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