978 research outputs found
Homology of spaces of non-resultant polynomial systems in R^2 and C^2
The resultant veriety in the space of systems of homogeneous polynomials of
given degrees consists of such systems having non-trivial solutions. We
calculate the integer cohomology groups of all spaces of non-resultant systems
of polynomials , and also the rational cohomology groups of similar
systems in
Extreme TeV Blazars and Lower Limits on Intergalactic Magnetic Fields
The intergalactic magnetic field (IGMF) in cosmic voids can be indirectly
probed through its effect on electromagnetic cascades initiated by a source of
TeV gamma rays, such as blazars, a subclass of active galactic nuclei. Blazars
that are sufficiently luminous at TeV energies, "extreme TeV blazars", can
produce detectable levels of secondary radiation from inverse Compton
scattering of the electrons in the cascade, provided that the IGMF is not too
large. We reveiw recent work in the literature which utilizes this idea to
derive constraints on the IGMF for three TeV-detected blazars-1ES 0229+200, 1ES
1218+304, and RGB J0710+591, and we also investigate four other hard-spectrum
TeV blazars in the same framework. Through a recently developed detailed 3D
particle tracking Monte Carlo simulation code, incorporating all major effects
of QED and cosmological expansion, we research effects of major uncertainties
such as the spectral properties of the source, uncertainty in the intensity of
the UV - far IR extragalactic background light (EBL), under-sampled Very High
Energy (VHE; energy > 100 GeV) coverage, past history of gamma-ray emission,
source vs. observer geometry, and jet AGN Doppler factor. The implications of
these effects on the recently reported lower limits of the IGMF are thoroughly
examined to conclude that presently available data are compatible with a zero
IGMF hypothesis.Comment: 2012 Fermi Symposium proceedings - eConf C12102
Simplified numerical form of universal finite type invariant of Gauss words
In the present paper, we study the finite type invariants of Gauss words. In
the Polyak algebra techniques, we reduce the determination of the group
structure to transformation of a matrix into its Smith normal form and we give
the simplified form of a universal finite type invariant by means of the
isomorphism of this transformation. The advantage of this process is that we
can implement it as a computer program. We obtain the universal finite type
invariant of degree 4, 5, and 6 explicitly. Moreover, as an application, we
give the complete classification of Gauss words of rank 4 and the partial
classification of Gauss words of rank 5 where the distinction of only one pair
remains.Comment: 12 pages, 3 table
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