1099368
Quantum effects with an x-ray free-electron laser.
A quantum kinetic equation coupled with Maxwell's equation is used to estimate the laser power required at an x-ray free-electron laser (XFEL) facility to expose intrinsically quantum effects in the process of QED vacuum decay via spontaneous pair production. A 9 -TW-peak XFEL laser with photon energy of 8.3 keV could be sufficient to initiate particle accumulation and the consequent formation of a plasma of spontaneously produced pairs. The evolution of the particle number in the plasma will exhibit non-Markovian aspects of the strong-field pair production process, and the plasma's internal currents will generate an electric field whose interference with that of the laser leads to plasma oscillations.
14771019
Pair production and optical lasers.
Electron-positron pair creation in a standing wave is explored using a parameter-free quantum kinetic equation. Field strengths and frequencies corresponding to modern optical lasers induce a material polarization of the QED vacuum, which may be characterized as a plasma of e+e- quasiparticle pairs with a density of approximately 10(20) cm-3. The plasma vanishes almost completely when the laser field is zero, leaving a very small residual pair density n(r) which is the true manifestation of vacuum decay. The average pair density per period is proportional to the laser intensity but independent of the frequency nu. The density of residual pairs also grows with laser intensity but n(r) proportional to nu(2). With optical lasers at the forefront of the current generation, these dynamical QED vacuum effects can plausibly generate 5-10 observable two-photon annihilation events per laser pulse.
14279889
The distribution function of the strong non-equilibrium systems of particles and anti-particles created from vacuum by electromagnetic field
We investigate some details of the back reaction (BR) problem formulated on the basis of the kinetic approach of authors to description of vacuum pair production in a strong electromagnetic field (Schwinger’s mechanism). Here we study numerically an evolution on the distribution functions of strong non-equilibrium systems bosons and fermions. The realized analysis is shown the regular dynamics in an absence of BR mechanism is destroyed at its account. As the result some large-scale structure is arisen an a background of small-scale chaotic motions. A Back-Reaction (BR) problem has been studied intensively in recent years in both high energy particle physics and especially in early cosmology. For simplicity, in this contribution we do not take into account the non-Abelian structure of color electric fields and concentrate on the back-reaction problem in application only to strong electromagnetic fields. However, the characteristics considered and the region of the field parameters used are of interest for the flux tube model applications to hadronic processes. We restrict ourselves to a simplest situation of a time-dependent space-homogeneous field. Under these restrictions, the peculiarity of our approach is based on making use of the exact kinetic equation (KE) [1, 2] which describes the evolution process of particle-antiparticle pair creation and annihilation in strong fields with the full zero charge. Our approach to the BR problem is based on the following exact Vlasov-like KE for vacuum pair creation and annihilation processes in a strong time-dependent space-homogeneous electric field [1, 2] 1) df(~ P , t) dt = ∂f(~ P , t) ∂t + eE(t) ∂f(~ P , t) ∂P3(t) = S(~ P , t) , (1) ) We use the units h̄ = c = 1 and the metric is chosen to be g = diag(1,−1,−1,−1).
119344902
Valence quark distributions in the pion
We calculate the pion's valence-quark momentum-fraction probability distribution using a Dyson-Schwinger equation model. Valence quarks with an active mass of 0.30 GeV carry 71% of the pion's momentum at a resolving scale q{sub 0}=0.54 GeV=1/(0.37 fm). The shape of the calculated distribution is characteristic of a strongly bound system and, evolved from q{sub 0} to q=2 GeV, it yields first, second, and third moments in agreement with lattice and phenomenological estimates, and valence-quarks carrying 49% of the pion's momentum. However, pointwise there is a discrepancy between our calculated distribution and that hitherto inferred from parametrizations of extant pion-nucleon Drell-Yan data.
44004941
Analysis of chiral and thermal susceptibilities
We calculate the chiral and thermal susceptibilities for two confining Dyson-Schwinger equation models of QCD with two light flavors, a quantitative analysis of which yields the critical exponents {beta} and {delta} that characterize the second-order chiral symmetry restoration transition. The method itself is of interest, minimizing the influence of numerical noise in the calculation of the order parameter for chiral symmetry breaking near the critical temperature. For the more realistic of the two models we estimate T{sub c}{approx}153 MeV and the non-mean-field values {beta}=0.46{plus_minus}0.04, {delta}=4.3{plus_minus}0.3, and 1/({beta}{delta})=0.54{plus_minus}0.05, which we discuss in comparison with the results of other models. {copyright} {ital 1998} {ital The American Physical Society}
8421267
A DYNAMICAL, CONFINING MODEL AND HOT QUARK STARS
Abstract We explore the consequences of an equation of state (EOS) obtained in a confining Dyson–Schwinger equation model of QCD for the structure and stability of nonstrange quark stars at finite- T , and compare the results with those obtained using a bag-model EOS. Both models support a temperature profile that varies over the star's volume and the consequences of this are model independent. However, in our model the analogue of the bag pressure is ( T , μ )-dependent, which is not the case in the bag model. This is a significant qualitative difference and comparing the results effects a primary goal of elucidating the sensitivity of quark star properties to the form of the EOS.
118578896
CHARACTERIZING AND PROPAGATING MODELING UNCERTAINTIES IN PHOTOMETRICALLY-DERIVED REDSHIFT DISTRIBUTIONS
The uncertainty in the redshift distributions of galaxies has a significant potential impact on the cosmological parameter values inferred from multi-band imaging surveys. The accuracy of the photometric redshifts measured in these surveys depends not only on the quality of the flux data, but also on a number of modeling assumptions that enter into both the training set and spectral energy distribution (SED) fitting methods of photometric redshift estimation. In this work we focus on the latter, considering two types of modeling uncertainties: uncertainties in the SED template set and uncertainties in the magnitude and type priors used in a Bayesian photometric redshift estimation method. We find that SED template selection effects dominate over magnitude prior errors. We introduce a method for parameterizing the resulting ignorance of the redshift distributions, and for propagating these uncertainties to uncertainties in cosmological parameters.
119184968
Clustering-based redshift estimation: comparison to spectroscopic redshifts
We investigate the potential and accuracy of clustering-based redshift estimation using the method proposed by M\'enard et al. (2013). This technique enables the inference of redshift distributions from measurements of the spatial clustering of arbitrary sources, using a set of reference objects for which redshifts are known. We apply it to a sample of spectroscopic galaxies from the Sloan Digital Sky Survey and show that, after carefully controlling the sampling efficiency over the sky, we can estimate redshift distributions with high accuracy. Probing the full colour space of the SDSS galaxies, we show that we can recover the corresponding mean redshifts with an accuracy ranging from $\delta$z=0.001 to 0.01. We indicate that this mapping can be used to infer the redshift probability distribution of a single galaxy. We show how the lack of information on the galaxy bias limits the accuracy of the inference and show comparisons between clustering redshifts and photometric redshifts for this dataset. This analysis demonstrates, using real data, that clustering-based redshift inference provides a powerful data-driven technique to explore the redshift distribution of arbitrary datasets, without any prior knowledge on the spectral energy distribution of the sources.
119204525
Tomographic magnification of Lyman-break galaxies in the Deep Lens Survey
Using about 450 000 galaxies in the Deep Lens Survey, we present a detection of the gravitational magnification of z > 4 Lyman-break galaxies by massive foreground galaxies with 0.4 7.5σ with a fixed σ8 and is found to be consistent with the expected redshift dependence of the Wilkinson Microwave Anisotropy Probe 7 Λ cold dark matter cosmology.
118589337
Improved photometric redshifts via enhanced estimates of system response, galaxy templates and magnitude priors
Wide, deep photometric surveys require robust photometric redshift estimates (photo-z's) for studies of large-scale structure. These estimates depend critically on accurate photometry. We describe the improvements to the photometric calibration and the photo-z estimates in the Deep Lens Survey (DLS) from correcting three of the inputs to the photo-z calculation: the system response as a function of wavelength, the spectral energy distribution templates, and template prior probabilities as a function of magnitude. We model the system response with a physical model of the MOSAIC camera's CCD, which corrects a 0.1 magnitude discrepancy in the colours of type M2 and later stars relative to the SDSS z-band photometry. We provide our estimated z-band response function for the use of other surveys that used MOSAIC before its recent detector upgrade. The improved throughput curve, template set, and Bayesian prior lead to a 20 per cent reduction in photo-z scatter and a reduction of the bias by a factor of more than two. This paper serves as both a photo-z data release description for DLS and a guide for testing the quality of photometry and resulting photo-z's generally.
12303947
The Star Formation History of Galaxies Measured from Individual Pixels. I. The Hubble Deep Field North
We analyze the photometric information contained in individual pixels of galaxies in the Hubble Deep Field North (HDF-N) using a new technique, pixel-z, that combines predictions of evolutionary synthesis models with photometric redshift template fitting. Each spectral energy distribution template is a result of modeling of the detailed physical processes affecting gas properties and star formation efficiency. The criteria chosen to generate the spectral energy distribution templates is that of sampling a wide range of physical characteristics such as age, star formation rate, obscuration, and metallicity. A key feature of our method is the sophisticated use of error analysis to generate error maps that define the reliability of the template fitting on pixel scales and allow for the separation of the interplay among dust, metallicity, and star formation histories. This technique offers a number of advantages over traditional integrated color studies. As a first application, we derive the star formation and metallicity histories of galaxies in the HDF-N. Our results show that the comoving density of star formation rate, determined from the UV luminosity density of sources in the HDF-N, increases monotonically with redshift out to at least redshift of 5. This behavior can plausibly be explained by a smooth increase of the UV luminosity density with redshift coupled with an increase in the number of star-forming regions as a function of redshift. We also find that the information contained in individual pixels in a galaxy can be linked to its morphological history. Finally, we derive the metal enrichment rate history of the universe and find it in good agreement with predictions based on the evolving H I content of Ly? QSO absorption-line systems.