Axionic Wormholes : More on their Classical and Quantum Aspects

As a system which is known to admit classical wormhole instanton solutions, Einstein-Kalb-Ramond (KR) antisymmetric tensor theory is revisited. As an untouched issue, the existence of fermionic zero modes in the background of classical axionic wormhole spacetime and its physical implications is addressed. In particular, in the context of a minisuperspace quantum cosmology model based on this Einstein-KR antisymmetric tensor theory, ``quantum wormhole'', defined as a state represented by a solution to the Wheeler-DeWitt equation satisfying an appropriate wormhole boundary condition, is discussed. An exact, analytic wave function for quantum wormholes is actually found. Finally, it is proposed that the minisuperspace model based on this theory in the presence of the cosmological constant may serve as an interesting simple system displaying an overall picture of entire universe's history from the deep quantum domain all the way to the classical domain.Comment: 41 pages, includes 6-figures, Revte

Classical and Quantum Anisotropic Wormholes in Pure General Relativity

In the homogeneous and isotropic Friedmann-Robertson-Walker minisuperspace model, it is known that there are no Euclidean wormhole solutions in the pure gravity system. Here it is demonstrated explicitly that in Taub cosmology, which is one of the simplest anisotropic cosmology models, wormhole solutions do exist in pure general relativity in both classical and quantum contexts.Comment: 13 pages, Revte

Supergravity Approach to Tachyon Potential in Brane-Antibrane Systems

Using an exact supergravity solution representing the Dp-\bar{Dp} system, it is demonstrated that one can construct a supergravity analogue of the tachyon potential. Remarkably, the (regularized) minimum value of the potential turns out to be V(T_{0})=-2m with m denoting the ADM mass of a single Dp-brane. This result, in a sense, appears to confirm that Sen's conjecture for the tachyon condensation on unstable D-branes is indeed correct although the analysis used here is semi-classical in nature and hence should be taken with some care. Also shown is the fact that the tachyon mass squared m^2_{T} (which has started out as being negative) can actually become positive definite and large as the tachyon rolls down toward the minimum of its potential. It indeed signals the possibility of successful condensation of the tachyon since it shows that near the minimum of its potential, tachyon can become heavy enough to disappear from the massless spectrum. Some cosmological implications of this tachyon potential in the context of ``rolling tachyons'' is also discussed.Comment: 26 pages, 2 eps figures, Corrected reference, To appear in JHE

Toward a Complete Analysis of the Global Structure of Kerr-Newman Spacetime

An attempt is made to supplement Carter's partial investigation of the global structure of Kerr-Newman spacetime on the symmetry axis. Namely, the global structure of \theta = const. timelike submanifolds of Kerr-Newman metric starting from the symmetry axis all the way down to the equatorial plane are studied by introducing a new time coordinate slightly different from the usual Boyer-Lindquist time coordinate. It turns out that the maximal anaytic extension of \theta = \theta_0 (0 \leq \theta_0 < \pi/2) submanifolds is the same as that of the symmetry axis first studied by Carter whereas \theta = \pi/2 equatorial plane has the topology identical to that of the Reissner-Nordstrom spacetime. General applicability of this method to Kerr-Newman-type black hole solutions in other gravity theories is discussed as well.Comment: 18 pages, Revte

Thermodynamics of Black Holes in Brans-Dicke Gravity

It has recently been argued that non-trivial Brans-Dicke black hole solutions different from the usual Schwarzschild solution could exist. We attemt here to ``censor'' these non-trivial Brans-Dicke black hole solutions by examining their thermodynamic properties. Quantities like Hawking temperature and entropy of the black holes are computed. Analysis of the behaviors of these thermodynamic quantities appears to show that even in Brans-Dicke gravity, the usual Schwarzschild spacetime turns out to be the only physically relevant uncharged static black hole solution.Comment: 14 pages, Revtex (appeared in a proceedings in Nuovo Cimento (1996)

Spinning closed superstring: as Nature's building block

Ever since its birth, up until its present development, the major role of string theory involves being the best candidate for the theory of quantum gravity and other species of interactions. In the present work, we would like to accomplish this goal by minimally extending its content while greatly simplifying its structure. To be more specific, by endowing the closed superstring with its spin, we successfully achieve this goal. This issue has been addressed in the first part of this work, entitled, "mission 1 of the work". In addition, we would like to make further developments on the selection of compactification manifolds that brings the string theory from the critical 10 dimensions down to four cosmology dimensions. Indeed, this issue has not been fully seriously and extensively explored in the literature. In the present work, therefore, we want to bring serious attention to this missing but non-trivial issue. This issue has been addressed in the second part of this work, entitled, "mission 2 of the work".Comment: 9 pages, 8 figure

Open string tachyon is the stringy inflaton

Regarding the current status of the superstring theory, despite its fully developed contents of all interactions in nature, it is no doubt that unfortunately it lacks a well established early universe cosmology content, that is, the inflationary universe. In the present work, we would like to address precisely this issue. To be more concrete, we would like to demonstrate that remarkably it is the well established open string tachyon condensation which is essentially equivalent to the stringy inflation that has been missing and hence long-seeking by nearly the entire string community.Comment: 20 pages, 1 figure. arXiv admin note: text overlap with arXiv:hep-ph/0106153 by other author

Removal of Closed Timelike Curves in Kerr-Newman Spacetime

A simple yet systematic new algorithm to investigate the global structure of Kerr-Newman spacetime is suggested. Namely, the global structure of \theta=const. timelike submanifolds of Kerr-Newman metric are studied by introducing a new time coordinate slightly different from the usual Boyer-Lindquist time coordinate. In addition, it is demonstrated that the possible causality violation thus far regarded to occur near the ring singularity via the development of closed timelike curves there is not really an unavoidable pathology which has plagued the Kerr-Newman solution but simply a gauge (coordinate) artifact as it disappears upon transforming from Boyer-Lindquist to the new time coordinate. This last point appears to lend support to the fact that, indeed, the Kerr-Newman spacetime is a legitimate solution to represent the interior as well as the exterior regions of a rotating, charged black hole spacetime.Comment: 14 pages, Revtex, Typos correcte

Quantum Brans-Dicke Gravity in Euclidean Path Integral Formulation

The conformal structure of Brans-Dicke gravity action is carefully studied. It is discussed that Brans-Dicke gravity action has definitely no conformal invariance. It is shown, however, that this lack of conformal invariance enables us to demonstrate that Brans-Dicke theory appears to have a better short-distance behavior than Einstein gravity as far as Euclidean path integral formulation for quantum gravity is concerned.Comment: 11 pages, Revte

Monopole Black Hole in Stringy gravity

The possible transition of large mass magnetic monopole solutions to monopole black hole solutions in Yang-Mills-Higgs theory with spontaneous symmetry breaking (SSB) coupled to the low energy effective theory of superstring with only dilatonic sector is studied. Our main motivation is to explore the effects of the dilaton field on the monopole black hole solutions. Working in the Einstein conformal gauge, it is explicitly shown, in terms of the Hawking evaporation of the monopole black hole, that the presence of the dilaton field appears to introduce a "mass dependent extra attractive interaction" in addition to that of the standard Einstein gravity into the system.Comment: 43 pages, 1 figur