82,503 research outputs found
Symplectic formulation of the type IIA nongeometric scalar potential
We study the four-dimensional (4D) scalar potential arising from a
generalized type IIA flux superpotential including the (non-)geometric fluxes.
First, we show that using a set of peculiar flux combinations, the 4D scalar
potential can be formulated into a very compact form. This is what we call as
the `symplectic formulation' from which one could easily anticipate the
ten-dimensional origin of the effective scalar potential. We support our
formulation through an alternate derivation of the scalar potential via
considering the Double Field Theory (DFT) reduction on a generic Calabi Yau
orientifold. In addition, we also exemplify the insights of our formulation
with explicit computations for two concrete toroidal examples using
orientifolds of the complex threefolds and .Comment: v4: 33 pages, typos fixed in eqn. (4.22) and (4.23), and some
cosmetic changes in the title; version to appear in PR
Broadband Epsilon-Near-Zero Metamaterials with Step-Like Metal-Dielectric Multilayer Structures
The concept of the broadband epsilon-near-zero meta-atom consisting of
layered stacks with specified metallic filling ratio and thickness is proposed
based on the Bergman spectral representation of the effective permittivity. The
step-like metal-dielectric multilayer structures are designed to achieve
realistic broadband epsilon-near-zero meta-atoms in optical frequency range.
These meta-atoms can be integrated as building blocks for unconventional
optical components with exotic electromagnetic properties over a wide frequency
range, such as the demonstrated broadband directional emission and phase front
shaping.Comment: 18 pages, 7 figure
Realizing broadband electromagnetic transparency with a graded-permittivity sphere
Broadband electromagnetic transparency phenomenon is realized with a
well-designed graded-permittivity sphere, which has an extremely low scattering
cross section over a wide frequency range, based on the generalized Mie
scattering theory and numerical simulation in full-wave condition. The dynamic
polarization cancellation is revealed by studying the variation of the
polarization with respect to the frequency. Furthermore, a properly-designed
multi-shell sphere is also proposed and examined in order to reduce the
rigorous conditions for realizing the broadband transparency in experiments.Comment: 15 pages, 4 figure
On Missing Bianchi Identities in Cohomology Formulation
In this article, we perform a deep analysis of the Bianchi identities in the
two known formulations developed for the four-dimensional effective type IIA
supergravity theory with (non-)geometric fluxes. In what we call the `first
formulation', fluxes are expressed in the real six-dimensional indices while in
the `second formulation', fluxes are written in the cohomology form. We find
that the set of flux constraints arising from these two known formulations are
not equivalent, and there are missing identities in the cohomology version
which need to be supplemented to match with the first formulation. By analyzing
two explicit examples, we conjecture a model independent form for (the most of)
the missing identities. These identities have been mostly overlooked in the
previous attempts of studying moduli stabilization, particularly for the models
developed in the beyond toroidal frameworks, where they could play some
important role.Comment: v2: 24 pages + 3 appendices, minor improvements and references added.
arXiv admin note: text overlap with arXiv:1712.07310; v3: minor updates,
published versio
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