1,471 research outputs found
Supersymmetry Breaking on Gauged Non-Abelian Vortices
There are a large number of systems characterized by a completely broken
gauge symmetry, but with an unbroken global color-flavor diagonal symmetry,
i.e., systems in the so-called color-flavor locked phase. If the gauge symmetry
breaking supports vortices, the latter develop non-Abelian orientational
zero-modes and become non-Abelian vortices, a subject of intense study in the
last several years. In this paper we consider the effects of weakly gauging the
full exact global flavor symmetry in such systems, deriving an effective
description of the light excitations in the presence of a vortex. Surprising
consequences are shown to follow. The fluctuations of the vortex orientational
modes get diffused to bulk modes through tunneling processes. When our model is
embedded in a supersymmetric theory, the vortex is still 1/2 BPS saturated, but
the vortex effective action breaks supersymmetry spontaneously.Comment: Latex, 24 pages, 1 figur
Vortex counting from field theory
The vortex partition function in 2d N = (2,2) U(N) gauge theory is derived
from the field theoretical point of view by using the moduli matrix approach.
The character for the tangent space at each moduli space fixed point is written
in terms of the moduli matrix, and then the vortex partition function is
obtained by applying the localization formula. We find that dealing with the
fermionic zero modes is crucial to obtain the vortex partition function with
the anti-fundamental and adjoint matters in addition to the fundamental chiral
multiplets. The orbifold vortex partition function is also investigated from
the field theoretical point of view.Comment: 21 pages, no 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
Structurally Parameterized d-Scattered Set
In -Scattered Set we are given an (edge-weighted) graph and are asked to
select at least vertices, so that the distance between any pair is at least
, thus generalizing Independent Set. We provide upper and lower bounds on
the complexity of this problem with respect to various standard graph
parameters. In particular, we show the following:
- For any , an -time algorithm, where
is the treewidth of the input graph.
- A tight SETH-based lower bound matching this algorithm's performance. These
generalize known results for Independent Set.
- -Scattered Set is W[1]-hard parameterized by vertex cover (for
edge-weighted graphs), or feedback vertex set (for unweighted graphs), even if
is an additional parameter.
- A single-exponential algorithm parameterized by vertex cover for unweighted
graphs, complementing the above-mentioned hardness.
- A -time algorithm parameterized by tree-depth
(), as well as a matching ETH-based lower bound, both for
unweighted graphs.
We complement these mostly negative results by providing an FPT approximation
scheme parameterized by treewidth. In particular, we give an algorithm which,
for any error parameter , runs in time
and returns a
-scattered set of size , if a -scattered set of the same
size exists
Quantum SUSY Algebra of -lumps in the Massive Grassmannian Sigma Model
We compute the SUSY algebra of the massive Grassmannian sigma
model in 2+1 dimensions. We first rederive the action of the model by using the
Scherk-Schwarz dimensional reduction from theory in 3+1
dimensions. Then, we perform the canonical quantization by using the Dirac
method. We find that a particular choice of the operator ordering yields the
quantum SUSY algebra of the -lumps with cental extension.Comment: 7 pages, references adde
Vortices and Monopoles in Mass-deformed SO and USp Gauge Theories
Effects of mass deformations on 1/2 Bogomol'nyi-Prasad-Sommerfield (BPS)
non-Abelian vortices are studied in 4d N=2 supersymmetric U(1) \times SO(2n)
and U(1) \times USp(2n) gauge theories, with Nf=2n quark multiplets. The 2d
N=(2,2) effective worldsheet sigma models on the Hermitian symmetric spaces
SO(2n)/U(n) and USp(2n)/U(n) found recently which describe the low-energy
excitations of the orientational moduli of the vortices, are generalized to the
respective massive sigma models. The continuous vortex moduli spaces are
replaced by a finite number (2^{n-1} or 2^{n}) of vortex solutions. The 1/2 BPS
kinks connecting different vortex vacua are magnetic monopoles in the 4d
theory, trapped inside the vortex core, with total configurations being 1/4 BPS
composite states. These configurations are systematically studied within the
semi-classical regime.Comment: 55 pages, 7 figure
Color Magnetic Flux Tubes in Dense QCD
QCD is expected to be in the color-flavor locking phase in high baryon
density, which exhibits color superconductivity. The most fundamental
topological objects in the color superconductor are non-Abelian vortices which
are topologically stable color magnetic flux tubes. We present numerical
solutions of the color magnetic flux tube for diverse choices of the coupling
constants. We also analytically study its asymptotic profiles and find that
they are different from the case of usual superconductors. We propose the width
of color magnetic fluxes and find that it is larger than naive expectation of
the Compton wave length of the massive gluon when the gluon mass is larger than
the scalar mass.Comment: 24 pages, 5 figures; v2: typos corrected, references added, minor
changes; v3: published versio
Radio-frequency operation of a double-island single-electron transistor
We present results on a double-island single-electron transistor (DISET)
operated at radio-frequency (rf) for fast and highly sensitive detection of
charge motion in the solid state. Using an intuitive definition for the charge
sensitivity, we compare a DISET to a conventional single-electron transistor
(SET). We find that a DISET can be more sensitive than a SET for identical,
minimum device resistances in the Coulomb blockade regime. This is of
particular importance for rf operation where ideal impedance matching to 50 Ohm
transmission lines is only possible for a limited range of device resistances.
We report a charge sensitivity of 5.6E-6 e/sqrt(Hz) for a rf-DISET, together
with a demonstration of single-shot detection of small (<=0.1e) charge signals
on microsecond timescales.Comment: 6 pages, 6 figure
Are "EIT Waves" Fast-Mode MHD Waves?
We examine the nature of large-scale, coronal, propagating wave fronts (``EIT
waves'') and find they are incongruous with solutions using fast-mode MHD
plane-wave theory. Specifically, we consider the following properties:
non-dispersive single pulse manifestions, observed velocities below the local
Alfven speed, and different pulses which travel at any number of constant
velocities, rather than at the ``predicted'' fast-mode speed. We discuss the
possibility of a soliton-like explanation for these phenomena, and show how it
is consistent with the above-mentioned aspects.Comment: to be published in the Astrophysical Journa
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
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