2,470 research outputs found
Quantum Theory of Neutrino Oscillations for Pedestrians - Simple Answers to Confusing Questions
Why are different mass states coherent? What is the correct formula for the
oscillation phase? How can textbook formulas for oscillations in time describe
experiments which never measure time? How can we treat the different velocities
and different transit times of different mass eigenstates and avoid incorrect
factors of two? How can textbook forumulas which describe coherence between
energy states be justified when Stodolsky's theorem states there is no
coherence between different energies? Is covariant relativistic quantum field
theory necessary to describe neutrino oscillations? How important is the
detector, which is at rest in the laboratory and cannot be Lorentz tranformed
to other frames?
These questions are answered by a simple rigorous calculation which includes
the quantum fluctuations in the position of the detector and in the transit
time between source and detector. The commonly used standard formula for
neutrino oscillation phases is confirmed. An "ideal" detector which measures
precisely the energy and momentum of the neutrino destroys all phases in the
initial wave packet and cannot observe oscillations. A realistic detector
preserves the phase differences between neutrinos having the same energy and
different momenta and confirms the standard formula. Whether phase differences
between neutrinos with different energies are observable or destroyed by the
detector is irrelevant.Comment: 10 pages, Introduction expanded to explain sources of confusion in
detai
The Sound of Fury: Teaching, Tempers, and White Privileged Resistance
This essay focuses on the resistance of students situated in positions of privilege in classrooms addressing issues of dominance, identity, and oppression related to race and racism. Examining the psycho/social history of two critical aspects of resistance – defensiveness (related to guilt and shame) and denial – the author draws from both practice and theory to explicate the roots of this resistance and offer specific, effective ways to support students in moving through resistance into responsibility
Dark Matter and Dark Radiation
We explore the feasibility and astrophysical consequences of a new long-range
U(1) gauge field ("dark electromagnetism") that couples only to dark matter,
not to the Standard Model. The dark matter consists of an equal number of
positive and negative charges under the new force, but annihilations are
suppressed if the dark matter mass is sufficiently high and the dark
fine-structure constant is sufficiently small. The correct relic
abundance can be obtained if the dark matter also couples to the conventional
weak interactions, and we verify that this is consistent with particle-physics
constraints. The primary limit on comes from the demand that the
dark matter be effectively collisionless in galactic dynamics, which implies
for TeV-scale dark matter. These values are
easily compatible with constraints from structure formation and primordial
nucleosynthesis. We raise the prospect of interesting new plasma effects in
dark matter dynamics, which remain to be explored.Comment: 14 pages, 6 figures Updated equations and figure
CLEO Results on Tau Michel Parameters
We present measurements of the tau Michel Parameters made by the CLEO
experiment. Three different analyses are performed: a spin-independent lepton
spectrum analysis and a second spin-dependent analysis using \vs\
events, and a third spin-dependent analysis using \vs\
events. the results are used to derive limits on the general
four-fermion couplings, the mass of the charged Higgs in the MSSM, and a
right-handed in left-right models. Many of these measurements are more
precise than the PDG world averages.Comment: Invited talk at the TAU'98 Workshop, 14-17 September 1998, Santander,
Spain. 7 pages, 7 figures, LaTeX -> postscrip
CP violation in unpolarized e^+ e^- to charginos at one loop level
We study CP violation in e^+ e^- to \tilde\chi_i^+\tilde\chi_j^- in the
framework of the MSSM. Though the cross section of this process is CP-even at
the tree level even for polarized electron-positron beams, we show that it
contains a CP-odd part at the one loop order and there are CP-odd observables
that can in principle be measured even using unpolarized electron-positron
beams. The relevant diagram calculations are briefly discussed and the results
of selected (box) diagram computations are shown.Comment: similar to Phys. Rev. D version, but corrected figs. 4, 5, 6 (factor
four
Diquark and light four-quark states
Four-quark states with different internal clusters are discussed within the
constituent quark model. It is pointed out that the diquark concept is not
meaningful in the construction of a tetraquark interpolating current in the QCD
sum rule approach, and hence existing sum-rule studies of four-quark states are
incomplete. An updated QCD sum-rule determination of the properties of diquark
clusters is then used as input for the constituent quark model to obtain the
masses of light tetraquark states ({\it i.e.\} a bound state of two
diquark clusters). The results support the identification of ,
and as the light tetraquark states, and seem to
be inconsistent with the tetraquark state interpretation of the new BES
observations of the near-threshold enhancements, X(1835) and X(1812),
with the possible exception that X(1576) may be an "exotic" first orbital
excitation of or .Comment: 7 pages, 4 eps figures, RevTex, two figures and some references
added, published version in PR
Interplay of gravitation and linear superposition of different mass eigenstates
The interplay of gravitation and the quantum-mechanical principle of linear
superposition induces a new set of neutrino oscillation phases. These ensure
that the flavor-oscillation clocks, inherent in the phenomenon of neutrino
oscillations, redshift precisely as required by Einstein's theory of
gravitation. The physical observability of these phases in the context of the
solar neutrino anomaly, type-II supernovae, and certain atomic systems is
briefly discussed
A Three-dimensional Deformable Brain Atlas for DBS Targeting. I. Methodology for Atlas Creation and Artifact Reduction.
BackgroundTargeting in deep brain stimulation (DBS) relies heavily on the ability to accurately localize particular anatomic brain structures. Direct targeting of subcortical structures has been limited by the ability to visualize relevant DBS targets.Methods and resultsIn this work, we describe the development and implementation, of a methodology utilized to create a three dimensional deformable atlas for DBS surgery. This atlas was designed to correspond to the print version of the Schaltenbrand-Bailey atlas structural contours. We employed a smoothing technique to reduce artifacts inherent in the print version.ConclusionsWe present the methodology used to create a three dimensional patient specific DBS atlas which may in the future be tested for clinical utility
- …