U(1) Axial Symmetry and Correlation Functions in the High Temperature Phase of QCD

Simple group-theoretical arguments are used to demonstrated that in the high temperature (chirally restored) phase of QCD with N massless flavours, all n-point correlation functions of quark bilinears are invariant under U(1) axial transformations provided n < N. In particular this implies that the two-point correlation function in the eta' channel is identical to that in the pion channel for N > 2. Unlike previous work, this result does not depend on the topological properties of QCD and can be formulated without explicit reference to functional integrals.Comment: 3 pages, RevTe

Relations Among Correlation Functions in the High Temperature Phase of QCD with Broken SU(3)

Group-theoretic arguments are used to determine the dependence of two-point correlators of quark bilinears on the current quark masses. The leading difference between $\pi$ and $\delta$ correlators is found to be of order $m_s$ times a U(1)$_{\scriptscriptstyle A}$-violating correlator. These general arguments are consistent with Schaefer's observation that if U(1)$_{\scriptscriptstyle A}$ violation persists to high enough temperatures then the strange $\eta$ can be lighter than the non-strange one.Comment: 8 page

The late-type stellar content of Magellanic Cloud clusters

New broad-band infrared photometric data have been obtained for 48 late-type giants in clusters in the Magellanic Clouds (MC). Visual spectrophotometry was obtained for a subset of these stars. These observations are combined with published data for MC cluster stars and then compared with similar data for MC field giants and with predictions of various evolutionary schemes for cool, luminous, carbon and oxygen rich stars. The MC cluster C stars are found to have a range in spectral energy distributions which is quite similar to that of MC field C stars. The luminosity function of the cluster C stars has a mean M_(bol) = —4.76 with a dispersion of ±0.36, also quite similar to the values for MC field C stars. However, the dispersion of the cluster C stars in M_K_0 at a given (J— K)_0 is between 2 and 3 times less than it is for the field C stars. This can arise if the present sample of clusters has a significantly smaller spread in age and/or metallicity than the progenitors of the field C stars. The LMC field contains M giants which are redder and more luminous than any so far found in LMC or SMC clusters. This is attributed to the presence in the LMC field of a significant population of stars which are younger and/or more metal rich than the stars in the cluster sample. Differences which are found to exist between the M star populations of the LMC and the SMC clusters are also attributed to age and/or metallicity effects. In all but one of the MC clusters which have both M and C stars, the faintest C star is brighter than the brightest M star. Such a “transition” luminosity appears to be correlated with the location of the cluster in the one-dimensional classification sequence of Searle, Wilkinson, and Bagnuolo, and it can be a useful criterion in the evaluation of theories of carbon star evolution. Finally, although the spectrophotometric data suggest that the LMC “halo-type” globular, NGC 1841 and 2257, have metallicities similar to one another and to that of M3, the locations of the NGC 1841 stars in a C-M diagram appear to be anomalous in the sense that its brightest stars have luminosities greater than the tips of giant branches of metal poor galactic globular clusters

What is the second parameter - The anomalous globular cluster NGC 7006

An infrared color-magnitude diagram for NGC 7006 and moderate dispersion digital optical spectra of eight of its members indicate a metal abundance of -1.5 dex with respect to the sun. However, the ratio of red to blue horizontal-branch stars is quite large and is what would be expected for a cluster of much higher metallicity. Molecular band strengths are determined for CO in four stars, and CH and CN in five stars, and it is found that none of these molecular bands are anomalously strong compared to the same molecular features in other globulars of similar metallicity but varying horizontal-branch type. This is contrary to the behavior predicted if the C, N, and O abundances are the 'second parameter' needed to explain anomalous horizontal-branch morphologies

The Extremely Red Objects Found Thus Far in the Caltech Faint Galaxy Redshift Survey

We discuss the very red objects found in the first field of the Caltech Faint Galaxy Redshift Survey, for which the observations and analysis are now complete. In this field, which is 15 arcmin$^2$ and at J005325+1234 there are 195 objects with $K_s < 20$ mag, of which 84% have redshifts. The sample includes 24 spectroscopically confirmed Galactic stars, 136 galaxies, three AGNs, and 32 objects without redshifts. About 10% of the sample has $(R-K) \ge 5$ mag. Four of these objects have redshifts, with $0.78 \le z \le 1.23$. Three of these are based on absorption features in the mid-UV, while the lowest redshift object shows the standard features near 4000\AA. Many of the objects still without redshifts have been observed spectroscopically, and no emission lines were seen in their spectra. We believe they are galaxies with $z \sim 1 - 1.5$ that are red due to their age and stellar content and not to some large amount of internal reddening from dust. Among the many other results from this survey of interest here is a determination of the median extinction in the mid-UV for objects with strong emission line spectra at $z \sim 1 - 1.3$. The result is extinction by a factor of $\sim$2 at 2400\AA.Comment: 6 pages, Latex, with 2 figures. To be published in the proceedings of the conference "Infrared Surveys: A Prelude to SIRTF

The oxygen-II luminosity density of the Universe

Equivalent widths of [OII] 3727 A lines are measured in 375 faint galaxy spectra taken as part of the Caltech Faint Galaxy Redshift Survey centered on the Hubble Deep Field. The sensitivity of the survey spectra to the [OII] line is computed as a function of magnitude, color and redshift. The luminosity function of galaxies in the [OII] line and the integrated luminosity density of the Universe in the [OII] line are computed as a function of redshift. It is found that the luminosity density in the [OII] line was a factor of ~10 higher at redshifts z~1 than it is at the present day. The simplest interpretation is that the star formation rate density of the Universe has declined dramatically since z~1.Comment: accepted for publication in Ap

Infrared photometry, bolometric luminosities, and effective temperatures for giant stars in 26 globular clusters

Infrared observations of 307 giant stars in 26 globular clusters are presented. The effects of H_2O absorption on the infrared colors are examined. The color-color correlations and color-magnitude diagrams, derived using an internally consistent set of distance moduli and reddenings, identify specific clusters with problematical reddenings or low quality optical data. The mean behavior of the color-color relationships is, in all cases, in good agreement with our earlier work

Globular cluster giant branches and the metallicity scale

Using the data base of Frogel, Persson, and Cohen and our earlier work, we derive characteristic parameters that describe the systematic behavior of the giants in each of 33 globular clusters. The globular cluster giant branches form a strictly homologous sequence in the H-R diagram, and their ordering correlates well with the metallicity scale published by Zinn. Nevertheless, when the giant branch parameters are used to define a metallicity ranking scheme, it appears that the Zinn abundance scale systematically underestimates the metallicity of clusters with exceptionally blue horizontal branches. The observed luminosities of the brightest giant in each cluster agree with the theoretical core helium flash luminosity; the small dispersion of these luminosities implies that at a given metallicity the intrinsic scatter in the absolute magnitude of horizontal-branch stars is less than 0.1 mag. The mean CO index increases as metallicity increases; analysis of the residuals from the mean relationships both of CO and of horizontal-branch type against metallicity imply that the CO abundance is unrelated to the second parameter problem. All metal-rich clusters with an adequate sample of stars show a spread in CO within each cluster comparable to that seen in 47 Tuc. Metal-poor clusters which exhibit a large star to star spread in CO are NGC 362, 2808, and 6656. The integrated light measurements of (V - K)_0 and CO published by Aaronson and colleagues correlate with the cluster parameters determined from measurements of individual stars in a manner that can be predicted from stellar evolutionary calculations for old populations. The integrated light of such old systems, at least from V to K, is therefore well understood