7,924 research outputs found
The deconfining phase transition in SU(N) gauge theories
We report on our ongoing investigation of the deconfining phase transition in
SU(4) and SU(6) gauge theories. We calculate the critical couplings while
taking care to avoid the influence of a nearby bulk phase transition. We
determine the latent heat of the phase transition and investigate the order and
the strength of the transition at large N. We also report on our determination
of the critical temperature expressed in units of the string tension in the
large N limit.Comment: Lattice 2002 (nonzerot), 3 pages, 2 figure
Features of SU(N) Gauge Theories
We review recent lattice results for the large limit of SU(N) gauge
theories. In particular, we focus on glueball masses, topology and its relation
to chiral symmetry breaking (relevant for phenomenology), on the tension of
strings connecting sources in higher representations of the gauge group
(relevant for models of confinement and as a comparative ground for theories
beyond the Standard Model) and on the finite temperature deconfinement phase
transition (relevant for RHIC-like experiments). In the final part we present
open challenges for the future.Comment: 6 pages, 3 figures; summary of the talk given by B. Lucini and the
poster presented by U. Wenger at the conference "Confinement 2003
The Green Bank Telescope H II Region Discovery Survey: IV. Helium and Carbon Recombination Lines
The Green Bank Telescope H II Region Discovery Survey (GBT HRDS) found
hundreds of previously unknown Galactic regions of massive star formation by
detecting hydrogen radio recombination line (RRL) emission from candidate H II
region targets. Since the HRDS nebulae lie at large distances from the Sun,
they are located in previously unprobed zones of the Galactic disk. Here we
derive the properties of helium and carbon RRL emission from HRDS nebulae. Our
target sample is the subset of the HRDS that has visible helium or carbon RRLs.
This criterion gives a total of 84 velocity components (14% of the HRDS) with
helium emission and 52 (9%) with carbon emission. For our highest quality
sources, the average ionic He-4+/H+ abundance ratio by number, , is 0.068
+/- 0.023 (1-sigma). This is the same ratio as that measured for the sample of
previously known Galactic H II regions. Nebulae without detected helium
emission give robust y+ upper limits. There are 5 RRL emission components with
y+ less than 0.04 and another 12 with upper limits below this value. These H II
regions must have either a very low He-4 abundance or contain a significant
amount of neutral helium. The HRDS has 20 nebulae with carbon RRL emission but
no helium emission at its sensitivity level. There is no correlation between
the carbon RRL parameters and the 8 microns mid-infrared morphology of these
nebulae.Comment: Accepted to ApJ. The survey website can be found here:
http://go.nrao.edu/hrd
Diffuse Ionized Gas in the Milky Way Disk
We analyze the diffuse ionized gas (DIG) in the first Galactic quadrant from
l=18deg to 40deg using radio recombination line (RRL) data from the Green Bank
Telescope. These data allow us to distinguish DIG emission from HII region
emission and thus study the diffuse gas essentially unaffected by confusion
from discrete sources. We find that the DIG has two dominant velocity
components, one centered around 100km/s associated with the luminous HII region
W43, and the other centered around 45km/s not associated with any large HII
region. Our analysis suggests that the two velocity components near W43 may be
caused by non-circular streaming motions originating near the end of the
Galactic bar. At lower Galactic longitudes, the two velocities may instead
arise from gas at two distinct distances from the Sun, with the most likely
distances being ~6kpc for the 100km/s component and ~12kpc for the 45km/s
component. We show that the intensity of diffuse Spitzer GLIMPSE 8.0um emission
caused by excitation of polyaromatic hydrocarbons (PAHs) is correlated with
both the locations of discrete HII regions and the intensity of the RRL
emission from the DIG. This implies that the soft ultra-violet photons
responsible for creating the infrared emission have a similar origin as the
harder ultra-violet photons required for the RRL emission. The 8.0um emission
increases with RRL intensity but flattens out for directions with the most
intense RRL emission, suggesting that PAHs are partially destroyed by the
energetic radiation field at these locations.Comment: Accepted for publication in ApJ (16 pages, 11 figures, 2 tables
Diffuse Ionized Gas in the Milky Way Disk
We analyze the diffuse ionized gas (DIG) in the first Galactic quadrant from
l=18deg to 40deg using radio recombination line (RRL) data from the Green Bank
Telescope. These data allow us to distinguish DIG emission from HII region
emission and thus study the diffuse gas essentially unaffected by confusion
from discrete sources. We find that the DIG has two dominant velocity
components, one centered around 100km/s associated with the luminous HII region
W43, and the other centered around 45km/s not associated with any large HII
region. Our analysis suggests that the two velocity components near W43 may be
caused by non-circular streaming motions originating near the end of the
Galactic bar. At lower Galactic longitudes, the two velocities may instead
arise from gas at two distinct distances from the Sun, with the most likely
distances being ~6kpc for the 100km/s component and ~12kpc for the 45km/s
component. We show that the intensity of diffuse Spitzer GLIMPSE 8.0um emission
caused by excitation of polyaromatic hydrocarbons (PAHs) is correlated with
both the locations of discrete HII regions and the intensity of the RRL
emission from the DIG. This implies that the soft ultra-violet photons
responsible for creating the infrared emission have a similar origin as the
harder ultra-violet photons required for the RRL emission. The 8.0um emission
increases with RRL intensity but flattens out for directions with the most
intense RRL emission, suggesting that PAHs are partially destroyed by the
energetic radiation field at these locations.Comment: Accepted for publication in ApJ (16 pages, 11 figures, 2 tables
High-Mass Star Formation in the Outer Scutum-Centaurus Arm
The Outer Scutum-Centaurus (OSC) spiral arm is the most distant molecular
spiral arm in the Milky Way, but until recently little was known about this
structure. Discovered by Dame and Thaddeus (2011), the OSC lies 15 kpc
from the Galactic Center. Due to the Galactic warp, it rises to nearly
4 above the Galactic Plane in the first Galactic quadrant, leaving it
unsampled by most Galactic plane surveys. Here we observe HII region candidates
spatially coincident with the OSC using the Very Large Array to image radio
continuum emission from 65 targets and the Green Bank Telescope to search for
ammonia and water maser emission from 75 targets. This sample, drawn from the
WISE Catalog of Galactic HII Regions, represents every HII region candidate
near the longitude-latitude (l,v) locus of the OSC. Coupled with their
characteristic mid-infrared morphologies, detection of radio continuum emission
strongly suggests that a target is a bona fide HII region. Detections of
associated ammonia or water maser emission allow us to derive a kinematic
distance and determine if the velocity of the region is consistent with that of
the OSC. Nearly 60% of the observed sources were detected in radio continuum,
and over 20% have ammonia or water maser detections. The velocities of these
sources mainly place them beyond the Solar orbit. These very distant high-mass
stars have stellar spectral types as early as O4. We associate high-mass star
formation at 2 new locations with the OSC, increasing the total number of
detected HII regions in the OSC to 12.Comment: 14 pages text and tables + 10 pages supplemental figure
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