227 research outputs found
Genus Two Surface and Quarter BPS Dyons: The Contour Prescription
Following the suggestion of hep-th/0506249 and hep-th/0612011, we represent
quarter BPS dyons in N=4 supersymmetric string theories as string network
configuration and explore the role of genus two surfaces in determining the
spectrum of such dyons. Our analysis leads to the correct contour prescription
for integrating the partition function to determine the spectrum in different
domains of the moduli space separated by the walls of marginal stability.Comment: LaTeX file, 25 page
Lattice Induced Transparency in Metasurfaces
Lattice modes are intrinsic to the periodic structures and their occurrence
can be easily tuned and controlled by changing the lattice constant of the
structural array. Previous studies have revealed excitation of sharp absorption
resonances due to lattice mode coupling with the plasmonic resonances. Here, we
report the first experimental observation of a lattice induced transparency
(LIT) by coupling the first order lattice mode (FOLM) to the structural
resonance of a metamaterial resonator at terahertz frequencies. The observed
sharp transparency is a result of the destructive interference between the
bright mode and the FOLM mediated dark mode. As the FOLM is swept across the
metamaterial resonance, the transparency band undergoes large change in its
bandwidth and resonance position. Besides controlling the transparency
behaviour, LIT also shows a huge enhancement in the Q-factor and record high
group delay of 28 ps, which could be pivotal in ultrasensitive sensing and slow
light device applications.Comment: 5 figure
Dynamics of supertubes
We find the evolution of arbitrary excitations on 2-charge supertubes, by
mapping the supertube to a string carrying traveling waves. We argue that when
the coupling is increased from zero the energy of excitation leaks off to
infinity, and when the coupling is increased still further a new set of long
lived excitations emerge. We relate the excitations at small and large
couplings to excitations in two different phases in the dual CFT. We conjecture
a way to distinguish bound states from unbound states among 3-charge BPS
geometries; this would identify black hole microstates among the complete set
of BPS geometries.Comment: 50 pages, 3 figure
New insights on the behaviour of solar wind protons and alphas in the Stream Interaction Region in solar cycle 23 and 24
Although the enhancements in the alpha-proton ratio in the solar wind
(expressed as ) in the Interplanetary Coronal Mass
Ejections (ICMEs) have been studied in the past, enhancements at the
stream interface region received very little attention so far. In this letter,
by extensively analyzing the stream interaction region (SIR) events observed in
solar cycle 23 and 24, we show that the stream interface of alphas starts
separating out from that of protons from the minimum of solar cycle 23. The
population of alpha particles are enhanced compared to protons at higher angles
between bulk velocity and local magnetic field (henceforth, bulk velocity
angle) in the fast wind region of SIRs if the background solar wind is taken as
reference. The analysis of differential velocities between alphas and protons
also reveals that the faster alpha particles accumulate near the fast wind side
of the stream interface region leading to enhancement of . The
investigation brings out, for the first time, the salient changes in
in SIRs for the two solar cycles and highlight the importances of bulk velocity
angle and differential velocity in the fast wind region for the changes in
in SIRs
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