1,979 research outputs found
Ultraviolet C II and Si III Transit Spectroscopy and Modeling of the Evaporating Atmosphere of GJ436b
Hydrogen gas evaporating from the atmosphere of the hot-Neptune GJ436b
absorbs over 50% of the stellar Ly emission during transit. Given the
planet's atmospheric composition and energy-limited escape rate, this hydrogen
outflow is expected to entrain heavier atoms such as C and O. We searched for C
and Si in the escaping atmosphere of GJ436b using far-ultraviolet HST COS G130M
observations made during the planet's extended H I transit. These observations
show no transit absorption in the C II 1334,1335 \AA\ and Si III 1206 \AA\
lines integrated over [-100, 100] km s, imposing 95% (2) upper
limits of 14% (C II) and 60% (Si III) depth on the transit of an opaque disk
and 22% (C II) and 49% (Si III) depth on an extended, highly asymmetric transit
similar to that of H I Ly. C is likely present in the outflow
according to a simulation we carried out using a spherically-symmetric,
photochemical-hydrodynamical model. This simulation predicts a 2% transit
over the integrated bandpass, consistent with the data. At line center, we
predict the C II transit depth to be as high as 19%. Our model predicts a
neutral hydrogen escape rate of g s (
g s for all species) for an upper atmosphere composed of hydrogen and
helium.Comment: 7 pages, 4 figures, 1 table; accepted to ApJ Letter
Using Spin Correlations to Distinguish Zh from ZA at the International Linear Collider
We investigate how to exploit the spin information imparted to the Z boson in
associated Higgs production at a future linear collider as an aid in
distinguishing between CP-even and CP-odd Higgs bosons. We apply a generalized
spin-basis analysis which allowsus to study the possibilities offered by
non-traditional choices of spin projection axis. In particular, we find that
the Z bosons produced in association with a CP-even Higgs via polarized
collisions are in a single transverse spin-state (>90% purity) when we use the
Zh-transverse basis, provided that the Z~bosons are not ultra-relativistic
(speed <0.9c). This same basis applied to the associated production of a CP-odd
Higgs yields Z's that are an approximately equal mixture of longitudinal and
transverse polarizations. We present a decay angular distribution which could
be used to distinguish between the CP-even and CP-odd cases. Finally, we make a
few brief remarks about how this distribution would be affected if the Higgs
boson turns out to not be a CP-eigenstate.Comment: 48 pages, 18 figures, revtex
Another possible way to determine the Neutrino Mass Hierarchy
We show that by combining high precision measurements of the atmospheric
delta m^2 in both the electron and muon neutrino (or anti-neutrino)
disappearance channels one can determine the neutrino mass hierarchy. The
required precision is a very challenging fraction of one per cent for both
measurements. At even higher precision, sensitivity to the cosine of the CP
violating phase is also possible. This method for determining the mass
hierarchy of the neutrino sector does not depend on matter effects.Comment: 12 pages, 3 postscript figures, late
Recovering Infinities in Graviton Scattering Amplitudes using Cutkosky rules
We use the Cutkosky rules as a tool for determining the infinities present in
graviton scattering amplitudes. We are able to confirm theoretical derivations
of counterterms in Einstein-Maxwell theory and to determine new results in the
Dirac-Einstein counter-Lagrangian.Comment: 10 pages, 4 Postscript figures, uses epsf.st
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