4,136 research outputs found
Echo of the Quantum Bounce
We identify a signature of quantum gravitational effects that survives from
the early universe to the current era: Fluctuations of quantum fields as seen
by comoving observers are significantly influenced by the history of the early
universe. In particular we show how the existence (or not) of a quantum bounce
leaves a trace in the background quantum noise that is not damped and would be
non-negligible even nowadays. Furthermore, we estimate an upper bound for the
typical energy and length scales where quantum effects are relevant. We discuss
how this signature might be observed and therefore used to build falsifiability
tests of quantum gravity theories.Comment: Revtex4.1. 2 Figures. V2: Content extended and edited to match
published versio
The Quantum Echo of the Early Universe
We show that the fluctuations of quantum fields as seen by late comoving
observers are significantly influenced by the history of the early Universe,
and therefore they transmit information about the nature of spacetime in
timescales when quantum gravitational effects were non-negligible. We discuss
how this may be observable even nowadays, and thus used to build falsifiability
tests of quantum gravity theories.Comment: 3 pages. 2 Figures. Proceedings Theory Canada 9. Published in
Canadian Journal of Physics.
(http://www.nrcresearchpress.com/doi/abs/10.1139/cjp-2014-0567
Violation of the strong Huygen's principle and timelike signals from the early Universe
We analyze the implications of the violations of the strong Huygens principle
in the transmission of information from the early universe to the current era
via massless fields. We show that much more information reaches us through
timelike channels (not mediated by real photons) than it is carried by rays of
light, which are usually regarded as the only carriers of information.Comment: 5 pages, 2 figures. RevTeX 4.1. V2: Updated to match published
version. Previous title "A glimpse of the early universe without real light"
modified to match Physical Review Letters published versio
Physical evolution in Loop Quantum Cosmology: The example of vacuum Bianchi I
We use the vacuum Bianchi I model as an example to investigate the concept of
physical evolution in Loop Quantum Cosmology (LQC) in the absence of the
massless scalar field which has been used so far in the literature as an
internal time. In order to retrieve the system dynamics when no such a suitable
clock field is present, we explore different constructions of families of
unitarily related partial observables. These observables are parameterized,
respectively, by: (i) one of the components of the densitized triad, and (ii)
its conjugate momentum; each of them playing the role of an evolution
parameter. Exploiting the properties of the considered example, we investigate
in detail the domains of applicability of each construction. In both cases the
observables possess a neat physical interpretation only in an approximate
sense. However, whereas in case (i) such interpretation is reasonably accurate
only for a portion of the evolution of the universe, in case (ii) it remains so
during all the evolution (at least in the physically interesting cases). The
constructed families of observables are next used to describe the evolution of
the Bianchi I universe. The performed analysis confirms the robustness of the
bounces, also in absence of matter fields, as well as the preservation of the
semiclassicality through them. The concept of evolution studied here and the
presented construction of observables are applicable to a wide class of models
in LQC, including quantizations of the Bianchi I model obtained with other
prescriptions for the improved dynamics.Comment: RevTex4, 22 pages, 4 figure
MEMS enabled Fabry-Perot cavity for cQED experiments
The development of novel experimental techniques in atomic physics is allowing for the manipulation and control of atoms in structured silicon chips. These new techniques to manipulate atoms in a chip require building micro systems on chip that support actuation, alignment control and tunability for each micro component, which requires a significant integration effort. One example of a new experimental technique in atomic physics is the realization of optical cavities which is a very attractive model for quantum information and communication, because it permits the study of light-matter effect. The important exigency of an integrated micro cavity consisting of a micro mirror and a fiber optics cable are; alignment between them to form a small cavity volume and actuation to allow for adjusment of the cavity length. In this Master thesis the fabrication of 1-D v-shape or chevron thermal actuator is proposed based on the following characteristics: the actuator exploits the thermal expansion property of silicon to generate mechanical actuation, offers linear in-plane displacement, large force in small area compared to other actuators schemes and a shuttle that is capable of carrying an optical fiber that creates an optical cavity between it and a micro-mirror. Additionally, fabrication and characterization techniques are also described for the highly reflective (99.9988\\%) micro-mirrors
Chemical Abundances of Planetary Nebulae in the Substructures of M31
We present deep spectroscopy of planetary nebulae (PNe) that are associated
with the substructures of the Andromeda Galaxy (M31). The spectra were obtained
with the OSIRIS spectrograph on the 10.4 m GTC. Seven targets were selected for
the observations, three in the Northern Spur and four associated with the Giant
Stream. The most distant target in our sample, with a rectified galactocentric
distance >100 kpc, was the first PN discovered in the outer streams of M31. The
[O III] 4363 auroral line was well detected in the spectra of all targets,
enabling electron temperature determination. Ionic abundances are derived based
on the [O III] temperatures, and elemental abundances of helium, nitrogen,
oxygen, neon, sulfur, and argon are estimated. The relatively low N/O and He/H
ratios as well as abundance ratios of alpha-elements indicate that our target
PNe might belong to populations as old as ~2 Gyr. Our PN sample, including the
current seven and the previous three observed by Fang et al., have rather
homogeneous oxygen abundances. The study of abundances and the spatial and
kinematical properties of our sample leads to the tempting conclusion that
their progenitors might belong to the same stellar population, which hints at a
possibility that the Northern Spur and the Giant Stream have the same origin.
This may be explained by the stellar orbit proposed by Merrett et al. Judging
from the position and kinematics, we emphasize that M32 might be responsible
for the two substructures. Deep spectroscopy of PNe in M32 will help to assess
this hypothesis.Comment: Accepted for publication in the ApJ. 23 pages, including 13 figures
and 7 table
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