648 research outputs found
Closed Strings in Misner Space: Cosmological Production of Winding Strings
Misner space, also known as the Lorentzian orbifold , is one
of the simplest examples of a cosmological singularity in string theory. In
this work, the study of weakly coupled closed strings on this space is pursued
in several directions: (i) physical states in the twisted sectors are found to
come in two kinds: short strings, which wind along the compact space-like
direction in the cosmological (Milne) regions, and long strings, which wind
along the compact time-like direction in the (Rindler) whiskers. The latter can
be viewed as infinitely long static open strings, stretching from Rindler
infinity to a finite radius and folding back onto themselves. (ii) As in the
Schwinger effect, tunneling between these states corresponds to local pair
production of winding strings. The tunneling rate approaches unity as the
winding number gets large, as a consequence of the singular geometry. (iii)
The one-loop string amplitude has singularities on the moduli space, associated
to periodic closed string trajectories in Euclidean time. In the untwisted
sector, they can be traced to the combined existence of CTCs and Regge
trajectories in the spectrum. In the twisted sectors, they indicate pair
production of winding strings. (iv) At a classical level and in sufficiently
low dimension, the condensation of winding strings can indeed lead to a bounce,
although the required initial conditions are not compatible with Misner
geometry at early times. (v) The semi-classical analysis of winding string pair
creation can be generalized to more general (off-shell) geometries. We show
that a regular geometry regularizes the divergence at large winding number.Comment: 46 pages, 5 figures, uses JHEP3.cls; v2: title changed and other
minor improvements, final version to appear in JCA
Closed Strings in Misner Space: Stringy Fuzziness with a Twist
Misner space, also known as the Lorentzian orbifold , is the
simplest tree-level solution of string theory with a cosmological singularity.
We compute tree-level scattering amplitudes involving twisted states, using
operator and current algebra techniques. We find that, due to zero-point
quantum fluctuations of the excited modes, twisted strings with a large winding
number are fuzzy on a scale , which can be much larger than
the string scale. Wave functions are smeared by an operator reminiscent of the Moyal-product of non-commutative
geometry, which, since is real, modulates the amplitude rather
than the phase of the wave function, and is purely gravitational in its origin.
We compute the scattering amplitude of two twisted states and one tachyon or
graviton, and find a finite result. The scattering amplitude of two twisted and
two untwisted states is found to diverge, due to the propagation of
intermediate winding strings with vanishing boost momentum. The scattering
amplitude of three twisted fields is computed by analytic continuation from
three-point amplitudes of states with non-zero in the Nappi-Witten plane
wave, and the non-locality of the three-point vertex is found to diverge for
certain kinematical configurations. Our results for the three-point amplitudes
allow in principle to compute, to leading order, the back-reaction on the
metric due to a condensation of coherent winding strings.Comment: 29 pages, Latex2e, uses JHEP3.cls; v3: minor corrections, final
version to appear in JCA
On Schwinger Pair Creation in Gravity and in Closed Superstring Theory
We investigate the Schwinger pair creation process in the context of
gravitational models with the back reaction of the electric field included in
the geometry. The background is also an exact solution of type II superstring
theory, where the electric field arises by Kaluza-Klein reduction. We obtain a
closed formula for the pair creation rate that incorporates the gravitational
back reaction. At weak fields it has the same structure as the general
Schwinger formula, albeit pairs are produced by a combination of Schwinger and
Unruh effect, the latter due to the presence of a Rindler horizon. In four
spacetime dimensions, the rate becomes constant at strong electric fields. For
states with mass of Kaluza-Klein origin, the rate has a power-like dependence
in the electric field, rather than the familiar (non-perturbative) exponential
dependence. We also reproduce the same formula from the string partition
function for winding string states. Finally, we comment on the generalization
to excited string states.Comment: 21 page
Matrix Description of Interacting Theories in Six Dimensions
We propose descriptions of interacting (2,0) supersymmetric theories without
gravity in six dimensions in the infinite momentum frame. They are based on the
large limit of quantum mechanics or 1+1 dimensional field theories on the
moduli space of instantons in \IR^4.Comment: 10 pages, harvmac bi
The abelian cosets of the Heisenberg group
In this paper we study the abelian cosets of the H(4) WZW model. They
coincide or are related to several interesting three-dimensional backgrounds
such as the Melvin model, the conical point-particle space-times and the null
orbifold. We perform a detailed CFT analysis of all the models and compute the
coset characters as well as some typical three-point couplings of coset
primaries.Comment: 26 pages; v2: minor typos corrected, also added section 3.3 and 4.3
with a few comments on a third class of geometries that have not been
discussed in v
D-instantons and Closed String Tachyons in Misner Space
We investigate closed string tachyon condensation in Misner space, a toy
model for big bang universe. In Misner space, we are able to condense tachyonic
modes of closed strings in the twisted sectors, which is supposed to remove the
big bang singularity. In order to examine this, we utilize D-instanton as a
probe. First, we study general properties of D-instanton by constructing
boundary state and effective action. Then, resorting to these, we are able to
show that tachyon condensation actually deforms the geometry such that the
singularity becomes milder.Comment: 24 pages, 1 figure, minor change
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