2,020 research outputs found
Natural extension of the Generalised Uncertainty Principle
We discuss a gedanken experiment for the simultaneous measurement of the
position and momentum of a particle in de Sitter spacetime. We propose an
extension of the so-called generalized uncertainty principle (GUP) which
implies the existence of a minimum observable momentum. The new GUP is directly
connected to the nonzero cosmological constant, which becomes a necessary
ingredient for a more complete picture of the quantum spacetime.Comment: 4 pages, 1 figure, v2 with added references, revised and extended as
published in CQ
Why we need to see the dark matter to understand the dark energy
The cosmological concordance model contains two separate constituents which
interact only gravitationally with themselves and everything else, the dark
matter and the dark energy. In the standard dark energy models, the dark matter
makes up some 20% of the total energy budget today, while the dark energy is
responsible for about 75%. Here we show that these numbers are only robust for
specific dark energy models and that in general we cannot measure the abundance
of the dark constituents separately without making strong assumptions.Comment: 4 pages, to be published in the Journal of Physics: Conference Series
as a contribution to the 2007 Europhysics Conference on High Energy Physic
Discovery of a Supernova Explosion at Half the Age of the Universe and its Cosmological Implications
The ultimate fate of the universe, infinite expansion or a big crunch, can be
determined by measuring the redshifts, apparent brightnesses, and intrinsic
luminosities of very distant supernovae. Recent developments have provided
tools that make such a program practicable: (1) Studies of relatively nearby
Type Ia supernovae (SNe Ia) have shown that their intrinsic luminosities can be
accurately determined; (2) New research techniques have made it possible to
schedule the discovery and follow-up observations of distant supernovae,
producing well over 50 very distant (z = 0.3 -- 0.7) SNe Ia to date. These
distant supernovae provide a record of changes in the expansion rate over the
past several billion years. By making precise measurements of supernovae at
still greater distances, and thus extending this expansion history back far
enough in time, we can distinguish the slowing caused by the gravitational
attraction of the universe's mass density Omega_M from the effect of a possibly
inflationary pressure caused by a cosmological constant Lambda. We report here
the first such measurements, with our discovery of a Type Ia supernova (SN
1997ap) at z = 0.83. Measurements at the Keck II 10-m telescope make this the
most distant spectroscopically confirmed supernova. Over two months of
photometry of SN 1997ap with the Hubble Space Telescope and ground-based
telescopes, when combined with previous measurements of nearer SNe Ia, suggests
that we may live in a low mass-density universe. Further supernovae at
comparable distances are currently scheduled for ground and space-based
observations.Comment: 12 pages and 4 figures (figure 4 is repeated in color and black and
white) Nature, scheduled for publication in the 1 January, 1998 issue. Also
available at http://www-supernova.lbl.go
An analysis method for time ordered data processing of Dark Matter experiments
The analysis of the time ordered data of Dark Matter experiments is becoming
more and more challenging with the increase of sensitivity in the ongoing and
forthcoming projects. Combined with the well-known level of background events,
this leads to a rather high level of pile-up in the data. Ionization,
scintillation as well as bolometric signals present common features in their
acquisition timeline: low frequency baselines, random gaussian noise, parasitic
noise and signal characterized by well-defined peaks. In particular, in the
case of long-lasting signals such as bolometric ones, the pile-up of events may
lead to an inaccurate reconstruction of the physical signal (misidentification
as well as fake events). We present a general method to detect and extract
signals in noisy data with a high pile-up rate and qe show that events from few
keV to hundreds of keV can be reconstructed in time ordered data presenting a
high pile-up rate. This method is based on an iterative detection and fitting
procedure combined with prior wavelet-based denoising of the data and baseline
subtraction. {We have tested this method on simulated data of the MACHe3
prototype experiment and shown that the iterative fitting procedure allows us
to recover the lowest energy events, of the order of a few keV, in the presence
of background signals from a few to hundreds of keV. Finally we applied this
method to the recent MACHe3 data to successfully measure the spectrum of
conversion electrons from Co57 source and also the spectrum of the background
cosmic muons
ELT Observations of Supernovae at the Edge of the Universe
We discuss the possibility of using Supernovae as tracers of the star
formation history of the Universe for the range of stellar masses
M and possibly beyond. We simulate the observations of 350 SNe, up to
, made with OWL (100m) telescope.Comment: 9 pages, 6 figures. To appear in "Exploring the Cosmic Frontier:
Astrophysical Instruments for the 21st Century", proceedings of the
conference held in Berlin, 18-21 May 200
An Interacting Two-Fluid Scenario for Dark Energy in FRW Universe
We study the evolution of the dark energy parameter within the scope of a
spatially flat and isotropic Friedmann-Robertson-Walker (FRW) model filled with
barotropic fluid and dark energy. To obtain the deterministic solution we
choose the scale factor which yields a time dependent
deceleration parameter (DP). In doing so we consider the case minimally coupled
with dark energy to the perfect fluid as well as direct interaction with it.Comment: 11 pages, accepted for publication in Chinese Physics Letters. Unlike
the previous version the new one contains the time depending deceleration
paramete
Self-tuning of the cosmological constant
Here, I discuss the cosmological constant (CC) problems, in particular paying
attention to the vanishing cosmological constant. There are three cosmological
constant problems in particle physics. Hawking's idea of calculating the
probability amplitude for our Universe is peaked at CC = 0 which I try to
obtain after the initial inflationary period using a self-tuning model. I
review what has been discussed on the Hawking type calculation, and present a
(probably) correct way to calculate the amplitude, and show that the
Kim-Kyae-Lee self-tuning model allows a finite range of parameters for the CC =
0 to have a singularly large probability, approached from the AdS side.Comment: 12 pages with 8 figure
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