3,859 research outputs found
Chaotic inflation with kinetic alignment of axion fields
N-flation is a radiatively stable scenario for chaotic inflation in which the displacements of N≫1 axions with decay constants f1≤…≤fN<MP lead to a super-Planckian effective displacement equal to the Pythagorean sum fPy of the fi. We show that mixing in the axion kinetic term generically leads to the phenomenon of kinetic alignment, allowing for effective displacements as large as N−−√fN≥fPy, even if f1,…,fN−1 are arbitrarily small. At the level of kinematics, the necessary alignment occurs with very high probability, because of eigenvector delocalization. We present conditions under which inflation can take place along an aligned direction. Our construction sharply reduces the challenge of realizing N-flation in string theory
Designing and testing inflationary models with Bayesian networks
Even simple inflationary scenarios have many free parameters. Beyond the
variables appearing in the inflationary action, these include dynamical initial
conditions, the number of fields, and couplings to other sectors. These
quantities are often ignored but cosmological observables can depend on the
unknown parameters. We use Bayesian networks to account for a large set of
inflationary parameters, deriving generative models for the primordial spectra
that are conditioned on a hierarchical set of prior probabilities describing
the initial conditions, reheating physics, and other free parameters. We use
--quadratic inflation as an illustrative example, finding that the number
of -folds between horizon exit for the pivot scale and the end of
inflation is typically the most important parameter, even when the number of
fields, their masses and initial conditions are unknown, along with possible
conditional dependencies between these parameters.Comment: 24 pages, 9 figures, 1 table; discussion update
Chemical enrichment of the pre-solar cloud by supernova dust grains
The presence of short-lived radioisotopes (SLRs) in solar system meteorites
has been interpreted as evidence that the solar system was exposed to a
supernova shortly before or during its formation. Yet results from
hydrodynamical models of SLR injection into the proto-solar cloud or disc
suggest that gas-phase mixing may not be efficient enough to reproduce the
observed abundances. As an alternative, we explore the injection of SLRs via
dust grains as a way to overcome the mixing barrier. We numerically model the
interaction of a supernova remnant containing SLR-rich dust grains with a
nearby molecular cloud. The dust grains are subject to drag forces and both
thermal and non-thermal sputtering. We confirm that the expanding gas shell
stalls upon impact with the dense cloud and that gas-phase SLR injection occurs
slowly due to hydrodynamical instabilities at the cloud surface. In contrast,
dust grains of sufficient size (> 1 micron) decouple from the gas and penetrate
into the cloud within 0.1 Myr. Once inside the cloud, the dust grains are
destroyed by sputtering, releasing SLRs and rapidly enriching the dense
(potentially star-forming) regions. Our results suggest that SLR transport on
dust grains is a viable mechanism to explain SLR enrichment.Comment: 15 pages, 10 figures, Accepted for publication in MNRAS. Movies can
be found here: http://user.physics.unc.edu/~mdgood86/research.htm
Effect of reheating on predictions following multiple-field inflation
We study the sensitivity of cosmological observables to the reheating phase
following inflation driven by many scalar fields. We describe a method which
allows semi-analytic treatment of the impact of perturbative reheating on
cosmological perturbations using the sudden decay approximation. Focusing on
-quadratic inflation, we show how the scalar spectral index and
tensor-to-scalar ratio are affected by the rates at which the scalar fields
decay into radiation. We find that for certain choices of decay rates,
reheating following multiple-field inflation can have a significant impact on
the prediction of cosmological observables.Comment: Published in PRD. 4 figures, 10 page
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