2,841 research outputs found
The curious case of large-N expansions on a (pseudo)sphere
We elucidate the large-N dynamics of one-dimensional sigma models with
spherical and hyperbolic target spaces and find a duality between the Lagrange
multiplier and the angular momentum. In the hyperbolic model we propose a new
class of operators based on the irreducible representations of hyperbolic
space. We also uncover unexpected zero modes which lead to the double scaling
of the 1/N expansion and explore these modes using Gelfand-Dikiy equations.Comment: 18 pages, 3 figure
Vacuum Decay in CFT and the Riemann-Hilbert problem
We study vacuum stability in 1+1 dimensional Conformal Field Theories with
external background fields. We show that the vacuum decay rate is given by a
non-local two-form. This two-form is a boundary term that must be added to the
effective in/out Lagrangian. The two-form is expressed in terms of a
Riemann-Hilbert decomposition for background gauge fields, and its novel
"functional" version in the gravitational case.Comment: 16 pages, 3 figure
Double Well Potential: Perturbation Theory, Tunneling, WKB (beyond instantons)
A simple approximate solution for the quantum-mechanical quartic oscillator
in the double-well regime at arbitrary is
presented. It is based on a combining of perturbation theory near true minima
of the potential, semi-classical approximation at large distances and a
description of tunneling under the barrier. It provides 9-10 significant digits
in energies and gives for wavefunctions the relative deviation in real
-space less than .Comment: 13 pages, invited talk at "Crossing the boundaries: Gauge dynamics at
strong coupling (Shifmania)", Minneapolis, May 14-17, 200
A Case Study on Investigation of Component Age Dependent Reliability Models - EC JRC Network on Use of Probabilistic Safety Assessments (PSA) for Evaluation of Aging Effects to the Safety of Energy Facilities - Task 4
The report presents the results of a case study on "Investigation of component age dependent reliability models" implemented by INPE and JRC IE in the frame of EC JRC Ageing PSA Network Task 4 activities. Several cases of Generalized Linear Model were proposed and investigated for the cases of continues and discrete data. The Fisher Chi-2 minimization approach was applied for goodness of fit test and parameters elaboration. Finally, uncertainty analysis was done for estimated parameters and model extrapolations. The results were analyzed and compared with other approaches.JRC.F.4-Nuclear design safet
Destruction of Neel order and local spin spirals in insulating La_{2-x}Sr_xCuO_4
Starting from the t-J model, we derive an effective field theory describing
the spin dynamics in the insulating phase of La_{2-x}Sr_xCuO_4, x < 0.055, at
low temperature. Using Monte Carlo simulations, we show that the destruction of
Neel order is driven by the single-hole localization length kappa. A phase
transition at 2% doping is consistent with the value of kappa known from the
variable range hopping conductivity. The static spin structure factor obtained
in our calculations is in perfect agreement with neutron scattering data over
the whole range of doping. We also demonstrate that topological defects (spin
vortex-antivortex pairs) are an intrinsic property of the spin-glass ground
state.Comment: 4 pages, 2 figure
FQHE interferometers in strong tunneling regime. The role of compactness of edge fields
We consider multiple-point tunneling in the interferometers formed between
edges of electron liquids with in general different filling factors in the
regime of the Fractional Quantum Hall effect (FQHE). We derive an effective
matrix Caldeira-Leggett models for the multiple tunneling contacts connected by
the chiral single-mode FQHE edges. It is shown that the compactness of the Wen-
Fr\"ohlich chiral boson fields describing the FQHE edge modes plays a crucial
role in eliminating the spurious non-locality of the electron transport
properties of the FQHE interferometers arising in the regime of strong
tunneling.Comment: 5 page
Regularisation of non-local actions in two-dimensional field theories
Taking the induced action for gauge fields coupled to affine currents as an
example, we show how loop calculations in non-local two-dimensional field
theories can be regulated. Our regularisation method for one loop is based on
the method of Pauli and Villars. We use it to calculate the renormalisation
factors for the corresponding effective actions, clearing up some discrepancies
in the literature. In particular, it will be shown explicitly that vector gauge
transformation invariance and Haar invariance of functional integral measures
impose different requirements, but they are related by a counterterm (which is
local in terms of group variables). For higher loops, we use the method of
covariant derivatives combined with Pauli-Villars to argue that the one loop
result remains unaltered.Comment: 29 pp, LATEX, LBL-33777, UCB-PTH-93/08, KUL-TF-93/2
An observation-based assessment of the influences of air temperature and snow depth on soil temperature in Russia
This study assessed trends in the variability of soil temperature (T-SOIL) using spatially averaged observation records from Russian meteorological land stations. The contributions of surface air temperature (SAT) and snow depth (SND) to T-SOIL variation were quantitatively evaluated. Composite time series of these data revealed positive trends during the period of 1921-2011, with accelerated increases since the 1970s. The T-SOIL warming rate over the entire period was faster than the SAT warming rate in both permafrost and non-permafrost regions, suggesting that SND contributes to T-SOIL warming. Statistical analysis revealed that the highest correlation between SND and T-SOIL was in eastern Siberia, which is underlain by permafrost. SND in this region accounted for 50% or more of the observed variation in T-SOIL. T-SOIL in the non-permafrost region of western Siberia was significantly correlated with changes in SAT. Thus, the main factors associated with T-SOIL variation differed between permafrost and non-permafrost regions. This finding underscores the importance of including SND data when assessing historical and future variations and trends of permafrost in the Northern Hemisphere
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