Worldline Green Functions for Arbitrary Feynman Diagrams

We propose a general method to obtain the scalar worldline Green function on an arbitrary 1D topological space, with which the first-quantized method of evaluating 1-loop Feynman diagrams can be generalized to calculate arbitrary ones. The electric analog of the worldline Green function problem is found and a compact expression for the worldline Green function is given, which has similar structure to the 2D bosonic Green function of the closed bosonic string.Comment: 20 pages, 6 figures; v2: typos corrected, references adde

Recycling Argon through Metamorphic Reactions: the Record in Symplectites

The 40Ar/39Ar ages of metamorphic micas that crystallized at high temperatures are commonly interpreted as cooling ages, with grains considered to have lost 40Ar via thermally-driven diffusion into the grain boundary network. Recently reported laser-ablation data suggest that the spatial distribution of Ar in metamorphic micas does not always conform to the patterns predicted by diffusion theory and that despite high metamorphic temperatures, argon was not removed efficiently from the local system during metamorphic evolution. In the Western Gneiss Region (WGR), Norway, felsic gneisses preserve microtextural evidence for the breakdown of phengite to biotite and plagioclase symplectites during near isothermal decompression from c. 20–25 to c. 8–12 kbar at ~700°C. These samples provide an ideal natural laboratory to assess whether the complete replacement of one K-bearing mineral by another at high temperatures completely ‘resets’ the Ar clock, or whether there is some inheritance of 40Ar in the neo-crystallized phase. The timing of the high-temperature portion of the WGR metamorphic cycle has been well constrained in previous studies. However, the timing of cooling following the overprint is still much debated. In-situ laser ablation spot dating in phengite, biotite-plagioclase symplectites and coarser, texturally later biotite yielded 40Ar/39Ar ages that span much of the metamorphic cycle. Together these data show that despite residence at temperatures of ~700°C, Ar is not completely removed by diffusive loss or during metamorphic recrystallization. Instead, Ar released during phengite breakdown appears to be partially reincorporated into the newly crystallizing biotite and plagioclase (or is trapped in fluid inclusions in those phases) within a close system. Our data show that the microtextural and petrographic evolution of the sample being dated provides a critical framework in which local 40Ar recycling can be tracked, thus potentially allowing 40Ar/39Ar dates to be linked more accurately to metamorphic history

Superconducting tantalum disulfide nanotapes; growth, structure and stoichiometry

Superconducting tantalum disulfide nanowires have been synthesised by surface-assisted chemical vapour transport (SACVT) methods and their crystal structure, morphology and stoichiometry studied by powder X-ray diffraction (PXD), scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and nanodiffraction. The evolution of morphology, stoichiometry and structure of materials grown by SACVT methods in the Ta-S system with reaction temperature was investigated systematically. High-aspect-ratio, superconducting disulfide nanowires are produced at intermediate reaction temperatures (650 degrees C). The superconducting wires are single crystalline, adopt the 2H polytypic structure (hexagonal space group P6(3)/mmc: a = 3.32(2) angstrom, c = 12.159(2) angstrom; c/a = 3.66) and grow in the <2<(1)over bar>(1) over bar0> direction. The nanowires are of rectangular cross-section forming nanotapes composed of bundles of much smaller fibres that grow cooperatively. At lower reaction temperatures nanowires close to a composition of TaS3 are produced whereas elevated temperatures yield platelets of 1T TaS2

Observation of correlated-photon statistics using a single detector

We report experimental observations of correlated-photon statistics in the single-photon detection rate. The usual quantum interference in a two-photon polarization interferometer always accompanies a dip in the single detector counting rate, regardless of whether a dip or peak is seen in the coincidence rate. This effect is explained by taking into account all possible photon number states that reach the detector, rather than considering just the state post-selected by the coincidence measurement. We also report an interferometeric scheme in which the interference peak or dip in coincidence corresponds directly to a peak or dip in the single-photon detection rate.Comment: 4 pages, two-column (minor errors corrected.

Examining subgrid models of supermassive black holes in cosmological simulation

While supermassive black holes (SMBHs) play an important role in galaxy and cluster evolution, at present they can only be included in large-scale cosmological simulation via subgrid techniques. However, these subgrid models have not been studied in a systematic fashion. Using a newly-developed fast, parallel spherical overdensity halo finder built into the simulation code FLASH, we perform a suite of dark matter-only cosmological simulations to study the effects of subgrid model choice on relations between SMBH mass and dark matter halo mass and velocity dispersion. We examine three aspects of SMBH subgrid models: the choice of initial black hole seed mass, the test for merging two black holes, and the frequency of applying the subgrid model. We also examine the role that merging can play in determining the relations, ignoring the complicating effects of SMBH-driven accretion and feedback. We find that the choice of subgrid model can dramatically affect the black hole merger rate, the cosmic SMBH mass density, and the low-redshift relations to halo properties. We also find that it is possible to reproduce observations of the low-redshift relations without accretion and feedback, depending on the choice of subgrid model.Comment: 12 pages, 12 figures, revised from referee comments, accepted by Ap

Detection of lensing substructure using ALMA observations of the dusty galaxy SDP.81

We study the abundance of substructure in the matter density near galaxies using ALMA Science Verification observations of the strong lensing system SDP.81. We present a method to measure the abundance of subhalos around galaxies using interferometric observations of gravitational lenses. Using simulated ALMA observations, we explore the effects of various systematics, including antenna phase errors and source priors, and show how such errors may be measured or marginalized. We apply our formalism to ALMA observations of SDP.81. We find evidence for the presence of a $M=10^{8.96\pm 0.12} M_{\odot}$ subhalo near one of the images, with a significance of $6.9\sigma$ in a joint fit to data from bands 6 and 7; the effect of the subhalo is also detected in both bands individually. We also derive constraints on the abundance of dark matter subhalos down to $M\sim 2\times 10^7 M_{\odot}$, pushing down to the mass regime of the smallest detected satellites in the Local Group, where there are significant discrepancies between the observed population of luminous galaxies and predicted dark matter subhalos. We find hints of additional substructure, warranting further study using the full SDP.81 dataset (including, for example, the spectroscopic imaging of the lensed carbon monoxide emission). We compare the results of this search to the predictions of $\Lambda$CDM halos, and find that given current uncertainties in the host halo properties of SDP.81, our measurements of substructure are consistent with theoretical expectations. Observations of larger samples of gravitational lenses with ALMA should be able to improve the constraints on the abundance of galactic substructure.Comment: 18 pages, 13 figures, Comments are welcom

Correlation between radio and broad-line emissions in radio-loud quasars

Radio emission is a good indicator of the jet power of radio-loud quasars, while the emission in broad-line can well represent the accretion disc radiation in quasars. We compile a sample of all sources of which the broad-line fluxes are available from 1 Jy, S4 and S5 radio source catalogues. A correlation between radio and broad-line emission for this sample of radio-loud quasars is presented, which is in favour of a close link between the accretion processes and the relativistic jets. The BL Lac objects seem to follow the statistical behaviour of the quasars, but with fainter broad-line emission.Comment: 9 pages, accepted for publication in MNRA

The number density of superdense early-type galaxies at 1<z<2 and the local cluster galaxies

Many of the early-type galaxies observed so far at z>1 turned out to have smaller radii with respect to that of a typical present-day early-type galaxy with comparable mass. This has generated the conviction that in the past early-type galaxies were more compact, hence denser, and that as a consequence, they should have increased their radius across the time to reconcile with the present-day ones. However, observations have not yet established whether the population of early-types in the early Universe was fully represented by compact galaxies nor if they were so much more numerous than in the present-day Universe to require an evolution of their sizes. Here we report the results of a study based on a complete sample of 34 early-type galaxies at 0.9<z_{spec}<1.92. We find a majority (62 per cent) of normal early-type galaxies similar to typical local ones, co-existing with compact early-types from ~2 to ~6 times smaller in spite of the same mass and redshift. The co-existence of normal and compact early-type galaxies at ~1.5 suggests that their build-up taken place in the first 3-4 Gyr, followed distinct paths. Also, we find that the number density of compact early-types at ~1.5 is consistent with the lower limits of the local number density of compact early-types derived from local clusters of galaxies. The similar number of compact early-types found in the early and in the present day Universe frustrates the hypothesized effective radius evolution while provides evidence that also compact ETGs were as we see them today 9-10 Gyr ago. Finally, the fact that (at least) most of the compact ETGs at high-z are accounted for by compact early-types in local cluster of galaxies implies that the former are the direct progenitors of the compact early-type cluster galaxies establishing a direct link between environment and early phases of assembly of ETGs.Comment: Published on MNRAS Letters (5 pages, 2 figures, 1 table

Journey to the M_BH -sigma relation: the fate of low mass black holes in the Universe

In this paper, we explore the establishment and evolution of the empirical correlation between black hole mass and velocity dispersion with redshift. We track the growth and accretion history of massive black holes starting from high redshift using two seeding models:(i) Population III remnants, and (ii) massive seeds from direct gas collapse. Although the seeds do not initially satisfy the $M_{\rm BH} - \sigma$ relation, the correlation is established and maintained at all times if self-regulating accretion episodes are associated with major mergers. The massive end of the $M_{\rm BH} - \sigma$ relation is established early, and lower mass MBHs migrate over time. How MBHs migrate toward the relation, the slope and the scatter of the relation all depend critically on the seeding model as well as the adopted self-regulation prescription. We expect flux limited AGN surveys and LISA to select accreting and merging MBHs respectively that have already migrated onto the \msigma relation. This is a consequence of major mergers being more common at high redshift for the most massive, biased, galaxies that anchor the \msigma relation early. We also predict the existence of a large population of low mass `hidden' MBHs at high redshift which can easily escape detection. Additionally, we find that if MBH seeds are massive, $\sim 10^5 M_{\odot}$, the low-mass end of the \msigma flattens towards this asymptotic value, creating a characteristic `plume'.Comment: 8 pages, 5 figures, MNRAS in pres

Hier ist wahrhaftig ein Loch im Himmel - The NGC 1999 dark globule is not a globule

The NGC 1999 reflection nebula features a dark patch with a size of ~10,000 AU, which has been interpreted as a small, dense foreground globule and possible site of imminent star formation. We present Herschel PACS far-infrared 70 and 160mum maps, which reveal a flux deficit at the location of the globule. We estimate the globule mass needed to produce such an absorption feature to be a few tenths to a few Msun. Inspired by this Herschel observation, we obtained APEX LABOCA and SABOCA submillimeter continuum maps, and Magellan PANIC near-infrared images of the region. We do not detect a submillimer source at the location of the Herschel flux decrement; furthermore our observations place an upper limit on the mass of the globule of ~2.4x10^-2 Msun. Indeed, the submillimeter maps appear to show a flux depression as well. Furthermore, the near-infrared images detect faint background stars that are less affected by extinction inside the dark patch than in its surroundings. We suggest that the dark patch is in fact a hole or cavity in the material producing the NGC 1999 reflection nebula, excavated by protostellar jets from the V 380 Ori multiple system.Comment: accepted for the A&A Herschel issue; 7 page