201 research outputs found
Stationarity of Inflation and Predictions of Quantum Cosmology
We describe several different regimes which are possible in inflationary
cosmology. The simplest one is inflation without self-reproduction of the
universe. In this scenario the universe is not stationary. The second regime,
which exists in a broad class of inflationary models, is eternal inflation with
the self-reproduction of inflationary domains. In this regime local properties
of domains with a given density and given values of fields do not depend on the
time when these domains were produced. The probability distribution to find a
domain with given properties in a self-reproducing universe may or may not be
stationary, depending on the choice of an inflationary model. We give examples
of models where each of these possibilities can be realized, and discuss some
implications of our results for quantum cosmology. In particular, we propose a
new mechanism which may help solving the cosmological constant problem.Comment: 30 pages, Stanford preprint SU-ITP-94-24, LaTe
Topological Defects as Seeds for Eternal Inflation
We investigate the global structure of inflationary universe both by
analytical methods and by computer simulations of stochastic processes in the
early Universe. We show that the global structure of the universe depends
crucially on the mechanism of inflation. In the simplest models of chaotic
inflation the Universe looks like a sea of thermalized phase surrounding
permanently self-reproducing inflationary domains. In the theories where
inflation occurs near a local extremum of the effective potential corresponding
to a metastable state, the Universe looks like de Sitter space surrounding
islands of thermalized phase. A similar picture appears even if the state is unstable but the effective potential has a discrete symmetry . In this case the Universe becomes divided into domains containing
different phases. These domains will be separated from each other by domain
walls. However, unlike ordinary domain walls, these domain walls will inflate,
and their thickness will exponentially grow. In the theories with continuous
symmetries inflation generates exponentially expanding strings and monopoles
surrounded by thermalized phase. Inflating topological defects will be stable,
and they will unceasingly produce new inflating topological defects. This means
that topological defects may play a role of indestructible seeds for eternal
inflation.Comment: 21 pages, 17 figures (not included), Stanford University preprint
SU--ITP--94--
From the Big Bang Theory to the Theory of a Stationary Universe
We consider chaotic inflation in the theories with the effective potentials
phi^n and e^{\alpha\phi}. In such theories inflationary domains containing
sufficiently large and homogeneous scalar field \phi permanently produce new
inflationary domains of a similar type. We show that under certain conditions
this process of the self-reproduction of the Universe can be described by a
stationary distribution of probability, which means that the fraction of the
physical volume of the Universe in a state with given properties (with given
values of fields, with a given density of matter, etc.) does not depend on
time, both at the stage of inflation and after it. This represents a strong
deviation of inflationary cosmology from the standard Big Bang paradigm. We
compare our approach with other approaches to quantum cosmology, and illustrate
some of the general conclusions mentioned above with the results of a computer
simulation of stochastic processes in the inflationary Universe.Comment: No changes to the file, but original figures are included. They
substantially help to understand this paper, as well as eternal inflation in
general, and what is now called the "multiverse" and the "string theory
landscape." High quality figures can be found at
http://www.stanford.edu/~alinde/LLMbigfigs
Inflation with
We discuss various models of inflationary universe with . A
homogeneous universe with may appear due to creation of the
universe "from nothing" in the theories where the effective potential becomes
very steep at large , or in the theories where the inflaton field
nonminimally couples to gravity. Inflation with generally requires
intermediate first order phase transition with the bubble formation, and with a
second stage of inflation inside the bubble. It is possible to realize this
scenario in the context of a theory of one scalar field, but typically it
requires artificially bent effective potentials and/or nonminimal kinetic
terms. It is much easier to obtain an open universe in the models involving two
scalar fields. However, these models have their own specific problems. We
propose three different models of this type which can describe an open
homogeneous inflationary universe.Comment: 29 pages, LaTeX, parameters of one of the models are slightly
modifie
Relaxing the Cosmological Moduli Problem
Typically the moduli fields acquire mass m =C H in the early universe, which
shifts the position of the minimum of their effective potential and leads to an
excessively large energy density of the oscillating moduli fields at the later
stages of the evolution of the universe. This constitutes the cosmological
moduli problem, or Polonyi field problem. We show that the cosmological moduli
problem can be solved or at least significantly relaxed in the theories in
which C >> 1, as well as in some models with C << 1.Comment: 9 pages, 3 Postscript figure
Quantum Creation of an Open Inflationary Universe
We discuss a dramatic difference between the description of the quantum
creation of an open universe using the Hartle-Hawking wave function and the
tunneling wave function. Recently Hawking and Turok have found that the
Hartle-Hawking wave function leads to a universe with Omega = 0.01, which is
much smaller that the observed value of Omega > 0.3. Galaxies in such a
universe would be about light years away from each other, so the
universe would be practically structureless. We will argue that the
Hartle-Hawking wave function does not describe the probability of the universe
creation. If one uses the tunneling wave function for the description of
creation of the universe, then in most inflationary models the universe should
have Omega = 1, which agrees with the standard expectation that inflation makes
the universe flat. The same result can be obtained in the theory of a
self-reproducing inflationary universe, independently of the issue of initial
conditions. However, there exist two classes of models where Omega may take any
value, from Omega > 1 to Omega << 1.Comment: 23 pages, 4 figures. New materials are added. In particular, we show
that boundary terms do not help to solve the problem of unacceptably small
Omega in the new model proposed by Hawking and Turok in hep-th/9803156. A
possibility to solve the cosmological constant problem in this model using
the tunneling wave function is discusse
Islands in the landscape
The string theory landscape consists of many metastable de Sitter vacua,
populated by eternal inflation. Tunneling between these vacua gives rise to a
dynamical system, which asymptotically settles down to an equilibrium state. We
investigate the effects of sinks to anti-de Sitter space, and show how their
existence can change probabilities in the landscape. Sinks can disturb the
thermal occupation numbers that would otherwise exist in the landscape and may
cause regions that were previously in thermal contact to be divided into
separate, thermally isolated islands.Comment: 31 pages, 8 figure
Subcarrier wave continuous-variable quantum key distribution with Gaussian modulation: composable security analysis
In this paper, we continue the study of the quantum cryptographic GG02 protocol, performed using the approach based on the subcarrier waves. We modify the scheme via heterodyne detection and perform security analysis for the full trusted hardware noise model in the presence of collective attacks with finite-key effects. It is shown that the system can potentially distribute the key even if the level of losses in the channel is above 9 dB. This result is consistent with the general technical level and comply with modern standards of practical CV-QKD systems. Finally, the system under consideration fully meets the criterion of composability.The work was done by Leading Research Center "National Center for Quantum Internet" of ITMO University by order of JSCo Russian Railways
Hard tube pulser for 150 MW klystron
The development of adequate modulators for high peak power klystrons is one of the focus points for linear collider R&D programs. For the DESY/THD Sband linear collider study 150MW RF pulse power at 50Hz repetition rate and 3mks pulse duration is required. Two different modulator schemes were investigated. One is the conventional line type pulser, using a pulse forming network and a step up transformer, the other one is a Hard Tube Pulser, using a DC power source at the full klystron voltage and a switch tube. The main advantages of a Hard Tube Pulser are short rise and fall times of the HV pulse, resulting in high efficiency and simpler design
Effects of exposure of rat erythrocytes to a hypogeomagnetic field
The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.Background:Hypomagnetic fields can disrupts the normal functioning of living organisms by a mechanism thought to involve oxidative stress. In erythrocytes, oxidative stress can inter alia lead to changes to hemoglobin content and to hemolysis. Objective:To study the effects of hypomagnetism on the state of rat erythrocytes in vitro. Methods:Rat erythrocytes were exposed to an attenuated magnetic field (AMF) or Earth’s magnetic field (EMF), in the presence of tert-butyl hydroperoxide (TBHP) as inducer of oxidative stress. Determinations: total hemoglobin (and its three forms – oxyhemoglobin, methemoglobin, and hemichrome) released from erythrocytes, spectral data (500–700 nm); oxygen radical concentrations, electron paramagnetic resonance. Results:AMF and EMF exposed erythrocytes were compared. After 4 h incubation at high TBHP concentrations (>700 μM), AMF exposed erythrocytes released significantly more (p<0.05) hemoglobin (Hb), mostly as methemoglobin (metHb). Conversely, after 24 h incubation at low TBHP concentrations (⩽350 μM), EMF exposed erythrocytes released significantly more (p<0.001) hemoglobin, with metHb as a significant proportion of the total Hb. Erythrocytes exposed to AMF generated more radicals than those exposed to the EMF. Conclusion:Under particular conditions of oxidative stress, hypomagnetic fields can disrupt the functional state of erythrocytes and promote cell death; an additive effect is implicated
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