6,260 research outputs found
Quantum Gravitational Contributions to the CMB Anisotropy Spectrum
We derive the primordial power spectrum of density fluctuations in the
framework of quantum cosmology. For this purpose we perform a Born-Oppenheimer
approximation to the Wheeler-DeWitt equation for an inflationary universe with
a scalar field. In this way we first recover the scale-invariant power spectrum
that is found as an approximation in the simplest inflationary models. We then
obtain quantum gravitational corrections to this spectrum and discuss whether
they lead to measurable signatures in the CMB anisotropy spectrum. The
non-observation so far of such corrections translates into an upper bound on
the energy scale of inflation.Comment: 4 pages, v3: sign error in Eq. (5) and its consequences correcte
Cosmological Constant from Decoherence
We address the issue why a cosmological constant (dark energy) possesses a
small positive value instead of being zero. Motivated by the cosmic landscape
picture, we mimic the dark energy by a scalar field with potential wells and
show that other degrees of freedom interacting with it can localize this field
by decoherence in one of the wells. Dark energy can then acquire a small
positive value. We also show that the additional degrees of freedom enhance the
tunneling rate between the wells. The consideration is performed in detail for
the case of two wells and then extended to a large number of wells.Comment: 39 pages, 2 figures, final versio
Can the Arrow of Time be understood from Quantum Cosmology?
I address the question whether the origin of the observed arrow of time can
be derived from quantum cosmology. After a general discussion of entropy in
cosmology and some numerical estimates, I give a brief introduction into
quantum geometrodynamics and argue that this may provide a sufficient framework
for studying this question. I then show that a natural boundary condition of
low initial entropy can be imposed on the universal wave function. The arrow of
time is then correlated with the size of the Universe and emerges from an
increasing amount of decoherence due to entanglement with unobserved degrees of
freedom. Remarks are also made concerning the arrow of time in multiverse
pictures and scenarios motivated by dark energy.Comment: 14 pages, to appear in "The Arrow of Time", ed. by L.
Mersini-Houghton and R. Vaa
Quantum Gravity Equation In Schroedinger Form In Minisuperspace Description
We start from classical Hamiltonian constraint of general relativity to
obtain the Einstein-Hamiltonian-Jacobi equation. We obtain a time parameter
prescription demanding that geometry itself determines the time, not the matter
field, such that the time so defined being equivalent to the time that enters
into the Schroedinger equation. Without any reference to the Wheeler-DeWitt
equation and without invoking the expansion of exponent in WKB wavefunction in
powers of Planck mass, we obtain an equation for quantum gravity in
Schroedinger form containing time. We restrict ourselves to a minisuperspace
description. Unlike matter field equation our equation is equivalent to the
Wheeler-DeWitt equation in the sense that our solutions reproduce also the
wavefunction of the Wheeler-DeWitt equation provided one evaluates the
normalization constant according to the wormhole dominance proposal recently
proposed by us.Comment: 11 Pages, ReVTeX, no figur
Remarks on the issue of time and complex numbers in canonical quantum gravity
We develop the idea that, as a result of the arbitrariness of the factor
ordering in Wheeler-DeWitt equation, gauge phases can not, in general, being
completely removed from the wave functional in quantum gravity. The latter may
be conveniently described by means of a remnant complex term in WDW equation
depending of the factor ordering. Taking this equation for granted we can
obtain WKB complex solutions and, therefore, we should be able to derive a
semiclassical time parameter for the Schroedinger equation corresponding to
matter fields in a given classical curved space.Comment: Typewritten using RevTex, to appear in Phys. Rev.
The effects of the interaction of polymeric materials with the space environment
Polymeric materials in low earth orbit will be exposed to a harmful environment mainly due to atomic oxygen and ultraviolet radiation. In geosynchronous earth orbit, the major hazards to such materials are energetic charged particles and ultraviolet radiation. The progress of studies on the effects of these hazards on a polyetherimide, a polyimide, and an epoxy adhesive is presented
Frequency response of intracavity laser coupling modulation
A resonant energy coupling between the atomic system and the oscillating optical mode leads to severe output distortion in intracavity laser coupling modulation. This anomalous behavior, which places a lower limit on the modulation frequency, is investigated in a case of a CO2 laser and compared with theoretical predictions
Space environmental effects on polymeric materials
Two of the major environmental hazards in the Geosynchronous Earth Orbit (GEO) are energetic charged particles and ultraviolet radiation. The charged particles, electrons and protons, range in energy from 0.1 to 4 MeV and each have a flux of 10 to the 8th sq cm/sec. Over a 30 year lifetime, materials in the GEO will have an absorbed dose from this radiation of 10 to the 10th rads. The ultraviolet radiation comes uninhibited from the sun with an irradiance of 1.4 kw/sq m. Radiation is known to initiate chain sission and crosslinking in polymeric materials, both of which affect their structural properties. The 30-year dose level from the combined radiation in the GEO exceeds the threshold for measurable damage in most polymer systems studied. Of further concern is possible synergistic effects from the simultaneous irradiation with charged particles and ultraviolet radiation. Most studies on radiation effects on polymeric materials use either electrons or ultraviolet radiation alone, or in a sequential combination
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