1,354 research outputs found
Strangeness hyperon-nucleon scattering in covariant chiral effective field theory
Motivated by the successes of covariant baryon chiral perturbation theory in
one-baryon systems and in heavy-light systems, we study relevance of
relativistic effects in hyperon-nucleon interactions with strangeness .
In this exploratory work, we follow the covariant framework developed by
Epelbaum and Gegelia to calculate the scattering amplitude at leading
order. By fitting the five low-energy constants to the experimental data, we
find that the cutoff dependence is mitigated, compared with the heavy-baryon
approach. Nevertheless, the description of the experimental data remains
quantitatively similar at leading order.Comment: The manuscript has been largely rewritten but the results remain
unchanged. To appear in Physical Review
C2H N=1-0 and N2H+ J=1-0 observations of Planck Galactic cold clumps
A survey of C2H N=1-0 and N2H+ J=1-0 toward Planck Galactic cold clumps
(PGCCs) was performed using the Purple Mountain Observatory's 13.7 m telescope.
C2H and N2H+ were chosen to study the chemical evolutionary states of PGCCs.
Among 121 observed molecular cores associated with PGCCs, 71 and 58 are
detected with C2H N=1-0 and N2H+ J=1-0, respectively. The detected lines of
most sources can be fitted with a single component with compatible Vlsr and
line widths, which confirms that these PGCC cores are very cold (with gas
temperatures 9-21 K) and quiescent while still dominanted by turbulence. The
ratio between the column densities of C2H and N2H+ (N(C2H)/N(N2H+)) is found to
be a good tracer for the evolutionary states of PGCC cores. Gas-grain chemical
model can reproduce the decreasing trend of N(C2H)/N(N2H+) as a function of
time. The cores with the lowest abundances of N2H+ (X[N2H+] < 10^{-10}) are the
youngest, and have nearly constant abundances of C2H. In evolved cores with
X[N2H+] ~ 1E-9, abundances of C2H drop quickly as the exhaustion of carbon
atoms. Although these PGCC cores are in different evolutionary states, they are
all quite young ( N(N2H+). Mapping observations are
carried out toward 20 PGCC cores. The PGCC cores in Cepheus have lower
N(C2H)/N(N2H+) and larger line widths compared with those in Taurus. This
implies that PGCC cores in Taurus are less chemically evolved than those in
Cepheus.Comment: 23 pages, 6 figures, 5 table
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