11 research outputs found
Chiral Imprint of a Cosmic Gauge Field on Primordial Gravitational Waves
A cosmological gauge field with isotropic stress-energy introduces parity
violation into the behavior of gravitational waves. We show that a primordial
spectrum of inflationary gravitational waves develops a preferred handedness,
left- or right-circularly polarized, depending on the abundance and coupling of
the gauge field during the radiation era. A modest abundance of the gauge field
would induce parity-violating correlations of the cosmic microwave background
temperature and polarization patterns that could be detected by current and
future experiments.Comment: 5 pages, 6 figure
Dark Energy Scaling from Dark Matter to Acceleration
The dark sector of the Universe need not be completely separable into
distinct dark matter and dark energy components. We consider a model of early
dark energy in which the dark energy mimics a dark matter component in both
evolution and perturbations at early times. Barotropic aether dark energy
scales as a fixed fraction, possibly greater than one, of the dark matter
density and has vanishing sound speed at early times before undergoing a
transition. This gives signatures not only in cosmic expansion but in sound
speed and inhomogeneities, and in number of effective neutrino species. Model
parameters describe the timing, sharpness of the transition, and the relative
abundance at early times. Upon comparison with current data, we find viable
regimes in which the dark energy behaves like dark matter at early times: for
transitions well before recombination the dark energy to dark matter fraction
can equal or exceed unity, while for transitions near recombination the ratio
can only be a few percent. After the transition, dark energy goes its separate
way, ultimately driving cosmic acceleration and approaching a cosmological
constant in this scenario.Comment: 10 pages, 8 figure
Cosmological Consequences of Classical Flavor-Space Locked Gauge Field Radiation
We propose a classical SU(2) gauge field in a flavor-space locked configuration as a species of radiation in the early Universe, and show that it would have a significant imprint on a primordial stochastic gravitational wave spectrum. In the flavor-space locked configuration, the electric and magnetic fields of each flavor are parallel and mutually orthogonal to other flavors, with isotropic and homogeneous stress energy. Due to the non-Abelian coupling, the gauge field breaks the symmetry between left- and right-circularly polarized gravitational waves. This broken chiral symmetry results in a unique signal: nonzero cross-correlation of the cosmic microwave background temperature and polarization, TB and EB , both of which should be zero in the standard, chiral symmetric case. We forecast the ability of current and future cosmic microwave background experiments to constrain this model. Furthermore, a wide range of behavior is shown to emerge, depending on the gauge field coupling, abundance, and allocation into electric and magnetic field energy density. The fluctuation power of primordial gravitational waves oscillates back and forth into fluctuations of the gauge field. In certain cases, the gravitational wave spectrum is shown to be suppressed or amplified by up to an order of magnitude depending on the initial conditions of the gauge field
Freezing Out Early Dark Energy
A phenomenological model of dark energy that tracks the baryonic and cold
dark matter at early times but resembles a cosmological constant at late times
is explored. In the transition between these two regimes, the dark energy
density drops rapidly as if it were a relic species that freezes out, during
which time the equation of state peaks at +1. Such an adjustment in the dark
energy density, as it shifts from scaling to potential-domination, could be the
signature of a trigger mechanism that helps explain the late-time cosmic
acceleration. We show that the non-negligible dark energy density at early
times, and the subsequent peak in the equation of state at the transition,
leave an imprint on the cosmic microwave background anisotropy pattern and the
rate of growth of large scale structure. The model introduces two new
parameters, consisting of the present-day equation of state and the redshift of
the freeze-out transition. A Monte Carlo Markov Chain analysis of a
ten-dimensional parameter space is performed to compare the model with
pre-Planck cosmic microwave background, large scale structure and supernova
data and measurements of the Hubble constant. We find that the transition
described by this model could have taken place as late as a redshift z~400. We
explore the capability of future cosmic microwave background and weak lensing
experiments to put tighter constraints on this model. The viability of this
model may suggest new directions in dark-energy model building that address the
coincidence problem.Comment: 11 pages, 15 figure