221 research outputs found
Neutrino oscillations in matter of varying density
We consider two-family neutrino oscillations in a medium of
continuously-varying density as a limit of the process in a series of
constant-density layers. We construct analytic expressions for the conversion
amplitude at high energies within a medium with a density profile that is
piecewise linear. We compare some cases to understand the type of effects that
depend on the order of the material traversed by a neutrino beam.Comment: 10 page
Neutrino Oscillations and Lepton Flavor Mixing
In view of the recent announcement on non-zero neutrino mass from
Super-Kamiokande experiment, it would be very timely to investigate all the
possible scenarios on masses and mixings of light neutrinos. Recently suggested
mass matrix texture for the quark CKM mixing, which can be originated from the
family permutation symmetry and its suitable breakings, is assumed for the
neutrino mass matrix and determined by the four combinations of solar,
atmospheric and LSND neutrino data and cosmological hot dark matter bound as
input constraints. The charged-lepton mass matrix is assumed to be diagonal so
that the neutrino mixing matrix can be identified directly as the lepton flavor
mixing matrix and no CP invariance violation originates from the leptonic
sector. The results favor hierarchical patterns for the neutrino masses, which
follow from the case when either solar-atmospheric data or solar-HDM
constraints are used.Comment: Latex, 9 page
On Neutrinos and Fermionic Mass Patterns
Recent data on neutrino mass differences are consistent with a hierarchical
neutrino mass structure strikingly similar to what is observed for the other
fermionic masses.Comment: 8pages, 2figure
Model of the Quark Mixing Matrix
The structure of the Cabibbo-Kobayashi-Maskawa (CKM) matrix is analyzed from
the standpoint of a composite model. A model is constructed with three families
of quarks, by taking tensor products of sufficient numbers of spin-1/2
representations and imagining the dominant terms in the mass matrix to arise
from spin-spin interactions. Generic results then obtained include the familiar
relation , and a less frequently
seen relation . The magnitudes of
and come out naturally to be of the right order. The phase in
the CKM matrix can be put in by hand, but its origin remains obscure.Comment: Presented by Mihir P. Worah at DPF 92 Meeting, Fermilab, November,
1992. 3 pages, LaTeX fil
Test of the Dimopouos-Hall-Raby Ansatz for Fermion Mass Matrices
By evolution of fermion mass matrices of the Fritzsch and the Georgi-Jarlskog
forms from the supersymmetric grand unified scale, DHR obtained predictions for
the quark masses and mixings. Using Monte Carlo methods we test these
predictions against the latest determinations of the mixings, the CP-violating
parameter epsilon_K and the B_d^0--Bbar_d^0 mixing parameter r_d. The
acceptable solutions closely specify the quark masses and mixings, but lie at
the edges of allowed regions at 90% confidence level.Comment: 11 pages, 1 figure (not included
Neutrino masses from universal Fermion mixing
If three right-handed neutrinos are added to the Standard Model, then, for
the three known generations, there are six quarks and six leptons. It is then
natural to assume that the symmetry considerations that have been applied to
the quark matrices are also valid for the lepton mass matrices. Under this
assumption, the solar and atmospheric neutrino data can be used to determine
the individual neutrino masses. Using the \chi^2 fit, it is found that the mass
of the lightest neutrino is (2-5)\times10^{-3} eV, that of the next heavier
neutrino is (10-13)\times10^{-3} eV, while the mass of the heaviest neutrino is
(52-54)\times10^{-3} eV.Comment: 27 pages, LaTeX, including several figure
On neutrino masses and leptonic mixing
Using recent data on neutrino oscillations, we argue that a hierarchical
solution for neutrino masses in a three-family context is possible, and that
the masses of the tau and mu neutrinos are very nearly determined within that
possibility. We also examine the predictions of a model that determines
neutrino and charged lepton mass matrices as well as its consistency with data.Comment: 13 pages, 6 figures, technical change to pdf, figures include
Large Lepton Mixings from Continuous Symmetries
Within the broad context of quark-lepton unification, we investigate the
implications of broken continuous family symmetries which result from requiring
that in the limit of exact symmetry, the Dirac mass matrices yield hierarchical
masses for the quarks and charged leptons, but lead to degenerate light
neutrino masses as a consequence of the seesaw mechanism, without requiring
hierarchical right-handed neutrino mass terms. Quark mixing is then naturally
small and proportional to the size of the perturbation, but lepton mixing is
large as a result of degenerate perturbation theory, shifted from maximal
mixing by the size of the perturbation. Within this approach, we study an
illustrative two-family prototype model with an SO(2) family symmetry, and
discuss extensions to three-family models.Comment: 23 page
A proposed framework for consensus-based lung tumour volume auto-segmentation in 4D computed tomography imaging.
This work aims to propose and validate a framework for tumour volume auto-segmentation based on ground-truth estimates derived from multi-physician input contours to expedite 4D-CT based lung tumour volume delineation. 4D-CT datasets of ten non-small cell lung cancer (NSCLC) patients were manually segmented by 6 physicians. Multi-expert ground truth (GT) estimates were constructed using the STAPLE algorithm for the gross tumour volume (GTV) on all respiratory phases. Next, using a deformable model-based method, multi-expert GT on each individual phase of the 4D-CT dataset was propagated to all other phases providing auto-segmented GTVs and motion encompassing internal gross target volumes (IGTVs) based on GT estimates (STAPLE) from each respiratory phase of the 4D-CT dataset. Accuracy assessment of auto-segmentation employed graph cuts for 3D-shape reconstruction and point-set registration-based analysis yielding volumetric and distance-based measures. STAPLE-based auto-segmented GTV accuracy ranged from (81.51 ± 1.92) to (97.27 ± 0.28)% volumetric overlap of the estimated ground truth. IGTV auto-segmentation showed significantly improved accuracies with reduced variance for all patients ranging from 90.87 to 98.57% volumetric overlap of the ground truth volume. Additional metrics supported these observations with statistical significance. Accuracy of auto-segmentation was shown to be largely independent of selection of the initial propagation phase. IGTV construction based on auto-segmented GTVs within the 4D-CT dataset provided accurate and reliable target volumes compared to manual segmentation-based GT estimates. While inter-/intra-observer effects were largely mitigated, the proposed segmentation workflow is more complex than that of current clinical practice and requires further development
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