11,995 research outputs found
Noncommutative open strings from Dirac quantization
We study Dirac commutators of canonical variables on D-branes with a constant
Neveu-Schwarz 2-form field by using the Dirac constraint quantization method,
and point out some subtleties appearing in previous works in analyzing
constraint structure of the brane system. Overcoming some ad hoc procedures, we
obtain desirable noncommutative coordinates exactly compatible with the result
of the conformal field theory in recent literatures. Furthermore, we find
interesting commutator relations of other canonical variables.Comment: 13 pages, revtex, Expressions are change
Massless vs. Massive Hawking Radiation in AdS Spacetime
We study massless and massive Hawking radiations on a two-dimensional AdS
spacetime. For the massless case, the quantum stress-energy tensor of a
massless scalar field on the AdS background is calculated, and the expected
null radiation is obtained. However, for the massive case, the scattering
analysis is performed in order to calculate the absorption and reflection
coefficients which are related to statistical Hawking temperature. On the
contrary to the massless case, we obtain a nonvanishing massive radiation.Comment: 13 pages, revtex, to appear in Phys. Lett.
Reduced-complexity transmit-beamforming codebook search algorithm
A two-stage reduced-complexity index search algorithm is proposed for finding the best vector in the codebook of quantised equal gain transmission based multiple-input multiple-output arrangements. When the number of transmit antennas is more than three, the normalised complexity is halved while maintaining the same symbol error rate as the benchmark
Decay Rate and Low-Energy Near-Horizon Dynamics of Acoustic Black Holes
We study the low-energy dynamics of an acoustic black hole near the sonic
horizon. For the experimental test of black hole evaporation in the laboratory,
the decay rate (greybody factor) of the acoustic black hole (sonic hole) can be
calculated by the usual low-energy perturbation method. As a consequence, we
obtain the decay rate of the sonic horizon from the absorption and the
reflection coefficients. Moreover, we show that the thermal emission from the
sonic horizon is only proportional to a control parameter which describes the
velocity of the fluid.Comment: 13pages, 3figures, RevTeX3, some minors corrected. version to appear
in PL
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