455 research outputs found
A new approach to equipment testing
Considerable controversy has arisen during the recent discussions over a new version of the RTCA DO160C/ED 14C Section 22 document at the European Committee for Aviation Electronics. Section 22 is concerned with lightning waveform tests to equipment. Investigations of some of these controversies with circuit analysis and measurements indicate the impedance characteristics required of the transient generators and the possibility of testing to a voltage limit even for current waveforms
Revisit relic gravitational waves based on the latest CMB observations
According to the CMB observations, Mielczarek (\cite{Mielczarek}) evaluated
the reheating temperature, which could help to determine the history of the
Universe. In this paper, we recalculate the reheating temperature using the new
data from WMAP 7 observations. Based on that, we list the approximate solutions
of relic gravitational waves (RGWs) for various frequency bands. With the
combination of the quantum normalization of RGWs when they are produced and the
CMB observations, we obtain the relation between the tensor-to-scalar ratio
and the inflation index for a given scalar spectral index . As a
comparison, the diagram in the slow-roll inflation model is also
given. Thus, the observational limits of from CMB lead to the constraints
on the value of . Then, we illustrate the energy density spectrum of
RGWs with the quantum normalization for different values of and the
corresponding . For comparison, the energy density spectra of RGWs with
parameters based on slow-roll inflation are also discussed. We find that the
values of affect the spectra of RGWs sensitively in the very high
frequencies. Based on the current and planed gravitational wave detectors, we
discuss the detectabilities of RGWs.Comment: 16 pages, 6 figures, accepted for publication in Class. Quantum Gra
Constraining super-critical string/brane cosmologies with astrophysical data
We discuss fits of unconventional dark energy models to the available data
from high-redshift supernovae, distant galaxies and baryon oscillations. The
models are based either on brane cosmologies or on Liouville strings in which a
relaxation dark energy is provided by a rolling dilaton field (Q-cosmology).
Such cosmologies feature the possibility of effective four-dimensional
negative-energy dust and/or exotic scaling of dark matter. We find evidence for
a negative-energy dust at the current era, as well as for exotic-scaling
(a^{-delta}) contributions to the energy density, with delta ~= 4, which could
be due to dark matter coupling with the dilaton in Q-cosmology models. We
conclude that Q-cosmology fits the data equally well with the LambdaCDM model
for a range of parameters that are in general expected from theoretical
considerations.Comment: 4 pages, 2 figures, Contributed to 11th International Conference on
Topics in Astroparticle and Underground Physics (TAUP 2009) 1-5 Jul 2009,
Rome, Italy; J. Phys. Conf. Series to appea
CMBPol Mission Concept Study: Prospects for polarized foreground removal
In this report we discuss the impact of polarized foregrounds on a future
CMBPol satellite mission. We review our current knowledge of Galactic polarized
emission at microwave frequencies, including synchrotron and thermal dust
emission. We use existing data and our understanding of the physical behavior
of the sources of foreground emission to generate sky templates, and start to
assess how well primordial gravitational wave signals can be separated from
foreground contaminants for a CMBPol mission. At the estimated foreground
minimum of ~100 GHz, the polarized foregrounds are expected to be lower than a
primordial polarization signal with tensor-to-scalar ratio r=0.01, in a small
patch (~1%) of the sky known to have low Galactic emission. Over 75% of the sky
we expect the foreground amplitude to exceed the primordial signal by about a
factor of eight at the foreground minimum and on scales of two degrees. Only on
the largest scales does the polarized foreground amplitude exceed the
primordial signal by a larger factor of about 20. The prospects for detecting
an r=0.01 signal including degree-scale measurements appear promising, with 5
sigma_r ~0.003 forecast from multiple methods. A mission that observes a range
of scales offers better prospects from the foregrounds perspective than one
targeting only the lowest few multipoles. We begin to explore how optimizing
the composition of frequency channels in the focal plane can maximize our
ability to perform component separation, with a range of typically 40 < nu <
300 GHz preferred for ten channels. Foreground cleaning methods are already in
place to tackle a CMBPol mission data set, and further investigation of the
optimization and detectability of the primordial signal will be useful for
mission design.Comment: 42 pages, 14 figures, Foreground Removal Working Group contribution
to the CMBPol Mission Concept Study, v2, matches AIP versio
MSSM Baryogenesis and Electric Dipole Moments: An Update on the Phenomenology
We explore the implications of electroweak baryogenesis for future searches
for permanent electric dipole moments in the context of the minimal
supersymmetric extension of the Standard Model (MSSM). From a cosmological
standpoint, we point out that regions of parameter space that over-produce
relic lightest supersymmetric particles can be salvaged only by assuming a
dilution of the particle relic density that makes it compatible with the dark
matter density: this dilution must occur after dark matter freeze-out, which
ordinarily takes place after electroweak baryogenesis, implying the same degree
of dilution for the generated baryon number density as well. We expand on
previous studies on the viable MSSM regions for baryogenesis, exploring for the
first time an orthogonal slice of the relevant parameter space, namely the
(tan\beta, m_A) plane, and the case of non-universal relative gaugino-higgsino
CP violating phases. The main result of our study is that in all cases lower
limits on the size of the electric dipole moments exist, and are typically on
the same order, or above, the expected sensitivity of the next generation of
experimental searches, implying that MSSM electroweak baryogenesis will be soon
conclusively tested.Comment: 23 pages, 10 figures, matches version published in JHE
Hubble Space Telescope Weak-lensing Study of the Galaxy Cluster XMMU J2235.3-2557 at z=1.4: A Surprisingly Massive Galaxy Cluster when the Universe is One-third of its Current Age
We present a weak-lensing analysis of the z=1.4 galaxy cluster XMMU
J2235.3-2557, based on deep Advanced Camera for Surveys images. Despite the
observational challenge set by the high redshift of the lens, we detect a
substantial lensing signal at the >~ 8 sigma level. This clear detection is
enabled in part by the high mass of the cluster, which is verified by our both
parametric and non-parametric estimation of the cluster mass. Assuming that the
cluster follows a Navarro-Frenk-White mass profile, we estimate that the
projected mass of the cluster within r=1 Mpc is (8.5+-1.7) x 10^14 solar mass,
where the error bar includes the statistical uncertainty of the shear profile,
the effect of possible interloping background structures, the scatter in
concentration parameter, and the error in our estimation of the mean redshift
of the background galaxies. The high X-ray temperature 8.6_{-1.2}^{+1.3} keV of
the cluster recently measured with Chandra is consistent with this high lensing
mass. When we adopt the 1-sigma lower limit as a mass threshold and use the
cosmological parameters favored by the Wilkinson Microwave Anisotropy Probe
5-year (WMAP5) result, the expected number of similarly massive clusters at z
>~ 1.4 in the 11 square degree survey is N ~ 0.005. Therefore, the discovery of
the cluster within the survey volume is a rare event with a probability < 1%,
and may open new scenarios in our current understanding of cluster formation
within the standard cosmological model.Comment: Accepted to ApJ for publication. 40 pages and 14 figure
A Millimeter-Wave Galactic Plane Survey With The BICEP Polarimeter
In addition to its potential to probe the Inflationary cosmological paradigm,
millimeter-wave polarimetry is a powerful tool for studying the Milky Way
galaxy's composition and magnetic field structure. Towards this end, presented
here are Stokes I, Q, and U maps of the Galactic plane from the millimeter-wave
polarimeter BICEP covering the Galactic longitude range 260 - 340 degrees in
three atmospheric transmission windows centered on 100, 150, and 220 GHz. The
maps sample an optical depth 1 < AV < 30, and are consistent with previous
characterizations of the Galactic millimeter-wave frequency spectrum and the
large-scale magnetic field structure permeating the interstellar medium.
Polarized emission is detected over the entire region within two degrees of the
Galactic plane and indicates that the large-scale magnetic field is oriented
parallel to the plane of the Galaxy. An observed trend of decreasing
polarization fraction with increasing total intensity rules out the simplest
model of a constant Galactic magnetic field throughout the Galaxy. Including
WMAP data in the analysis, the degree-scale frequency spectrum of Galactic
polarization fraction is plotted between 23 and 220 GHz for the first time. A
generally increasing trend of polarization fraction with electromagnetic
frequency is found, which varies from 0.5%-1.5%at frequencies below 50 GHz to
2.5%-3.5%above 90 GHz. The BICEP and WMAP data are fit to a two-component
(synchrotron and dust) model showing that the higher frequency BICEP data are
necessary to tightly constrain the amplitude and spectral index of Galactic
dust. Furthermore, the dust amplitude predicted by this two-component fit is
consistent with model predictions of dust emission in the BICEP bands
The Galactic Halo in Mixed Dark Matter Cosmologies
A possible solution to the small scale problems of the cold dark matter (CDM)
scenario is that the dark matter consists of two components, a cold and a warm
one. We perform a set of high resolution simulations of the Milky Way halo
varying the mass of the WDM particle () and the cosmic dark matter
mass fraction in the WDM component (). The scaling ansatz
introduced in combined analysis of LHC and astroparticle searches postulates
that the relative contribution of each dark matter component is the same
locally as on average in the Universe (e.g. ). Here we find however, that the normalised local WDM fraction ( / ) depends strongly on for 1 keV. Using the scaling ansatz can therefore introduce significant
errors into the interpretation of dark matter searches. To correct this issue a
simple formula that fits the local dark matter densities of each component is
provided.Comment: 19 pages, 10 figures, accepted for publication in JCA
Primordial Black Holes, Eternal Inflation, and the Inflationary Parameter Space after WMAP5
We consider constraints on inflation driven by a single, minimally coupled
scalar field in the light of the WMAP5 dataset, as well as ACBAR and the
SuperNova Legacy Survey. We use the Slow Roll Reconstruction algorithm to
derive optimal constraints on the inflationary parameter space. The scale
dependence in the slope of the scalar spectrum permitted by WMAP5 is large
enough to lead to viable models where the small scale perturbations have a
substantial amplitude when extrapolated to the end of inflation. We find that
excluding parameter values which would cause the overproduction of primordial
black holes or even the onset of eternal inflation leads to potentially
significant constraints on the slow roll parameters. Finally, we present a more
sophisticated approach to including priors based on the total duration of
inflation, and discuss the resulting restrictions on the inflationary parameter
space.Comment: v2: version published in JCAP. Minor clarifications and references
adde
Late transient acceleration of the universe in string theory on
Recently, in Gong {\em et al} \cite{GWW07} and Wang and Santos \cite{WS07} it
was shown that the effective cosmological constant on each of the two orbifold
branes can be easily lowered to its current observational value, by using the
large extra dimensions in the framework of both M-Theory and string theory on
. In this paper, we study the current acceleration of the
universe, using the formulas developed in \cite{WS07}. We first construct
explicitly time-dependent solution to the 10-dimensional bulk of the
Neveu-Schwarz/Neveu-Schwarz sector, compactified on a 5-dimensional torus.
Then, we write down the generalized Friedmann equations on each of the two
dynamical branes, and fit the models to the 182 gold supernova Ia data and the
BAO parameter from SDSS, using both of our MINUIT and Monte-Carlo Markov Chain
(MCMC) codes. With the best fitting values of the parameters involved as
initial conditions, we integrate the generalized Friedmann equations
numerically and find the future evolution of the universe. We find that it
depends on the choice of the radion potentials of the
branes. In particular, when choosing them to be the Goldberger-Wise potentials,
, we find that
the current acceleration of the universe driven by the effective cosmological
constant is only temporary. Due to the effects of the potentials, the universe
will be finally in its decelerating expansion phase again. We also study the
proper distance between the two branes, and find that it remains almost
constant during the whole future evolution of the universe in all the models
considered.Comment: revtex4, 18 figures. Typos corrected and new References added.
Version to be published in JCA
- …