1,880 research outputs found
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
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
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
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
Colloquium : disclination loops, point defects, and all that in nematic liquid crystals
The homotopy theory of topological defects is a powerful tool for organizing and unifying many ideas across a broad range of physical systems. Recently, experimental progress was made in controlling and measuring colloidal inclusions in liquid crystalline phases. The topological structure of these systems is quite rich but, at the same time, subtle. Motivated by experiment and the power of topological reasoning, the classification of defects in uniaxial nematic liquid crystals was reviewed and expounded upon. Particular attention was paid to the ambiguities that arise in these systems, which have no counterpart in the much-storied XY model or the Heisenberg ferromagnet
On Explicit Point Multi-Monopoles in SU(2) Gauge Theory
It is well known that the Dirac monopole solution with the U(1) gauge group
embedded into the group SU(2) is equivalent to the SU(2) Wu-Yang point monopole
solution having no Dirac string singularity. We consider a multi-center
configuration of m Dirac monopoles and n anti-monopoles and its embedding into
SU(2) gauge theory. Using geometric methods, we construct an explicit solution
of the SU(2) Yang-Mills equations which generalizes the Wu-Yang solution to the
case of m monopoles and n anti-monopoles located at arbitrary points in R^3.Comment: 1+7 pages, LaTe
Explicit Non-Abelian Monopoles and Instantons in SU(N) Pure Yang-Mills Theory
It is well known that there are no static non-Abelian monopole solutions in
pure Yang-Mills theory on Minkowski space R^{3,1}. We show that such solutions
exist in SU(N) gauge theory on the spaces R^2\times S^2 and R^1\times S^1\times
S^2 with Minkowski signature (-+++). In the temporal gauge they are solutions
of pure Yang-Mills theory on T^1\times S^2, where T^1 is R^1 or S^1. Namely,
imposing SO(3)-invariance and some reality conditions, we consistently reduce
the Yang-Mills model on the above spaces to a non-Abelian analog of the \phi^4
kink model whose static solutions give SU(N) monopole (-antimonopole)
configurations on the space R^{1,1}\times S^2 via the above-mentioned
correspondence. These solutions can also be considered as instanton
configurations of Yang-Mills theory in 2+1 dimensions. The kink model on
R^1\times S^1 admits also periodic sphaleron-type solutions describing chains
of n kink-antikink pairs spaced around the circle S^1 with arbitrary n>0. They
correspond to chains of n static monopole-antimonopole pairs on the space
R^1\times S^1\times S^2 which can also be interpreted as instanton
configurations in 2+1 dimensional pure Yang-Mills theory at finite temperature
(thermal time circle). We also describe similar solutions in Euclidean SU(N)
gauge theory on S^1\times S^3 interpreted as chains of n
instanton-antiinstanton pairs.Comment: 16 pages; v2: subsection on topological charges added, title
expanded, some coefficients corrected, version to appear in PR
Case study of ozone anomalies over northern Russia in the 2015/2016 winter: measurements and numerical modelling
Episodes of extremely low ozone columns were observed over the territory of
Russia in the Arctic winter of 2015/2016 and the beginning of spring 2016. We
compare total ozone columns (TOCs) from different remote sensing techniques
(satellite and ground-based observations) with results of numerical modelling
over the territory of the Urals and Siberia for this period. We demonstrate
that the provided monitoring systems (including the new Russian Infrared
Fourier Spectrometer IKFS-2) and modern three-dimensional atmospheric models
can capture the observed TOC anomalies. However, the results of observations
and modelling show differences of up to 20 %–30 % in TOC
measurements. Analysis of the role of chemical and dynamical processes
demonstrates that the observed short-term TOC variability is not a result of
local photochemical loss initiated by heterogeneous halogen activation on
particles of polar stratospheric clouds that formed under low temperatures in
the mid-winter.</p
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