536 research outputs found
Effective non-intercommutation of local cosmic strings at high collision speeds
We present evidence that Abrikosov-Nielsen-Olesen (ANO) strings pass through
each other for very high speeds of approach due to a double intercommutation.
In near-perpendicular collisions numerical simulations give threshold speeds
bounded above by for type I, and by for deep type
II strings. The second intercommutation occurs because at ultra high collision
speeds, the connecting segments formed by the first intercommutation are nearly
static and almost antiparallel, which gives them time to interact and
annihilate. A simple model explains the rough features of the threshold
velocity dependence with the incidence angle. For deep type II strings and
large incidence angles a second effect becomes dominant, the formation of a
loop that catches up with the interpolating segments. The loop is related to
the observed vortex - antivortex reemergence in two-dimensions. In this case
the critical value for double intercommutation can become much lower.Comment: 5 pages, 4 figures. data points added, plots for deep type II regime
showing lower critical velocities, some minor changes in tex
An Empirical Approach to Cosmological Galaxy Survey Simulation: Application to SPHEREx Low-Resolution Spectroscopy
Highly accurate models of the galaxy population over cosmological volumes are
necessary in order to predict the performance of upcoming cosmological
missions. We present a data-driven model of the galaxy population constrained
by deep 0.1-8 imaging and spectroscopic data in the COSMOS survey,
with the immediate goal of simulating the spectroscopic redshift performance of
the proposed SPHEREx mission. SPHEREx will obtain over the full-sky
spectrophotometry at moderate spatial resolution () over the wavelength
range 0.75-4.18 and over the wavelength range 4.18-5
. We show that our simulation accurately reproduces a range of known
galaxy properties, encapsulating the full complexity of the galaxy population
and enables realistic, full end-to-end simulations to predict mission
performance. Finally, we discuss potential applications of the simulation
framework to future cosmology missions and give a description of released data
products
Constraints on Cosmology from the Cosmic Microwave Background Power Spectrum of the 2500 deg^2 SPT-SZ Survey
We explore extensions to the ΛCDM cosmology using measurements of the cosmic microwave background (CMB) from the recent SPT-SZ survey, along with data from WMAP7 and measurements of H_0 and baryon acoustic oscillation (BAO). We check for consistency within ΛCDM between these data sets, and find some tension. The CMB alone gives weak support to physics beyond ΛCDM, due to a slight trend relative to ΛCDM of decreasing power toward smaller angular scales. While it may be due to statistical fluctuation, this trend could also be explained by several extensions. We consider running of the primordial spectral index (dn_s /d ln k), as well as two extensions that modify the damping tail power (the primordial helium abundance Y_p and the effective number of neutrino species N_(eff)) and one that modifies the large-scale power due to the integrated Sachs-Wolfe effect (the sum of neutrino masses ∑m_ν). These extensions have similar observational consequences and are partially degenerate when considered simultaneously. Of the six one-parameter extensions considered, we find CMB to have the largest preference for dn_s/d ln k with –0.046 0 from CMB+BAO+H_0 + SPT_(CL). The median value is (0.32 ± 0.11) eV, a factor of six above the lower bound set by neutrino oscillation observations. All data sets except H_0 show some preference for massive neutrinos; data combinations including H_0 favor nonzero masses only if BAO data are also included. We also constrain the two-parameter extensions N_(eff) + ∑m_ν and N_(eff) + Y_p to explore constraints on additional light species and big bang nucleosynthesis, respectively
Future CMB Constraints on Early, Cold, or Stressed Dark Energy
We investigate future constraints on early dark energy (EDE) achievable by
the Planck and CMBPol experiments, including cosmic microwave background (CMB)
lensing. For the dark energy, we include the possibility of clustering through
a sound speed c_s^2 <1 (cold dark energy) and anisotropic stresses
parameterized with a viscosity parameter c_vis^2. We discuss the degeneracies
between cosmological parameters and EDE parameters. In particular we show that
the presence of anisotropic stresses in EDE models can substantially undermine
the determination of the EDE sound speed parameter c_s^2. The constraints on
EDE primordial energy density are however unaffected. We also calculate the
future CMB constraints on neutrino masses and find that they are weakened by a
factor of 2 when allowing for the presence of EDE, and highly biased if it is
incorrectly ignored.Comment: 12 pages, 19 figure
Constraints on massive sterile neutrino species from current and future cosmological data
Sterile massive neutrinos are a natural extension of the Standard Model of
elementary particles. The energy density of the extra sterile massive states
affects cosmological measurements in an analogous way to that of active
neutrino species. We perform here an analysis of current cosmological data and
derive bounds on the masses of the active and the sterile neutrino states as
well as on the number of sterile states. The so-called (3+2) models with three
sub-eV active massive neutrinos plus two sub-eV massive sterile species is well
within the 95% CL allowed regions when considering cosmological data only. If
the two extra sterile states have thermal abundances at decoupling, Big Bang
Nucleosynthesis bounds compromise the viability of (3+2) models. Forecasts from
future cosmological data on the active and sterile neutrino parameters are also
presented. Independent measurements of the neutrino mass from tritium beta
decay experiments and of the Hubble constant could shed light on sub-eV massive
sterile neutrino scenarios.Comment: 9 pages, 7 figures. Journal versio
Kinematic Constraints on Formation of Bound States of Cosmic Strings - Field Theoretical Approach
Superstring theory predicts the potential formation of string networks with
bound states ending in junctions. Kinematic constraints for junction formation
have been derived within the Nambu-Goto thin string approximation. Here we test
these constraints numerically in the framework of the Abelian-Higgs model in
the Type-I regime and report on good agreement with the analytical predictions.
We also demonstrate that strings can effectively pass through each other when
they meet at speeds slightly above the critical velocity permitting bound state
formation. This is due to reconnection effects that are beyond the scope of the
Nambu-Goto approximation.Comment: 6 pages, 12 eps figures - matches the published versio
Learning on electrical circuits while playing 'E&E electrical endeavours' : design research on a serious game optimizing for conceptual understanding
In a two year design research project, a serious game was developed in a close collaboration of educational researchers, game-designers and secondary school teachers. In a first round, the game was used in classroom employing an open-inquiry format. It was found that the game had a strong impact on the student’s conceptual development but that it provoked the construction of misconceptions. The game was then adapted and partially redesigned on the basis of the evaluation outcomes and additional expert-review. Also the way of using the game in classroom was redesigned and written down in a teachers’ guide. In a second round this pedagogical approach to using the game in classroom alternating open inquiry type gaming-episodes with guided reflection and internalisation episodes, was used. Again a strong impact on students’ conceptual understanding of electrical circuits was found. Significantly less misconceptions occurred. The results indicate that the close collaboration of school teachers, educational experts and game designers was fruitful for improving the serious game and its use in school practice. Moreover it became clear that serious games have a potential to strongly contribute to students’ conceptual understanding, in particular by the mental model implicitly represented in the game´s layout and structure
Shifting the Universe: Early Dark Energy and Standard Rulers
The presence of dark energy at high redshift influences both the cosmic sound
horizon and the distance to last scattering of the cosmic microwave background.
We demonstrate that through the degeneracy in their ratio, early dark energy
can lie hidden in the CMB temperature and polarization spectra, leading to an
unrecognized shift in the sound horizon. If the sound horizon is then used as a
standard ruler, as in baryon acoustic oscillations, then the derived
cosmological parameters can be nontrivially biased. Fitting for the absolute
ruler scale (just as supernovae must be fit for the absolute candle magnitude)
removes the bias but decreases the leverage of the BAO technique by a factor 2.Comment: 6 pages, 3 figure
Ecologische atlas van de Paarse Strandloper en de Steenloper aan de Vlaamse kust 1947-2005: Aantalsevolutie, terreingebruik, activiteitsritme en gedrag van de Paarse Strandloper (<i>Calidris maritima</i>) en de Steenloper (<i>Arenaria interpres</i>) aan de Vlaamse kust, 1947-2005 = Numbers, habitat use, activity system and behaviour of the Purple Sandpiper (<i>Calidris maritima</i>) and the Turnstone (<i>Arenaria interpres</i>) on the Flemish coast, Belgium, 1947-2005
- …