229 research outputs found
T-Duality and Non-Local Realizations of Supersymmetry in String Theory
We study non-local realizations of extended worldsheet supersymmetries and
the associated space-time supersymmetries which arise under a T-duality
transformation. These non-local effects appear when the supersymmetries do not
commute with the isometry with respect to which T-duality is performed.Comment: 6 pages, Latex, Talk presented at the Workshop on Strings, Gravity
and Related Topics, Trieste, 29-30 June 199
Is there an imprint of Planck scale physics on inflationary cosmology?
We study the effects of the trans-Planckian dispersion relation on the
spectrum of the primordial density perturbations during inflation. In contrast
to the earlier analyses, we do not assume any specific form of the dispersion
relation and allow the initial state of the field to be arbitrary. We obtain
the spectrum of vacuum fluctuations of the quantum field by considering a
scalar field satisfying the linear wave equation with higher spatial derivative
terms propagating in the de Sitter space-time. We show that the power spectrum
does not strongly depend on the dispersion relation and that the form of the
dispersion relation does not play a significant role in obtaining the
corrections to the scale invariant spectrum. We also show that the signatures
of the deviations from the flat scale-invariant spectrum from the CMBR
observations due to quantum gravitational effects cannot be differentiated from
the standard inflationary scenario with an arbitrary initial state.Comment: 6 pages, uses RevTex4; References added; Final versio
Holographic bounds on the UV cutoff scale in inflationary cosmology
We discuss how holographic bounds can be applied to the quantum fluctuations
of the inflaton. In general the holographic principle will lead to a bound on
the UV cutoff scale of the effective theory of inflation, but it will depend on
the coarse-graining prescription involved in calculating the entropy. We
propose that the entanglement entropy is a natural measure of the entropy of
the quantum perturbations, and show which kind of bound on the cutoff it leads
to. Such bounds are related to whether the effects of new physics will show up
in the CMB.Comment: 19 pages, 2 figures;(V3):Comments and references adde
Effective Field Theories and Inflation
We investigate the possible influence of very-high-energy physics on
inflationary predictions focussing on whether effective field theories can
allow effects which are parametrically larger than order H^2/M^2, where M is
the scale of heavy physics and H is the Hubble scale at horizon exit. By
investigating supersymmetric hybrid inflation models, we show that decoupling
does not preclude heavy-physics having effects for the CMB with observable size
even if H^2/M^2 << O(1%), although their presence can only be inferred from
observations given some a priori assumptions about the inflationary mechanism.
Our analysis differs from the results of hep-th/0210233, in which other kinds
of heavy-physics effects were found which could alter inflationary predictions
for CMB fluctuations, inasmuch as the heavy-physics can be integrated out here
to produce an effective field theory description of low-energy physics. We
argue, as in hep-th/0210233, that the potential presence of heavy-physics
effects in the CMB does not alter the predictions of inflation for generic
models, but does make the search for deviations from standard predictions
worthwhile.Comment: 19 pages, LaTeX, no figures, uses JHEP
Penrose limits and Green-Schwarz strings
We discuss the Green-Schwarz action for type IIB strings in general
plane-wave backgrounds obtained as Penrose limits from any IIB supergravity
solutions with vanishing background fermions. Using the normal-coordinate
expansion in superspace, we prove that the light-cone action is necessarily
quadratic in the fermionic coordinates. This proof is valid for more general
pp-wave backgrounds under certain conditions. We also write down the complete
quadratic action for general bosonic on-shell backgrounds in a form in which
its geometrical meaning is manifest both in the Einstein and string frames.
When the dilaton and 1-form field strength are vanishing, and the other field
strengths are constant, our string-frame action reduces, up to conventions, to
the one which has been written down using the supercovariant derivative.Comment: 18 pages, latex, no figures; (v2) relation to ref.14 clarified; (v3)
typos corrected, minor change
The Bekenstein Formula and String Theory (N-brane Theory)
A review of recent progress in string theory concerning the Bekenstein
formula for black hole entropy is given. Topics discussed include p-branes,
D-branes and supersymmetry; the correspondence principle; the D- and M-brane
approach to black hole entropy; the D-brane analogue of Hawking radiation, and
information loss; D-branes as probes of black holes; and the Matrix theory
approach to charged and neutral black holes. Some introductory material is
included.Comment: 53 pages, LaTeX. v3: Typos fixed, minor updates, references added,
brief Note Added on AdS/CF
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