394 research outputs found
One Loop Graviton Self-Energy In A Locally De Sitter Background
The graviton tadpole has recently been computed at two loops in a locally de
Sitter background. We apply intermediate results of this work to exhibit the
graviton self-energy at one loop. This quantity is interesting both to check
the accuracy of the first calculation and to understand the relaxation effect
it reveals. In the former context we show that the self-energy obeys the
appropriate Ward identity. We also show that its flat space limit agrees with
the flat space result obtained by Capper in what should be the same gauge.Comment: 35 pages, plain TeX, 4 Postscript files, uses psfig.sty, revised June
1996 for publication in Physical Review
Two Loop Scalar Bilinears for Inflationary SQED
We evaluate the one and two loop contributions to the expectation values of
two coincident and gauge invariant scalar bilinears in the theory of massless,
minimally coupled scalar quantum electrodynamics on a locally de Sitter
background. One of these bilinears is the product of two covariantly
differentiated scalars, the other is the product of two undifferentiated
scalars. The computations are done using dimensional regularization and the
Schwinger-Keldysh formalism. Our results are in perfect agreement with the
stochastic predictions at this order.Comment: 43 pages, LaTeX 2epsilon, 5 figures (using axodraw.sty) Version 2 has
updated references and important corrections to Tables 3-5 and to eqns
(139-141), (145-146), (153-155), (158) and (160
Reintegrating FARC's Female Combatants: The Challenges of Addressing Gender Binaries in Transitional Justice
Against the backdrop of the 2016 Colombian plebiscite and the subsequent peace treaty, the female Revolutionary Armed Forces of Colombia/Fuerzas Armadas Revolucionarias de Colombia (FARC) face insurmountable obstacles in returning to civilian life. Long-standing gender disparity, largely amplified by socio-economic inequality, manifested with an estimated 40% female guerrilla membership. This article argues that the financial incentives, physical protection and sense of equality offered by FARC posed a strong lure to females who were otherwise at a natural disadvantage within Colombian society, resulting in a large number of female combatants facing gender-specific challenges now that FARC has formally ended their existence as an armed group. Whilst considering female victims of human rights (HR) violations, deeper consideration is given to the symbiotic and conflicting duality of a female who may fulfill the roles of both victim and abuser, and the inability of present transitional justice (TJ) mechanisms to approach and adequately address such a dyad
Integral field spectroscopy of protoplanetary disks in Orion with VLT FLAMES
We discuss integral field spectroscopy of proplyds in M42 using the FLAMES
Argus unit and report the first detection of recombination lines of C II and O
II from the archetypical Laques-Vidal-2 object. These lines can provide
important new diagnostics of the physical conditions in proplyds. We also draw
attention to the future capabilities of the MUSE spectrograph in relation to
similar studies.Comment: 5 pages; 3 figs; To appear in proceedings of "Science with the VLT in
the ELT era" (ESO Garching, Oct. 2007
The Quantum Gravitationally Induced Stress Tensor
We derive non-perturbative relations between the expectation value of the
invariant element in a homogeneous and isotropic state and the quantum
gravitationally induced pressure and energy density. By exploiting previously
obtained bounds for the maximum possible growth of perturbative corrections to
a locally de Sitter background we show that the two loop result dominates all
higher orders. We also show that the quantum gravitational slowing of inflation
becomes non-perturbatively strong earlier than previously expected.Comment: 13 pages, LaTeX 2 epsilo
Primordial Density Perturbations and Reheating from Gravity
We consider the presence and evolution of primordial density perturbations in
a cosmological model based on a simple ansatz which captures -- by providing a
set of effective gravitational field equations -- the strength of the enhanced
quantum loop effects that can arise during inflation. After deriving the
general equations that perturbations obey, we concentrate on scalar
perturbations and show that their evolution is quite different than that of
conventional inflationary models but still phenomenologically acceptable. The
main reason for this novel evolution is the presence of an oscillating regime
after the end of inflation which makes all super-horizon scalar modes
oscillate. The same reason allows for a natural and very fast reheating
mechanism for the universe.Comment: 37 pages, 2 figures, uses LaTeX2
Reply to `Can infrared gravitons screen ?'
We reply to the recent criticism by Garriga and Tanaka of our proposal that
quantum gravitational loop corrections may lead to a secular screening of the
effective cosmological constant. Their argument rests upon a renormalization
scheme in which the composite operator is defined to be the trace of the renormalized field equations.
Although this is a peculiar prescription, we show that it {\it does not
preclude secular screening}. Moreover, we show that a constant Ricci scalar
{\it does not even classically} imply a constant expansion rate. Other
important points are: (1) the quantity of Garriga and Tanaka is
neither a properly defined composite operator, nor is it constant; (2) gauge
dependence does not render a Green's function devoid of physical content; (3)
scalar models on a non-dynamical de Sitter background (for which there is no
gauge issue) can induce arbitrarily large secular contributions to the stress
tensor; (4) the same secular corrections appear in observable quantities in
quantum gravity; and (5) the prospects seem good for deriving a simple
stochastic formulation of quantum gravity in which the leading secular effects
can be summed and for which the expectation values of even complicated, gauge
invariant operators can be computed at leading order.Comment: 17 pages, no figures, uses LaTeX 2epsilon. Version 2 adds important
points about R_ren being neither finite nor constant, and that a constant
Ricci scalar is not even classically an indicator of de Sitter expansion.
Version 3 corrects some typoes and updates the reference
Properties of the ionized gas in HH202. I: Results from integral field spectroscopy with PMAS
We present results from integral field spectroscopy with the Potsdam
multi-Aperture Spectrograph of the head of the Herbig-Haro object HH 202 with a
spatial sampling of 1"x1". We have obtained maps of different emission lines,
physical conditions --such as electron temperature and density-- and ionic
abundances from recombination and collisionally excited lines. We present the
first map of the Balmer temperature and of the temperature fluctuation
parameter, t^2. We have calculated the t^2 in the plane of the sky, which is
substantially smaller than that determined along the line of sight. We have
mapped the abundance discrepancy factor of O^{2+}, ADF(O^{2+}), finding its
maximum value at the HH 202-S position. We have explored the relations between
the ADF(O^{2+}) and the electron density, the Balmer and [O III] temperatures,
the ionization degree as well as the t^2 parameter. We do not find clear
correlations between these properties and the results seem to support that the
ADF and t^2 are independent phenomena. We have found a weak negative
correlation between the O^{2+} abundance determined from recombination lines
and the temperature, which is the expected behaviour in an ionized nebula,
hence it seems that there is not evidence for the presence of super-metal rich
droplets in H II regions.Comment: 12 pages, 11 figures. Accepted for publication in MNRA
General plane wave mode functions for scalar-driven cosmology
We give a solution for plane wave scalar, vector and tensor mode functions in
the presence of any homogeneous, isotropic and spatially flat cosmology which
is driven by a single, minimally coupled scalar. The solution is obtained by
rescaling the various mode functions so that they reduce, with a suitable scale
factor and a suitable time variable, to those of a massless, minimally coupled
scalar. We then express the general solution in terms of co-moving time and the
original scale factor.Comment: 6 pages, revtex4, no figures, revised version corrects an
embarrassing mistake (in the published version) for the parameter q_C.
Affected eqns are 45 and 6
One Loop Back Reaction On Power Law Inflation
We consider quantum mechanical corrections to a homogeneous, isotropic and
spatially flat geometry whose scale factor expands classically as a general
power of the co-moving time. The effects of both gravitons and the scalar
inflaton are computed at one loop using the manifestly causal formalism of
Schwinger with the Feynman rules recently developed by Iliopoulos {\it et al.}
We find no significant effect, in marked contrast with the result obtained by
Mukhanov {\it et al.} for chaotic inflation based on a quadratic potential. By
applying the canonical technique of Mukhanov {\it et al.} to the exponential
potentials of power law inflation, we show that the two methods produce the
same results, within the approximations employed, for these backgrounds. We
therefore conclude that the shape of the inflaton potential can have an
enormous impact on the one loop back-reaction.Comment: 28 pages, LaTeX 2 epsilo
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