516 research outputs found
How do Neutrinos Propagate ? - Wave-Packet Treatment of Neutrino Oscillation
The wave-packet treatment of neutrino oscillation developed previously is
extended to the case in which momentum distribution functions are taken to be a
Gaussian form with both central values and dispersions depending on the mass
eigenstates of the neutrinos. It is shown among other things that the velocity
of the neutrino wave packets does not in general agree with what one would
expect classically and that relativistic neutrinos emitted from pions
nevertheless do follow, to a good approximation, the classical trajectory.Comment: 13 page. No figure. Typeset using PTPTeX.st
Isospin-symmetry breaking in superallowed Fermi beta-decay due to isospin-nonconserving forces
We investigate isospin-symmetry breaking effects in the sd-shell region with
large-scale shell-model calculations, aiming to understand the recent anomalies
observed in superallowed Fermi beta-decay. We begin with calculations of
Coulomb displacement energies (CDE's) and triplet displacement energies (TDE's)
by adding the T=1,J=0 isospin nonconserving (INC) interaction into the usual
isospin-invariant Hamiltonian. It is found that CDE's and TDE's can be
systematically described with high accuracy. A total number of 122 one- and
two-proton separation energies are predicted accordingly, and locations of the
proton drip-line and candidates for proton-emitters are thereby suggested.
However, attempt to explain the anomalies in the superallowed Fermi beta-decay
fails because these well-fitted T=1,J=0 INC interactions are found no effects
on the nuclear matrix elements. It is demonstrated that the observed large
isospin-breaking correction in the 32Cl beta-decay, the large isospin-mixing in
the 31Cl beta-decay, and the small isospin-mixing in the 23Al beta-decay can be
consistently understood by introducing additional T=1,J=2 INC interactions
related to the s1/2 orbit.Comment: 7 pages, 3 figures, accepted in Phys. Lett.
The Water-ice Feature in Near-infrared Disk-scattered Light around HD 142527:Micron-sized Icy Grains Lifted up to the Disk Surface?
We study the m scattering feature of water ice detected in the outer
disk of HD 142527 by performing radiative transfer simulations. We show that an
ice mass abundance at the outer disk surface of HD 142527 is much lower than
estimated in a previous study. It is even lower than inferred from far-infrared
ice observations, implying ice disruption at the disk surface. Next, we
demonstrate that a polarization fraction of disk-scattered light varies across
the ice-band wavelengths depending on ice grain properties; hence, polarimetric
spectra would be another tool for characterizing water-ice properties. Finally,
we argue that the observed reddish disk-scattered light is due to grains with a
few microns in size. To explain the presence of such grains at the disk
surface, we need a mechanism that can efficiently oppose dust settling. If we
assume turbulent mixing, our estimate requires ,
where is a non-dimensional parameter describing the vertical diffusion
coefficient of grains. Future observations probing gas kinematics would be
helpful to elucidate vertical grain dynamics in the outer disk of HD 142527.Comment: 21 pages, 14 figures, 1 table; Accepted for publication in Ap
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