2,711 research outputs found
Dark energy in motion
Recent large-scale peculiar velocity surveys suggest that large matter
volumes could be moving with appreciable velocity with respect to the CMB rest
frame. If confirmed, such results could conflict with the Cosmological
Principle according to which the matter and CMB rest frames should converge on
very large scales. In this work we explore the possibility that such large
scale bulk flows are due, not to the motion of matter with respect to the CMB,
but to the flow of dark energy with respect to matter. Indeed, when dark energy
is moving, the usual definition of the CMB rest frame as that in which the CMB
dipole vanishes is not appropriate. We find instead that the dipole vanishes
for observers at rest with respect to the cosmic center of mass, i.e. in motion
with respect to the background radiation.Comment: 9 pages, 1 figure. Essay selected for "Honorable Mention" in the 2006
Awards for Essays on Gravitation (Gravity Research Foundation
Ecotheology and the Parables of Jesus: Creative Re-readings of Parables In Light of the Environmental Crisis
In this paper I demonstrate how adopting a scriptural hermeneutic based in Rosemary Radford Ruether’s prophetic principle can cultivate the ability of Christian communities to interpret Scripture based on their own community context. I will provide an interpretive framework for rethinking relationships between humans, nature, and the Divine that can serve as a correction for entrenched reading practices that reinforce Christianity’s complicity in environmental degradation. I use reader-response theory to conduct literary-critical readings of three well-known parables from the Gospel of Luke. The parabolic structure of orientation, disorientation, and reorientation informs my view of the parables as inherently subversive and on the side of the marginalized and oppressed in society. I propose applying this reading practice to three parables with the goal of reorienting social norms to be radically inclusive: love, neighborliness and hospitality, thereby challenging the dominant paradigms of hierarchical binaries, anthropocentrism, and utilitarianism
Ecotheology and the Parables of Jesus: Creative Re-readings of Parables In Light of the Environmental Crisis
In this paper I demonstrate how adopting a scriptural hermeneutic based in Rosemary Radford Ruether’s prophetic principle can cultivate the ability of Christian communities to interpret Scripture based on their own community context. I will provide an interpretive framework for rethinking relationships between humans, nature, and the Divine that can serve as a correction for entrenched reading practices that reinforce Christianity’s complicity in environmental degradation. I use reader-response theory to conduct literary-critical readings of three well-known parables from the Gospel of Luke. The parabolic structure of orientation, disorientation, and reorientation informs my view of the parables as inherently subversive and on the side of the marginalized and oppressed in society. I propose applying this reading practice to three parables with the goal of reorienting social norms to be radically inclusive: love, neighborliness and hospitality, thereby challenging the dominant paradigms of hierarchical binaries, anthropocentrism, and utilitarianism
Dynamics of a Dark Matter Field with a Quartic Self-Interaction Potential
It may prove useful in cosmology to understand the behavior of the energy
distribution in a scalar field that interacts only with gravity and with itself
by a pure quartic potential, because if such a field existed it would be
gravitationally produced, as a squeezed state, during inflation. It is known
that the mean energy density in such a field after inflation varies with the
expansion of the universe in the same way as radiation. I show that if the
field initially is close to homogeneous, with small energy density contrast
delta rho /rho and coherence length L, the energy density fluctuations behave
like acoustic oscillations in an ideal relativistic fluid for a time on the
order of L/|delta rho /rho|. This ends with the appearance of features that
resemble shock waves, but interact in a close to elastic way that reversibly
disturbs the energy distribution.Comment: 7 pages, 5 figures, submitted to Phys Rev
Noninteracting dark matter
Since an acceptable dark matter candidate may interact only weakly with
ordinary matter and radiation, it is of interest to consider the limiting case
where the dark matter interacts only with gravity and itself, the matter
originating by the gravitational particle production at the end of inflation.
We use the bounds on the present dark mass density and the measured large-scale
fluctuations in the thermal cosmic background radiation to constrain the two
parameters in a self-interaction potential that is a sum of quadratic and
quartic terms in a single scalar dark matter field that is minimally coupled to
gravity. In quintessential inflation, where the temperature at the end of
inflation is relatively low, the field starts acting like cold dark matter
relatively late, shortly before the epoch of equal mass densities in matter and
radiation. This could have observable consequences for galaxy formation. We
respond to recent criticisms of the quintessential inflation scenario, since
these issues also apply to elements of the noninteracting dark matter picture.Comment: 37 pages, 3 figure
Issues for the Next Generation of Galaxy Surveys
I argue that the weight of the available evidence favours the conclusions
that galaxies are unbiased tracers of mass, the mean mass density (excluding a
cosmological constant or its equivalent) is less than the critical Einstein-de
Sitter value, and an isocurvature model for structure formation offers a viable
and arguably attractive model for the early assembly of galaxies. If valid
these conclusions complicate our work of adding structure formation to the
standard model for cosmology, but it seems sensible to pay attention to
evidence.Comment: 14 pages, 3 postscript figures, uses rspublic.st
Adiabatic instability in coupled dark energy-dark matter models
We consider theories in which there exists a nontrivial coupling between the
dark matter sector and the sector responsible for the acceleration of the
universe. Such theories can possess an adiabatic regime in which the
quintessence field always sits at the minimum of its effective potential, which
is set by the local dark matter density. We show that if the coupling strength
is much larger than gravitational, then the adiabatic regime is always subject
to an instability. The instability, which can also be thought of as a type of
Jeans instability, is characterized by a negative sound speed squared of an
effective coupled dark matter/dark energy fluid, and results in the exponential
growth of small scale modes. We discuss the role of the instability in specific
coupled CDM and Mass Varying Neutrino (MaVaN) models of dark energy, and
clarify for these theories the regimes in which the instability can be evaded
due to non-adiabaticity or weak coupling.Comment: 20 pages, 2 figures; final published versio
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