The 100 and 160 micron maps of the dust reemission from the nucleus and inner-arm regions of NGC 6946

Dust reemission from the Scd galaxy NGC 6946 has been measured at 100 and 160 microns with the 32-channel University of Chicago Far-Infrared Camera. Researchers present fully sampled maps of the nucleus and inner spiral arms at 45 seconds resolution. The far-infrared morphology of the galaxy is a bright peak centered on a diffuse disk, where the peak occurs about 24 seconds NE of the Dressel and Condon optical center. The 100/160 micron color temperature is correlated with the H alpha surface brightness. Assuming the distance from Earth to the galaxy is 10.1 Mpc, researchers determine that Tc is 32 K at the nucleus and at radius 5.4 kpc, where there is a concentration of H II regions. In the intermediate annulus of relatively low H alpha surface brightness, the temperature drops to a local minimum of 25 K at radius 3 kpc. The ratio of reradiated to transmitted stellar luminosity is approx. 3.0 at the nucleus and approx. 0.9 for the disk. The optical depth at 100 micron increases from .0005 at the edges of our map to .0035 at the far infrared radiation (FIR) peak. Combining our observations with a fully sampled map of similar spatial extent in CO(1 greater than 0), researchers determine that the ratio F sub IR/I sub CO at the center of the galaxy is almost twice that for the disk, where the value is more or less constant

Integrable vortex-type equations on the two-sphere

We consider the Yang-Mills instanton equations on the four-dimensional manifold S^2xSigma, where Sigma is a compact Riemann surface of genus g>1 or its covering space H^2=SU(1,1)/U(1). Introducing a natural ansatz for the gauge potential, we reduce the instanton equations on S^2xSigma to vortex-type equations on the sphere S^2. It is shown that when the scalar curvature of the manifold S^2xSigma vanishes, the vortex-type equations are integrable, i.e. can be obtained as compatibility conditions of two linear equations (Lax pair) which are written down explicitly. Thus, the standard methods of integrable systems can be applied for constructing their solutions. However, even if the scalar curvature of S^2xSigma does not vanish, the vortex equations are well defined and have solutions for any values of the topological charge N. We show that any solution to the vortex equations on S^2 with a fixed topological charge N corresponds to a Yang-Mills instanton on S^2xSigma of charge (g-1)N.Comment: 14 pages; v2: clarifying comments added, published versio

Gravitational Waves Probe the Coalescence Rate of Massive Black Hole Binaries

We calculate the expected nHz--$\mu$Hz gravitational wave (GW) spectrum from coalescing Massive Black Hole (MBH) binaries resulting from mergers of their host galaxies. We consider detection of this spectrum by precision pulsar timing and a future Pulsar Timing Array. The spectrum depends on the merger rate of massive galaxies, the demographics of MBHs at low and high redshift, and the dynamics of MBH binaries. We apply recent theoretical and observational work on all of these fronts. The spectrum has a characteristic strain $h_c(f)~10^{-15} (f/yr^{-1})^{-2/3}$, just below the detection limit from recent analysis of precision pulsar timing measurements. However, the amplitude of the spectrum is still very uncertain owing to approximations in the theoretical formulation of the model, to our lack of knowledge of the merger rate and MBH population at high redshift, and to the dynamical problem of removing enough angular momentum from the MBH binary to reach a GW-dominated regime.Comment: 31 Pages, 8 Figures, small changes to match the published versio

Spectral triples and the super-Virasoro algebra

We construct infinite dimensional spectral triples associated with representations of the super-Virasoro algebra. In particular the irreducible, unitary positive energy representation of the Ramond algebra with central charge c and minimal lowest weight h=c/24 is graded and gives rise to a net of even theta-summable spectral triples with non-zero Fredholm index. The irreducible unitary positive energy representations of the Neveu-Schwarz algebra give rise to nets of even theta-summable generalised spectral triples where there is no Dirac operator but only a superderivation.Comment: 27 pages; v2: a comment concerning the difficulty in defining cyclic cocycles in the NS case have been adde

Two-hadron interference fragmentation functions. Part I: general framework

We investigate the properties of interference fragmentation functions measurable from the distribution of two hadrons produced in the same jet in the current fragmentation region of a hard process. We discuss the azimuthal angular dependences in the leading order cross section of two-hadron inclusive lepton-nucleon scattering as an example how these interference fragmentation functions can be addressed separately.Comment: RevTeX, 7 figures, first part of a work split in two, second part forthcoming in few day

Quark Masses: An Environmental Impact Statement

We investigate worlds that lie on a slice through the parameter space of the Standard Model over which quark masses vary. We allow as many as three quarks to participate in nuclei, while fixing the mass of the electron and the average mass of the lightest baryon flavor multiplet. We classify as "congenial" worlds that satisfy the environmental constraint that the quark masses allow for stable nuclei with charges one, six, and eight, making organic chemistry possible. Whether a congenial world actually produces observers depends on a multitude of historical contingencies, beginning with primordial nucleosynthesis, which we do not explore. Such constraints may be independently superimposed on our results. Environmental constraints such as the ones we study may be combined with information about the a priori distribution of quark masses over the landscape of possible universes to determine whether the measured values of the quark masses are determined environmentally, but our analysis is independent of such an anthropic approach. We estimate baryon masses as functions of quark masses and nuclear masses as functions of baryon masses. We check for the stability of nuclei against fission, strong particle emission, and weak nucleon emission. For two light quarks with charges 2/3 and -1/3, we find a band of congeniality roughly 29 MeV wide in their mass difference. We also find another, less robust region of congeniality with one light, charge -1/3 quark, and two heavier, approximately degenerate charge -1/3 and 2/3 quarks. No other assignment of light quark charges yields congenial worlds with two baryons participating in nuclei. We identify and discuss the region in quark-mass space where nuclei would be made from three or more baryon species.Comment: 40 pages, 16 figures (in color), 4 tables. See paper for a more detailed abstract. v4: Cleaning up minor typo

Semi-inclusive vector meson production in DIS

We analyze one-particle inclusive DIS in the case when a spin-1 hadron (such as a vector meson) is observed in the final state. We consider only leading order contributions in 1/Q, but we include transverse momentum of partons. Several new fragmentation functions appear in cross sections. One of them can be measured in connection with the transverse-spin disbtribution function h_1.Comment: 3 pages, uses sprocl.sty, talk given at the DIS2000 conference, Liverpool, England, April 2000, to appear in the conference proceeding

Bounds on transverse momentum dependent distribution and fragmentation functions

We give bounds on the distribution and fragmentation functions that appear at leading order in deep inelastic 1-particle inclusive leptoproduction or in Drell-Yan processes. These bounds simply follow from positivity of the defining matrix elements and are an important guidance in estimating the magnitude of the azimuthal and spin asymmetries in these processes.Comment: 5 pages, Revtex, 3 Postscript figures, version with minor changes, to be published in Physical Review Letter

Explicit Non-Abelian Monopoles and Instantons in SU(N) Pure Yang-Mills Theory

It is well known that there are no static non-Abelian monopole solutions in pure Yang-Mills theory on Minkowski space R^{3,1}. We show that such solutions exist in SU(N) gauge theory on the spaces R^2\times S^2 and R^1\times S^1\times S^2 with Minkowski signature (-+++). In the temporal gauge they are solutions of pure Yang-Mills theory on T^1\times S^2, where T^1 is R^1 or S^1. Namely, imposing SO(3)-invariance and some reality conditions, we consistently reduce the Yang-Mills model on the above spaces to a non-Abelian analog of the \phi^4 kink model whose static solutions give SU(N) monopole (-antimonopole) configurations on the space R^{1,1}\times S^2 via the above-mentioned correspondence. These solutions can also be considered as instanton configurations of Yang-Mills theory in 2+1 dimensions. The kink model on R^1\times S^1 admits also periodic sphaleron-type solutions describing chains of n kink-antikink pairs spaced around the circle S^1 with arbitrary n>0. They correspond to chains of n static monopole-antimonopole pairs on the space R^1\times S^1\times S^2 which can also be interpreted as instanton configurations in 2+1 dimensional pure Yang-Mills theory at finite temperature (thermal time circle). We also describe similar solutions in Euclidean SU(N) gauge theory on S^1\times S^3 interpreted as chains of n instanton-antiinstanton pairs.Comment: 16 pages; v2: subsection on topological charges added, title expanded, some coefficients corrected, version to appear in PR

Two-hadron semi-inclusive production including subleading twist

We extend the analysis of two-hadron fragmentation functions to the subleading twist, discussing also the issue of color gauge invariance. Our results can be used anywhere two unpolarized hadrons are semi-inclusively produced in the same fragmentation region, also at moderate values of the hard scale Q. Here, we consider the example of polarized deep-inelastic production of two hadrons and we give a complete list of cross sections and spin asymmetries up to subleading twist. Among the results, we highlight the possibility of extracting the transversity distribution with longitudinally polarized targets and also the twist-3 distribution e(x), which is related to the pion-nucleon sigma term and to the strangeness content of the nucleon.Comment: 16 pages, RevTeX4, 5 figures, revised notation of several formulae, added text in Secs. III-V, added reference