141,304 research outputs found
The largest oxigen bearing organic molecule repository
We present the first detection of complex aldehydes and isomers in three
typical molecular clouds located within 200pc of the center of our Galaxy.
We find very large abundances of these complex organic molecules (COMs) in
the central molecular zone (CMZ), which we attribute to the ejection of COMs
from grain mantles by shocks. The relative abundances of the different COMs
with respect to that of CH3OH are strikingly similar for the three sources,
located in very different environments in the CMZ. The similar relative
abundances point toward a unique grain mantle composition in the CMZ. Studying
the Galactic center clouds and objects in the Galactic disk having large
abundances of COMs, we find that more saturated molecules are more abundant
than the non-saturated ones. We also find differences between the relative
abundance between COMs in the CMZ and the Galactic disk, suggesting different
chemical histories of the grain mantles between the two regions in the Galaxy
for the complex aldehydes. Different possibilities for the grain chemistry on
the icy mantles in the GC clouds are briefly discussed. Cosmic rays can play an
important role in the grain chemistry. With these new detections, the molecular
clouds in the Galactic center appear to be one of the best laboratories for
studying the formation of COMs in the Galaxy.Comment: 20 pages, 4 figures, accepted in Ap
Improving alpha_QED(M_Z^2) and the charm mass by analytic continuation
The standard determination of the QED coupling on the Z pole is performed
using the latest available data for R. The direct application of analytic
continuation techniques is found not to improve the accuracy of the value of
\alpha(M_Z^2). However they help to resolve an ambiguity in the values of R in
the energy region \sqrt{s} < 2 GeV, which, in turn, reduces the uncertainty in
\alpha(M_Z^2). Moreover, they provide a sensitive determination of the mass of
the charm quark. The favoured solution, which uses the inclusive data for R for
\sqrt{s} < 2 GeV, has a pole mass m_c = 1.33-1.40 GeV and \alpha^{-1}(M_Z^2) =
128.972 +/- 0.026; whereas if the sum of the exclusive channels is used to
determine R in this region, we find \alpha^{-1}(M_Z^2) = 128.941 +/- 0.029.Comment: LaTeX, 23 pages, 7 eps figures, typos removed, accepted by Eur. Phys.
J.
Nucleon-Nucleon Interactions from Dispersion Relations: Coupled Partial Waves
We consider nucleon-nucleon interactions from chiral effective field theory
applying the N/D method. The case of coupled partial waves is now treated,
extending Ref. [1] where the uncoupled case was studied. As a result three N/D
elastic-like equations have to be solved for every set of three independent
partial waves coupled. As in the previous reference the input for this method
is the discontinuity along the left-hand cut of the nucleon-nucleon partial
wave amplitudes. It can be calculated perturbatively in chiral perturbation
theory because it involves only irreducible two-nucleon intermediate states. We
apply here our method to the leading order result consisting of one-pion
exchange as the source for the discontinuity along the left-hand cut. The
linear integral equations for the N/D method must be solved in the presence of
L - 1 constraints, with L the orbital angular momentum, in order to satisfy the
proper threshold behavior for L>= 2. We dedicate special attention to satisfy
the requirements of unitarity in coupled channels. We also focus on the
specific issue of the deuteron pole position in the 3S1-3D1 scattering. Our
final amplitudes are based on dispersion relations and chiral effective field
theory, being independent of any explicit regulator. They are amenable to a
systematic improvement order by order in the chiral expansion.Comment: 11 pages. Extends the work of uncoupled partial waves of M.
Albaladejo and J. A. Oller, Phys. Rev. C 84, 054009 (2011) to the case of
coupled partial waves. This version matches the published version. Discussion
about the deuteron enlarged. Some references adde
The Matrix Product Approach to Quantum Spin Ladders
We present a manifestly rotational invariant formulation of the matrix
product method valid for spin chains and ladders. We apply it to 2 legged spin
ladders with spins 1/2, 1 and 3/2 and different magnetic structures labelled by
the exchange coupling constants, which can be ferromagnetic or
antiferromagnetic along the legs and the rungs of the ladder We compute ground
state energy densities, correlation lengths and string order parameters. We
present numerical evidence of the duality properties of the 3 different non
ferromagnetic spin 1/2 ladders. We show that the long range topological order
characteristic of isolated spin 1 chains is broken by the interchain coupling.
The string order correlation function decays exponentially with a finite
correlation length that we compute. A physical picture of the spin 1 ladder is
given in terms of a collection of resonating spin 1 chains. Finally for ladders
with spin equal or greater than 3/2 we define a class of AKLT states whose
matrix product coefficients are given by 9-j symbols.Comment: REVTEX file, 16 pages, 12 figures, 6 Table
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