23,164 research outputs found
Dark energy: a quantum fossil from the inflationary Universe?
The discovery of dark energy (DE) as the physical cause for the accelerated
expansion of the Universe is the most remarkable experimental finding of modern
cosmology. However, it leads to insurmountable theoretical difficulties from
the point of view of fundamental physics. Inflation, on the other hand,
constitutes another crucial ingredient, which seems necessary to solve other
cosmological conundrums and provides the primeval quantum seeds for structure
formation. One may wonder if there is any deep relationship between these two
paradigms. In this work, we suggest that the existence of the DE in the present
Universe could be linked to the quantum field theoretical mechanism that may
have triggered primordial inflation in the early Universe. This mechanism,
based on quantum conformal symmetry, induces a logarithmic,
asymptotically-free, running of the gravitational coupling. If this evolution
persists in the present Universe, and if matter is conserved, the general
covariance of Einstein's equations demands the existence of dynamical DE in the
form of a running cosmological term whose variation follows a power law of the
redshift.Comment: LaTeX, 14 pages, extended discussion. References added. Accepted in
J. Phys. A: Mathematical and Theoretica
Region of the anomalous compression under Bondi-Hoyle accretion
We investigate the properties of an axisymmetric non-magnetized gas flow
without angular momentum on a small compact object, in particular, on a
Schwarzschild black hole in the supersonic region near the object; the velocity
of the object itself is assumed to be low compared to the speed of sound at
infinity. First of all, we see that the streamlines intersect (i.e., a caustic
forms) on the symmetry axis at a certain distance from the center on the
front side if the pressure gradient is neglected. The characteristic radial
size of the region, in which the streamlines emerging from the sonic surface at
an angle no larger than to the axis intersect, is To refine the flow structure in this region, we numerically
compute the system in the adiabatic approximation without ignoring the
pressure. We estimate the parameters of the inferred region with anomalously
high matter temperature and density accompanied by anomalously high energy
release.Comment: 10 pages, 2 figure
Glaciological and volcanological studies in the Wrangell Mountains, Alaska
There are no author-identified significant results in this report
Deterministic and cascadable conditional phase gate for photonic qubits
Previous analyses of conditional \phi-phase gates for photonic qubits that
treat cross-phase modulation (XPM) in a causal, multimode, quantum field
setting suggest that a large (~\pi rad) nonlinear phase shift is always
accompanied by fidelity-degrading noise [J. H. Shapiro, Phys. Rev. A 73, 062305
(2006); J. Gea-Banacloche, Phys. Rev. A 81, 043823 (2010)]. Using an atomic
V-system to model an XPM medium, we present a conditional phase gate that, for
sufficiently small nonzero \phi, has high fidelity. The gate is made cascadable
by using using a special measurement, principal mode projection, to exploit the
quantum Zeno effect and preclude the accumulation of fidelity-degrading
departures from the principal-mode Hilbert space when both control and target
photons illuminate the gate
Qudit-Basis Universal Quantum Computation using Interactions
We prove that universal quantum computation can be realized---using only
linear optics and (three-wave mixing) interactions---in any
-dimensional qudit basis of the -pump-photon subspace. First, we
exhibit a strictly universal gate set for the qubit basis in the
one-pump-photon subspace. Next, we demonstrate qutrit-basis universality by
proving that Hamiltonians and photon-number operators generate the
full Lie algebra in the two-pump-photon subspace, and showing
how the qutrit controlled- gate can be implemented with only linear optics
and interactions. We then use proof by induction to obtain our
general qudit result. Our induction proof relies on coherent photon
injection/subtraction, a technique enabled by interaction between
the encoding modes and ancillary modes. Finally, we show that coherent photon
injection is more than a conceptual tool in that it offers a route to preparing
high-photon-number Fock states from single-photon Fock states.Comment: 9 pages, 3 figure
Is There a Relationship between the Density of Primordial Black Holes in a Galaxy and the Rate of Cosmological Gamma-Ray Bursts?
The rate of accretion of matter from a solar-type star onto a primordial
black hole (PBH) that passes through it is calculated. The probability that a
PBH is captured into an orbit around a star in a galaxy is found. The mean
lifetime of the PBH in such an orbit and the rate of orbital captures of PBHs
in the galaxy are calculated. It is shown that this rate does not depend on the
mass of the PBH. This mechanism cannot make an appreciable contribution to the
rate of observed gamma-ray bursts. The density of PBHs in the galaxy can reach
a critical value - the density of the mass of dark matter in the galaxy.Comment: 7 page
Vegetative and geologic mapping of the western Seward Peninsula, Alaska, based on ERTS-1 imagery
ERTS-1 scene 1009-22095 (Western Seward Peninsula, Alaska) has been studied, partly as a training exercise, to evaluate whether direct visual examination of individual and custom color-composite prints can provide new information on the vegetation and geology of this relatively well known area of Alaska. The vegetation analysis reveals seven major vegetation types, only four of which are described on existing vegetation maps. In addition, the ERTS analysis provides greater detail than the existing maps on the areal distribution of vegetation types. The geologic analysis demonstrates that most of the major rock units and geomorphic boundaries shown on the available geologic maps could also be identified on the ERTS data. Several major high-angle faults were observed, but the zones of thrust faults which are much less obvious
Cosmology with variable parameters and effective equation of state for Dark Energy
A cosmological constant, Lambda, is the most natural candidate to explain the
origin of the dark energy (DE) component in the Universe. However, due to
experimental evidence that the equation of state (EOS) of the DE could be
evolving with time/redshift (including the possibility that it might behave
phantom-like near our time) has led theorists to emphasize that there might be
a dynamical field (or some suitable combination of them) that could explain the
behavior of the DE. While this is of course one possibility, here we show that
there is no imperative need to invoke such dynamical fields and that a variable
cosmological constant (including perhaps a variable Newton's constant too) may
account in a natural way for all these features.Comment: LaTeX, 9 pages, 1 figure. Talk given at the 7th Intern. Workshop on
Quantum Field Theory Under the Influence of External Conditions (QFEXT 05
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