120,586 research outputs found
Theory of electron-phonon interaction in a nonequilibrium open electronic system
We study the effects of time-independent nonequilibrium drive on an open 2D
electron gas system coupled to 2D longitudinal acoustic phonons using the
Keldysh path integral method. The layer electron-phonon system is defined at
the two-dimensional interface between a pair of three-dimensional Fermi liquid
leads, which act both as a particle pump and an infinite bath. The
nonequilibrium steady state is achieved in the layer by assuming the leads to
be thermally equilibrated at two different chemical potentials. This subjects
the layer to an out-of-plane voltage and drives a steady-state charge
current perpendicular to the system. We compute the effects of small voltages
(V\ll\w_D) on the in-plane electron-phonon scattering rate and the electron
effective mass at zero temperature. We also find that the obtained
onequilibrium modification to the acoustic phonon velocity and the Thomas-Fermi
screening length reveal the possibility of tuning these quantities with the
external voltage.Comment: 14 pages, 4 figure
The Effects of the Massless O(alpha_s^2), O(\alpha\alpha_s), O(\alpha^2) QCD and QED Corrections and of the Massive Contributions to Gamma(H^0\rightarrow b\overline{b})
We consider in detail various theoretical uncertainties of the perturbative
predictions for the decay width of process in
the region . We calculate the order
-contributions to the expression for
through the pole quark mass and demonstrate that they are important for the
elimination of the numerical difference between the corresponding expression
and the one through the running -quark mass. The order
and massless and order massive corrections to
are also calculated. The importance of the latter
contributions for modeling of the threshold effects is demonstrated. The
troubles with identifying of the 4 recent L3 events with the decay of a Standard Higgs boson are discussed.Comment: 16 pages, 6 figures (can be optained by mail after the request from
the authers, e-mails: [email protected]; [email protected]); LATEX,
modified version of ENSLAPP.-A.-407/92 preprin
Interfering directed paths and the sign phase transition
We revisit the question of the "sign phase transition" for interfering
directed paths with real amplitudes in a random medium. The sign of the total
amplitude of the paths to a given point may be viewed as an Ising order
parameter, so we suggest that a coarse-grained theory for system is a dynamic
Ising model coupled to a Kardar-Parisi-Zhang (KPZ) model. It appears that when
the KPZ model is in its strong-coupling ("pinned") phase, the Ising model does
not have a stable ferromagnetic phase, so there is no sign phase transition. We
investigate this numerically for the case of {\ss}1+1 dimensions, demonstrating
the instability of the Ising ordered phase there.Comment: 4 pages, 4 figure
A criterion for the nature of the superconducting transition in strongly interacting field theories : Holographic approach
It is beyond the present techniques based on perturbation theory to reveal
the nature of phase transitions in strongly interacting field theories.
Recently, the holographic approach has provided us with an effective dual
description, mapping strongly coupled conformal field theories to classical
gravity theories. Resorting to the holographic superconductor model, we propose
a general criterion for the nature of the superconducting phase transition
based on effective interactions between vortices. We find "tricritical" points
in terms of the chemical potential for U(1) charges and an effective
Ginzburg-Landau parameter, where vortices do not interact to separate the
second order (repulsive) from the first order (attractive) transitions. We
interpret the first order transition as the Coleman-Weinberg mechanism, arguing
that it is relevant to superconducting instabilities around quantum
criticality.Comment: 7 pages, 7 figure
Thermal stability of metastable magnetic skyrmions: Entropic narrowing and significance of internal eigenmodes
We compute annihilation rates of metastable magnetic skyrmions using a form
of Langer's theory in the intermediate-to-high damping (IHD) regime. For a
N\'eel skyrmion, a Bloch skyrmion, and an antiskyrmion, we look at two possible
paths to annihilation: collapse and escape through a boundary. We also study
the effects of a curved vs. a flat boundary, a second skyrmion and a
non-magnetic defect. We find that the skyrmion's internal modes play a dominant
role in the thermally activated transitions compared to the spin-wave
excitations and that the relative contribution of internal modes depends on the
nature of the transition process. Our calculations for a small skyrmion
stabilized at zero-field show that collapse on a defect is the most probable
path. In the absence of a defect, the annihilation is largely dominated by
escape mechanisms, even though in this case the activation energy is higher
than that of collapse processes. Escape through a flat boundary is found more
probable than through a curved boundary. The potential source of stability of
metastable skyrmions is therefore found not to lie in high activation energies,
nor in the dynamics at the transition state, but comes from entropic narrowing
in the saddle point region which leads to lowered attempt frequencies. This
narrowing effect is found to be primarily associated with the skyrmion's
internal modes.Comment: 14 pages, 9 figure
The BFKL Pomeron within Physical Renormalization Schemes and Scales
In this lecture the next-to-leading order (NLO) corrections to the QCD
Pomeron intercept obtained from the Balitsky-Fadin-Kuraev-Lipatov (BFKL)
equation are discussed. It is shown that the BFKL Pomeron intercept when
evaluated in non-Abelian physical renormalization schemes with
Brodsky-Lepage-Mackenzie (BLM) optimal scale setting does not exhibit the
serious problems encountered in the modified minimal subtraction (bar{MS})
scheme. The results obtained provide an opportunity for applications of the NLO
BFKL resummation to high-energy phenomenology.
One of such applications for virtual gamma-gamma total cross section shows a
good agreement with preliminary data at CERN LEP.Comment: Presented at XXXXV PNPI Winter School, Repino, St.Petersburg, Russia,
19-25 Feb., 2001; Latex, 16 pages, 5 figure
Diamagnetic response of Aharonov-Bohm rings: Impurity backward scatterings
We report a theoretical calculation on the persistent currents of disordered
normal-metal rings. It is shown that the diamagnetic responses of the rings in
the vicinity of the zero magnetic field are attributed to multiple backward
scatterings off the impurities. We observe the transition from the paramagnetic
response to the diamagnetic one as the strength of disorder grows using both
the analytic calculation and the numerical exact diagonalization.Comment: final versio
Path sampling for lifetimes of metastable magnetic skyrmions and direct comparison with Kramers' method
We perform a direct comparison between Kramers' method in many dimensions --
i.e., Langer's theory -- adapted to magnetic spin systems, and a path sampling
method in the form of forward flux sampling, as a means to compute collapse
rates of metastable magnetic skyrmions. We show that a good agreement is
obtained between the two methods. We report variations of the attempt frequency
associated with skyrmion collapse by three to four orders of magnitude when
varying the applied magnetic field by 5 of the exchange strength, which
confirms the existence of a strong entropic contribution to the lifetime of
skyrmions. This demonstrates that in complex systems, the knowledge of the rate
prefactor, in addition to the internal energy barrier, is essential in order to
properly estimate a lifetime.Comment: 5 pages, 5 figures (main text), 8 pages including supplemental
materia
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