531 research outputs found
Ward Identity for Membranes
Ward identities in the case of scattering of antisymmetric three form RR
gauge fields off a D2-brane target has been studied in type-IIA theory.Comment: 10 pages, Revtex, Version to appear in Phys.Lett.
Duality and Integrability of Two Dimensional String Effective Action
We present a prescription for constructing the monodromy matrix, , for invariant string effective actions and derive its
transformation properties under the -duality group. This allows us to
construct for new backgrounds, starting from known ones,
which are related by -duality. As an application, we derive the monodromy
matrix for the exactly solvable Nappi-Witten model, both when B=0 and .Comment: 6pages, revtex, to be published in Physics Letters
The Holography Hypothesis in Pre-Big-Bang Cosmology with String Sources
The holographic ratio in Pre-big bang string cosmology is obtained in the
presence string sources. An iterative procedure is adopted to solve the
equations of motion and derive the ratio in four dimensional world. First the
zeroth order ratio is computed in the remote past, i.e. at , then
the holographic ratio is obtained taking into account the evolution of the
backgrounds following the iterative procedure. The corrections to the zeroth
order value of the ratio depends on the form of the initial number distribution
of the strings chosen. Moreover, we estimate the holographic ratio in the
recent past (i.e. when ) and in the remote past (i.e. when
), , in different dimensions in the
Einstein frame and in the string frame. We find that in the first case it has
similar time dependences in both the frames, especially in four dimensions the
ratio is explicitly computed to be the same in the two cases, whereas for
case the time dependence is different.Comment: 33 pages, latex, five figure
Dualities and Hidden Supersymmetry in String Quantum Cosmology
A supersymmetric approach to string quantum cosmology based on the
non-compact, global duality symmetries of the effective action is developed. An
N=2 supersymmetric action is derived whose bosonic component is the
Neveu-Schwarz/Neveu-Schwarz sector of the --dimensional effective action
compactified on a --torus. A representation for the supercharges is found
and the form of the zero-and one-fermion quantum states is determined. The
purely bosonic component of the wavefunction is unique and manifestly invariant
under the symmetry of the action. The formalism applies to a wide class of
non-linear sigma-models.Comment: 18 pages, plain Latex, no figure
Open Membranes, p-Branes and Noncommutativity of Boundary String Coordinates
We study the dynamics of an open membrane with a cylindrical topology, in the
background of a constant three form, whose boundary is attached to p-branes.
The boundary closed string is coupled to a two form potential to ensure gauge
invariance. We use the action, due to Bergshoeff, London and Townsend, to study
the noncommutativity properties of the boundary string coordinates. The
constrained Hamiltonian formalism due to Dirac is used to derive the
noncommutativity of coordinates. The chain of constraints is found to be finite
for a suitable gauge choice, unlike the case of the static gauge, where the
chain has an infinite sequence of terms. It is conjectured that the formulation
of closed string field theory may necessitate introduction of a star product
which is both noncommutative and nonassociative.Comment: 32page
Duality, Monodromy and Integrability of Two Dimensional String Effective Action
The monodromy matrix, , is constructed for two dimensional
tree level string effective action. The pole structure of is
derived using its factorizability property. It is found that the monodromy
matrix transforms non-trivially under the non-compact T-duality group, which
leaves the effective action invariant and this can be used to construct the
monodromy matrix for more complicated backgrounds starting from simpler ones.
We construct, explicitly, for the exactly solvable
Nappi-Witten model, both when B=0 and , where these ideas can be
directly checked. We consider well known charged black hole solutions in the
heterotic string theory which can be generated by T-duality transformations
from a spherically symmetric `seed' Schwarzschild solution. We construct the
monodromy matrix for the Schwarzschild black hole background of the heterotic
string theory.Comment: 20 pages, to be published in Physical Review
A numerical simulation of pre-big bang cosmology
We analyse numerically the onset of pre-big bang inflation in an
inhomogeneous, spherically symmetric Universe. Adding a small dilatonic
perturbation to a trivial (Milne) background, we find that suitable regions of
space undergo dilaton-driven inflation and quickly become spatially flat
(). Numerical calculations are pushed close enough to the big
bang singularity to allow cross checks against previously proposed analytic
asymptotic solutions.Comment: 19 pages, revtex, matlab code available at
http://www.fis.unipr.it/~onofr
The Holography Hypothesis and Pre-Big Bang Cosmology
The consequences of holography hypothesis are investigated for the
Pre-big-bang string cosmological models. The evolution equations are obtained
from the tree level string effective action. It is shown that is bounded
by a constant in each case, being the entropy within the volume bounded by
the horizon of area .Comment: 11 pages, revtex, 1 eps fil
Proof of dispersion relations for the amplitude in theories with a compactified space dimension
The analyticity properties of the scattering amplitude in the nonforward direction are investigated for a field theory in the manifold . A scalar field theory of mass is considered in Minkowski space to start with. Subsequently, one spatial dimension is compactified to a circle. The mass spectrum of the resulting theory is: (a) a massive scalar of mass, , same as the original five dimensional theory and (b) a tower of massive Kaluza-Klein states. We derive nonforward dispersion relations for scattering of the excited Kaluza-Klein states in the Lehmann-Symanzik-Zimmermann formulation of the theory. In order to accomplish this object, first we generalize the Jost-Lehmann-Dyson theorem for a relativistic field theory with a compact spatial dimension. Next, we show the existence of the Lehmann-Martin ellipse inside which the partial wave expansion converges. It is proved that the scattering amplitude satisfies fixed- dispersion relations when lies within the Lehmann-Martin ellipse
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