664798
Stretched strings in noncommutative field theory
Motivated by recent discussions of IR-UV mixing in noncommutative field theories, we perform a detailed analysis of the nonplanar amplitudes of the bosonic open string in the presence of an external B field at the one-loop level. We carefully isolate, at the string theory level, the contribution which is responsible for the IR-UV behavior in the field theory limit. We show that it is a pure open string effect by deriving it from the factorization of the one-loop amplitude into the disk amplitudes of intermediate open string insertions. We suggest that it is natural to understand IR-UV mixing as the creation of intermediate ''stretched strings.'' (c) 2000 The American Physical Society.
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.}
119468101
Open String Star as a Continuous Moyal Product
We establish that the open string star product in the zero momentum sector can be described as a continuous tensor product of mutually commuting two dimensional Moyal star products. Let the continuous variable κ [0, ∞) parametrize the eigenvalues of the Neumann matrices; then the noncommutativity parameter is given by θ(κ) = 2tanh (πκ/4). For each κ, the Moyal coordinates are a linear combination of even position modes, and the Fourier transform of a linear combination of odd position modes. The commuting coordinate at κ = 0 is identified as the momentum carried by half the string. We discuss the relation to Bars' work, and attempt to write the string field action as a noncommutative field theory.
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.
119533356
SU(5) monopoles and the dual standard model
We find the spectrum of magnetic monopoles produced in the symmetry breaking SU(5){r_arrow}[SU(3){times}SU(2){times}U(1){prime}]/Z{sub 6} by constructing classical bound states of the fundamental monopoles. The spectrum of monopoles is found to correspond to the spectrum of one family of standard model fermions and, hence, is a starting point for constructing the dual standard model. At this level, however, there is an extra monopole state {emdash} the {open_quotes}diquark{close_quotes} monopole {emdash} with no corresponding standard model fermion. If the SU(3) factor now breaks down to Z{sub 3}, the monopoles with nontrivial SU(3) charge get confined by strings in SU(3) singlets. Another outcome of this symmetry breaking is that the diquark monopole becomes unstable (metastable) to fragmentation into fundamental monopoles and the one-one correspondence with the standard model fermions is restored. We discuss the fate of the monopoles if the [SU(2){times}U(1){prime}]/Z{sub 2} factor breaks down to U(1){sub Q} by a Higgs mechanism as in the electroweak model. Here we find that monopoles that are misaligned with the vacuum get connected by strings even though the electroweak symmetry breaking does not admit topological strings. We discuss the lowest order quantum corrections to the mass spectrum of monopoles. {copyright} {ital 1997} {ital The American Physical Society}
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.
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.
119217684
Quasi-normal modes of a massless scalar field around the 5D Ricci-flat black string
As one candidate of the higher dimensional black holes, the 5D Ricci-flat black string is considered in this paper. By means of a non-trivial potential Vn, the quasi-normal modes of a massless scalar field around this black string space are studied. By using the classical third-order WKB approximation, we carefully analyze the evolution of frequencies in two aspects, one is the induced cosmological constant Λ and the other is the quantum number n. The massless scalar field decays more slowly because of the existence of the fifth dimension and the induced cosmological constant. If an extra dimension has in fact existed near the black hole, the quasi-normal frequencies may have some indication of it.
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.
119204651
Gauged Kaluza-Klein AdS pseudo-supergravity
Abstract We obtain the pseudo-supergravity extension of the D -dimensional Kaluza–Klein theory, which is the circle reduction of pure gravity in D + 1 dimensions. The fermionic partners are pseudo-gravitino and pseudo-dilatino. The full Lagrangian is invariant under the pseudo-supersymmetric transformation, up to quadratic order in fermion fields. We find that the theory possesses a U ( 1 ) global symmetry that can be gauged so that all the fermions are charged under the Kaluza–Klein vector. The gauging process generates a scalar potential that has a maximum, leading to the AdS vacuum. Whist the highest dimension for gauged AdS supergravity is seven, our gauged AdS pseudo-supergravities can exist in arbitrary dimensions.
14992212
CORRESPONDENCE BETWEEN 5D RICCI-FLAT COSMOLOGICAL MODELS AND QUINTESSENCE DARK ENERGY MODELS
We study the accelerating expansion and the induced dark energy of the 5D Ricci-flat universe which is characterized by having a big bounce as opposed to a big bang. We show that the arbitrary function μ(t) contained in the 5D solutions can be rewritten in terms of the redshift z as a new arbitrary function f(z), and we find that there is a correspondence between this f(z) and the potential V(ϕ) of the 4D quintessence models. Using this correspondence, the arbitrary function f(z) and the 5D solution could be specified for a given form of the potential V(ϕ).