53540181
Existence and stability of multiple solutions to the gap equation
We argue by way of examples that, as a nonlinear integral equation, the gap equation can and does possess many physically distinct solutions for the dressed-quark propagator. The examples are drawn from a class that is successful in describing a broad range of hadron physics observables. We apply the homotopy continuation method to each of our four exemplars and thereby find all solutions that exist within the interesting domains of light current-quark masses and interaction strengths; and simultaneously provide an explanation of the nature and number of the solutions, many of which may be associated with dynamical chiral symmetry breaking. Introducing a stability criterion based on the scalar and pseudoscalar susceptibilities we demonstrate, however, that for any nonzero current-quark mass only the regular Nambu solution of the gap equation is stable against perturbations. This guarantees that the existence of multiple solutions to the gap equation cannot complicate the description of phenomena in hadron physics. Dynamical chiral symmetry breaking (DCSB) is a particularly striking feature of the Standard Model, playing an important role in formation of the visible matter in the Universe [1]. It is apparent in the existence of a strongly momentum-dependent chiral-limit dressedquark mass function, M(p 2 ), which is obtained in solutions of models for QCD’s gap equation that provide a realistic description of hadron properties [2–4], and in a sharp increase in M(p 2 ) at p 2 . 2GeV 2 when the current-quark mass is nonzero but light. The latter is seen in both Dyson-Schwinger equation (DSE) studies [5– 7] and numerical simulations of lattice-regularised QCD [8–10]. This behaviour of the mass function must be part of any treatment of continuum strong QCD that aims to be considered realistic. The gap equation is a nonlinear integral equation. The nonlinearity gives it the power to express nonperturbative phenomena; and also leads to the curiosity that the solution is not unique. Mathematically, this should have been anticipated. However, perhaps surprisingly, it has only been established relatively recently that on a bounded, measurable domain of non-negative currentquark mass, realistic models of the QCD’s gap equation simultaneously admit more than one nonequivalent DCSB solution and also distinct solutions that may unambiguously be connected with the realization of chiral symmetry in the Wigner mode [11–13]. This feature can potentially create problems; e.g., if the additional solu
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.
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).
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.
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}
54796299
Galaxy-Mass Correlations on 10 Mpc Scales in the Deep Lens Survey
We examine the projected correlation of galaxies with mass from small scales (<few hundred kpc), where individual dark matter halos dominate, out to 15 Mpc, where correlated large-scale structure dominates. We investigate these profiles as a function of galaxy luminosity and redshift. Selecting 0.8 million galaxies in the Deep Lens Survey, we use photometric redshifts and stacked weak gravitational lensing shear tomography out to radial scales of 1° from the centers of foreground galaxies. We detect correlated mass density from multiple halos and large-scale structure at radii larger than the virial radius and find the first observational evidence for growth in the galaxy-mass correlation on 10 Mpc scales with decreasing redshift and fixed range of luminosity. For a fixed range of redshift, we find a scaling of projected halo mass with rest-frame luminosity similar to previous studies at lower redshift. We control systematic errors in shape measurement and photometric redshift, enforce volume completeness through absolute magnitude cuts, and explore residual sample selection effects via simulations.
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.
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.
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.
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.