163 research outputs found
Open-closed string correspondence: D-brane decay in curved space
This paper analyzes the effect of curved closed string backgrounds on the
stability of D-branes within boundary string field theory. We identify the
non-local open string background that implements shifts in the closed string
background and analyze the tachyonic sector off-shell. The renormalization
group flow reveals some characteristic properties, which are expected for a
curved background, like the absence of a stable space-filling brane. In
3-dimensions we describe tachyon condensation processes to lower-dimensional
branes, including a curved 2-dimensional brane. We argue that this 2-brane is
perturbatively stable. This is in agreement with the known maximally symmetric
WZW-branes and provides further support to the bulk-boundary factorization
approach to open-closed string correspondence.Comment: 23 pages, harvma
Quantitative differentiation of coal, char and soil organic matter in an Australian coal minesoil
Sending femtosecond pulses in circles: highly non-paraxial accelerating beams
We use caustic beam shaping on 100 fs pulses to experimentally generate
non-paraxial accelerating beams along a 60 degree circular arc, moving
laterally by 14 \mum over a 28 \mum propagation length. This is the highest
degree of transverse acceleration reported to our knowledge. Using diffraction
integral theory and numerical beam propagation simulations, we show that
circular acceleration trajectories represent a unique class of non-paraxial
diffraction-free beam profile which also preserves the femtosecond temporal
structure in the vicinity of the caustic
Five-Brane Superpotentials, Blow-Up Geometries and SU(3) Structure Manifolds
We investigate the dynamics of space-time filling five-branes wrapped on
curves in heterotic and orientifold Calabi-Yau compactifications. We first
study the leading N=1 scalar potential on the infinite deformation space of the
brane-curve around a supersymmetric configuration. The higher order potential
is also determined by a brane superpotential which we compute for a subset of
light deformations. We argue that these deformations map to new complex
structure deformations of a non-Calabi-Yau manifold which is obtained by
blowing up the brane-curve into a four-cycle and by replacing the brane by
background fluxes. This translates the original brane-bulk system into a
unifying geometrical formulation. Using this blow-up geometry we compute the
complete set of open-closed Picard-Fuchs differential equations and identify
the brane superpotential at special points in the field space for five-branes
in toric Calabi-Yau hypersurfaces. This has an interpretation in open mirror
symmetry and enables us to list compact disk instanton invariants. As a first
step towards promoting the blow-up geometry to a supersymmetric heterotic
background we propose a non-Kaehler SU(3) structure and an identification of
the three-form flux.Comment: 95 pages, 4 figures; v2: Minor corrections, references update
High average and peak power femtosecond large-pitch photonic-crystal-fiber laser
We report on the generation of high-average-power and high-peak-power ultrashort pulses from a mode-locked fiber laser operating in the all-normal-dispersion regime. As gain medium, a large-mode-area ytterbium-doped large-pitch photonic-crystal fiber is used. The self-starting fiber laser delivers 27 W of average power at 50:57 MHz repetition rate, resulting in 534 nJ of pulse energy. The laser produces positively chirped 2 ps output pulses, which are compressed down to sub-100 fs, leading to pulse peak powers as high as 3:2 MW. © 2011 Optical Society of America
Remarks on quiver gauge theories from open topological string theory
We study effective quiver gauge theories arising from a stack of D3-branes on certain Calabi-Yau singularities. Our point of view is a first principle approach via open topological string theory. This means that we construct the natural A-infinity-structure of open string amplitudes in the associated D-brane category. Then we show that it precisely reproduces the results of the method of brane tilings, without having to resort to any effective field theory computations. In particular, we prove a general and simple formula for effective superpotentials
Open mirror symmetry for Pfaffian Calabi-Yau 3-folds
We investigate the open mirror symmetry of certain non-complete intersection
Calabi- Yau 3-folds, so called pfaffian Calabi-Yau. We perform the prediction
of the number of disk invariants of several examples by using the direct
integration method proposed recently and the open mirror symmetry. We treat
several pfaffian Calabi-Yau 3-folds in and branes with two
discrete vacua. Some models have the two special points in its moduli space,
around both of which we can consider different A-model mirror partners. We
compute disc invariants for both cases. This study is the first application of
the open mirror symmetry to the compact non-complete intersections in toric
variety.Comment: 64 pages; v2: typos corrected, minor changes, references added; v3:
published version, minor corrections and improvement
Compact ultrafast oscillators and high performance ultrafast amplifiers based on ytterbium-doped fibers
This chapter reviews the fundamentals and achievements of ultrashort pulse generation and amplification in ytterbium-doped fibers. Compact and ultrastable passively mode-locked fiber oscillators represent an ideal seed source for high performance femtosecond fiber amplification systems, which have been scaled towards kW-level average power and pulse energies well above the mJ-level. These laser systems will have significant impact in numerous scientific and industrial applications. © Springer International Publishing Switzerland 2016
The Physics of the Colloidal Glass Transition
As one increases the concentration of a colloidal suspension, the system
exhibits a dramatic increase in viscosity. Structurally, the system resembles a
liquid, yet motions within the suspension are slow enough that it can be
considered essentially frozen. This kinetic arrest is the colloidal glass
transition. For several decades, colloids have served as a valuable model
system for understanding the glass transition in molecular systems. The spatial
and temporal scales involved allow these systems to be studied by a wide
variety of experimental techniques. The focus of this review is the current
state of understanding of the colloidal glass transition. A brief introduction
is given to important experimental techniques used to study the glass
transition in colloids. We describe features of colloidal systems near and in
glassy states, including tremendous increases in viscosity and relaxation
times, dynamical heterogeneity, and ageing, among others. We also compare and
contrast the glass transition in colloids to that in molecular liquids. Other
glassy systems are briefly discussed, as well as recently developed synthesis
techniques that will keep these systems rich with interesting physics for years
to come.Comment: 56 pages, 18 figures, Revie
- …