16 research outputs found
Neutrinoless double-beta decay with three or four neutrino mixing
Considering the scheme with mixing of three neutrinos and a mass hierarchy
that can accommodate the results of solar and atmospheric neutrino experiments,
it is shown that the results of solar neutrino experiments imply a lower bound
for the effective Majorana mass in neutrinoless double-beta decay, under the
natural assumptions that massive neutrinos are Majorana particles and there are
no unlikely fine-tuned cancellations among the contributions of the different
neutrino masses. Considering the four-neutrino schemes that can accommodate
also the results of the LSND experiment, it is shown that only one of them is
compatible with the results of neutrinoless double-beta decay experiments and
with the measurement of the abundances of primordial elements produced in
Big-Bang Nucleosynthesis. It is shown that in this scheme, under the
assumptions that massive neutrinos are Majorana particles and there are no
cancellations among the contributions of the different neutrino masses, the
results of the LSND experiment imply a lower bound for the effective Majorana
mass in neutrinoless double-beta decay.Comment: 18 pages including 2 figures, RevTe
Revisiting Cardassian Model and Cosmic Constraint
In this paper, we revisit the Cardassian model in which the radiation energy
component is included. It is important for early epoch when the radiation
cannot be neglected because the equation of state (EoS) of the effective dark
energy becomes time variable. Therefore, it is not equivalent to the
quintessence model with a constant EoS anymore. This situation was almost
overlooked in the literature. By using the recent released Union2 557 of type
Ia supernovae (SN Ia), the baryon acoustic oscillation (BAO) from Sloan Digital
Sky Survey and the WiggleZ data points, the full information of cosmic
microwave background (CMB) measurement given by the seven-year Wilkinson
Microwave Anisotropy Probe observation, we constrain the Cardassian model via
the Markov Chain Monte Carlo (MCMC) method. A tight constraint is obtained: in regions. The
deviation of Cardassian model from quintessence model is shown in CMB
anisotropic power spectra at high l's parts due to the evolution of EoS. But it
is about the order of 0.1% which cannot be discriminated by current data sets.
The Cardassian model is consistent with current cosmic observational data sets.Comment: 6 pages, 5 figures, match the published versio
Cosmology at the Millennium
One hundred years ago we did not know how stars generate energy, the age of
the Universe was thought to be only millions of years, and our Milky Way galaxy
was the only galaxy known. Today, we know that we live in an evolving and
expanding Universe comprising billions of galaxies, all held together by dark
matter. With the hot big-bang model, we can trace the evolution of the Universe
from the hot soup of quarks and leptons that existed a fraction of a second
after the beginning to the formation of galaxies a few billion years later, and
finally to the Universe we see today 13 billion years after the big bang, with
its clusters of galaxies, superclusters, voids, and great walls. The attractive
force of gravity acting on tiny primeval inhomogeneities in the distribution of
matter gave rise to all the structure seen today. A paradigm based upon deep
connections between cosmology and elementary particle physics -- inflation +
cold dark matter -- holds the promise of extending our understanding to an even
more fundamental level and much earlier times, as well as shedding light on the
unification of the forces and particles of nature. As we enter the 21st
century, a flood of observations is testing this paradigm.Comment: 44 pages LaTeX with 14 eps figures. To be published in the Centennial
Volume of Reviews of Modern Physic
Revisiting Generalized Chaplygin Gas as a Unified Dark Matter and Dark Energy Model
In this paper, we revisit generalized Chaplygin gas (GCG) model as a unified
dark matter and dark energy model. The energy density of GCG model is given as
,
where and are two model parameters which will be constrained by
type Ia supernova as standard candles, baryon acoustic oscillation as standard
rulers and the seventh year full WMAP data points. In this paper, we will not
separate GCG into dark matter and dark energy parts any more as adopted in the
literatures. By using Markov Chain Monte Carlo method, we find the result:
and .Comment: 6 pages, 4 figure
Observational Constraints on Chaplygin Quartessence: Background Results
We derive the constraints set by several experiments on the quartessence
Chaplygin model (QCM). In this scenario, a single fluid component drives the
Universe from a nonrelativistic matter-dominated phase to an accelerated
expansion phase behaving, first, like dark matter and in a more recent epoch
like dark energy. We consider current data from SNIa experiments, statistics of
gravitational lensing, FR IIb radio galaxies, and x-ray gas mass fraction in
galaxy clusters. We investigate the constraints from this data set on flat
Chaplygin quartessence cosmologies. The observables considered here are
dependent essentially on the background geometry, and not on the specific form
of the QCM fluctuations. We obtain the confidence region on the two parameters
of the model from a combined analysis of all the above tests. We find that the
best-fit occurs close to the CDM limit (). The standard
Chaplygin quartessence () is also allowed by the data, but only at
the level.Comment: Replaced to match the published version, references update
Cosmological parameters from SDSS and WMAP
We measure cosmological parameters using the three-dimensional power spectrum
P(k) from over 200,000 galaxies in the Sloan Digital Sky Survey (SDSS) in
combination with WMAP and other data. Our results are consistent with a
``vanilla'' flat adiabatic Lambda-CDM model without tilt (n=1), running tilt,
tensor modes or massive neutrinos. Adding SDSS information more than halves the
WMAP-only error bars on some parameters, tightening 1 sigma constraints on the
Hubble parameter from h~0.74+0.18-0.07 to h~0.70+0.04-0.03, on the matter
density from Omega_m~0.25+/-0.10 to Omega_m~0.30+/-0.04 (1 sigma) and on
neutrino masses from <11 eV to <0.6 eV (95%). SDSS helps even more when
dropping prior assumptions about curvature, neutrinos, tensor modes and the
equation of state. Our results are in substantial agreement with the joint
analysis of WMAP and the 2dF Galaxy Redshift Survey, which is an impressive
consistency check with independent redshift survey data and analysis
techniques. In this paper, we place particular emphasis on clarifying the
physical origin of the constraints, i.e., what we do and do not know when using
different data sets and prior assumptions. For instance, dropping the
assumption that space is perfectly flat, the WMAP-only constraint on the
measured age of the Universe tightens from t0~16.3+2.3-1.8 Gyr to
t0~14.1+1.0-0.9 Gyr by adding SDSS and SN Ia data. Including tensors, running
tilt, neutrino mass and equation of state in the list of free parameters, many
constraints are still quite weak, but future cosmological measurements from
SDSS and other sources should allow these to be substantially tightened.Comment: Minor revisions to match accepted PRD version. SDSS data and ppt
figures available at http://www.hep.upenn.edu/~max/sdsspars.htm
Cosmological parameters from CMB and other data: a Monte-Carlo approach
We present a fast Markov Chain Monte-Carlo exploration of cosmological
parameter space. We perform a joint analysis of results from recent CMB
experiments and provide parameter constraints, including sigma_8, from the CMB
independent of other data. We next combine data from the CMB, HST Key Project,
2dF galaxy redshift survey, supernovae Ia and big-bang nucleosynthesis. The
Monte Carlo method allows the rapid investigation of a large number of
parameters, and we present results from 6 and 9 parameter analyses of flat
models, and an 11 parameter analysis of non-flat models. Our results include
constraints on the neutrino mass (m_nu < 0.3eV), equation of state of the dark
energy, and the tensor amplitude, as well as demonstrating the effect of
additional parameters on the base parameter constraints. In a series of
appendices we describe the many uses of importance sampling, including
computing results from new data and accuracy correction of results generated
from an approximate method. We also discuss the different ways of converting
parameter samples to parameter constraints, the effect of the prior, assess the
goodness of fit and consistency, and describe the use of analytic
marginalization over normalization parameters.Comment: Quintessence results now include perturbations. Changes to match
version accepted by PRD. MCMC code and data are available at
http://cosmologist.info/cosmomc/ along with a B&W printer-friendly version of
the pape
Modified Chaplygin Gas as a Unified Dark Matter and Dark Energy Model and Cosmic Constraints
A modified Chaplygin gas model (MCG),
,
as a unified dark matter model and dark energy model is constrained by using
current available cosmic observational data points which include type Ia
supernovae, baryon acoustic oscillation and the seventh year full WMAP data
points. As a contrast to the consideration in the literatures, we {\it do not}
separate the MCG into two components, i.e. dark mater and dark energy
component, but we take it as a whole energy component-a unified dark sector. By
using Markov Chain Monte Carlo method, a tight constraint is obtained: , and .}Comment: 6 pages, 3 figure
Testing dark energy beyond the cosmological constant barrier
Although well motivated from theoretical arguments, the cosmological constant
\emph{barrier}, i.e., the imposition that the equation-of-state parameter of
dark energy () is , seems to introduce
bias in the parameter determination from statistical analyses of observational
data. In this regard, \emph{phantom} dark energy or \emph{superquintessence}
has been proposed in which the usual imposition is relaxed.
Here, we study possible observational limits to the \emph{phantom} behavior of
the dark energy from recent distance estimates of galaxy clusters obtained from
interferometric measurements of the Sunyaev-Zel'dovich effect/X-ray
observations, Type Ia supernova data and CMB measurements. We find that there
is much \emph{observationally} acceptable parameter space beyond the
\emph{barrier}, thus opening the possibility of existence of more exotic forms
of energy in the Universe.Comment: 5 pages, 5 figures, to appear in Phys. Rev.
Baryons: What, When and Where?
We review the current state of empirical knowledge of the total budget of
baryonic matter in the Universe as observed since the epoch of reionization.
Our summary examines on three milestone redshifts since the reionization of H
in the IGM, z = 3, 1, and 0, with emphasis on the endpoints. We review the
observational techniques used to discover and characterize the phases of
baryons. In the spirit of the meeting, the level is aimed at a diverse and
non-expert audience and additional attention is given to describe how space
missions expected to launch within the next decade will impact this scientific
field.Comment: Proceedings Review for "Astrophysics in the Next Decade: JWST and
Concurrent Facilities", ed. X. Tielens, 38 pages, 10 color figures. Revised
to address comments from the communit