1,599 research outputs found
Collective Field Description of Matrix Cosmologies
We study the Das-Jevicki collective field description of arbitrary classical
solutions in the c=1 matrix model, which are believed to describe nontrivial
spacetime backgrounds in 2d string theory. Our analysis naturally includes the
case of a Fermi droplet cosmology: a finite size droplet of Fermi fluid, made
up of a finite number of eigenvalues. We analyze properties of the coordinates
in which the metric in the collective field theory is trivial, and comment on
the form of the interaction terms in these coordinates.Comment: 16 pages, 1 figure. v2: Typos corrected, JHEP styl
Particle Production in Matrix Cosmology
We consider cosmological particle production in 1+1 dimensional string
theory. The process is described most efficiently in terms of anomalies, but we
also discuss the explicit mode expansions. In matrix cosmology the usual vacuum
ambiguity of quantum fields in time-dependent backgrounds is resolved by the
underlying matrix model. This leads to a finite energy density for the "in"
state which cancels the effect of anomalous particle production.Comment: 24 pages, 1 figure; v2: references added, minor change
Branes as Stable Holomorphic Line Bundles On the Non-Commutative Torus
It was recently suggested by A. Kapustin that turning on a -field, and
allowing some discrepancy between the left and and right-moving complex
structures, must induce an identification of B-branes with holomorphic line
bundles on a non-commutative complex torus. We translate the stability
condition for the branes into this language and identify the stable topological
branes with previously proposed non-commutative instanton equations. This
involves certain topological identities whose derivation has become familiar in
non-commutative field theory. It is crucial for these identities that the
instantons are localized. We therefore explore the case of non-constant field
strength, whose non-linearities are dealt with thanks to the rank-one
Seiberg--Witten map.Comment: 12 pages, LaTe
Rolling Tachyon Boundary State, Conserved Charges and Two Dimensional String Theory
The boundary state associated with the rolling tachyon solution on an
unstable D-brane contains a part that decays exponentially in the asymptotic
past and the asymptotic future, but it also contains other parts which either
remain constant or grow exponentially in the past or future. We argue that the
time dependence of the latter parts is completely determined by the requirement
of BRST invariance of the boundary state, and hence they contain information
about certain conserved charges in the system. We also examine this in the
context of the unstable D0-brane in two dimensional string theory where these
conserved charges produce closed string background associated with the discrete
states, and show that these charges are in one to one correspondence with the
symmetry generators in the matrix model description of this theory.Comment: LaTeX file, 37 pages; v3: references added; v4: minor change
Black-hole information puzzle: A generic string-inspired approach
Given the insight steming from string theory, the origin of the black-hole
(BH) information puzzle is traced back to the assumption that it is physically
meaningful to trace out the density matrix over negative-frequency Hawking
particles. Instead, treating them as virtual particles necessarily absorbed by
the BH in a manner consistent with the laws of BH thermodynamics, and tracing
out the density matrix only over physical BH states, the complete evaporation
becomes compatible with unitarity.Comment: 8 pages, revised, title changed, to appear in Eur. Phys. J.
On The Problem of Particle Production in c=1 Matrix Model
We reconsider and analyze in detail the problem of particle production in the
time dependent background of matrix model where the Fermi sea drains away
at late time. In addition to the moving mirror method, which has already been
discussed in hep-th/0403169 and hep-th/0403275, we describe yet another method
of computing the Bogolubov coefficients which gives the same result. We
emphasize that these Bogolubov coefficients are approximately correct for small
value of the deformation parameter.
We also study the time evolution of the collective field theory stress-tensor
with a special point-splitting regularization. Our computations go beyond the
approximation of the previous treatments and are valid at large coordinate
distances from the boundary at a finite time and up-to a finite coordinate
distance from the boundary at late time. In this region of validity our
regularization produces a certain singular term that is precisely canceled by
the collective field theory counter term in the present background. The energy
and momentum densities fall off exponentially at large distance from the
boundary to the values corresponding to the static background. This clearly
shows that the radiated energy reaches the asymptotic region signaling the
space-time decay.Comment: 37 pages, 5 figures. Section 6 is modified to clarify main
accomplishments of the paper including a discussion comparing stress-tensor
analysis with those preexisted in literature. Other modifications include
minor changes in the text and addition of one reference. Version accepted for
publication in JHE
Photoelectron Spectra Of Amorphous Sixhy Alloy Films: The Effect Of Microstructure On The Si-2p Level Shift
Depending on the deposition conditions, amorphous SixH y alloy films prepared by planar rf reactive magnetron sputtering exhibit one of three types of microstructure: (i) type A with no discernible microstructural features down to the 20-Ă… level and with a smooth uniform density; (ii) type B consisting of high-density regions of 50-200-Ă… lateral dimensions separated by a low-density network; and (iii) a two-level (type C) microstructure consisting of 300-500-Ă… dimensions columns separated by a pronounced low-density network. The columns, in turn, are composed of 50-200-Ă… dimension high-density regions interspersed with low-density network. The Si-2p level in these alloy films, determined by x-ray photoelectron spectroscopy, is observed to be strongly influenced by the microstructure of the film. A shift in the Si-2p level, systematically varying with the hydrogen concentration, is observed in alloy films with type B and type C microstructures. No shift is observed, irrespective of the hydrogen concentration, in alloy films with type A microstructure. The photoelectron spectra are examined in the light of the vibrational spectra of the films as measured by Fourier transform infrared techniques. The dependence of the Si-2p level shift on the microstructure and the variation with hydrogen concentration are explained qualitatively in terms of the differences in the silicon-hydrogen bonding in amorphous SixHy films with dissimilar microstructures.6072530253
Large-N Collective Fields and Holography
We propose that the euclidean bilocal collective field theory of critical
large-N vector models provides a complete definition of the proposed dual
theory of higher spin fields in anti de-Sitter spaces. We show how this bilocal
field can be decomposed into an infinite number of even spin fields in one more
dimension. The collective field has a nontrivial classical solution which leads
to a O(N) thermodynamic entropy characteristic of the lower dimensional theory,
as required by general considerations of holography. A subtle cancellation of
the entropy coming from the bulk fields in one higher dimension with O(1)
contributions from the classical solution ensures that the subleading terms in
thermodynamic quantities are of the expected form. While the spin components of
the collective field transform properly under dilatational, translational and
rotational isometries of , special conformal transformations mix fields of
different spins indicating a need for a nonlocal map between the two sets of
fields. We discuss the nature of the propagating degrees of freedom through a
hamiltonian form of collective field theory and argue that nonsinglet states
which are present in an euclidean version are related to nontrivial
backgrounds.Comment: 27 pages, harvmac. v2: references adde
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