctuation, i.e., size of Kondo screening
cloud, L_K=\hbar v_F/ T_K. We obtain different expressions of T_K(\phi) for (i)
L_c \ll L_K \ll L, (ii) L_c \ll L \ll L_K, and (iii) L \ll L_c \ll L_K, where L
is the size of the ring. T_K is markedly modulated by \phi in cases (ii) and
(iii), whereas it hardly depends on \phi in case (i). We also derive
logarithmic corrections to the conductance at temperature T\gg T_K and an
analytical expression of the conductance at T\ll T_K, on the basis of the
scaling analysis.Comment: 21pages, 10 figure
Kondo Effect in Multiple-Dot Systems
We study the Kondo effect in multiple-dot systems for which the inter- as
well as intra-dot Coulomb repulsions are strong, and the inter-dot tunneling is
small. The application of the Ward-Takahashi identity to the inter-dot
dynamical susceptibility enables us to analytically calculate the conductance
for a double-dot system by using the Bethe-ansatz exact solution of the SU(4)
impurity Anderson model. It is clarified how the inter-dot Kondo effect
enhances or suppresses the conductance under the control of the gate voltage
and the magnetic field. We then extend our analysis to multiple-dot systems
including more than two dots, and discuss their characteristic transport
properties by taking a triple-dot system as an example.Comment: 8 pages, 9 figure
Multi-parameter scaling of the Kondo effect in quantum dots with an even number of electrons
We address a recent theoretical discrepancy concerning the Kondo effect in
quantum dots with an even number of electrons where spin-singlet and -triplet
states are nearly degenerate. We show that the discrepancy arises from the fact
that the Kondo scaling involves many parameters, which makes the results depend
on concrete microscopic models. We illustrate this by the scaling calculations
of the Kondo temperature, , as a function of the energy difference between
the singlet and triplet states . decreases with
increasing , showing a crossover from a power law with a universal
exponent to that with a nonuniversal exponent. The crossover depends on the
initial parameters of the model.Comment: 8 pages, 3 figure
Enhanced spin Hall effect by tuning antidot potential: Proposal for a spin filter
We propose an efficient spin filter including an antidot fabricated on
semiconductor heterostructures with strong spin-orbit interaction. The antidot
creates a tunable potential on two-dimensional electron gas in the
heterostructures, which may be attractive as well as repulsive. Our idea is
based on the enhancement of extrinsic spin Hall effect by resonant scattering
when the attractive potential is properly tuned. Numerical studies for three-
and four-terminal devices indicate that the efficiency of the spin filter can
be more than 50% by tuning the potential to the resonant condition.Comment: 11 pages, 10 figure
Radius Stabilization in a Supersymmetric Warped Compactification
A supersymmetric (SUSY) model of radius stabilization is constructed for the
S^1/Z_2 warped compactifications with a hypermultiplet in five dimensions.
Requiring the continuity of scalar field across the boundaries, we obtain
radius stabilization preserving SUSY, realizing the SUSY extension of the
Goldberger-Wise mechanism. Even if we allow discontinuities of the Z_2 odd
field across the boundary, we always obtain SUSY preservation but obtain the
radius stabilization only when the discontinuity is fixed by other mechanism.Comment: 6 pages, revtex, Errors of the products of distributions are
corrected and the results are reanalyzed, references added, final version to
appear in PR
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