58,092 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
Second quantized Frobenius algebras
We show that given a Frobenius algebra there is a unique notion of its second
quantization, which is the sum over all symmetric group quotients of n--th
tensor powers, where the quotients are given by symmetric group twisted
Frobenius algebras. To this end, we consider the setting of Frobenius algebras
given by functors from geometric categories whose objects are endowed with
geometric group actions and prove structural results, which in turn yield a
constructive realization in the case of n--th tensor powers and the natural
permutation action. We also show that naturally graded symmetric group twisted
Frobenius algebras have a unique algebra structure already determined by their
underlying additive data together with a choice of super--grading. Furthermore
we discuss several notions of discrete torsion andshow that indeed a
non--trivial discrete torsion leads to a non--trivial super structure on the
second quantization.Comment: 39p. Latex. New version fixes sign mistake and includes the full
description of discrete torsio
- …