214 research outputs found
Magnetooptics in Gold and Silver NanoSizes Low-Dimensional Objects
The spectra of optical absorption and of magnetic circular dichroism (MCD) have been measured in the 350–1150 nm wavelength range for a set of colloidal solutions containing Au and Ag nanoparticles. The average size of Au nanoparticles was 6 nm and having thiolate coatings with different degrees of chirality. (The average size of Ag nanoparticles was 14 nm and having citrate coatings) The form of absorption and MCD spectra suggests the dipole character of interband transitions involving the 5d–6(sp) for Au orbitals and 4d–5(sp) for Ag orbitals. The absence (within the experimental error) of the MCD spectra dependence on the coating type rules out the hypothesis on the orbital nature of the observed magnetism. We argue that the spin polarization plays the dominant role in the magnetism both for Au and Ag nanoparticles.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3534
Burkhardt-Cottingham sum rule and forward spin polarizabilities in Heavy Baryon Chiral Perturbation Theory
We study spin-dependent sum rules for forward virtual Compton
scattering(VVCS) off the nucleon in heavy baryon chiral perturbation theory at
order . We show how these sum rules can be evaluated from low energy
expansions (in the virtual photon energy) of the forward VVCS amplitudes. We
study in particular the Burkhardt -Cottingham sum rule in HBChPT and higher
terms in the low energy expansion, which can be related to the generalized
forward spin polarizabilities of the nucleon. The dependence of these
observables on the photon virtuality can be accessed, at small and
intermediate values, from existing and forthcoming data at Jefferson Lab.Comment: 16 pages,4 fig
Disordered Dirac Fermions: Multifractality Termination and Logarithmic Conformal Field Theories
We reexamine in detail the problem of fermions interacting with a non-Abelian
random vector potential. Without resorting to the replica or supersymmetry
approaches, we show that in the limit of infinite disorder strength the theory
possesses an exact solution which takes the form of a logarithmic conformal
field theory. We show that the proper treatment of the locality conditions in
the SU(2) theory leads to the termination of the multifractal spectrum, or in
other words to the termination of the infinite hierarchies of
negative-dimensional operators that were thought to occur. Based on arguments
of logarithmic degeneracies, we conjecture that such a termination mechanism
should be present for general SU(N). Moreover, our results lead to the
conclusion that the previous replica solution of this problem yields incorrect
results.Comment: Revised version, to appear in Nucl. Phys.
A Matrix Model Dual of Type 0B String Theory in Two Dimensions
We propose that type 0B string theory in two dimensions admits a dual
description in terms of a one dimensional bosonic matrix model of a hermitian
matrix. The potential in the matrix model is symmetric with respect to the
parity-like Z_2 transformation of the matrix. The two sectors in the theory,
namely the NSNS and RR scalar sectors correspond to two classes of operators in
the matrix model, even and odd under the Z_2 symmetry respectively. We provide
evidence that the matrix model successfully reconstructs the perturbative
S-matrix of the string theory, and reproduces the closed string emission
amplitude from unstable D-branes. Following recent work in two dimensional
bosonic string, we argue that the matrix model can be identified with the
theory describing N unstable D0-branes in type 0B theory. We also argue that
type 0A theory is described in terms of the quantum mechanics of
brane-antibrane systems.Comment: Latex, 20 pages, typos corrected, explanations added, references
adde
Compton Scattering and the Spin Structure of the Nucleon at Low Energies
We analyze polarized Compton scattering which provides information on the
spin-structure of the nucleon. For scattering processes with photon energies up
to 100 MeV the spin-structure dependence can be encoded into four independent
parameters-the so-called spin-polarizabilities of the
nucleon, which we calculate within the framework of the "small scale expansion"
in SU(2) baryon chiral perturbation theory. Specific application is made to
"forward" and "backward" spin- polarizabilities.Comment: 8 pages revtex file, separation between pion-pole and regular
contributions detailed + minor wording changes, results and conclusions
unchange
D-brane Decay in Two-Dimensional String Theory
We consider unstable D0-branes of two dimensional string theory, described by
the boundary state of Zamolodchikov and Zamolodchikov [hep-th/0101152]
multiplied by the Neumann boundary state for the time coordinate . In the
dual description in terms of the matrix model, this D0-brane is described
by a matrix eigenvalue on top of the upside down harmonic oscillator potential.
As suggested by McGreevy and Verlinde [hep-th/0304224], an eigenvalue rolling
down the potential describes D-brane decay. As the eigenvalue moves down the
potential to the asymptotic region it can be described as a free relativistic
fermion. Bosonizing this fermion we get a description of the state in terms of
a coherent state of the tachyon field in the asymptotic region, up to a
non-local linear field redefinition by an energy-dependent phase. This coherent
state agrees with the exponential of the closed string one-point function on a
disk with Sen's marginal boundary interaction for which describes D0-brane
decay.Comment: 19 pages, harvmac, minor change
The Hitchin functionals and the topological B-model at one loop
The quantization in quadratic order of the Hitchin functional, which defines
by critical points a Calabi-Yau structure on a six-dimensional manifold, is
performed. The conjectured relation between the topological B-model and the
Hitchin functional is studied at one loop. It is found that the genus one free
energy of the topological B-model disagrees with the one-loop free energy of
the minimal Hitchin functional. However, the topological B-model does agree at
one-loop order with the extended Hitchin functional, which also defines by
critical points a generalized Calabi-Yau structure. The dependence of the
one-loop result on a background metric is studied, and a gravitational anomaly
is found for both the B-model and the extended Hitchin model. The anomaly
reduces to a volume-dependent factor if one computes for only Ricci-flat Kahler
metrics.Comment: 33 pages, LaTe
Notes on D-branes in 2D Type 0 String Theory
In this paper we construct complete macroscopic operators in two dimensional
type 0 string theory. They represent D-branes localized in the time direction.
We give another equivalent description of them as deformed Fermi surfaces. We
also discuss a continuous array of such D-branes and show that it can be
described by a matrix model with a deformed potential. For appropriate values
of parameters, we find that it has an additional new sector hidden inside its
strongly coupled region.Comment: harvmac, 18 pages, 2 figures, references adde
The Neveu-Schwarz and Ramond Algebras of Logarithmic Superconformal Field Theory
We describe the general features of the Neveu-Schwarz and Ramond sectors of
logarithmic conformal field theories with N=1 supersymmetry. Three particular
systems are examined in some detail -- D-brane recoil, a superconformal
extension of the c=-2 model, and the supersymmetric SU(2)_2 WZW model.Comment: 65 pages AMSTeX; Typos corrected, references added and update
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