49,063 research outputs found
Sub-THz radiation mechanisms in solar flares
Observations in the sub-THz range of large solar flares have revealed a
mysterious spectral component increasing with frequency and hence distinct from
the microwave component commonly accepted to be produced by gyrosynchrotron
(GS) emission from accelerated electrons. Evidently, having a distinct sub-THz
component requires either a distinct emission mechanism (compared to the GS
one), or different properties of electrons and location, or both. We find,
however, that the list of possible emission mechanisms is incomplete. This
Letter proposes a more complete list of emission mechanisms, capable of
producing a sub-THz component, both well-known and new in this context and
calculates a representative set of their spectra produced by a) free-free
emission, b) gyrosynchrotron emission, c) synchrotron emission from
relativistic positrons/electrons, d) diffusive radiation, and e) Cherenkov
emission. We discuss the possible role of the mechanisms in forming the sub-THz
emission and emphasize their diagnostics potential for flares.Comment: Submitted to ApJL, 5 figures, minor revision to match resubmitted
versio
The geometry of the double gyroid wire network: quantum and classical
Quantum wire networks have recently become of great interest. Here we deal
with a novel nano material structure of a Double Gyroid wire network. We use
methods of commutative and non-commutative geometry to describe this wire
network. Its non--commutative geometry is closely related to non-commutative
3-tori as we discuss in detail.Comment: pdflatex 9 Figures. Minor changes, some typos and formulation
Re-gauging groupoid, symmetries and degeneracies for graph Hamiltonians and applications to the Gyroid wire network
We study a class of graph Hamiltonians given by a type of quiver representation to which we can associate (non)-commutative geometries. By selecting gauging data, these geometries are realized by matrices through an explicit construction or a Kan extension. We describe the changes in gauge via the action of a re-gauging groupoid. It acts via matrices that give rise to a noncommutative 2-cocycle and hence to a groupoid extension (gerbe). We furthermore show that automorphisms of the underlying graph of the quiver can be lifted to extended symmetry groups of re-gaugings. In the commutative case, we deduce that the extended symmetries act via a projective representation. This yields isotypical decompositions and super-selection rules. We apply these results to the primitive cubic, diamond, gyroid and honeycomb wire networks using representation theory for projective groups and show that all the degeneracies in the spectra are consequences of these enhanced symmetries. This includes the Dirac points of the G(yroid) and the honeycomb systems
Open/closed string topology and moduli space actions via open/closed Hochschild actions
In this paper we extend our correlation functions to the open/closed case.
This gives rise to actions of an open/closed version of the Sullivan PROP as
well as an action of the relevant moduli space. There are several unexpected
structures and conditions that arise in this extension which are forced upon us
by considering the open sector. For string topology type operations, one cannot
just consider graphs, but has to take punctures into account and one has to
restrict the underlying Frobenius algebras. In the moduli space, one first has
to pass to a smaller moduli space which is closed under open/closed duality and
then consider covers in order to account for the punctures
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