6,272 research outputs found
Large-field CO(1--0) observations toward the Galactic historical supernova remnants: a large cavity around Tycho's supernova remnant
The investigation of the interaction between the supernova remnants (SNRs)
and interstellar gas is not only necessary to improve our knowledge of SNRs,
but also to understand the nature of the progenitor systems. As a part of the
Milky Way Imaging Scroll Painting CO line survey (MWISP), we study the
interstellar gas surrounding the Galactic historical SNRs, using the PMO
13.7-meter telescope. In this work, we present large-field
(32) and high-sensitivity CO(1-0) molecular line
observations toward Tycho's SNR. The CO observations reveal, from the outside
in, large molecular clouds, stream-like structures, and an inner rim around
Tycho's SNR. We derived the basic properties (column density, mass, and
kinematics) of these objects based on the CO observations. The large molecular
clouds individually show an arc toward the remnant center, outlining a large
cavity with radii of 0.30.6 (or 13 pc 27
pc at a distance of 2.5 kpc) around the remnant. The CO line broadenings and
asymmetries detected in the surrounding clouds, the observed expansion of the
cavity, in concert with enhanced CO(2-1)/(1-0) intensity ratio detected
in previous studies, suggest the interaction of the large cavity with a wind in
the region. After excluding the scenario of a large bubble produced by bright
massive stars, we suggest that the large cavity could be explained by accretion
wind from the progenitor system of Tycho's supernova. Nevertheless, the
possibility of the random distribution of a large cavity around Tycho's SNR
cannot be ruled out thus far. Further observations are needed to confirm the
physical association of the large cavity with Tycho's SNR.Comment: 15 pages, 9 figures, updated according to the A&A proo
Proton Spin Structure from Measurable Parton Distributions
We present a systematic study of the proton spin structure in terms of
measurable parton distributions. For a transversely-polarizedproton, we derive
a polarization sum rule from the leading generalized parton distributions
appearing in hard exclusive processes. For a longitudinally-polarized proton,
we obtain a helicity decomposition from well-known quark and gluon helicity
distributions and orbital angular-momentum contributions. The latter is shown
to be related to measurable subleading generalized parton distributions and
quantum-phase space Wigner distributions.Comment: 7 pages, title change
One-Loop Matching for Parton Distributions: Non-Singlet Case
We derive one-loop matching condition for non-singlet quark distributions in
transverse-momentum cut-off scheme, including unpolarized, helicity and
transversity distributions. The matching is between the quasi-distribution
defined by static correlation at finite nucleon momentum and the light-cone
distribution measurable in experiments. The result is useful for extracting the
latter from the former in a lattice QCD calculation.Comment: 10 pages, 1 figur
One-Loop Matching for Generalized Parton Distributions
We present the one-loop matching condition for the unpolarized and polarized
generalized quark distributions in the non-singlet case. The matching condition
links the quasi distributions defined in terms of spacelike correlators at
finite nucleon momentum to the light-cone distributions, and is useful for
extracting the latter from the former in a lattice QCD calculation. Our results
show that at one-loop and leading power accuracy the matching for the
light-cone generalized quark distribution () is non-trivial,
whereas no matching is required for (). Therefore, () can be smoothly approached by its quasi counterpart in the large momentum
limit. We also present the matching for the distribution amplitude of the pion.Comment: 16 pages, 1 figur
Probing Parton Orbital Angular Momentum in Longitudinally Polarized Nucleon
While the total orbital angular momentum (OAM) of a definite quark flavor in
a longitudinally-polarized nucleon can be obtained through a sum rule involving
twist-two generalized parton distribution (GPDs), its distribution as a
function of parton momentum in light-front coordinates is more complicated to
define and measure because it involves intrinsically twist-three effects. In
this paper, we consider two different parton OAM distributions. The first is
manifestly gauge invariant, and its moments are local operators and calculable
in lattice QCD. We show that it can potentially be measured through twist-three
GPDs. The second is the much-debated canonical OAM distribution natural in
free-field theory and light-cone gauge. We show the latter in light-cone gauge
can also be related to twist-three GPDs as well as quantum phase-space Wigner
distributions, both being measurable in high-energy experiments.Comment: 14 pages, no figur
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