6,726 research outputs found
Green Bank Telescope observations of low column density HI around NGC 2997 and NGC 6946
Observations of ongoing HI accretion in nearby galaxies have only identified
about 10% of the needed fuel to sustain star formation in these galaxies. Most
of these observations have been conducted using interferometers and may have
missed lower column density, diffuse, HI gas that may trace the missing 90% of
gas. Such gas may represent the so-called "cold flows" predicted by current
theories of galaxy formation to have never been heated above the virial
temperature of the dark matter halo. As a first attempt to identify such cold
flows around nearby galaxies and complete the census of HI down to N(HI)~10^18
cm^-2, I used the Robert C. Byrd Green Bank Telescope (GBT) to map the
circumgalactic (r < 100-200 kpc) HI environment around NGC 2997 and NGC 6946.
The resulting GBT observations cover a four square degree area around each
galaxy with a 5-sigma detection limit of N(HI)~10^18 cm^-2 over a 20 km/s
linewidth. This project complements absorption line studies, which are
well-suited to the regime of lower N(HI). Around NGC 2997, the GBT HI data
reveal an extended HI disk and all of its surrounding gas-rich satellite
galaxies, but no filamentary features. Furthermore, the HI mass as measured
with the GBT is only 7% higher than past interferometric measurements. After
correcting for resolution differences, the HI extent of the galaxy is 23%
larger at the N(HI)~1.2x10^18 cm^-2 level as measured by the GBT. On the other
hand, the HI observations of NGC 6946 reveal a filamentary feature apparently
connecting NGC 6946 with its nearest companions. This HI filament has
N(HI)~10^18 cm^-2 and a FWHM of 55+-5 km/s and was invisible in past
interferometer observations. The properties of this filament are broadly
consistent with being a cold flow or debris from a past tidal interaction
between NGC 6946 and its satellites.Comment: 19 pages, 7 figures. Accepted for publication in A
Reply to ``Comment on `Majoron emitting neutrinoless double beta decay in the electroweak chiral gauge extensions' ''
We demonstrate that in the process of deducing the constraint on the
electroweak mixing angle in our paper, we have indeed been working
with three mass scales while implementing (331) model.Comment: Revtex, 3pages, Reply to hep-ph/9902448, Submitted to Phys. Rev.
Neutrinos and Electromagnetic Gauge Invariance
It is discussed a recently proposed connection among U(1)
electromagnetic gauge invariance and the nature of the neutrino mass terms in
the framework of \mbox {SU(3)}_C\otimes G_W \otimes {\mbox U(1)}_N, =
SU(3), extensions of the Standard Model. The impossibility of that
connection, also in the extended case = SU(4), is demonstrated.Comment: 10 pages, Revtex 3.0, no figure
Polarization effects in double open-charm production at LHCb
Double open-charm production is one of the most promising channels to
disentangle single from double parton scattering (DPS) and study different
properties of DPS. Several studies of the DPS contributions have been made. A
missing ingredient so far has been the study of polarization effects, arising
from spin correlations between the two partons inside an unpolarized proton. We
investigate the impact polarization has on the double open-charm cross section.
We show that the longitudinally polarized gluons can give significant
contributions to the cross section, but for most of the considered kinematic
region only have a moderate effect on the shape. We compare our findings to the
LHCb data in the D0D0 final state, identify observables where polarization does
have an impact on the distribution of the final state particles, and suggest
measurements which could lead to first experimental indications of, or limits
on, polarization in DPS.Comment: 16 pages, 13 figure
Dijet imbalance in hadronic collisions
The imbalance of dijets produced in hadronic collisions has been used to
extract the average transverse momentum of partons inside the hadrons. In this
paper we discuss new contributions to the dijet imbalance that could complicate
or even hamper this extraction. They are due to polarization of initial state
partons inside unpolarized hadrons that can arise in the presence of nonzero
parton transverse momentum. Transversely polarized quarks and linearly
polarized gluons produce specific azimuthal dependences of the two jets that in
principle are not suppressed. Their effects cannot be isolated just by looking
at the angular deviation from the back-to-back situation, rather they enter jet
broadening observables. In this way they directly affect the extraction of the
average transverse momentum of unpolarized partons that is thought to be
extracted. We discuss appropriately weighted cross sections to isolate the
additional contributions.Comment: 15 pages, 2 figures; revised version, published in Phys. Rev.
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