440 research outputs found
Floquet–Bloch solutions in a sawtooth photonic crystal
Band structure of a sawtooth photonic crystal for optical wave propagation along the axis of periodicity is investigated. Floquet-Bloch solutions are found and illustrated for the bandgaps, allowed bands, and bandedges of the crystal. Special attention is given to the cases where Floquet-Bloch solutions become periodic functions
Matrix Model Conjecture for Exact BS Periods and Nekrasov Functions
We give a concise summary of the impressive recent development unifying a
number of different fundamental subjects. The quiver Nekrasov functions
(generalized hypergeometric series) form a full basis for all conformal blocks
of the Virasoro algebra and are sufficient to provide the same for some
(special) conformal blocks of W-algebras. They can be described in terms of
Seiberg-Witten theory, with the SW differential given by the 1-point resolvent
in the DV phase of the quiver (discrete or conformal) matrix model
(\beta-ensemble), dS = ydz + O(\epsilon^2) = \sum_p \epsilon^{2p}
\rho_\beta^{(p|1)}(z), where \epsilon and \beta are related to the LNS
parameters \epsilon_1 and \epsilon_2. This provides explicit formulas for
conformal blocks in terms of analytically continued contour integrals and
resolves the old puzzle of the free-field description of generic conformal
blocks through the Dotsenko-Fateev integrals. Most important, this completes
the GKMMM description of SW theory in terms of integrability theory with the
help of exact BS integrals, and provides an extended manifestation of the basic
principle which states that the effective actions are the tau-functions of
integrable hierarchies.Comment: 14 page
Bipolar supercurrent in graphene
Graphene -a recently discovered one-atom-thick layer of graphite- constitutes
a new model system in condensed matter physics, because it is the first
material in which charge carriers behave as massless chiral relativistic
particles. The anomalous quantization of the Hall conductance, which is now
understood theoretically, is one of the experimental signatures of the peculiar
transport properties of relativistic electrons in graphene. Other unusual
phenomena, like the finite conductivity of order 4e^2/h at the charge
neutrality (or Dirac) point, have come as a surprise and remain to be
explained. Here, we study the Josephson effect in graphene. Our experiments
rely on mesoscopic superconducting junctions consisting of a graphene layer
contacted by two closely spaced superconducting electrodes, where the charge
density can be controlled by means of a gate electrode. We observe a
supercurrent that, depending on the gate voltage, is carried by either
electrons in the conduction band or by holes in the valence band. More
importantly, we find that not only the normal state conductance of graphene is
finite, but also a finite supercurrent can flow at zero charge density. Our
observations shed light on the special role of time reversal symmetry in
graphene and constitute the first demonstration of phase coherent electronic
transport at the Dirac point.Comment: Under review, 12 pages, 4 Figs., suppl. info (v2 identical, resolved
file problems
The Overall Coefficient of the Two-loop Superstring Amplitude Using Pure Spinors
Using the results recently obtained for computing integrals over
(non-minimal) pure spinor superspace, we compute the coefficient of the
massless two-loop four-point amplitude from first principles. Contrasting with
the mathematical difficulties in the RNS formalism where unknown normalizations
of chiral determinant formulae force the two-loop coefficient to be determined
only indirectly through factorization, the computation in the pure spinor
formalism can be smoothly carried out.Comment: 29 pages, harvmac TeX. v2: add reference
The matrix model version of AGT conjecture and CIV-DV prepotential
Recently exact formulas were provided for partition function of conformal
(multi-Penner) beta-ensemble in the Dijkgraaf-Vafa phase, which, if interpreted
as Dotsenko-Fateev correlator of screenings and analytically continued in the
number of screening insertions, represents generic Virasoro conformal blocks.
Actually these formulas describe the lowest terms of the q_a-expansion, where
q_a parameterize the shape of the Penner potential, and are exact in the
filling numbers N_a. At the same time, the older theory of CIV-DV prepotential,
straightforwardly extended to arbitrary beta and to non-polynomial potentials,
provides an alternative expansion: in powers of N_a and exact in q_a. We check
that the two expansions coincide in the overlapping region, i.e. for the lowest
terms of expansions in both q_a and N_a. This coincidence is somewhat
non-trivial, since the two methods use different integration contours:
integrals in one case are of the B-function (Euler-Selberg) type, while in the
other case they are Gaussian integrals.Comment: 27 pages, 1 figur
Non-Perturbative Topological Strings And Conformal Blocks
We give a non-perturbative completion of a class of closed topological string
theories in terms of building blocks of dual open strings. In the specific case
where the open string is given by a matrix model these blocks correspond to a
choice of integration contour. We then apply this definition to the AGT setup
where the dual matrix model has logarithmic potential and is conjecturally
equivalent to Liouville conformal field theory. By studying the natural
contours of these matrix integrals and their monodromy properties, we propose a
precise map between topological string blocks and Liouville conformal blocks.
Remarkably, this description makes use of the light-cone diagrams of closed
string field theory, where the critical points of the matrix potential
correspond to string interaction points.Comment: 36 page
Classical conformal blocks from TBA for the elliptic Calogero-Moser system
The so-called Poghossian identities connecting the toric and spherical
blocks, the AGT relation on the torus and the Nekrasov-Shatashvili formula for
the elliptic Calogero-Moser Yang's (eCMY) functional are used to derive certain
expressions for the classical 4-point block on the sphere. The main motivation
for this line of research is the longstanding open problem of uniformization of
the 4-punctured Riemann sphere, where the 4-point classical block plays a
crucial role. It is found that the obtained representation for certain 4-point
classical blocks implies the relation between the accessory parameter of the
Fuchsian uniformization of the 4-punctured sphere and the eCMY functional.
Additionally, a relation between the 4-point classical block and the ,
twisted superpotential is found and further used to re-derive the
instanton sector of the Seiberg-Witten prepotential of the , supersymmetric gauge theory from the classical block.Comment: 25 pages, no figures, latex+JHEP3, published versio
Elevated temperature lasing from injection microdisk lasers on silicon
The combination of high operation temperatures and small diode lasers directly grown on silicon substrates is essential for their application in future photonic integrated circuits. In this letter, results are presented for quantum dot III–V-on-Si microdisk diode lasers tested at elevated temperatures. To the best of our knowledge, we have demonstrated the first uncooled microlasers with diameter of 30 µm capable of operating in the continuous wave regime at 60 °C. In the lasing regime, the emission spectra contain one very intense line with a full-width at half-maximum of 30 pm; the side mode suppression ratio reaches 18 dB. Because of self-heating, the actual temperature of the active region is close to 100 °C. Under pulsed excitation, the maximal lasing temperature is 110 °C
Azimuthal anisotropy and correlations at large transverse momenta in and Au+Au collisions at = 200 GeV
Results on high transverse momentum charged particle emission with respect to
the reaction plane are presented for Au+Au collisions at =
200 GeV. Two- and four-particle correlations results are presented as well as a
comparison of azimuthal correlations in Au+Au collisions to those in at
the same energy. Elliptic anisotropy, , is found to reach its maximum at
GeV/c, then decrease slowly and remain significant up to
-- 10 GeV/c. Stronger suppression is found in the back-to-back
high- particle correlations for particles emitted out-of-plane compared to
those emitted in-plane. The centrality dependence of at intermediate
is compared to simple models based on jet quenching.Comment: 4 figures. Published version as PRL 93, 252301 (2004
Modeling electromagnetic form factors of light and heavy pseudoscalar mesons
The electromagnetic form factors of light and heavy pseudoscalar mesons are
calculated within two covariant constituent-quark models, a light-front and a
dispersion relation approach. We investigate the details and physical origins
of the model dependence of various hadronic observables: the weak decay
constant, the charge radius and the elastic electromagnetic form factor.Comment: 6 pages, 4 figures, use revtex4. Figure 2 and references are
corrected. Acknoledgments are adde
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