257 research outputs found
Initial correlations effects on decoherence at zero temperature
We consider a free charged particle interacting with an electromagnetic bath
at zero temperature. The dipole approximation is used to treat the bath
wavelengths larger than the width of the particle wave packet. The effect of
these wavelengths is described then by a linear Hamiltonian whose form is
analogous to phenomenological Hamiltonians previously adopted to describe the
free particle-bath interaction. We study how the time dependence of decoherence
evolution is related with initial particle-bath correlations. We show that
decoherence is related to the time dependent dressing of the particle. Moreover
because decoherence induced by the T=0 bath is very rapid, we make some
considerations on the conditions under which interference may be experimentally
observed.Comment: 16 pages, 1 figur
Inflating Lorentzian Wormholes
It has been speculated that Lorentzian wormholes of the Morris- Thorne type
might be allowed by the laws of physics at submicroscopic, e.g. Planck, scales
and that a sufficiently advanced civilization might be able to enlarge them to
classical size. The purpose of this paper is to explore the possibility that
inflation might provide a natural mechanism for the enlargement of such
wormholes to macroscopic size. A new classical metric is presented for a
Lorentzian wormhole which is imbedded in a flat deSitter space. It is shown
that the throat and proper length of the wormhole inflate. The resulting
properties and stress-energy tensor associated with this metric are discussed.Comment: 24 pg
Stochastic Theory of Relativistic Particles Moving in a Quantum Field: II. Scalar Abraham-Lorentz-Dirac-Langevin Equation, Radiation Reaction and Vacuum Fluctuations
We apply the open systems concept and the influence functional formalism
introduced in Paper I to establish a stochastic theory of relativistic moving
spinless particles in a quantum scalar field. The stochastic regime resting
between the quantum and semi-classical captures the statistical mechanical
attributes of the full theory. Applying the particle-centric world-line
quantization formulation to the quantum field theory of scalar QED we derive a
time-dependent (scalar) Abraham-Lorentz-Dirac (ALD) equation and show that it
is the correct semiclassical limit for nonlinear particle-field systems without
the need of making the dipole or non-relativistic approximations. Progressing
to the stochastic regime, we derive multiparticle ALD-Langevin equations for
nonlinearly coupled particle-field systems. With these equations we show how to
address time-dependent dissipation/noise/renormalization in the semiclassical
and stochastic limits of QED. We clarify the the relation of radiation
reaction, quantum dissipation and vacuum fluctuations and the role that initial
conditions may play in producing non-Lorentz invariant noise. We emphasize the
fundamental role of decoherence in reaching the semiclassical limit, which also
suggests the correct way to think about the issues of runaway solutions and
preacceleration from the presence of third derivative terms in the ALD
equation. We show that the semiclassical self-consistent solutions obtained in
this way are ``paradox'' and pathology free both technically and conceptually.
This self-consistent treatment serves as a new platform for investigations into
problems related to relativistic moving charges.Comment: RevTex; 20 pages, 3 figures, Replaced version has corrected typos,
slightly modified derivation, improved discussion including new section with
comparisons to related work, and expanded reference
The absolute infrared magnitudes of type Ia supernovae
The absolute luminosities and homogeneity of early-time infrared (IR) light
curves of type Ia supernovae are examined. Eight supernovae are considered.
These are selected to have accurately known epochs of maximum blue light as
well as having reliable distance estimates and/or good light curve coverage.
Two approaches to extinction correction are considered. Owing to the low
extinction in the IR, the differences in the corrections via the two methods
are small. Absolute magnitude light curves in the J, H and K-bands are derived.
Six of the events, including five established ``Branch-normal'' supernovae show
similar coeval magnitudes. Two of these, SNe 1989B and 1998bu, were observed
near maximum infrared light. This occurs about 5 days {\it before} maximum blue
light. Absolute peak magnitudes of about -19.0, -18.7 and -18.8 in J, H & K
respectively were obtained. The two spectroscopically peculiar supernovae in
the sample, SNe 1986G and 1991T, also show atypical IR behaviour. The light
curves of the six similar supernovae can be represented fairly consistently
with a single light curve in each of the three bands. In all three IR bands the
dispersion in absolute magnitude is about 0.15 mag, and this can be accounted
for within the uncertainties of the individual light curves. No significant
variation of absolute IR magnitude with B-band light curve decline rate, Delta
m_{15}(B), is seen over the range 0.87<Delta m_{15}(B)<1.31. However, the data
are insufficient to allow us to decide whether or not the decline rate relation
is weaker in the IR than in the optical region. IR light curves of type Ia
supernovae should eventually provide cosmological distance estimates which are
of equal or even superior quality to those obtained in optical studies.Comment: 19 pages, 9 figures, MNRAS in press (includes Referee's changes
Testing A (Stringy) Model of Quantum Gravity
I discuss a specific model of space-time foam, inspired by the modern
non-perturbative approach to string theory (D-branes). The model views our
world as a three brane, intersecting with D-particles that represent stringy
quantum gravity effects, which can be real or virtual. In this picture, matter
is represented generically by (closed or open) strings on the D3 brane
propagating in such a background. Scattering of the (matter) strings off the
D-particles causes recoil of the latter, which in turn results in a distortion
of the surrounding space-time fluid and the formation of (microscopic, i.e.
Planckian size) horizons around the defects. As a mean-field result, the
dispersion relation of the various particle excitations is modified, leading to
non-trivial optical properties of the space time, for instance a non-trivial
refractive index for the case of photons or other massless probes. Such models
make falsifiable predictions, that may be tested experimentally in the
foreseeable future. I describe a few such tests, ranging from observations of
light from distant gamma-ray-bursters and ultra high energy cosmic rays, to
tests using gravity-wave interferometric devices and terrestrial particle
physics experients involving, for instance, neutral kaons.Comment: 25 pages LATEX, four figures incorporated, uses special proceedings
style. Invited talk at the third international conference on Dark Matter in
Astro and Particle Physics, DARK2000, Heidelberg, Germany, July 10-15 200
Climate-sensitive health priorities in Nunatsiavut, Canada
Background: This exploratory study used participatory methods to identify, characterize, and rank climate-sensitive health priorities in Nunatsiavut, Labrador, Canada. Methods: A mixed method study design was used and involved collecting both qualitative and quantitative data at regional, community, and individual levels. In-depth interviews with regional health representatives were conducted throughout Nunatsiavut (n = 11). In addition, three PhotoVoice workshops were held with Rigolet community members (n = 11), where participants took photos of areas, items, or concepts that expressed how climate change is impacting their health. The workshop groups shared their photographs, discussed the stories and messages behind them, and then grouped photos into re-occurring themes. Two community surveys were administered in Rigolet to capture data on observed climatic and environmental changes in the area, and perceived impacts on health, wellbeing, and lifestyles (n = 187). Results: Climate-sensitive health pathways were described in terms of inter-relationships between environmental and social determinants of Inuit health. The climate-sensitive health priorities for the region included food security, water security, mental health and wellbeing, new hazards and safety concerns, and health services and delivery. Conclusions: The results highlight several climate-sensitive health priorities that are specific to the Nunatsiavut region, and suggest approaching health research and adaptation planning from an EcoHealth perspective
Spin Flavor Conversion of Neutrinos in Loop Quantum Gravity
Loop quantum gravity theory incorporates a new scale length which
induces a Lorentz invariance breakdown. This scale can be either an universal
constant or can be fixed by the momentum of particles ().
Effects of the scale parameter and helicity terms occurring in the
dispersion relation of fermions are reviewed in the framework of spin-flip
conversion of neutrino flavors.Comment: 7 pages, no figur
Vacuum Energy Density Fluctuations in Minkowski and Casimir States via Smeared Quantum Fields and Point Separation
We present calculations of the variance of fluctuations and of the mean of
the energy momentum tensor of a massless scalar field for the Minkowski and
Casimir vacua as a function of an intrinsic scale defined by a smeared field or
by point separation. We point out that contrary to prior claims, the ratio of
variance to mean-squared being of the order unity is not necessarily a good
criterion for measuring the invalidity of semiclassical gravity. For the
Casimir topology we obtain expressions for the variance to mean-squared ratio
as a function of the intrinsic scale (defined by a smeared field) compared to
the extrinsic scale (defined by the separation of the plates, or the
periodicity of space). Our results make it possible to identify the spatial
extent where negative energy density prevails which could be useful for
studying quantum field effects in worm holes and baby universe, and for
examining the design feasibility of real-life `time-machines'.
For the Minkowski vacuum we find that the ratio of the variance to the
mean-squared, calculated from the coincidence limit, is identical to the value
of the Casimir case at the same limit for spatial point separation while
identical to the value of a hot flat space result with a temporal
point-separation. We analyze the origin of divergences in the fluctuations of
the energy density and discuss choices in formulating a procedure for their
removal, thus raising new questions into the uniqueness and even the very
meaning of regularization of the energy momentum tensor for quantum fields in
curved or even flat spacetimes when spacetime is viewed as having an extended
structure.Comment: 41 pages, 2 figure
Back-Reaction on the Topological Degrees of Freedom in (2+1)-Dimensional Spacetime
We investigate the back-reaction effect of the quantum field on the
topological degrees of freedom in (2+1)-dimensional toroidal universe, . Constructing a homogeneous model of the toroidal
universe, we examine explicitly the back-reaction effect of the Casimir energy
of a massless, conformally coupled scalar field, with a conformal vacuum. The
back-reaction causes an instability of the universe: The torus becomes thinner
and thinner as it evolves, while its total 2-volume (area) becomes smaller and
smaller. The back-reaction caused by the Casimir energy can be compared with
the influence of the negative cosmological constant: Both of them make the
system unstable and the torus becomes thinner and thinner in shape. On the
other hand, the Casimir energy is a complicated function of the Teichm\"uller
parameters causing highly non-trivial dynamical evolutions,
while the cosmological constant is simply a constant.
Since the spatial section is a 2-torus, we shall write down the partition
function of this system, fixing the path-integral measure for gravity modes,
with the help of the techniques developed in string theories. We show
explicitly that the partition function expressed in terms of the canonical
variables corresponding to the (redundantly large) original phase space, is
reduced to the partition function defined in terms of the physical-phase-space
variables with a standard Liouville measure. This result is compatible with the
general theory of the path integral for the 1st-class constrained systems.Comment: 42 pages, phyzzx.tex, Figures will be sent on reques
Decoherence, einselection, and the quantum origins of the classical
Decoherence is caused by the interaction with the environment. Environment
monitors certain observables of the system, destroying interference between the
pointer states corresponding to their eigenvalues. This leads to
environment-induced superselection or einselection, a quantum process
associated with selective loss of information. Einselected pointer states are
stable. They can retain correlations with the rest of the Universe in spite of
the environment. Einselection enforces classicality by imposing an effective
ban on the vast majority of the Hilbert space, eliminating especially the
flagrantly non-local "Schr\"odinger cat" states. Classical structure of phase
space emerges from the quantum Hilbert space in the appropriate macroscopic
limit: Combination of einselection with dynamics leads to the idealizations of
a point and of a classical trajectory. In measurements, einselection replaces
quantum entanglement between the apparatus and the measured system with the
classical correlation.Comment: Final version of the review, with brutally compressed figures. Apart
from the changes introduced in the editorial process the text is identical
with that in the Rev. Mod. Phys. July issue. Also available from
http://www.vjquantuminfo.or
- …