52,636 research outputs found
Nonequilibrium noise correlations in a point contact of helical edge states
We investigate theoretically the nonequilibrium finite-frequency current
noise in a four-terminal quantum point contact of interacting helical edge
states at a finite bias voltage. Special focus is put on the effects of the
single-particle and two-particle scattering between the two helical edge states
on the fractional charge quasiparticle excitations shown in the nonequilibrium
current noise spectra. Via the Keldysh perturbative approach, we find that the
effects of the single-particle and the two-particle scattering processes on the
current noise depend sensitively on the Luttinger liquid parameter. Moreover,
the Fano factors for the auto- and cross correlations of the currents in the
terminals are distinct from the ones for tunneling between the chiral edge
states in the quantum Hall liquid. The current noise spectra in the
single-particle-scattering-dominated and the two-particle-scattering-dominated
regime are shown. Experimental implications of our results on the transport
through the helical edges in two-dimensional topological insulators are
discussed.Comment: 10 pages, 8 figure
Trade, International Business Cycles, and the Optimum Currency Area
This paper studies the co-movement of intra-Asian business cycles. Based on the regional bilateral trade statistics and using three de-trending techniques to examine several macroeconomic fundamentals, the negative trade effects prevailing in the cases of economic activity such as real GDP and industrial production indicate that tighter intra- Asian trade may most likely lead to more idiosyncratic business cycles and hence lower correlations of economic activity between Asian nations. Given this result, it is believed that for the foreseeable future, the creation of an Asian-Pacific monetary union and the corresponding currency area may be unsuitable and will not be recommended
Exploring soft constraints on effective actions
We study effective actions for simultaneous breaking of space-time and
internal symmetries. Novel features arise due to the mixing of Goldstone modes
under the broken symmetries which, in contrast to the usual Adler's zero, leads
to non-vanishing soft limits. Such scenarios are common for spontaneously
broken SCFT's. We explicitly test these soft theorems for sYM
in the Coulomb branch both perturbatively and non-perturbatively. We explore
the soft constraints systematically utilizing recursion relations. In the pure
dilaton sector of a general CFT, we show that all amplitudes up to order are completely determined in terms of the -point
amplitudes at order with . Terms with at most one derivative
acting on each dilaton insertion are completely fixed and coincide with those
appearing in the conformal DBI, i.e. DBI in AdS. With maximal supersymmetry,
the effective actions are further constrained, leading to new
non-renormalization theorems. In particular, the effective action is fixed up
to eight derivatives in terms of just one unknown four-point coefficient and
one more coefficient for ten-derivative terms. Finally, we also study the
interplay between scale and conformal invariance in this context.Comment: 20+4 pages, 1 figure; v2: references added, typos corrected; v3:
typos corrected, JHEP versio
Criterion for transformation of transverse domain wall to vortex or antivortex wall in soft magnetic thin-film nanostripes
We report on the criterion for the dynamic transformation of the internal
structure of moving domain walls (DWs) in soft magnetic thin-film nanostripes
above the Walker threshold field, Hw. In order for the process of
transformation from transverse wall (TW) to vortex wall (VW) or antivortex wall
(AVW) occurs, the edge-soliton core of the TW-type DW should grow sufficiently
to the full width at half maximum of the out-of-plane magnetizations of the
core area of the stabilized vortex (or antivortex) by moving inward along the
transverse (width) direction. Upon completion of the nucleation of the vortex
(antivortex) core, the VW (AVW) is stabilized, and then its core accompanies
the gyrotropic motion in a potential well (hill) of a given nanostripe. Field
strengths exceeding the Hw, which is the onset field of DW velocity breakdown,
are not sufficient but necessary conditions for dynamic DW transformation
Photon splitting in atomic fields
Photon splitting due to vacuum polarization in the electric field of an atom
is considered. We survey different theoretical approaches to the description of
this nonlinear QED process and several attempts of its experimental
observation. We present the results of the lowest-order perturbation theory as
well as those obtained within the quasiclassical approximation being exact in
the external field strength. The experiment where photon splitting was really
observed for the first time is discussed in details. The results of this
experiment are compared with recent theoretical estimations.Comment: 45 pages, 24 figure
Momentum Flow Correlations from Event Shapes: Factorized Soft Gluons and Soft-Collinear Effective Theory
The distributions of two-jet event shapes contain information on
hadronization in QCD. Near the two-jet limit, these distributions can be
described by convolutions of nonperturbative event shape functions with the
same distributions calculated in resummed perturbation theory. The shape
functions, in turn, are determined by correlations of momentum flow operators
with each other and with light-like Wilson lines, which describe the coupling
of soft, wide-angle radiation to jets. We observe that leading power
corrections to the mean values of event shapes are determined by the
correlation of a single momentum flow operator with the relevant Wilson lines.
This generalizes arguments for the universality of leading power corrections
based on the low-scale behavior of the running coupling or resummation. We also
show how a study of the angularity event shapes can provide information on
correlations involving multiple momentum flow operators, giving a window to the
system of QCD dynamics that underlies the variety of event shape functions. In
deriving these results, we review, develop and compare factorization techniques
in conventional perturbative QCD and soft-collinear effective theory (SCET). We
give special emphasis to the elimination of double counting of momentum regions
in these two formalisms.Comment: 25 pages revtex
Dynamical renormalization group approach to the Altarelli-Parisi-Lipatov equations
The Altarelli-Parisi-Lipatov equations for the parton distribution functions
are rederived using the dynamical renormalization group approach to quantum
kinetics. This method systematically treats the ln Q^2 corrections that arises
in perturbation theory as a renormalization of the parton distribution function
and unambiguously indicates that the strong coupling must be allowed to run
with the scale in the evolution kernel. To leading logarithmic accuracy the
evolution equation is Markovian and the logarithmic divergences in the
perturbative expansion are identified with the secular divergences (terms that
grow in time) that emerge in a perturbative treatment of the kinetic equations
in nonequilibrium systems. The resummation of the leading logarithms by the
Altarelli-Parisi-Lipatov equation is thus similar to the resummation of the
leading secular terms by the Boltzmann kinetic equation.Comment: 8 pages, version to appear in Phys. Rev.
On Resource-bounded versions of the van Lambalgen theorem
The van Lambalgen theorem is a surprising result in algorithmic information
theory concerning the symmetry of relative randomness. It establishes that for
any pair of infinite sequences and , is Martin-L\"of random and
is Martin-L\"of random relative to if and only if the interleaved sequence
is Martin-L\"of random. This implies that is relative random
to if and only if is random relative to \cite{vanLambalgen},
\cite{Nies09}, \cite{HirschfeldtBook}. This paper studies the validity of this
phenomenon for different notions of time-bounded relative randomness.
We prove the classical van Lambalgen theorem using martingales and Kolmogorov
compressibility. We establish the failure of relative randomness in these
settings, for both time-bounded martingales and time-bounded Kolmogorov
complexity. We adapt our classical proofs when applicable to the time-bounded
setting, and construct counterexamples when they fail. The mode of failure of
the theorem may depend on the notion of time-bounded randomness
Ground state of graphite ribbons with zigzag edges
We study the interaction effects on the ground state of nanographite ribbons
with zigzag edges. Within the mean-field approximation, we found that there are
two possible phases: the superconducting (SC) phase and the excitonic insulator
(EI). The two phases are separated by a first-order transition point. After
taking into account the low-lying fluctuations around the mean-field solutions,
the SC phase becomes a spin liquid phase with one gapless charge mode.
On the other hand, all excitations in the EI phase, especially the spin
excitations, are gapped.Comment: 6 pages, 3 figure
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