836 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
Neveu-Schwarz Five-Branes And Matrix String Theory On K3
The Matrix theory description of Type IIA string theory on a compact K3
surface as the theory of Neveu-Schwarz five-branes on is
analyzed. The full multiplet of space-time BPS states is identified in the
five-brane world-volume as fluxes.Comment: harvmac, 12 pages, some changes in the T-duality on K3 sectio
Branes, central charges and U-duality invariant BPS conditions
In extended supergravity theories there are -brane solutions preserving
different numbers of supersymmetries, depending on the charges, the spacetime
dimension and the number of original supersymmetries (8, 16 or 32). We find
U-duality invariant conditions on the quantized charges which specify the
number of supersymmetries preserved with a particular charge configuration.
These conditions relate U-duality invariants to the picture of intersecting
branes. The analysis is carried out for all extended supergravities with 16 or
32 supersymmetries in various dimensions.Comment: 15 pages, no figures, typos correcte
Propagation of a string across the cosmological singularity
Our results concern the transition of a quantum string through the
singularity of the compactified Milne (CM) space. We restrict our analysis to
the string winding around the compact dimension (CD) of spacetime. The CD
undergoes contraction to a point followed by re-expansion. We demonstrate that
both classical and quantum dynamics of considered string are well defined. Most
of presently available calculations strongly suggest that the singularity of a
time dependent orbifold is useless as a model of the cosmological singularity.
We believe that our results bring, to some extent, this claim into question.Comment: 9 pages, 2 figures, revtex4; version accepted for publication in
Class. Quantum Gra
Thermal Correlators in Holographic Models with Lifshitz scaling
We study finite temperature effects in two distinct holographic models that
exhibit Lifshitz scaling, looking to identify model independent features in the
dual strong coupling physics. We consider the thermodynamics of black branes
and find different low-temperature behavior of the specific heat. Deformation
away from criticality leads to non-trivial temperature dependence of
correlation functions and we study how the characteristic length scale in the
two point function of scalar operators varies as a function of temperature and
deformation parameters.Comment: 28 pages, 8 figures; typos corrected, references added, published
versio
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
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