4 research outputs found
Thermal Inflation and the Gravitational Wave Background
We consider the impact of thermal inflation -- a short, secondary period of
inflation that can arise in supersymmetric scenarios -- on the stochastic
gravitational wave background. We show that while the primordial inflationary
gravitational wave background is essentially unchanged at CMB scales, it is
massively diluted at solar system scales and would be unobservable by a BBO
style experiment. Conversely, bubble collisions at the end of thermal inflation
can generate a new stochastic background. We calculate the likely properties of
the bubbles created during this phase transition, and show that the expected
amplitude and frequency of this signal would fall within the BBO range.Comment: 21 pages, 4 figures; accepted for JCAP; a reference added; table
reformatte
Stochastic Gravitational Wave Production After Inflation
In many models of inflation, the period of accelerated expansion ends with
preheating, a highly non-thermal phase of evolution during which the inflaton
pumps energy into a specific set of momentum modes of field(s) to which it is
coupled. This necessarily induces large, transient density inhomogeneities
which can source a significant spectrum of gravitational waves. In this paper,
we consider the generic properties of gravitational waves produced during
preheating, perform detailed calculations of the spectrum for several specific
inflationary models, and identify problems that require further study. In
particular, we argue that if these gravitational waves exist they will
necessarily fall within the frequency range that is feasible for direct
detection experiments -- from laboratory through to solar system scales. We
extract the gravitational wave spectrum from numerical simulations of
preheating after and inflation, and find
that they lead to a gravitational wave amplitude of around . This is considerably higher than the amplitude of the primordial
gravitational waves produced during inflation. However, the typical wavelength
of these gravitational waves is considerably shorter than LIGO scales, although
in extreme cases they may be visible at scales accessible to the proposed BBO
mission. We survey possible experimental approaches to detecting any
gravitational wave background generated during preheating.Comment: 11 pages. Updated references. Minor clarification
A status report on the observability of cosmic bubble collisions
In the picture of eternal inflation as driven by a scalar potential with
multiple minima, our observable universe resides inside one of many bubbles
formed from transitions out of a false vacuum. These bubbles necessarily
collide, upsetting the homogeneity and isotropy of our bubble interior, and
possibly leading to detectable signatures in the observable portion of our
bubble, potentially in the Cosmic Microwave Background or other precision
cosmological probes. This constitutes a direct experimental test of eternal
inflation and the landscape of string theory vacua. Assessing this possibility
roughly splits into answering three questions: What happens in a generic bubble
collision? What observational effects might be expected? How likely are we to
observe a collision? In this review we report the current progress on each of
these questions, improve upon a few of the existing results, and attempt to lay
out directions for future work.Comment: Review article; comments very welcome. 24 pages + 4 appendices; 19
color figures. (Revised version adds two figures, minor edits.
Probing reheating temperature of the universe with gravitational wave background
Thermal history of the universe after big-bang nucleosynthesis (BBN) is well
understood both theoretically and observationally, and recent cosmological
observations also begin to reveal the inflationary dynamics. However, the epoch
between inflation and BBN is scarcely known. In this paper we show that the
detection of the stochastic gravitational wave background around 1Hz provides
useful information about thermal history well before BBN. In particular, the
reheating temperature of the universe may be determined by future space-based
laser interferometer experiments such as DECIGO and/or BBO if it is around
10^{6-9} GeV, depending on the tensor-to-scalar ratio and dilution factor
.Comment: 20 pages, 8 figure