6 research outputs found
Gravitational waves from oscillons after inflation
We investigate the production of gravitational waves during preheating after
inflation in the common case of field potentials that are asymmetric around the
minimum. In particular, we study the impact of oscillons, comparatively long
lived and spatially localized regions where a scalar field (e.g. the inflaton)
oscillates with large amplitude. Contrary to a previous study, which considered
a symmetric potential, we find that oscillons in asymmetric potentials
associated with a phase transition can generate a pronounced peak in the
spectrum of gravitational waves, that largely exceeds the linear preheating
spectrum. We discuss the possible implications of this enhanced amplitude of
gravitational waves. For instance, for low scale inflation models, the
contribution from the oscillons can strongly enhance the observation prospects
at current and future gravitational wave detectors.Comment: 5 pages, 3 figures; v2: version published in PRL; v3: includes
Erratum (submitted to PRL
What can we learn from the stochastic gravitational wave background produced by oscillons?
The stochastic gravitational wave (GW) background provides a fascinating
window to the physics of the very early universe. Beyond the nearly
scale-invariant primordial GW spectrum produced during inflation, a spectrum
with a much richer structure is typically generated during the preheating phase
after inflation (or after some other phase transition at lower energies). This
raises the question of what one can learn from a future observation of the
stochastic gravitational wave background spectrum about the underlying physics
during preheating. Recently, it has been shown that during preheating
non-perturbative quasi-stable objects like oscillons can act as strong sources
for GW, leading to characteristic features such as distinct peaks in the
spectrum. In this paper, we study the GW production from oscillons using
semi-analytical techniques. In particular, we discuss how the GW spectrum is
affected by the parameters that characterise a given oscillon system, e.g. by
the background cosmology, the asymmetry of the oscillons and the evolution of
the number density of the oscillons. We compare our semi-analytic results with
numerical lattice simulations for a hilltop inflation model and a KKLT
scenario, which differ strongly in some of these characteristics, and find very
good agreement.Comment: 25 pages + Appendix, 16 figure
False vacuum energy dominated inflation with large and the importance of
We investigate to which extent and under which circumstances false vacuum
energy () dominated slow-roll inflation is compatible with a large
tensor-to-scalar ratio , as indicated by the recent BICEP2
measurement. With we refer to a constant contribution to the inflaton
potential, present before a phase transition takes place and absent in the true
vacuum of the theory, like e.g. in hybrid inflation. Based on model-independent
considerations, we derive an upper bound on the possible amount of
domination and highlight the importance of higher-order runnings of the scalar
spectral index (beyond ) in order to realise scenarios of
dominated inflation. We study the conditions for domination explicitly
with an inflaton potential reconstruction around the inflaton field value 50
e-folds before the end of inflation, taking into account the present
observational data. To this end, we provide the up-to-date parameter
constraints within CDM + + + using the
cosmological parameter estimation code Monte Python together with the Boltzmann
code CLASS.Comment: 16 pages, 5 figures; v2: matches publication in JCA
Oscillons from String Moduli
A generic feature of string compactifications is the presence of many scalar
fields, called moduli. Moduli are usually displaced from their
post-inflationary minimum during inflation. Their relaxation to the minimum
could lead to the production of oscillons: localised, long-lived, non-linear
excitations of the scalar fields. Here we discuss under which conditions
oscillons can be produced in string cosmology and illustrate their production
and potential phenomenology with two explicit examples: the case of an
initially displaced volume modulus in the KKLT scenario and the case of a
displaced blow-up Kaehler modulus in the Large Volume Scenario (LVS). One, in
principle, observable consequence of oscillon dynamics is the production of
gravitational waves which, contrary to those produced from preheating after
high scale inflation, could have lower frequencies, closer to the currently
observable range. We also show that, for the considered parameter ranges,
oscillating fibre and volume moduli do not develop any significant
non-perturbative dynamics. Furthermore, we find that the vacua in the LVS and
the KKLT scenario are stable against local overshootings of the field into the
decompatification region, which provides an additional check on the longevity
of these metastable configurations.Comment: 32 pages + appendix, 23 figures, for videos of the simulations see
https://particlesandcosmology.unibas.ch/downloads/oscillons-from-string-moduli-movies.htm
Properties of Oscillons in Hilltop Potentials: energies, shapes, and lifetimes
Oscillons are spatially localised strong fluctuations of a scalar field. They can e.g. form after inflation when the scalar field potential is shallower than quadratic away from the minimum. Although oscillons are not protected by topology, they can be remarkably stable and have a significant impact on the (p)reheating phase. In this work we investigate the properties of oscillons in hilltop-shaped potentials, in particular the typical energies, shapes and lifetimes. In the first part of the paper, we simulate oscillon creation and stabilization with (3+1)-dimensional classical lattice simulations, and extract the typical energies, radii and amplitudes of the oscillons. In the second part we approximate the oscillons as spherically symmetric, and simulate single oscillons until their decay. We find that typical oscillons live up to about 10(4)-10(5) field oscillations, with the individual lifetime of the oscillons depending mainly on the initial shape of the oscillon and the power-law coefficient characterising the particular hilltop model. We also observe a breathing mode in the oscillon radii and amplitudes, and find that stronger breathing implies shorter lifetimes
Parametric resonance after hilltop inflation caused by an inhomogeneous inflaton field
We study preheating after hilltop inflation where the inflaton couples to another scalar field, e.g. a right-handed sneutrino, which provides a mechanism for generating the correct initial conditions for inflation and also a decay channel for the inflaton that allows for reheating and non-thermal leptogenesis. In the presence of such a coupling, we find that after the phases of tachyonic preheating and tachyonic oscillations, during which the inflaton field becomes inhomogeneous, there can be a subsequent preheating phase where the fluctuations of the other field get resonantly enhanced, from initial vacuum fluctuations up to amplitudes of the same order (and even larger) as the ones of the inflaton field. This resonant enhancement differs from the usual parametric resonance as the inflaton field is inhomogeneous at the time the enhancement takes place. We study this effect using lattice simulations as well as semi-analytically with a generalized Floquet analysis for inhomogeneous background fields