13,780 research outputs found
Graviton Loop Corrections to Vacuum Polarization in de Sitter in a General Covariant Gauge
We evaluate the one-graviton loop contribution to the vacuum polarization on
de Sitter background in a 1-parameter family of exact, de Sitter invariant
gauges. Our result is computed using dimensional regularization and fully
renormalized with BPHZ counterterms, which must include a noninvariant owing to
the time-ordered interactions. Because the graviton propagator engenders a
physical breaking of de Sitter invariance two structure functions are needed to
express the result. In addition to its relevance for the gauge issue this is
the first time a covariant gauge graviton propagator has been used to compute a
noncoincident loop. A number of identities are derived which should facilitate
further graviton loop computations.Comment: 61 pages, 1 figure, 11 tables, version 2 (63 pages) revised for
publication in CQ
One loop graviton corrections to dynamical photons in de Sitter
We employ a recent, general gauge computation of the one loop graviton
contribution to the vacuum polarization on de Sitter to solve for one loop
corrections to the photon mode function. The vacuum polarization takes the form
of a gauge independent, spin 2 contribution and a gauge dependent, spin 0
contribution. We show that the leading secular corrections derive entirely from
the spin 2 contribution.Comment: 41 pages, no figures, uses LaTeX2
Single Graviton Loop Contribution to the Self-Mass of a Massless, Conformally Coupled Scalar on de Sitter Background
We use a simplified formalism to re-compute the single graviton loop
contribution to the self-mass of a massless, conformally coupled scalar on de
Sitter background which was originally made by Boran, Kahya and Park [1-3]. Our
result resolves the problem with the flat space correspondence limit that was
pointed out by Fr\"ob [4]. We discuss how this computation will be used in a
long-term project to purge the linearized effective field equation of gauge
dependence.Comment: 26 pages, 1 figure, uses LaTeX 2e. Version 2 revised slightly for
publicatio
Duality Symmetry in Momentum Frame
Siegel's action is generalized to the D=2(p+1) (p even) dimensional
space-time. The investigation of self-duality of chiral p-forms is extended to
the momentum frame, using Siegel's action of chiral bosons in two space-time
dimensions and its generalization in higher dimensions as examples. The whole
procedure of investigation is realized in the momentum space which relates to
the configuration space through the Fourier transformation of fields. These
actions correspond to non-local Lagrangians in the momentum frame. The
self-duality of them with respect to dualization of chiral fields is uncovered.
The relationship between two self-dual tensors in momentum space, whose similar
form appears in configuration space, plays an important role in the
calculation, that is, its application realizes solving algebraically an
integral equation.Comment: 11 pages, no figures, to appear in Phys. Rev.
A Trouble with Ho\v{r}ava-Lifshitz Gravity
We study the structure of the phase space in Ho\v{r}ava-Lifshitz theory. With
the constraints derived from the action, the phase space is described by five
fields, thus there is a lack of canonical structure. The Poisson brackets of
the Hamiltonian density do not form a closed structure, resulting in many new
constraints. Taking these new constraints into account, it appears that there
is no degree of freedom left, or the phase space is reduced to one with an odd
number of fields.Comment: 12 pages, some discussions, comments and references added, JHEP styl
A blowout jet associated with one obvious extreme-ultraviolet wave and one complicated coronal mass ejection event
In this paper, we present a detailed analysis of a coronal blowout jet
eruption which was associated with an obvious extreme-ultraviolet (EUV) wave
and one complicated coronal mass ejection (CME) event based on the
multi-wavelength and multi-view-angle observations from {\sl Solar Dynamics
Observatory} and {\sl Solar Terrestrial Relations Observatory}. It is found
that the triggering of the blowout jet was due to the emergence and
cancellation of magnetic fluxes on the photosphere. During the rising stage of
the jet, the EUV wave appeared just ahead of the jet top, lasting about 4
minutes and at a speed of 458 - \speed{762}. In addition, obvious dark material
is observed along the EUV jet body, which confirms the observation of a
mini-filament eruption at the jet base in the chromosphere. Interestingly, two
distinct but overlapped CME structures can be observed in corona together with
the eruption of the blowout jet. One is in narrow jet-shape, while the other
one is in bubble-shape. The jet-shaped component was unambiguously related with
the outwardly running jet itself, while the bubble-like one might either be
produced due to the reconstruction of the high coronal fields or by the
internal reconnection during the mini-filament ejection according to the
double-CME blowout jet model firstly proposed by Shen et al. (2012b),
suggesting more observational evidence should be supplied to clear the current
ambiguity based on large samples of blowout jets in future studies.Comment: APJ, Accepted October 19, 201
Selective Jamming of LoRaWAN using Commodity Hardware
Long range, low power networks are rapidly gaining acceptance in the Internet
of Things (IoT) due to their ability to economically support long-range sensing
and control applications while providing multi-year battery life. LoRa is a key
example of this new class of network and is being deployed at large scale in
several countries worldwide. As these networks move out of the lab and into the
real world, they expose a large cyber-physical attack surface. Securing these
networks is therefore both critical and urgent. This paper highlights security
issues in LoRa and LoRaWAN that arise due to the choice of a robust but slow
modulation type in the protocol. We exploit these issues to develop a suite of
practical attacks based around selective jamming. These attacks are conducted
and evaluated using commodity hardware. The paper concludes by suggesting a
range of countermeasures that can be used to mitigate the attacks.Comment: Mobiquitous 2017, November 7-10, 2017, Melbourne, VIC, Australi
The parameters identification and validation for IGBT based on optimization algorithm
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