8,479 research outputs found
Oscillating Strings and Non-Abelian T-dual Klebanov-Witten Background
We study oscillating string solutions in the Klebanov-Witten and its
non-Abelian T-dual background dualised along an SU(2) isometry. We find the
string energy as the function of oscillation number and angular momentum. We
show that for a particular set of T-dual co-ordinates both the background have
equal string states. We also study the string states where the strings are
expanding and contracting in the T-dual co-ordinate direction. We expect the
presence of the superconformal field theory dual operators whose anomalous
dimensions depend on T-dual co-ordinate.Comment: 13 pages, references added, to appear in PR
Spiky strings on AdS3 x S3 with NS-NS flux
We study rigidly rotating strings in the background of AdS3 x S3 with
Neveu-Schwarz (NS) fluxes. We find two interesting limiting cases corresponding
to the known giant magnon and the new single spike solution of strings in the
above background and write down the dispersion relations among various
conserved charges. We use proper regularization to find the correct relations
among them. We further study the circular and infinite spiky strings on AdS and
study their properties.Comment: 19 pages, added clarification, typos fixe
Highly Excited Core Resonances in Photoionization of Fe XVII : Implications for Plasma Opacities
A comprehensive study of high-accuracy photoionization cross sections is
carried out using the relativistic Breit-Pauli R-matrix (BPRM) method for (hnu
+ Fe XVII --> Fe XVIII + e). Owing to its importance in high-temperature
plasmas the calculations cover a large energy range, particularly the myriad
photoexciation-of-core (PEC) resonances including the n = 3 levels not
heretofore considered. The calculations employ a close coupling wave function
expansion of 60 levels of the core ion Fe XVIII ranging over a wide energy
range of nearly 900 eV between the n = 2 and n = 3 levels. Strong coupling
effects due to dipole transition arrays 2p^5 --> 2p^4 (3s,3d) manifest
themselves as large PEC resonances throughout this range, and enhance the
effective photoionization cross sections orders of magnitude above the
background. Comparisons with the erstwhile Opacity Project (OP) and other
previous calculations shows that the currently available cross sections
considerably underestimate the bound-free cross sections. A
level-identification scheme is used for spectroscopic designation of the 454
bound fine structure levels of Fe XVII. Level-specific photoionization cross
sections are computed for all levels. In addition, partial cross sections for
leaving the core ion Fe XVII in the ground state are also obtained. These
results should be relevant to modeling of astrophysical and laboratory plasma
sources requiring (i) photoionization rates, (ii) extensive
non-local-thermodynamic-equilibrium models, (iii) total unified electron-ion
recombination rates including radiative and dielectronic recombination, and
(iv) plasma opacities. We particularly examine PEC and non-PEC resonance
strengths and emphasize their expanded role to incorporate inner-shell
excitations for improved opacities, as shown by the computed monochromatic
opacity of Fe XVII.Comment: 12 pages, 5 figures, Physical Review A (in press
Geometric phase for a dimerized disordered continuum: Topological shot noise
Geometric phase shift associated with an electron propagating through a
dimerized-disordered continuum is shown to be 0, or (modulo 2),
according as the associated circuit traversed in the two-dimensional parameter
space excludes, or encircles a certain singularity. This phase-shift is a
topological invariant. Its discontinuous dependence on the electron energy and
disorder implies a statistical spectral and conductance fluctuation in a
corresponding mesoscopic system. Inasmuch as the fluctuation derives from the
discreteness of the phase shift, it may aptly be called a topological
shot-noise.Comment: 10 pages(LATEX) + 1 figure, (revised version). Will appear in
Europhys. Let
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