11,064 research outputs found
Fermi Coordinates and Penrose Limits
We propose a formulation of the Penrose plane wave limit in terms of null
Fermi coordinates. This provides a physically intuitive (Fermi coordinates are
direct measures of geodesic distance in space-time) and manifestly covariant
description of the expansion around the plane wave metric in terms of
components of the curvature tensor of the original metric, and generalises the
covariant description of the lowest order Penrose limit metric itself, obtained
in hep-th/0312029. We describe in some detail the construction of null Fermi
coordinates and the corresponding expansion of the metric, and then study
various aspects of the higher order corrections to the Penrose limit. In
particular, we observe that in general the first-order corrected metric is such
that it admits a light-cone gauge description in string theory. We also
establish a formal analogue of the Weyl tensor peeling theorem for the Penrose
limit expansion in any dimension, and we give a simple derivation of the
leading (quadratic) corrections to the Penrose limit of AdS_5 x S^5.Comment: 25 page
On the Hagedorn Behaviour of Singular Scale-Invariant Plane Waves
As a step towards understanding the properties of string theory in
time-dependent and singular spacetimes, we study the divergence of density
operators for string ensembles in singular scale-invariant plane waves, i.e.
those plane waves that arise as the Penrose limits of generic power-law
spacetime singularities. We show that the scale invariance implies that the
Hagedorn behaviour of bosonic and supersymmetric strings in these backgrounds,
even with the inclusion of RR or NS fields, is the same as that of strings in
flat space. This is in marked contrast to the behaviour of strings in the BFHP
plane wave which exhibit quantitatively and qualitatively different
thermodynamic properties.Comment: 15 pages, LaTeX2e, v2: JHEP3.cls, one reference adde
Penrose Limits and Spacetime Singularities
We give a covariant characterisation of the Penrose plane wave limit: the
plane wave profile matrix is the restriction of the null geodesic
deviation matrix (curvature tensor) of the original spacetime metric to the
null geodesic, evaluated in a comoving frame. We also consider the Penrose
limits of spacetime singularities and show that for a large class of black
hole, cosmological and null singularities (of Szekeres-Iyer ``power-law
type''), including those of the FRW and Schwarzschild metrics, the result is a
singular homogeneous plane wave with profile , the scale
invariance of the latter reflecting the power-law behaviour of the
singularities.Comment: 9 pages, LaTeX2e; v2: additional references and cosmetic correction
The Refractive Index of Curved Spacetime II: QED, Penrose Limits and Black Holes
This work considers the way that quantum loop effects modify the propagation
of light in curved space. The calculation of the refractive index for scalar
QED is reviewed and then extended for the first time to QED with spinor
particles in the loop. It is shown how, in both cases, the low frequency phase
velocity can be greater than c, as found originally by Drummond and Hathrell,
but causality is respected in the sense that retarded Green functions vanish
outside the lightcone. A "phenomenology" of the refractive index is then
presented for black holes, FRW universes and gravitational waves. In some
cases, some of the polarization states propagate with a refractive index having
a negative imaginary part indicating a potential breakdown of the optical
theorem in curved space and possible instabilities.Comment: 62 pages, 14 figures, some signs corrected in formulae and graph
Goedel, Penrose, anti-Mach: extra supersymmetries of time-dependent plane waves
We prove that M-theory plane waves with extra supersymmetries are necessarily
homogeneous (but possibly time-dependent), and we show by explicit construction
that such time-dependent plane waves can admit extra supersymmetries. To that
end we study the Penrose limits of Goedel-like metrics, show that the Penrose
limit of the M-theory Goedel metric (with 20 supercharges) is generically a
time-dependent homogeneous plane wave of the anti-Mach type, and display the
four extra Killings spinors in that case. We conclude with some general remarks
on the Killing spinor equations for homogeneous plane waves.Comment: 20 pages, LaTeX2
Tsirik - fold the leaves so that others may be guided: A study of how the BriBri women are preserving their culture to ensure a sustainable future for their community
Bananas are one of Costa Rica’s largest exports, along with coffee, palm oil, and cocoa. The banana plantations are large-scale, are most often run by multinational companies, and are considered to be run as enclave economies (Equal Exchange, 2016). This monoculture crop production has been globally accused of human rights abuses said to include, but not be limited to, violating the rights of indigenous people and loss in culture and tradition. For this paper, I studied the effects that large-scale agricultural corporations have on the BriBri, a matriarchal and indigenous group who live on the Caribbean coast of Costa Rica. As I will show in this paper, the large-scale agricultural programs are affecting the health and fertility of the women of the tribe, as well as redefining gender roles. These changes have further policy implications for the culture and livelihood of the BriBri community. The BriBri have combated many of the negative effects of the commercialization of agriculture by creating and sustaining an agrotourism business model that is helping to preserve and revitalize the BriBri culture.
Many academics have speculated on the effects of tourism on indigenous peoples and ask whether tourism tourism in indigenous communities is a promising opportunity for development or a lurking undercover threat. In this study, I examine how agrotourism influences the identity of the BriBri people, specifically the women, as well as how it encourages the revitalization of the culture, tradition, and language of the BriBri. This paper will further provide recommendations of how the BriBri can continue to preserve their culture, and how the Costa Rican government can reinforce the treaties they signed to stand with indigenous people. The BriBri model has global significance because it stands as an alternative for other indigenous groups facing similar situations, by encouraging the use of tradition, culture, and lifestyle to find solutions to their own situations
PP-wave and Non-supersymmetric Gauge Theory
We extend the pp-wave correspondence to a non supersymmetric example. The
model is the type 0B string theory on the pp-wave R-R background. We explicitly
solve the model and give the spectrum of physical states. The field theory
counterpart is given by a sector of the large N SU(N) x SU(N) CFT living on a
stack of N electric and N magnetic D3-branes. The relevant effective coupling
constant is g_{eff}=g_sN/J^2. The string theory has a tachyon in the spectrum,
whose light-cone energy can be exactly computed as a function of g_{eff}. We
argue that the perturbative analysis in g_{eff} in the dual gauge theory is
reliable, with corrections of non perturbative type. We find a precise
state/operator map, showing that the first perturbative corrections to the
anomalous dimensions of the operators have the behavior expected from the
string analysis.Comment: 19 pages. Revised versio
Randall-Sundrum Zero Mode as a Penrose Limit
A generalization of the limiting procedure of Penrose, which allows non-zero
cosmological constants and takes into account metrics that contain homogeneous
functions of degree zero, is presented. It is shown that any spacetime which
admits a spacelike conformal Killing vector has a limit which is conformal to
plane waves. If the spacetime is an Einstein space, its limit exists only if
the cosmological constant is negative or zero. When the conformal Killing
vector is hypersurface orthogonal, the limits of Einstein spacetimes are
certain AdS plane waves. In this case the nonlinear version of the
Randall-Sundrum zero mode is obtained as the limit of the brane world
scenarios.Comment: 8 pages,LaTe
Penrose limits, supergravity and brane dynamics
We investigate the Penrose limits of classical string and M-theory
backgrounds. We prove that the number of (super)symmetries of a supergravity
background never decreases in the limit. We classify all the possible Penrose
limits of AdS x S spacetimes and of supergravity brane solutions. We also
present the Penrose limits of various other solutions: intersecting branes,
supersymmetric black holes and strings in diverse dimensions, and cosmological
models. We explore the Penrose limit of an isometrically embedded spacetime and
find a generalisation to spaces with more than one time. Finally, we show that
the Penrose limit is a large tension limit for all branes including those with
fields of Born--Infeld type.Comment: 67 page
String Interactions in PP-Waves
We argue that string interactions in a PP-wave spacetime are governed by an
effective coupling g_{eff}=g_s(\mu p^+\apm)f(\mu p^+ \apm) where f(\mu p^+
\apm) is proportional to the light cone energy of the string states involved
in the interaction. This simply follows from generalities of a Matrix String
description of this background. nicely interpolates between the
expected result () for flat space (small \mu p^+\apm) and a recently
conjectured expression from the perturbative gauge theory side (large \mu
p^+\apm).Comment: 8 page
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