35,674 research outputs found
Quantum criticality in Kondo quantum dot coupled to helical edge states of interacting 2D topological insulators
We investigate theoretically the quantum phase transition (QPT) between the
one-channel Kondo (1CK) and two-channel Kondo (2CK) fixed points in a quantum
dot coupled to helical edge states of interacting 2D topological insulators
(2DTI) with Luttinger parameter . The model has been studied in Ref. 21,
and was mapped onto an anisotropic two-channel Kondo model via bosonization.
For K<1, the strong coupling 2CK fixed point was argued to be stable for
infinitesimally weak tunnelings between dot and the 2DTI based on a simple
scaling dimensional analysis[21]. We re-examine this model beyond the bare
scaling dimension analysis via a 1-loop renormalization group (RG) approach
combined with bosonization and re-fermionization techniques near weak-coupling
and strong-coupling (2CK) fixed points. We find for K -->1 that the 2CK fixed
point can be unstable towards the 1CK fixed point and the system may undergo a
quantum phase transition between 1CK and 2CK fixed points. The QPT in our model
comes as a result of the combined Kondo and the helical Luttinger physics in
2DTI, and it serves as the first example of the 1CK-2CK QPT that is accessible
by the controlled RG approach. We extract quantum critical and crossover
behaviors from various thermodynamical quantities near the transition. Our
results are robust against particle-hole asymmetry for 1/2<K<1.Comment: 17 pages, 9 figures, more details added, typos corrected, revised
Sec. IV, V, Appendix A and
Time evolution towards q-Gaussian stationary states through unified Ito-Stratonovich stochastic equation
We consider a class of single-particle one-dimensional stochastic equations
which include external field, additive and multiplicative noises. We use a
parameter which enables the unification of the traditional
It\^o and Stratonovich approaches, now recovered respectively as the
and particular cases to derive the associated Fokker-Planck
equation (FPE). These FPE is a {\it linear} one, and its stationary state is
given by a -Gaussian distribution with , where characterizes the
strength of the confining external field, and is the (normalized)
amplitude of the multiplicative noise. We also calculate the standard kurtosis
and the -generalized kurtosis (i.e., the standard
kurtosis but using the escort distribution instead of the direct one). Through
these two quantities we numerically follow the time evolution of the
distributions. Finally, we exhibit how these quantities can be used as
convenient calibrations for determining the index from numerical data
obtained through experiments, observations or numerical computations.Comment: 9 pages, 2 figure
Strong Collapse Turbulence in Quintic Nonlinear Schr\"odinger Equation
We consider the quintic one dimensional nonlinear Schr\"odinger equation with
forcing and both linear and nonlinear dissipation. Quintic nonlinearity results
in multiple collapse events randomly distributed in space and time forming
forced turbulence. Without dissipation each of these collapses produces finite
time singularity but dissipative terms prevents actual formation of
singularity. In statistical steady state of the developed turbulence the
spatial correlation function has a universal form with the correlation length
determined by the modulational instability scale. The amplitude fluctuations at
that scale are nearly-Gaussian while the large amplitude tail of probability
density function (PDF) is strongly non-Gaussian with power-like behavior. The
small amplitude nearly-Gaussian fluctuations seed formation of large collapse
events. The universal spatio-temporal form of these events together with the
PDF for their maximum amplitudes define the power-like tail of PDF for large
amplitude fluctuations, i.e., the intermittency of strong turbulence.Comment: 14 pages, 17 figure
Radion Potential and Brane Dynamics
We examine the cosmology of the Randall-Sundrum model in a dynamic setting
where scalar fields are present in the bulk as well as the branes. This
generates a mechanism similar to that of Goldberger-Wise for radion
stabilization and the recovery of late-cosmology features in the branes. Due to
the induced radion dynamics, the inflating branes roll towards the minimum of
the radion potential, thereby exiting inflation and reheating the Universe. In
the slow roll part of the potential, the 'TeV' branes have maximum inflation
rate and energy as their coupling to the radion and bulk modes have minimum
suppresion. Hence, when rolling down the steep end of the potential towards the
stable point, the radion field (which appears as the inflaton of the effective
4D theory in the branes) decays very fast, reheats the Universe .This process
results decayin a decrease of brane's canonical vacuum energy .
However, at the minimum of the potential is small but not
neccessarily zero and the fine-tuning issue remains .Density perturbation
constraints introduce an upper bound when the radion stabilizies. Due to the
large radion mass and strong suppression to the bulk modes, moduli problems and
bulk reheating do not occur. The reheat temperature and a sufficient number of
e-folding constraints for the brane-universe are also satisfied. The model
therefore recovers the radiation dominated FRW universe.Comment: 16 pages, 3 figures,extraneous sentences removed, 2 footnotes added,
some typos correcte
Thermomechanical behavior of plasma-sprayed ZrO2-Y2O3 coatings influenced by plasticity, creep and oxidation
Thermocycling of ceramic-coated turbomachine components produces high thermomechanical stresses that are mitigated by plasticity and creep but aggravated by oxidation, with residual stresses exacerbated by all three. These residual stresses, coupled with the thermocyclic loading, lead to high compressive stresses that cause the coating to spall. A ceramic-coated gas path seal is modeled with consideration given to creep, plasticity, and oxidation. The resulting stresses and possible failure modes are discussed
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