541,303 research outputs found
Diagnostics of the molecular component of PDRs with mechanical heating. II: line intensities and ratios
CO observations in active galactic nuclei and star-bursts reveal high kinetic
temperatures. Those environments are thought to be very turbulent due to
dynamic phenomena such as outflows and high supernova rates. We investigate the
effect of mechanical heating (MH) on atomic fine-structure and molecular lines,
and their ratios. We use those ratios as a diagnostic to constrain the amount
of MH in an object and also study its significance on estimating the H2 mass.
Equilibrium PDRs models were used to compute the thermal and chemical balance
for the clouds. The equilibria were solved for numerically using the optimized
version of the Leiden PDR-XDR code. Large velocity gradient calculations were
done as post-processing on the output of the PDR models using RADEX. High-J CO
line ratios are very sensitive to MH. Emission becomes at least one order of
magnitude brighter in clouds with n~10^5~cm^-3 and a star formation rate of 1
Solar Mass per year (corresponding to a MH rate of 2 * 10^-19 erg cm^-3 s^-1).
Emission of low-J CO lines is not as sensitive to MH, but they do become
brighter in response to MH. Generally, for all of the lines we considered, MH
increases excitation temperatures and decreases the optical depth at the line
centre. Hence line ratios are also affected, strongly in some cases. Ratios
involving HCN are a good diagnostic for MH, such as HCN(1-0)/CO(1-0) and
HCN(1-0)/HCO^+(1-0). Both ratios increase by a factor 3 or more for a MH
equivalent to > 5 percent of the surface heating, as opposed to pure PDRs. The
first major conclusion is that low-J to high-J intensity ratios will yield a
good estimate of the MH rate (as opposed to only low-J ratios). The second one
is that the MH rate should be taken into account when determining A_V or
equivalently N_H, and consequently the cloud mass. Ignoring MH will also lead
to large errors in density and radiation field estimates.Comment: 38 pages, to appear in A&
Anti-dark and Mexican-hat solitons in the Sasa-Satsuma equation on the continuous wave background
In this letter, via the Darboux transformation method we construct new
analytic soliton solutions for the Sasa-Satsuma equation which describes the
femtosecond pulses propagation in a monomode fiber. We reveal that two
different types of femtosecond solitons, i.e., the anti-dark (AD) and
Mexican-hat (MH) solitons, can form on a continuous wave (CW) background, and
numerically study their stability under small initial perturbations. Different
from the common bright and dark solitons, the AD and MH solitons can exhibit
both the resonant and elastic interactions, as well as various
partially/completely inelastic interactions which are composed of such two
fundamental interactions. In addition, we find that the energy exchange between
some interacting soliton and the CW background may lead to one AD soliton
changing into an MH one, or one MH soliton into an AD one.Comment: 12 pages, 6 figure
Three-Loop Predictions for the Light Higgs Mass in the MSSM
The Minimal Supersymmetric Extension of the Standard Model (MSSM) features a
light Higgs boson, the mass Mh of which is predicted by the theory. Given that
the LHC will be able to measure the mass of a light Higgs with great accuracy,
a precise theoretical calculation of Mh yields an important test of the MSSM.
In order to deliver this precision, we present three-loop radiative
corrections of O(alpha_t*alpha_s^2) and provide a computer code that combines
our results with corrections to Mh at lower loop orders that are available in
the literature.Comment: 3 pages, 1 figure, contribution to the proceedings of the conference
"Physics at LHC 2010
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