14591909
Closed strings from decaying D-branes
We compute the emission of closed string radiation from homogeneous rolling tachyons. For an unstable decaying Dp-brane the radiated energy is infinite to leading order for p ≤ 2 and finite for 2$>p > 2. The closed string state produced by a decaying brane is closely related to the state produced by D-instantons at a critical Euclidean distance from t = 0. In the case of a D0 brane one can cutoff this divergence so that we get a finite energy final state which would be the state that the brane decays into.
7373383
Supergravity couplings of noncommutative D-branes
Abstract We discuss the supergravity couplings of noncommutative D-branes by considering the disk amplitudes with one closed string insertion. The result confirms a recent proposal for the general form of the noncommutative Yang–Mills operators coupling to the massless closed string modes. The construction involves smearing Yang–Mills field variables along an open Wilson line. For multiple D-branes interacting with background supergravity fields, this prescription reduces, in the B =0 limit, to the “symmetrized trace” prescription, and the supergravity fields are seen to be functionals of the nonabelian scalar fields on the branes.
14851960
UV finite brane decay
The decay of an unstable D-brane via closed string emission and open string pair production is considered in subcritical string theory with a spacelike linear dilaton. The decay rate is given by the imaginary part of the annulus, which has ambiguities corresponding to the choices of incoming closed and open string vacua. An exact expression for the full annulus diagram is computed with a natural choice of incoming vacua. It is found that the ultraviolet divergences present in critical string theory in both of these processes are absent for any nonzero spacelike dilaton. Implications for the vexing issue of the tachyon dust are discussed.
17322710
Quantum hair, instantons, and black hole thermodynamics: some new results
Abstract We present results obtained by a consideration of the non-classical energy-momentum tensor associated with Euclidean instantons outside the event horizon of black holes. We demonstrate here how this allows for an analytic estimate to be made of the effect of discrete quantum hair on the temperature of the black hole, in which the role of violations of the weak energy condition associated with instantons is made explicit, and in which the previous results of Coleman, Preskill, and Wilczek are extended. Last, we demonstrate how the existence of a non-classical electric field outside the event horizon of black holes, uncovered by these authors, can be identified with a well-known effect in the Abelian Higgs mode] in two dimensions. In this case, there is a one-to-one connection between the discrete charge of a black hole and a topological phase in two dimensions.
16866051
Dirty Black Holes and Hairy Black Holes.
An approach based on considerations of the nonclassical energy momentum tensor outside the event horizon of a black hole provides additional physical insight into the nature of discrete quantum hair on black holes and its effect on black hole temperature. Our analysis both extends previous work based on the Euclidean action techniques and corrects an omission in that work. We also raise several issues related to the effects of instantons on black hole thermodynamics and the relation between these effects and results in two dimensional quantum field theory. {copyright} {ital 1996 The American Physical Society.}
15969913
Perturbed Electroweak Strings and Fermion Zero Modes
Abstract The effect of perturbations of electroweak strings on quark zero modes is studied in 2+1 and 3+1 dimensions. As first discovered by Naculich, it is found that the bosonic perturbations that destabilize the string give a mass to the zero modes and also lift their degeneracy. The effect of the zero modes on the stability of the string is discussed qualitatively and, based on general arguments, we conjecture that the fermionic vacuum instability found by Naculich should lead to a distortion of the bosonic string but not be responsible for decay.
20448840
Statefinder parameters for interacting phantom energy with dark matter
In this paper we apply the statefinder parameters to the interacting phantom energy with dark matter. There are two kinds of scaling solution in this model. It is found that the evolving trajectories of these two scaling solutions in the statefinder parameter plane are quite different, and that they are also different from the statefinder diagnostic of other dark energy models.
14287684
Correspondence Between DGP Brane Cosmology and $5D$ Ricci-flat Cosmology
We discuss the correspondence between the DGP brane cosmology and 5D Ricci-flat cosmology by letting their metrics equal each other. By this correspondence, a specific geometrical property of the arbitrary integral constant I in DGP metric is given and it is related to the curvature of 5D bulk. At the same time, the relation of arbitrary functions μ and ν in a class of Ricci-flat solutions is obtained from DGP brane metric.
11595061
DARK ENERGY IN GLOBAL BRANE UNIVERSE
We discuss the exact solutions of brane universes and the results indicate that the Friedmann equations on the branes are modified with a new density term. Then, we assume the new term as the density of dark energy. Using Wetterich's parametrization equation of state (EOS) of dark energy, we obtain that the new term varies with the redshift z. Finally, the evolutions of the mass density parameter Ω2, dark energy density parameter Ωx and deceleration parameter q2 are studied.
119247810
Killing spinors for the bosonic string and Kaluza–Klein theory with scalar potentials
The paper consists mainly of two parts. In the first part, we obtain well-defined Killing spinor equations for the low-energy effective action of the bosonic string with the conformal anomaly term. We show that the conformal anomaly term is the only scalar potential that one can add into the action that is consistent with the Killing spinor equations. In the second part, we demonstrate that Kaluza–Klein theory can be gauged so that the Killing spinors are charged under the Kaluza–Klein vector. This gauging process generates a scalar potential with a maximum that gives rise to an AdS spacetime. We also construct solutions of these theories.
118482632
The Numerical Solution of Scalar Field for Nariai Case in 5D Ricci-flat SdS Black String Space with Polynomial Approximation
As one exact candidate of the higher dimensional black hole, the 5D Ricci-flat Schwarzschild-de Sitter black string space presents something interesting. In this paper, we give a numerical solution to the real scalar field around the Nariai black hole by the polynomial approximation. Unlike the previous tangent approximation, this fitting function makes a perfect match in the leading intermediate region and gives a good description near both the event and the cosmological horizons. We can read from our results that the wave is close to a harmonic one with the tortoise coordinate. Furthermore, with the actual radial coordinate the waves pile up almost equally near the both horizons.