69 research outputs found
The New Era of Precision Cosmology: Testing Gravity at Large Scales
Cosmic acceleration may be the biggest phenomenological mystery in cosmology today. Various explanations for its cause have been proposed, including the cosmological constant, dark energy and modified gravities. Structure formation provides a strong test of any cosmic acceleration model because a successful dark energy model must not inhibit the development of observed large-scale structures. Traditional approaches to studies of structure formation in the presence of dark energy ore modified gravity implement the Press & Schechter formalism (PGF). However, does the PGF apply in all cosmologies? The search is on for a better understanding of universality in the PGF In this talk, I explore the potential for universality and talk about what dark matter haloes may be able to tell us about cosmology. I will also discuss the implications of this and new cosmological experiments for better understanding our theory of gravity
Cosmic Acceleration As Quantum Gravity Phenomenology
The discovery of cosmic acceleration has prompted the need for a new understanding of cosmology. The presence of this acceleration is often described as the dark energy problem or the Lambda problem.The simplest explanation is that the acceleration is due to addition of a cosmological constant to Einstein's equation, but this resolution is unsatisfactory as it leaves several unanswered questions. Although General Relativity has been tested in the strong-field limit, the apparent dark energy may be urging us to consider experimental cosmology as such a test for large scales. In this vein, I have pursued a study of modifications to Einstein's gravity as well as possible related quantum gravity phenomenology.
Not only must the details of modified gravities be worked out, but their impact on other astrophysics must be checked. For example, structure formation provides a strong test of any cosmic acceleration model because a successful dark energy model must not inhibit the development of observed large-scale structures. Traditional approaches to studies of structure formation in the presence of dark energy or a modified gravity implement the Press & Schechter formalism. I explore the potential for universality in the Press & Schechter formalism and what dark matter haloes may be able to tell us about cosmology
Constraining bosonic asymmetric dark matter with neutron star mass-radius measurements
Neutron stars can accumulate asymmetric dark matter (ADM) in their interiors,
which affects the neutron star's measurable properties and makes compact
objects prime targets to search for ADM. In this work, we use Bayesian
inference to explore potential neutron star mass-radius measurements, from
current and future x-ray telescopes, to constrain the bosonic ADM parameters
for the case where bosonic ADM has accumulated in the neutron star interior. We
find that the current uncertainties in the baryonic equation of state do not
allow for constraints on the ADM parameter space to be made. However, we also
find that ADM cannot be excluded and the inclusion of bosonic ADM in neutron
star cores relaxes the constraints on the baryonic equation of state space. If
the baryonic equation of state were more tightly constrained independent of
ADM, we find that statements about the ADM parameter space could be made. In
particular, we find that the high bosonic ADM particle mass () and low
effective self-interaction strength ( regime is disfavored due
to the observationally and theoretically motivated constraint that neutron
stars must have at least a mass of . However, within the
remaining parameter space, and are individually
unconstrained. On the other hand, the ADM mass-fraction, i.e., the fraction of
ADM mass inside the neutron star, can be constrained by such neutron star
measurements.Comment: 19 pages, 7 figures. This paper was made to be as similar to the PRD
version as possibl
Preheating after multifield inflation with nonminimal couplings, II: Resonance Structure
This is the second in a series of papers on preheating in inflationary models
comprised of multiple scalar fields coupled nonminimally to gravity. In this
paper, we work in the rigid-spacetime approximation and consider field
trajectories within the single-field attractor, which is a generic feature of
these models. We construct the Floquet charts to find regions of parameter
space in which particle production is efficient for both the adiabatic and
isocurvature modes, and analyze the resonance structure using analytic and
semi-analytic techniques. Particle production in the adiabatic direction is
characterized by the existence of an asymptotic scaling solution at large
values of the nonminimal couplings, , in which the dominant
instability band arises in the long-wavelength limit, for comoving wavenumbers
. However, the large- regime is not reached until
. In the intermediate regime, with , the resonance structure depends strongly on wavenumber and
couplings. The resonance structure for isocurvature perturbations is distinct
and more complicated than its adiabatic counterpart. An intermediate regime,
for , is again evident. For large values of
, the Floquet chart consists of densely spaced, nearly parallel
instability bands, suggesting a very efficient preheating behavior. The
increased efficiency arises from features of the nontrivial field-space
manifold in the Einstein frame, which itself arises from the fields' nonminimal
couplings in the Jordan frame, and has no analogue in models with minimal
couplings. Quantitatively, the approach to the large- asymptotic
solution for isocurvature modes is slower than in the case of the adiabatic
modes.Comment: 46 pages, 23 figures. References added and minor edits made to match
published versio
Preheating after multifield inflation with nonminimal couplings, III: Dynamical spacetime results
This paper concludes our semi-analytic study of preheating in inflationary
models comprised of multiple scalar fields coupled nonminimally to gravity.
Using the covariant framework of paper I in this series, we extend the
rigid-spacetime results of paper II by considering both the expansion of the
universe during preheating, as well as the effect of the coupled metric
perturbations on particle production. The adiabatic and isocurvature
perturbations are governed by different effective masses that scale differently
with the nonminimal couplings and evolve differently in time. The effective
mass for the adiabatic modes is dominated by contributions from the coupled
metric perturbations immediately after inflation. The metric perturbations
contribute an oscillating tachyonic term that enhances an early period of
significant particle production for the adiabatic modes, which ceases on a
time-scale governed by the nonminimal couplings . The effective mass of
the isocurvature perturbations, on the other hand, is dominated by
contributions from the fields' potential and from the curvature of the
field-space manifold (in the Einstein frame), the balance between which shifts
on a time-scale governed by . As in papers I and II, we identify
distinct behavior depending on whether the nonminimal couplings are small
(), intermediate (),
or large ().Comment: 34 pages, 11 figures. References added and minor edits made to match
published versio
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