32252191
Memory effects and thermodynamics in strong field plasmas
We study the evolution of a strong field plasma using a quantum Vlasov equation with a non-Markovian source term and a simple collision term, and calculate the time dependence of the energy and number density, and the temperature. The evolution of a plasma produced with BNL RHIC-like initial conditions is well described by a low density approximation to the source term. However, non-Markovian aspects should be retained to obtain an accurate description of the early stages of a CERN LHC-like plasma. (c) 2000 The American Physical Society.
121729939
Diquark condensation and the quark-quark interaction
We employ a bispinor gap equation to study superfluidity at nonzero chemical potential, {mu}{ne}0, in two- and three-color QCD, exploring the gap's sensitivity to the nature of the quark-quark interaction. The two-color theory, QC{sub 2}D, is an excellent exemplar; the order of truncation of the quark-quark scattering kernel K has no qualitative impact, which allows a straightforward elucidation of the effects of {mu} when the coupling is strong. In the three-color theory the rainbow-ladder truncation admits diquark bound states, a defect that is eliminated by an improvement of K. The corrected gap equation describes a superfluid phase that is semiquantitatively similar to that obtained using the rainbow truncation. A model study suggests that the width of the superfluid gap and the transition point in QC{sub 2}D provide reliable quantitative estimates of those quantities in QCD. (c) 1999 The American Physical Society.
119080896
Concerning the quark condensate
A continuum expression for the trace of the massive dressed-quark propagator is used to explicate a connection between the infrared limit of the QCD Dirac operator's spectrum and the quark condensate appearing in the operator product expansion. This connection is verified via comparison with a lattice-QCD simulation. The pseudoscalar vacuum polarization provides a good approximation to the condensate over a larger range of current-quark masses.
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.
119018652
Facets of confinement and dynamical chiral symmetry breaking
Abstract.The gap equation is a cornerstone in understanding dynamical chiral symmetry breaking and may also provide clues to confinement. A symmetry-preserving truncation of its kernel enables proofs of important results and the development of an efficacious phenomenology. We describe a model of the kernel that yields: a momentum-dependent dressed-quark propagator in fair agreement with quenched lattice-QCD results; and chiral limit values, $f_\pi^0 = 68 $MeV and $\langle \bar q q \rangle = -(190 {\rm MeV})^3$. It is compared with models inferred from studies of the gauge sector.
7794133
Deconfinement at finite chemical potential.
Abstract In a confining, renormalisable, Dyson-Schwinger equation model of two-flavour QCD we explore the chemical-potential dependence of the dressed-quark propagator, which provides a means of determining the behaviour of the chiral and deconfinement order parameters, and low-energy pion observables. We find coincident, first order deconfinement and chiral symmetry restoration transitions at μ c =375 MeV. f π is insensitive to μ until μ≈μ 0 :=0.7 μ c when it begins to increase rapidly. m π is weakly dependent on μ , decreasing slowly with μ and reaching a minimum 6% less than its μ =0 value at μ = μ 0 . In a two-flavour free-quark gas at μ = μ c the baryon number density would be approximately 3 ρ 0 , where ρ 0 =0.16 fm −3 ; while in such a gas at μ 0 the density is ρ 0 .
16712090
The DRaGONS Survey: A Search for High Redshift Radio Galaxies And Heavily Obscured AGNs
We present the first results from the Distant Radio Galaxies Optically Non-detected in the SDSS (DRaGONS) Survey. Using a novel selection technique for identifying high redshift radio galaxy (HzRG) candidates, a large sample of bright (S_{1.4GHz} > 100mJy) radio sources from the FIRST survey having no optical counterpart in the SDSS is compiled. K-band imaging with the FLAMINGOS instrument on the 4-meter telescope at Kitt Peak for 96 such candidates allows preliminary identification of HzRG candidates through the well-known K-z relation. Of the initial candidates, we identify 70 with magnitudes brighter than K \approx 19.5, and compute limiting magnitudes for the remainder. Assigning redshifts based on the K-z Hubble diagram gives a mean redshift for our sample of z=2.5 and a median redshift of z=2.0. This selection is also sensitive to a previously unseen population of anomalously red radio galaxies (r-K > 6.5-7), which may indicate significant obscuration at moderate redshifts. These obscured objects can be used to test the completeness of QSO surveys to the effects of reddenning. More than ten percent of our sample falls into this category, which may represent a sizable radio loud population missing from current optically selected AGN samples. We additionally identify 479 bright Extremely Red Objects (EROs) in the fields surrounding our HzRG candidates, to a magnitude of K=17.5, within a non-contiguous area of 2.38 square degrees. This constitutes a small overdensity of EROs surrounding the radio galaxy candidates over random fields, and we see possible evidence for a physical association of the EROs with the radio galaxies. However, examining the clustering of all K < 19.0 galaxies around the radio targets reveals no evidence of a global galaxy excess.
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.
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.
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.