3,415 research outputs found
The 1/N-expansion, quantum-classical correspondence and nonclassical states generation in dissipative higher-order anharmonic oscillators
We develop a method for the determination of thecdynamics of dissipative
quantum systems in the limit of large number of quanta N, based on the
1/N-expansion of Heidmann et al. [ Opt. Commun. 54, 189 (1985) ] and the
quantum-classical correspondence. Using this method, we find analytically the
dynamics of nonclassical states generation in the higher-order anharmonic
dissipative oscillators for an arbitrary temperature of a reservoir. We show
that the quantum correction to the classical motion increases with time
quadratically up to some maximal value, which is dependent on the degree of
nonlinearity and a damping constant, and then it decreases. Similarities and
differences with the corresponding behavior of the quantum corrections to the
classical motion in the Hamiltonian chaotic systems are discussed. We also
compare our results obtained for some limiting cases with the results obtained
by using other semiclassical tools and discuss the conditions for validity of
our approach.Comment: 15 pages, RevTEX (EPSF-style), 3 figs. Replaced with final version
(stylistic corrections
Decomposable representations and Lagrangian submanifolds of moduli spaces associated to surface groups
In this paper, we construct a Lagrangian submanifold of the moduli space
associated to the fundamental group of a punctured Riemann surface (the space
of representations of this fundamental group into a compact connected Lie
group). This Lagrangian submanifold is obtained as the fixed-point set of an
anti-symplectic involution defined on the moduli space. The notion of
decomposable representation provides a geometric interpretation of this
Lagrangian submanifold
Nested T-duality
We identify the obstructions for T-dualizing the boundary WZW model and make
explicit how they depend on the geometry of branes. In particular, the
obstructions disappear for certain brane configurations associated to
non-regular elements of the Cartan torus. It is shown in this case that the
boundary WZW model is "nested" in the twisted boundary WZW model as the
dynamical subsystem of the latter.Comment: 13 page
Evidence for short-range antiferromagnetic fluctuations in Kondo-insulating YbB12
The spin dynamics of mixed-valence YbB12 has been studied by inelastic
neutron scattering on a high-quality single crystal. In the Kondo-insulating
regime realized at low temperature, the spectra exhibit a spin-gap structure
with two sharp, dispersive, in-gap excitations at E = 14.5 and approximately 20
meV. The lower mode is shown to be associated with short-range correlations
near the antiferromagnetic wave vector q0 = (1/2, 1/2, 1/2). Its properties are
in overall agreement with those expected for a "spin exciton'' branch in an
indirect hybridization gap semiconductor.Comment: 4 pages, 4 figures ; submitted to Physical Review Letter
Hamiltonian Quantization of Chern-Simons theory with SL(2,C) Group
We analyze the hamiltonian quantization of Chern-Simons theory associated to
the universal covering of the Lorentz group SO(3,1). The algebra of observables
is generated by finite dimensional spin networks drawn on a punctured
topological surface. Our main result is a construction of a unitary
representation of this algebra. For this purpose, we use the formalism of
combinatorial quantization of Chern-Simons theory, i.e we quantize the algebra
of polynomial functions on the space of flat SL(2,C)-connections on a
topological surface with punctures. This algebra admits a unitary
representation acting on an Hilbert space which consists in wave packets of
spin-networks associated to principal unitary representations of the quantum
Lorentz group. This representation is constructed using only Clebsch-Gordan
decomposition of a tensor product of a finite dimensional representation with a
principal unitary representation. The proof of unitarity of this representation
is non trivial and is a consequence of properties of intertwiners which are
studied in depth. We analyze the relationship between the insertion of a
puncture colored with a principal representation and the presence of a
world-line of a massive spinning particle in de Sitter space.Comment: 78 pages. Packages include
Gauging the Wess-Zumino term of a sigma model with boundary
We investigate the gauging of the Wess-Zumino term of a sigma model with
boundary. We derive a set of obstructions to gauging and we interpret them as
the conditions for the Wess-Zumino term to extend to a closed form in a
suitable equivariant relative de Rham complex. We illustrate this with the
two-dimensional sigma model and we show that the new obstructions due to the
boundary can be interpreted in terms of Courant algebroids. We specialise to
the case of the Wess-Zumino-Witten model, where it is proved that there always
exist suitable boundary conditions which allow gauging any subgroup which can
be gauged in the absence of a boundary. We illustrate this with two natural
classes of gaugings: (twisted) diagonal subgroups with boundary conditions
given by (twisted) conjugacy classes, and chiral isotropic subgroups with
boundary conditions given by cosets.Comment: 18 pages (minor changes in response to referee report
Physical phase space of lattice Yang-Mills theory and the moduli space of flat connections on a Riemann surface
It is shown that the physical phase space of \g-deformed Hamiltonian
lattice Yang-Mills theory, which was recently proposed in refs.[1,2], coincides
as a Poisson manifold with the moduli space of flat connections on a Riemann
surface with handles and therefore with the physical phase space of
the corresponding -dimensional Chern-Simons model, where and are
correspondingly a total number of links and vertices of the lattice. The
deformation parameter \g is identified with and is an
integer entering the Chern-Simons action.Comment: 12 pages, latex, no figure
Defect loops in gauged Wess-Zumino-Witten models
We consider loop observables in gauged Wess-Zumino-Witten models, and study
the action of renormalization group flows on them. In the WZW model based on a
compact Lie group G, we analyze at the classical level how the space of
renormalizable defects is reduced upon the imposition of global and affine
symmetries. We identify families of loop observables which are invariant with
respect to an affine symmetry corresponding to a subgroup H of G, and show that
they descend to gauge-invariant defects in the gauged model based on G/H. We
study the flows acting on these families perturbatively, and quantize the fixed
points of the flows exactly. From their action on boundary states, we present a
derivation of the "generalized Affleck-Ludwig rule, which describes a large
class of boundary renormalization group flows in rational conformal field
theories.Comment: 43 pages, 2 figures. v2: a few typos corrected, version to be
published in JHE
Boundary three-point function on AdS2 D-branes
Using the H3+-Liouville relation, I explicitly compute the boundary
three-point function on AdS2 D-branes in H3+, and check that it exhibits the
expected symmetry properties and has the correct geometrical limit. I then find
a simple relation between this boundary three-point function and certain fusing
matrix elements, which suggests a formal correspondence between the AdS2
D-branes and discrete representations of the symmetry group. Concluding
speculations deal with the fuzzy geometry of AdS2 D-branes, strings in the
Minkowskian AdS3, and the hypothetical existence of new D-branes in H3+.Comment: 27 pages, v2: significant clarifications added in sections 4.3 and
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