435 research outputs found
Dual Actions for Born-Infeld and Dp-Brane Theories
Dual actions with respect to U(1) gauge fields for Born-Infeld and -brane
theories are reexamined. Taking into account an additional condition, i.e. a
corollary to the field equation of the auxiliary metric, one obtains an
alternative dual action that does not involve the infinite power series in the
auxiliary metric given by ref. \cite{s14}, but just picks out the first term
from the series formally. New effective interactions of the theories are
revealed. That is, the new dual action gives rise to an effective interaction
in terms of one interaction term rather than infinite terms of different
(higher) orders of interactions physically. However, the price paid for
eliminating the infinite power series is that the new action is not quadratic
but highly nonlinear in the Hodge dual of a -form field strength. This
non-linearity is inevitable to the requirement the two dual actions are
equivalent.Comment: v1: 11 pages, no figures; v2: explanation of effective interactions
added; v3: concision made; v4: minor modification mad
Stabilization of Extra Dimensions at Tree Level
By considering the effects of string winding and momentum modes on a time
dependent background, we find a method by which six compact dimensions become
stabilized naturally at the self-dual radius while three dimensions grow large.Comment: 15 pages, 2 figures, minor typos correcte
Higher Dimensional Taub-NUTs and Taub-Bolts in Einstein-Maxwell Gravity
We present a class of higher dimensional solutions to Einstein-Maxwell
equations in d-dimensions. These solutions are asymptotically locally flat,
de-Sitter, or anti-de Sitter space-times. The solutions we obtained depend on
two extra parameters other than the mass and the nut charge. These two
parameters are the electric charge, q and the electric potential at infinity,
V, which has a non-trivial contribution. We Analyze the conditions one can
impose to obtain Taub-Nut or Taub-Bolt space-times, including the
four-dimensional case. We found that in the nut case these conditions coincide
with that coming from the regularity of the one-form potential at the horizon.
Furthermore, the mass parameter for the higher dimensional solutions depends on
the nut charge and the electric charge or the potential at infinity.Comment: 11 pages, LaTe
Time-dependent backgrounds from supergravity with gauged non-compact R-symmetry
We obtain a general class of time-dependent, asymptotically de Sitter
backgrounds which solve the first order bosonic equations that extremize the
action for supergravity with gauged non-compact -symmetry. These backgrounds
correspond only to neutral fields with the correct sign of kinetic energy.
Within N=2 five-dimensional supergravity with vector-superfields we provide
examples of multi-centered charged black holes in asymptotic de Sitter space,
whose spatial part is given by a time-dependent hyper-K\"ahler space. Reducing
these backgrounds to four dimensions yields asymptotically de Sitter
multi-centered charged black hole backgrounds and we show that they are related
to an instanton configuration by a massive T-duality over time. Within N=2
gauged supergravity in four (and five)-dimensions with hyper-multiplets there
could also be neutral cosmological backgrounds that are regular and correspond
to the different de Sitter spaces at early and late times.Comment: 28 pages, Latex; minor changes and add reference
Numerical experiments with p F- and q D-strings: the formation of (p,q) bound states
We investigate the behaviour of (p,q) string networks, focusing on two
aspects: (1) modelling more realistic (p,q) string networks than the Z_N
networks used so far and (2) investigating the effect of long-range
interactions on the evolution of the network. We model the network with no
long-range interactions using two sets of fields, complex scalars coupled to
gauge fields, with a potential chosen such that the two types of strings will
form bound states. This way we can model junctions of 3 strings with different
tension; in Z_N models used so far in simulations all the strings have
identical tensions. In order to introduce long-range interactions we also study
a network in which one of the scalars forms global strings. We observe that in
the absence of long-range interactions the formation of bound states has a
significant influence on the evolution of the network. When long-range
interactions are turned on the bound states are short-lived and have a minimal
effect on the network evolution.Comment: 17 pages, 8 figures, JCAP styl
A class of solvable Lie algebras and their Casimir Invariants
A nilpotent Lie algebra n_{n,1} with an (n-1) dimensional Abelian ideal is
studied. All indecomposable solvable Lie algebras with n_{n,1} as their
nilradical are obtained. Their dimension is at most n+2. The generalized
Casimir invariants of n_{n,1} and of its solvable extensions are calculated.
For n=4 these algebras figure in the Petrov classification of Einstein spaces.
For larger values of n they can be used in a more general classification of
Riemannian manifolds.Comment: 16 page
Backlund Transformations, D-Branes, and Fluxes in Minimal Type 0 Strings
We study the Type 0A string theory in the (2,4k) superconformal minimal model
backgrounds, focusing on the fully non-perturbative string equations which
define the partition function of the model. The equations admit a parameter,
Gamma, which in the spacetime interpretation controls the number of background
D-branes, or R-R flux units, depending upon which weak coupling regime is
taken. We study the properties of the string equations (often focusing on the
(2,4) model in particular) and their physical solutions. The solutions are the
potential for an associated Schrodinger problem whose wavefunction is that of
an extended D-brane probe. We perform a numerical study of the spectrum of this
system for varying Gamma and establish that when Gamma is a positive integer
the equations' solutions have special properties consistent with the spacetime
interpretation. We also show that a natural solution-generating transformation
(that changes Gamma by an integer) is the Backlund transformation of the KdV
hierarchy specialized to (scale invariant) solitons at zero velocity. Our
results suggest that the localized D-branes of the minimal string theories are
directly related to the solitons of the KdV hierarchy. Further, we observe an
interesting transition when Gamma=-1.Comment: 17 pages, 3 figure
Constraining the string scale: from Planck to Weak and back again
String and field theory ideas have greatly influenced each other since the so
called second string revolution. We review this interrelation paying particular
attention to its phenomenological implications. Our guiding principle is the
radical shift in the way that we think about the fundamental scale, in
particular the way in which string models have been able to accommodate values
from the Planck GeV down to the electroweak scale
TeV.Comment: Invited review aimed at an experimental audienc
Vacuum Plane Waves in 4+1 D and Exact solutions to Einstein's Equations in 3+1 D
In this paper we derive homogeneous vacuum plane-wave solutions to Einstein's
field equations in 4+1 dimensions. The solutions come in five different types
of which three generalise the vacuum plane-wave solutions in 3+1 dimensions to
the 4+1 dimensional case. By doing a Kaluza-Klein reduction we obtain solutions
to the Einstein-Maxwell equations in 3+1 dimensions. The solutions generalise
the vacuum plane-wave spacetimes of Bianchi class B to the non-vacuum case and
describe spatially homogeneous spacetimes containing an extremely tilted fluid.
Also, using a similar reduction we obtain 3+1 dimensional solutions to the
Einstein equations with a scalar field.Comment: 16 pages, no figure
Quark Soup al dente: Applied Superstring Theory
We discuss the application of the AdS/CFT correspondence to possibly gain new
physical insights for the strongly coupled quark-gluon plasma. This article
provides an informal summary of a talk given by RCM at the 18th International
Conference on General Relativity and Gravitation in July 2007.Comment: This article provides an informal summary of a talk given by RCM at
the 18th International Conference on General Relativity and Gravitation in
July 200
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