1,724,525 research outputs found
Primordial magnetic fields from the post-inflationary universe
No full textWe explore cosmological magnetogenesis in the post-inflationary universe, when the inflaton oscillates around its potential minimum and the universe is effectively dominated by cold matter. During this epoch prior to reheating, large-scale magnetic fields can be significantly produced by the cosmological background. By considering magnetogenesis both during and after inflation, we demonstrate that magnetic fields stronger than 10-15 G can be generated on Mpc scales without having strong couplings in the theory, or producing too large electric fields that would dominate the universe. © 2014 IOP Publishing Ltd and Sissa Medialab srl
Monopole-antimonopole pair production in primordial magnetic fields
Get PDFWe show that monopoles can be pair produced by cosmological magnetic fields in the early Universe. The pair production gives rise to relic monopoles and, at the same time, induces a self-screening of the magnetic fields. By studying these effects we derive limits on the monopole mass and also on the initial amplitude of primordial magnetic fields. Monopoles of GUT scale mass can even be produced if primordial magnetic fields exist at sufficiently high redshifts
Watada, E. et al., and Kobayashi, T.
No full textData for our paper in Mol Cell Biol (2020) "Age-dependent ribosomal DNA variations in mice
Axionlike Origin of the Primordial Density Perturbation
Get PDFWe show that an axionlike field coupled to a new confining gauge group can generate the primordial density perturbation in the postinflation Universe. The axion decay constant and strong coupling scale are uniquely determined by observations of the density perturbation, which further suggest a temporal deconfinement of the gauge group after inflation. The resulting temperature-dependent axion potential, together with its periodic nature, gives rise to the red-tilted density perturbation, with a positive local-type non-Gaussianity of order unity
Density perturbations from curvatons revisited
No full textWe investigate density perturbations sourced by a curvaton with a generic energy potential. The key feature of a curvaton potential which deviates from a quadratic is that the curvaton experiences a non-uniform onset of its oscillation. This sources additional contributions to the resulting density perturbations, and we especially find that curvaton potentials that are flatter compared to a quadratic lead to enhancement of the linear and second-order density perturbations, while steepened potentials can generate strongly scale-dependent non-Gaussianity. As such examples, we study pseudo-Nambu- Goldstone curvatons and self-interacting curvatons. Our analyses are analytic, and thus provide a systematic framework for studying curvatons in general. The discussion in this paper are based on [1, 2]. © Published under licence by IOP Publishing Ltd
Al<sub>x</sub>Ga<sub>1-x</sub>As synthesis by knock-on effect of atoms from Al films on GaAs by As<sup>+</sup> implantation
No full textThe synthesis of AlxGa1-xAs by depositing thin films of Al on GaAs substrates and irradiating with arsenic ions has been studied using photoluminescence, transmission electron microscopy and secondary ion mass spectrometry. Following implantation secondary ion mass spectrometry has identified appreciable levels of Al to a depth of about 0.25µm. AlGaAs emission within the photoluminescence spectra was seen for samples implanted with 1 x 1017 cm-2 of As+ at 150 keV through an Al-film of thickness 580 Angstrom and annealed at 950°C for 25sec. Transmission electron microscopy showed these layers to be single-crystal but characterised by dislocation loops of varying sizes
Large Tensor-to-Scalar Ratio in Small-Field Inflation
No full textWe show that density perturbations seeded by the inflaton can be suppressed when having additional light degrees of freedom contributing to the production of perturbations. The inflaton fluctuations affect the light field dynamics by modulating the length of the inflationary period and, hence, produce additional density perturbations in the postinflationary era. Such perturbations can cancel those generated during inflation as both originate from the same inflaton fluctuations. This allows production of large gravitational waves from small-field inflation, which is normally forbidden by the Lyth bound on the inflaton field excursion. We also find that the field bound is taken over by the light scalar when the inflaton-induced perturbations are suppressed and, thus, present a generalized form of the Lyth bound that applies to the total field space. The novel mechanism allows violation of the usual consistency relation r≤-8nT for the tensor spectral index. © 2013 American Physical Society
Effects of light fields during inflation
No full textIn the inflationary universe, there can be light fields other than the inflaton. We explore a possibility that such light fields source the primordial perturbations, while minimally affecting the inflaton dynamics. We show that during inflation, fluctuations of the light fields can be converted to adiabatic curvature perturbations, which accumulate and become significant by the end of the inflationary era. An additional goal of this work is to distinguish between light fields which can/cannot be ignored during inflation. Such criteria become useful for examining cosmological scenarios with multiple fields. As concrete examples, our results are applied to D-brane inflation models. We consider effects from KK modes (oscillation modes) of wrapped branes in monodromy-driven large-field models, and angular directions of throat geometries in warped D-brane inflation. © 2010 The American Physical Society
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