2,215 research outputs found
Past electron-positron g-2 experiments yielded sharpest bound on CPT violation for point particles
In our past experiments on a single electron and positron we measured the
cyclotron and spin-cyclotron difference frequencies omega_c and omega_a and the
ratios a = omega_a/ omega_c at omega_c = 141 Ghz for e^- and e^+ and later,
only for e^-, also at 164 Ghz. Here, we do extract from these data, as had not
done before, a new and very different figure of merit for violation of CPT
symmetry, one similar to the widely recognized impressive limit |m_Kaon -
m_Antikaon|/m_Kaon < 10^-18 for the K-mesons composed of two quarks. That
expression may be seen as comparing experimental relativistic masses of
particle states before and after the C, P, T operations had transformed
particle into antiparticle. Such a similar figure of merit for a non-composite
and quite different lepton, found by us from our Delta a = a^- - a^+ data, was
even smaller, h_bar |omega_a^- - omega_a^+|/2m_0 c^2 = |Delta a| h_bar
omega_c/2m_0 c^2) < 3(12) 10^-22.Comment: Improved content, Editorially approved for publication in PRL, LATEX
file, 5 pages, no figures, 16
Glucose availability and sensitivity to anoxia of isolated rat peripheral nerve
The contrast between resistance to ischemia and ischemic lesions in peripheral nerves of diabetic patients was explored by in vitro experiments. Isolated and desheathed rat peroneal nerves were incubated in the following solutions with different glucose availability: 1) 25 mM glucose, 2) 2.5 mM glucose, and 3) 2.5 mM glucose plus 10 mM 2-deoxy-D-glucose. Additionally, the buffering power of all of these solutions was modified. Compound nerve action potential (CNAP), extracellular pH, and extracellular potassium activity (aKe) were measured simultaneously before, during, and after a period of 30 min of anoxia. An increase in glucose availability led to a slower decline in CNAP and to a smaller rise in aKe during anoxia. This resistance to anoxia was accompanied by an enhanced extracellular acidosis. Postanoxic recovery of CNAP was always complete in 25 mM HCO3(-)-buffered solutions. In 5 mM HCO3- and in HCO3(-)-free solutions, however, nerves incubated in 25 mM glucose did not recover functionally after anoxia, whereas nerves bathed in solutions 2 or 3 showed a complete restitution of CNAP. We conclude that high glucose availability and low PO2 in the combination with decreased buffering power and/or inhibition of HCO3(-)-dependent pH regulation mechanisms may damage peripheral mammalian nerves due to a pronounced intracellular acidosis
Possible Spontaneous Breaking of Lorentz and CPT Symmetry
One possible ramification of unified theories of nature such as string theory
that may underlie the conventional standard model is the possible spontaneous
breakdown of Lorentz and CPT symmetry. In this talk, the formalism for
inclusion of such effects into a low-energy effective field theory is
presented. An extension of the standard model that includes Lorentz- and
CPT-breaking terms is developed. The restriction of the standard model
extension to the QED sector is then discussed.Comment: Talk presented at Non-Accelerator New Physics, Dubna, Russia, July
199
Completing the bedrock mapping of southern Baffin Island, Nunavut; plutonic suites and regional stratigraphy
This paper summarizes the field observations and initial interpretations following eight weeks of regional and targeted bed-
rock mapping on south-central Baffin Island, Nunavut. The 2015 field campaign completes a two-decade mission to update
the geoscience knowledge for the whole of Baffin Island south of latitude 70°N. The bedrock in the area is dominated by a
Paleoproterozoic metaplutonic suite, ranging in composition from gabbro to syenogranite, with crosscutting relations indi-
cating a progression from mafic to silicic magmatism. Phase-equilibria modelling reveals that the prevailing upper-amphi-
bolite– to lower-granulite–facies metamorphic conditions overlap the stability limits of magnetite and orthopyroxene for a
typical granitoid bulk composition, which is consistent with field observations of the discontinuous presence of both phases
throughout the map area. This result is also consistent with regional aeromagnetic data that show complex structures within
relatively homogeneous map units, which are primarily attributed to variations in the abundance of magnetite. The granitoid
rocks are interpreted as part of the middle Paleoproterozoic Cumberland Batholith.
Metasedimentary rocks, including quartzite, pelite, marble and metagreywacke, are present as enclaves and screens within
and between plutonic bodies. An examination of the ‘ghost’stratigraphy suggests that the metasedimentary rocks through-
out most of the map area can be correlated with the middle Paleoproterozoic Lake Harbour Group, except in the northeast,
where the unique presence of greywacke suggests a middle Paleoproterozoic Piling Group affinity. This transition in strata
is consistent with the proposal that a middle Paleoproterozoic tectonic suture (the Baffin suture) associated with the Trans-
Hudson Orogen runs through Cumberland Sound. Completion of the bedrock mapping in southern Baffin Island indicates
that the region offers a world-class exposure of a reworked Paleoproterozoic convergent margin, which affords valuable in-
sight into a variety of magmatic and tectonic processes that can be applied to younger collisional belt
Gravitationally induced electromagnetism at the Compton scale
It is shown that Einstein gravity tends to modify the electric and magnetic
fields appreciably at distances of the order of the Compton wavelength. At that
distance the gravitational field becomes spin dominated rather than mass
dominated. The gravitational field couples to the electromagnetic field via the
Einstein-Maxwell equations which in the simplest model causes the electrostatic
field of charged spinning particles to acquire an oblate structure relative to
the spin direction. For electrons and protons, a pure Coulomb field is
therefore likely to be incompatible with general relativity at the Compton
scale. In the simplest model, the magnetic dipole corresponds to the Dirac
g-factor, g=2. Also, it follows from the form of the electric field that the
electric dipole moment vanishes, in agreement with current experimental limits
for the electron. Quantitatively, the classical Einstein-Maxwell theory
predicts the magnetic and electric dipoles of the electron to an accuracy of
about one part in 10^{-3} or better. Going to the next multipole order, one
finds that the first non-vanishing higher multipole is the electric quadrupole
moment which is predicted to be -124 barn for the electron. Any non-zero value
of the electric quadrupole moment for the electron or the proton would be a
clear sign of curvature due to the implied violation of rotation invariance.
There is also a possible spherical modification of the Coulomb force
proportional to r^{-4}. However, the size of this effect is well below current
experimental limits. The corrections to the hydrogen spectrum are expected to
be small but possibly detectable.Comment: 11 pages, 3 figures: revised version published in Class. Quantum
Grav. 23 (2006) 3111-3122; Conclusions unchange
CPT and Lorentz Tests in Penning Traps
A theoretical analysis is performed of Penning-trap experiments testing CPT
and Lorentz symmetry through measurements of anomalous magnetic moments and
charge-to-mass ratios. Possible CPT and Lorentz violations arising from
spontaneous symmetry breaking at a fundamental level are treated in the context
of a general extension of the SU(3) x SU(2) x U(1) standard model and its
restriction to quantum electrodynamics. We describe signals that might appear
in principle, introduce suitable figures of merit, and estimate CPT and Lorentz
bounds attainable in present and future Penning-trap experiments. Experiments
measuring anomaly frequencies are found to provide the sharpest tests of CPT
symmetry. Bounds are attainable of approximately in the
electron-positron case and of for a suggested experiment with
protons and antiprotons. Searches for diurnal frequency variations in these
experiments could also limit certain types of Lorentz violation to the level of
in the electron-positron system and others at the level of
in the proton-antiproton system. In contrast, measurements comparing
cyclotron frequencies are sensitive within the present theoretical framework to
different kinds of Lorentz violation that preserve CPT. Constraints could be
obtained on one figure of merit in the electron-positron system at the level of
, on another in the proton-antiproton system at , and on a
third at using comparisons of ions with antiprotons.Comment: 31 pages, published in Physical Review
Ptarmigan Fiord basement-cover thrust imbricates, Baffin Island, Nunavut
The rocks at Ptarmigan Fiord on the Hall Peninsula of Baffin Island underwent midcrustal deformation during the formation
of the Paleoproterozoic Trans-Hudson Orogen. The structural style in the region is dominated by imbricate panels of
Archean basement orthogneiss and Paleoproterozoic supracrustal strata, interpreted to have been deformed by thick-
skinned ductile thrusting. Basement rocks comprise amphibolite-facies metatonalite, metagranodiorite, metaquartz-diorite
and metamonzogranite, and cover rocks comprise amphibolite-facies migmatitic pelitic and semipelitic schist, psammitic
schist, amphibolite, calcsilicate and quartzite. The S 1a penetrative foliation is variably present in basement rocks and consis-
tently present in cover rocks, and is defined by alignment of biotite, sillimanite and leucogranite that formed before and dur-
ing the thermal metamorphic peak. The S 1a foliation was deformed by F 1b isoclinal folds with an amplitude of 100 m. These
structures are interpreted as forming during a D 1 east-west crustal shortening event. Basement and cover imbrication oc-
curred after the thermal metamorphic peak and is interpreted as D 2 thick-skinned ductile thrusting. Ductile thrust faults at
the base of seven basement-cover slices are identified on the basis of repetition of units and strain localization, and are inter-
preted as predominantly south-to-southeast verging on the basis of shear-sense indicators. There are two structural panels of
D 2 thrust imbricates, one in the northwestern part of the map area and one in the eastern part of the map area. Map-scale
crosscutting relationships indicate that the northwestern panel overthrusted the eastern panel on a southeasterly T 2c -di-
rected thrust fault, following a F 2b folding event that folded the T 2a basement-cover thrust imbricates in the eastern panel.
The Ptarmigan Fiord area contains a world-class exposure of thick-skinned structures as they are spectacularly delineated
by belts of distinctive grey-weathering Archean basement rocks and brown- to black-weathering Paleoproterozoic supra-
crustal rocks
Lorentz and CPT tests with spin-polarized solids
Experiments using macroscopic samples of spin-polarized matter offer
exceptional sensitivity to Lorentz and CPT violation in the electron sector.
Data from existing experiments with a spin-polarized torsion pendulum provide
sensitivity in this sector rivaling that of all other existing experiments and
could reveal spontaneous violation of Lorentz symmetry at the Planck scale.Comment: 4 pages, accepted for publication in Physical Review Letter
Constraints on Lorentz violation from clock-comparison experiments
Constraints from clock-comparison experiments on violations of Lorentz and
CPT symmetry are investigated in the context of a general Lorentz-violating
extension of the standard model. The experimental signals are shown to depend
on the atomic and ionic species used as clocks. Certain experiments usually
regarded as establishing comparable bounds are in this context sensitive to
different types of Lorentz violation. Some considerations relevant to possible
future measurements are presented. All these experiments are potentially
sensitive to Lorentz-violating physics at the Planck scale.Comment: accepted for publication in Physical Review D; scheduled for issue of
December 1, 199
Signals for CPT and Lorentz Violation in Neutral-Meson Oscillations
Experimental signals for indirect CPT violation in the neutral-meson systems
are studied in the context of a general CPT- and Lorentz-violating
standard-model extension. In this explicit theory, some CPT observables depend
on the meson momentum and exhibit diurnal variations. The consequences for CPT
tests vary significantly with the specific experimental scenario. The wide
range of possible effects is illustrated for two types of CPT experiment
presently underway, one involving boosted uncorrelated kaons and the other
involving unboosted correlated kaon pairs.Comment: Accepted in Physical Review D, scheduled for December 1999 issu
- …