76 research outputs found
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
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
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
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
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
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
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
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