4,074 research outputs found
Lorentz violation from gamma-ray bursts
The constancy of light speed is a basic assumption in Einstein's special
relativity, and consequently the Lorentz invariance is a fundamental symmetry
of space-time in modern physics. However, it is speculated that the speed of
light becomes energy-dependent due to the Lorentz invariance violation~(LV) in
various new physics theories. We analyse the data of the energetic photons from
the gamma-ray bursts (GRBs) by the Fermi Gamma-Ray Space Telescope, and find
more events to support the energy dependence in the light speed with both
linear and quadratic form corrections. We provide two scenarios to understand
all the new-released Pass~8 data of bright GRBs by the Fermi-LAT Collaboration,
with predictions from such scenarios being testable by future detected GRBs.Comment: 7 latex pages, 2 figures, final version for journal publicatio
Circulant Arrays on Cyclic Subgroups of Finite Fields: Rank Analysis and Construction of Quasi-Cyclic LDPC Codes
This paper consists of three parts. The first part presents a large class of
new binary quasi-cyclic (QC)-LDPC codes with girth of at least 6 whose
parity-check matrices are constructed based on cyclic subgroups of finite
fields. Experimental results show that the codes constructed perform well over
the binary-input AWGN channel with iterative decoding using the sum-product
algorithm (SPA). The second part analyzes the ranks of the parity-check
matrices of codes constructed based on finite fields with characteristic of 2
and gives combinatorial expressions for these ranks. The third part identifies
a subclass of constructed QC-LDPC codes that have large minimum distances.
Decoding of codes in this subclass with the SPA converges very fast.Comment: 26 pages, 6 figures, submitted to IEEE Transaction on Communication
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