697 research outputs found
Dynamics of false vacuum bubbles: beyond the thin shell approximation
We numerically study the dynamics of false vacuum bubbles which are inside an
almost flat background; we assumed spherical symmetry and the size of the
bubble is smaller than the size of the background horizon. According to the
thin shell approximation and the null energy condition, if the bubble is
outside of a Schwarzschild black hole, unless we assume Farhi-Guth-Guven
tunneling, expanding and inflating solutions are impossible. In this paper, we
extend our method to beyond the thin shell approximation: we include the
dynamics of fields and assume that the transition layer between a true vacuum
and a false vacuum has non-zero thickness. If a shell has sufficiently low
energy, as expected from the thin shell approximation, it collapses (Type 1).
However, if the shell has sufficiently large energy, it tends to expand. Here,
via the field dynamics, field values of inside of the shell slowly roll down to
the true vacuum and hence the shell does not inflate (Type 2). If we add
sufficient exotic matters to regularize the curvature near the shell, inflation
may be possible without assuming Farhi-Guth-Guven tunneling. In this case, a
wormhole is dynamically generated around the shell (Type 3). By tuning our
simulation parameters, we could find transitions between Type 1 and Type 2, as
well as between Type 2 and Type 3. Between Type 2 and Type 3, we could find
another class of solutions (Type 4). Finally, we discuss the generation of a
bubble universe and the violation of unitarity. We conclude that the existence
of a certain combination of exotic matter fields violates unitarity.Comment: 40 pages, 41 figure
Mass inflation in f(R) gravity: A conjecture on the resolution of the mass inflation singularity
We study gravitational collapse of a charged black hole in f(R) gravity using
double-null formalism. We require cosmological stability to f(R) models; we
used the Starobinsky model and the R + (1/2)cR^2 model. Charged black holes in
f(R) gravity can have a new type of singularity due to higher curvature
corrections, the so-called f(R)-induced singularity, although it is highly
model-dependent. As the advanced time increases, the internal structure will
approach the Cauchy horizon, which may not be an inner apparent horizon. There
is mass inflation as one approaches the Cauchy horizon and hence the Cauchy
horizon may be a curvature singularity with nonzero area. However, the Ricci
scalar is finite for an out-going null observer. This can be integrated as
follows: Cosmologically stable higher curvature corrections of the Ricci scalar
made it bounded even in the presence of mass inflation. Finally, we conjecture
that if there is a general action including general higher curvature
corrections with cosmological stability, then the corrections can make all
curvature components finite even in the presence of mass inflation. This might
help us to resolve the problem of inner horizon instability of regular black
hole models.Comment: 31 pages, 15 figure
Density functional theory of phase coexistence in weakly polydisperse fluids
The recently proposed universal relations between the moments of the
polydispersity distributions of a phase-separated weakly polydisperse system
are analyzed in detail using the numerical results obtained by solving a simple
density functional theory of a polydisperse fluid. It is shown that universal
properties are the exception rather than the rule.Comment: 10 pages, 2 figures, to appear in PR
Quantum optical coherence tomography with dispersion cancellation
We propose a new technique, called quantum optical coherence tomography
(QOCT), for carrying out tomographic measurements with dispersion-cancelled
resolution. The technique can also be used to extract the frequency-dependent
refractive index of the medium. QOCT makes use of a two-photon interferometer
in which a swept delay permits a coincidence interferogram to be traced. The
technique bears a resemblance to classical optical coherence tomography (OCT).
However, it makes use of a nonclassical entangled twin-photon light source that
permits measurements to be made at depths greater than those accessible via
OCT, which suffers from the deleterious effects of sample dispersion. Aside
from the dispersion cancellation, QOCT offers higher sensitivity than OCT as
well as an enhancement of resolution by a factor of 2 for the same source
bandwidth. QOCT and OCT are compared using an idealized sample.Comment: 19 pages, 4 figure
The influence of nonlinearities on the symmetric hydrodynamic response of a 10,000 TEU Container ship
The prediction of wave-induced motions and loads is of great importance for the design of marine structures. Linear potential flow hydrodynamic models are already used in different parts of the ship design development and appraisal process. However, the industry demands for design innovation and the possibilities offered by modern technology imply the need to also understand the modelling assumptions and associated influences of nonlinear hydrodynamic actions on ship response. At first instance, this paper presents the taxonomy of different Fluid Structure Interaction (FSI) methods that may be used for the assessment of ship motions and loads. Consequently, it documents in a practical way the effects of weakly nonlinear hydrodynamics on the symmetric wave-induced responses for a 10,000TEU Container ship. It is shown that the weakly nonlinear FSI models may be useful for the prediction of symmetric wave-induced loads and responses of such ship not only in way of amidships but also at the extremities of the hull. It is concluded that validation of hydrodynamic radiation and diffraction forces and their respective influence on ship response should be especially considered for those cases where the variations of the hull wetted surface in time may be noticeable
Creep behavior of copper-chromium in-situ composite
Creep deformation and fracture behaviors were investigated on a deformation-processed Cu-Cr in-situ composite over a temperature range of 200 °C to 650 °C. It was found that the creep resistance increases significantly with the introduction of Cr fibers into Cu. The stress exponent and the activation energy for creep of the composite at high temperatures (≥400 °C) were observed to be 5.5 and 180 to 216 kJ/mol, respectively. The observation that the stress exponent and the activation energy for creep of the composite at high temperatures (≥400 °C) are close to those of pure Cu suggests that the creep deformation of the composite is dominated by the deformation of the Cu matrix. The high stress exponent at low temperatures (200 °C and 300 °C) is thought be associated with the as-swaged microstructure, which contains elongated dislocation cells and subgrains that are stable and act as strong athermal obstacles at low temperatures. The mechanism of damage was found to be similar for all the creep tests performed, but the distribution and extent of damage were found to be very sensitive to the test temperature
Complementarity, quantum erasure and delayed choice with modified Mach-Zehnder interferometers
Often cited dictums in Quantum Mechanics include "observation disturbance
causes loss of interference" and "ignorance is interference". In this paper we
propose and describe a series of experiments with modified Mach-Zehnder
interferometers showing that one has to be careful when applying such dictums.
We are able to show that without interacting in any way with the light quantum
(or quanta) expected to behave "wave-like", interference fringes can be lost by
simply gaining (or having the potential to gain) the which-path knowledge.
Erasing this information may revive the interference fringes. Delayed choice
can be added, arriving to an experiment in line with Wheeler's original
proposal. We also show that ignorance is not always synonym with having the
interference fringes. The often-invoked "collapse of the wavefunction" is found
to be a non-necessary ingredient to describe our experiments.Comment: 8 pages, 3 figures; to appear in EPJ
Multiorder coherent Raman scattering of a quantum probe field
We study the multiorder coherent Raman scattering of a quantum probe field in
a far-off-resonance medium with a prepared coherence. Under the conditions of
negligible dispersion and limited bandwidth, we derive a Bessel-function
solution for the sideband field operators. We analytically and numerically
calculate various quantum statistical characteristics of the sideband fields.
We show that the multiorder coherent Raman process can replicate the
statistical properties of a single-mode quantum probe field into a broad comb
of generated Raman sidebands. We also study the mixing and modulation of photon
statistical properties in the case of two-mode input. We show that the prepared
Raman coherence and the medium length can be used as control parameters to
switch a sideband field from one type of photon statistics to another type, or
from a non-squeezed state to a squeezed state and vice versa.Comment: 12 pages, 7 figures, to be published in Phys. Rev.
Single Photons on Pseudo-Demand from Stored Parametric Down-Conversion
We describe the results of a parametric down-conversion experiment in which
the detection of one photon of a pair causes the other photon to be switched
into a storage loop. The stored photon can then be switched out of the loop at
a later time chosen by the user, providing a single photon for potential use in
a variety of quantum information processing applications. Although the stored
single photon is only available at periodic time intervals, those times can be
chosen to match the cycle time of a quantum computer by using pulsed
down-conversion. The potential use of the storage loop as a photonic quantum
memory device is also discussed.Comment: 8 pages, 7 Figs., RevTe
Multi-parameter Entanglement in Quantum Interferometry
The role of multi-parameter entanglement in quantum interference from
collinear type-II spontaneous parametric down-conversion is explored using a
variety of aperture shapes and sizes, in regimes of both ultrafast and
continuous-wave pumping. We have developed and experimentally verified a theory
of down-conversion which considers a quantum state that can be concurrently
entangled in frequency, wavevector, and polarization. In particular, we
demonstrate deviations from the familiar triangular interference dip, such as
asymmetry and peaking. These findings improve our capacity to control the
quantum state produced by spontaneous parametric down-conversion, and should
prove useful to those pursuing the many proposed applications of down-converted
light.Comment: submitted to Physical Review
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