2,698 research outputs found

### The wave function discord

Linde's proposal of a Euclidean path integral with the ``wrong'' sign of
Euclidean action is often identified with the tunneling proposal for the wave
function of the universe. However, the two proposals are in fact quite
different. I illustrate the difference and point out that recent criticism by
Hawking and Turok does not apply to the tunneling proposal.Comment: 7 pages, 2 figure

### The No-Boundary Wave Function and the Duration of the Inflationary Period

For the simplest minisuperspace model based on a homogeneous, isotropic
metric and a minimally coupled scalar field we derive analytic expressions for
the caustic which separates Euklidean and Minkowskian region and its breakdown
value \p_*. This value represents the prediction of the no-boundary wave
function for the scalar field at the beginning of inflation. We use our results
to search for inflationary models which can render the no-boundary wave
function consistent with the requirement of a sufficiently long inflationary
period.Comment: 11 pages, TUM-HEP-206/94, 2 figures (added as uu-encoded postscript
file

### Scaling of cosmic string loops

We study the spectrum of loops as a part of a complete network of cosmic
strings in flat spacetime. After a long transient regime, characterized by
production of small loops at the scale of the initial conditions, it appears
that a true scaling regime takes over. In this final regime the characteristic
length of loops scales as $0.1 t$, in contrast to earlier simulations which
found tiny loops. We expect the expanding-universe behavior to be qualitatively
similar. The large loop sizes have important cosmological implications. In
particular, the nucleosynthesis bound becomes $G\mu \lesssim 10^{-7}$, much
tighter than before.Comment: Added discussion of gravitational wave bounds; other minor change

### Ultra high energy neutrinos from hidden-sector topological defects

We study Topological Defects (TD) in hidden (mirror) matter as possible
sources of ultra-high energy neutrinos. The hidden/mirror and ordinary matter
are assumed to interact very weakly through gravity or superheavy particles. An
inflationary scenario is outlined in which superheavy defects are formed in
hidden/mirror matter (and not in ordinary matter), and at the same time the
density of mirror matter produced at the end of inflation is much smaller than
that of ordinary matter. Superheavy particles produced by hidden-sector TD and
the products of their decays are all sterile in our world. Only mirror
neutrinos oscillate into ordinary neutrinos. We show that oscillations with
maximal mixing of neutrinos from both worlds are possible and that values of
$\Delta m^2$, needed for for solution of solar-neutrino and
atmospheric-neutrino problems, allow the oscillation of ultra-high energy
neutrinos on a timescale of the age of the Universe. A model of mass-degenerate
visible and mirror neutrinos with maximal mixing is constructed. Constraints on
UHE neutrino fluxes are obtained. The estimated fluxes can be 3 orders of
magnitude higher than those from ordinary matter. Detection of these fluxes is
briefly discussed.Comment: Revtex, 31 page

### Non-linear dynamics of cosmic strings with non-scaling loops

At early stages the dynamics of cosmic string networks is expected to be
influenced by an excessive production of small loops at the scales of initial
conditions l_{min}. To understand the late time behavior we propose a very
simple analytical model of strings with a non-scaling population of loops. The
complicated non-linear dynamics is described by only a single parameter N ~
2/(1-C(l_{min})) where C(l) is a correlation function of the string tangent
vectors. The model predicts an appearance of two new length scales: the
coherence length \xi ~ t/N^2 and the cross-correlation length \chi ~ t/N. At
the onset of evolution N ~ 10 and at late times N is expected to grow
logarithmically due to cosmological stretching and emission of small loops. The
very late time evolution might be modified further when the gravitational
back-reaction scale grows larger than l_{min}.Comment: 5 pages, minor corrections, accepted for publication in Physical
Review

### WKB Wave Functions with the Induced Gravity Theory

The Wheeler-DeWitt equation for the induced gravity theory is constructed in
the minisuperspace approximation, and then solved using the WKB method under
three types of boundary condition proposed respectively by Hartle & Hawking
(``no boundary''), Linde and Vilenkin (``tunneling from nothing''). It is found
that no matter how the gravitational and cosmological ``constants'' vary in the
classical models, they will acquire constant values when the universe comes
from quantum creation, and that, in particular, the resulting tunneling wave
function under the Linde or Vilenkin boundary condition reaches its maximum
value if the cosmological constant vanishes.Comment: 10 pages, no figure, LaTex fil

### Schroedinger Wheeler-DeWitt Equation In Multidimensional Cosmology

We study multidimensional cosmology to obtain the wavefunction of the
universe using wormhole dominance proposal. Using a prescription for time we
obtain the Schroedinger-Wheeler-DeWitt equation without any reference to WD
equation and WKB ansatz for WD wavefunction. It is found that the
Hartle-Hawking or wormhole-dominated boundary conditions serve as a seed for
inflation as well as for Gaussian type ansatz to Schroedinger-Wheeler-DeWitt
equation.Comment: 10 Pages, LaTeX, no figur

### Iso-curvature fluctuations through axion trapping by cosmic string wakes

We consider wake-like density fluctuations produced by cosmic strings at the
quark-hadron transition in the early universe. We show that low momentum axions
which are produced through the radiation from the axionic string at an earlier
stage, may get trapped inside these wakes due to delayed hadronization in these
overdense regions. As the interfaces, bordering the wakes, collapse, the axions
pick-up momentum from the walls and finally leave the wake regions. These
axions thus can produce large scale iso-curvature fluctuations. We have
calculated the detailed profile of these axionic density fluctuations and
discuss its astrophysical consequences.Comment: 23 pages, 4 figures, RevTe

### Effects of friction on cosmic strings

We study the evolution of cosmic strings taking into account the frictional
force due to the surrounding radiation. We consider small perturbations on
straight strings, oscillation of circular loops and small perturbations on
circular loops. For straight strings, friction exponentially suppresses
perturbations whose co-moving scale crosses the horizon before cosmological
time $t_*\sim \mu^{-2}$ (in Planck units), where $\mu$ is the string tension.
Loops with size much smaller than $t_*$ will be approximately circular at the
time when they start the relativistic collapse. We investigate the possibility
that such loops will form black holes. We find that the number of black holes
which are formed through this process is well bellow present observational
limits, so this does not give any lower or upper bounds on $\mu$. We also
consider the case of straight strings attached to walls and circular holes that
can spontaneously nucleate on metastable domain walls.Comment: 32 pages, TUTP-93-

### Tunneling in quantum cosmology: numerical study of particle creation

We consider a minisuperspace model for a closed universe with small and
positive cosmological constant, filled with a massive scalar field conformally
coupled to gravity. In the quantum version of this model, the universe may
undergo a tunneling transition through an effective barrier between regions of
small and large scale factor. We solve numerically the minisuperspace
Wheeler--De Witt equation with tunneling boundary conditions for the wave
function of the universe, and find that tunneling in quantum cosmology is quite
different from that in quantum mechanics. Namely, the matter degree of freedom
gets excited under the barrier, provided its interaction with the scale factor
is not too weak, and makes a strong back reaction onto tunneling. In the
semiclassical limit of small values of cosmological constant, the matter energy
behind the barrier is close to the height of the barrier: the system ``climbs
up'' the barrier, and then evolves classically from its top. These features are
even more pronounced for inhomogeneous modes of matter field. Extrapolating to
field theory we thus argue that high momentum particles are copiously created
in the tunneling process. Nevertheless, we find empirical evidence for the
semiclassical-type scaling with the cosmological constant of the wave function
under and behind the barrier.Comment: 29 pages, 17 figure

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