5,140 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
Thermal expansion of liquid Ti–6Al–4V measured by electrostatic levitation
The liquid density of Ti–6Al–4V was measured over a temperature range from 1661 to 1997 K that included undercooling by as much as 280 K. The sample was levitated in an electrostatic levitator and video imaging technique was used to capture the volume changes as a function of temperature. Over the temperature range the liquid density can be expressed by rholiq(T)=4123–0.254 (T–Tm) kg/m^3, where the melting temperature Tm is 1943 K. The corresponding volume expansion coefficient is alphaliq=6.05×10^–5 K^–1 near Tm
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.
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
Dilaton driven Hawking radiation in AdS black hole
A recent study shows that Hawking radiation of the massless scalar field does
not appear on the two-dimensional AdS black hole background. We study this
issue by investigating absorption and reflection coefficients under dilaton
coupling with the matter field. If the scalar field does not couple to the
dilaton, then it is fully absorbed into the black hole without any outgoing
mode. On the other hand, once it couples to the dilaton field, the outgoing
mode of the massless scalar field exists and the nontrivial Hawking radiation
is obtained. Finally, we comment on this dilaton dependence of Hawking
radiation in connection with a three-dimensional black hole.Comment: 13 pages, revtex, no figures, version to appear in Phys. Lett.
Absorption cross section and Hawking radiation in two-dimensional AdS black hole
We calculate the absorption coefficient of scalar field on the background of
the two-dimensional AdS black hole, which is of relevance to Hawking radiation.
For the massless scalar field, we find that there does not exist any massless
radiation.Comment: 6 pages, revtex, no figure
Quasinormal Modes and Choptuik Scaling in the Near Extremal Reissner-Nordstr{\"o} Black Hole
We study quasinormal modes of massless scalar and fermion fields in the near
extremal Reissner-Nordstr{\"o}m black hole, and relate them to Choptuik scaling
form following a recently proposed analytic approach. For both massless cases,
quasinormal modes are shown to be proportional to the black hole horizon and
the Hawking temperature, and the critical exponents are the same, although for
the fermionic case there are two possible discrete quasinormal modes. In
addition, the critical exponent of the massive boson is also equivalent to that
of the massless case. Finally, we discuss quasinormal modes and critical
exponents in the other models, and obtain some different critical exponents
between massless boson and massive one.Comment: 13 pages, Refs. and comments are added. To appear in Phys. Lett.
Duality of Quasilocal Gravitational Energy and Charges with Non-orthogonal Boundaries
We study the duality of quasilocal energy and charges with non-orthogonal
boundaries in the (2+1)-dimensional low-energy string theory. Quasilocal
quantities shown in the previous work and some new variables arisen from
considering the non-orthogonal boundaries as well are presented, and the boost
relations between those quantities are discussed. Moreover, we show that the
dual properties of quasilocal variables such as quasilocal energy density,
momentum densities, surface stress densities, dilaton pressure densities, and
Neuve-Schwarz(NS) charge density, are still valid in the moving observer's
frame.Comment: 19pages, 1figure, RevTe
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