115 research outputs found
Bubble fluctuations in inflation
In the context of the open inflationary universe, we calculate the amplitude
of quantum fluctuations which deform the bubble shape. These give rise to
scalar field fluctuations in the open Friedman-Robertson-Walker universe which
is contained inside the bubble. One can transform to a new gauge in which
matter looks perfectly smooth, and then the perturbations behave as tensor
modes (gravitational waves of very long wavelength). For , where
is the density parameter, the microwave temperature anisotropies
produced by these modes are of order . Here, is the expansion rate during inflation, is
the intrinsic radius of the bubble at the time of nucleation, is the
bubble wall tension and labels the different multipoles (). The
gravitational backreaction of the bubble has been ignored. In this
approximation, , and the new effect can be much larger than the
one due to ordinary gravitational waves generated during inflation (unless, of
course, gets too close to one, in which case the new effect
disappears).Comment: 17 pages, 3 figs, LaTeX, epsfig.sty, available at
ftp://ftp.ifae.es/preprint/ft/uabft387.p
Gravity Waves from Instantons
We perform a first principles computation of the spectrum of gravity waves
produced in open inflationary universes. The background spacetime is taken to
be the continuation of an instanton saddle point of the Euclidean no boundary
path integral. The two-point tensor correlator is computed directly from the
path integral and is shown to be unique and well behaved in the infrared. We
discuss the tensor contribution to the cosmic microwave background anisotropy
and show how it may provide an observational discriminant between different
types of primordial instantons.Comment: 19 pages, RevTex file, including two postscript figure file
Cosmological Perturbations from the No Boundary Euclidean Path Integral
We compute, from first principles, the quantum fluctuations about instanton
saddle points of the Euclidean path integral for Einstein gravity coupled to a
scalar field. The Euclidean two-point correlator is analytically continued into
the Lorentzian region where it describes the quantum mechanical vacuum
fluctuations in the state described by no boundary proposal initial conditions.
We concentrate on the density perturbations in open inflationary universes
produced from cosmological instantons, describing the differences between
non-singular Coleman-De Luccia and singular Hawking-Turok instantons. We show
how the Euclidean path integral uniquely specifies the fluctuations in both
cases.Comment: 21 pages, RevTex file, including five postscript figure file
In vitro propagation of cedar (Cedrela odorata L.) from juvenile shoots
Garriga, M (Garriga, Miguel); Caligari, PDS (Caligari, Peter D. S.). Univ Talca, Inst Biol Vegetal & Biotecnol, Talca, ChileCedrela odorata L. is one of the most important timber species currently traded in the Caribbean and Central America; however, it has been intensively exploited. In vitro techniques and clonal propagation can help to develop new plantations and assist in establishing improvement programs for this species. The aim of this study was to develop a protocol to establish in vitro conditions and to micropropagate this species from nodal explants from juvenile cuttings taken from field trees. Disinfection of node explants with 5% propiconazole CE 25 during 3 min resulted in 100% explant disinfection and 60% morphogenic response on those established explants. Shoot development was optimized by cultivating in vitro node explants in Murashige and Skoog basal medium supplemented with 2 mg L(-1) 6-bencilaminopurine and 3 mg L(-1) naphthaleneacetic acid. This medium resulted in 100% shoot development from the in vitro node explants with a 3.93 cm mean height. Rooting was also stimulated 6 wk after individualization of the regenerated plants on the same micropropagation medium with a mean of 3.9 roots per plant. In vitro plants did not show morphologic differences when compared to ex vitro seeds
A prescription for probabilities in eternal inflation
Some of the parameters we call ``constants of Nature'' may in fact be
variables related to the local values of some dynamical fields. During
inflation, these variables are randomized by quantum fluctuations. In cases
when the variable in question (call it ) takes values in a continuous
range, all thermalized regions in the universe are statistically equivalent,
and a gauge invariant procedure for calculating the probability distribution
for is known. This is the so-called ``spherical cutoff method''. In
order to find the probability distribution for it suffices to consider a
large spherical patch in a single thermalized region. Here, we generalize this
method to the case when the range of is discontinuous and there are
several different types of thermalized region. We first formulate a set of
requirements that any such generalization should satisfy, and then introduce a
prescription that meets all the requirements. We finally apply this
prescription to calculate the relative probability for different bubble
universes in the open inflation scenario.Comment: 15 pages, 5 figure
Primordial Gravitational Waves From Open Inflation
We calculate the spectrum of gravitational waves generated during inflation
in open inflationary models. In such models an initial epoch of
old inflation solves the horizon and flatness problems, and during this first
epoch of inflation the quantum state of the graviton field rapidly approaches
the Bunch-Davies vacuum. Then old inflation ends by the nucleation of a single
bubble, inside of which there is a shortened epoch of slow-roll inflation
giving today. In this paper we re-express the Bunch-Davies vacuum
for the graviton field in terms of the hyperbolic modes inside the bubble and
propagate these modes forward in time into the present era. We derive the
expression for the contribution from these gravity waves to the cosmic
microwave background anisotropy including the effect of a finite energy
difference across the bubble wall.Comment: 40 pages, TEX with phyzzx macro, 5 figure
Unambiguous probabilities in an eternally inflating universe
``Constants of Nature'' and cosmological parameters may in fact be variables
related to some slowly-varying fields. In models of eternal inflation, such
fields will take different values in different parts of the universe. Here I
show how one can assign probabilities to values of the ``constants'' measured
by a typical observer. This method does not suffer from ambiguities previously
discussed in the literature.Comment: 7 pages, Final version (minor changes), to appear in Phys. Rev. Let
Recycling universe
If the effective cosmological constant is non-zero, our observable universe
may enter a stage of exponential expansion. In such case, regions of it may
tunnel back to the false vacuum of an inflaton scalar field, and inflation with
a high expansion rate may resume in those regions. An ``ideal'' eternal
observer would then witness an infinite succession of cycles from false vacuum
to true, and back. Within each cycle, the entire history of a hot universe
would be replayed. If there were several minima of the inflaton potential, our
ideal observer would visit each one of these minima with a frequency which
depends on the shape of the potential. We generalize the formalism of
stochastic inflation to analyze the global structure of the universe when this
`recycling' process is taken into account.Comment: 43 pages, 10 figure
Quantized gravitational waves in the Milne universe
The quantization of gravitational waves in the Milne universe is discussed.
The relation between positive frequency functions of the gravitational waves in
the Milne universe and those in the Minkowski universe is clarified.
Implications to the one-bubble open inflation scenario are also discussed.Comment: 26 pages, 1 figure, revtex. submitted to Phys. Rev. D1
The density parameter and the Anthropic Principle
In the context of open inflation, we calculate the probability distribution
for the density parameter . A large class of two field models of open
inflation do not lead to infinite open universes, but to an ensemble of
inflating islands of finite size, or ``quasi-open'' universes, where the
density parameter takes a range of values. Assuming we are typical observers,
the models make definite predictions for the value we are most likely
to observe. When compared with observations, these predictions can be used to
constrain the parameters of the models. We also argue that obsevers should not
be surprised to find themselves living at the time when curvature is about to
dominate.Comment: Revised version, to be published in Phys. Rev.
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