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 AdS2_2 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 AdS2_2 black hole

A recent study shows that Hawking radiation of the massless scalar field does not appear on the two-dimensional AdS$_2$ 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