4,899 research outputs found
Constraints on a Parity-even/Time-Reversal-odd Interaction
Time-Reversal-Invariance non-conservation has for the first time been
unequivocally demonstrated in a direct measurement, one of the results of the
CPLEAR experiment. What is the situation then with regard to
time-reversal-invariance non-conservation in systems other than the neutral
kaon system? Two classes of tests of time-reversal-invariance need to be
distinguished: the first one deals with parity violating
(P-odd)/time-reversal-invariance non-conserving (T-odd) interactions, while the
second one deals with P-even/T-odd interactions (assuming CPT conservation this
implies C-conjugation non-conservation). Limits on a P-odd/T-odd interaction
follow from measurements of the electric dipole moment of the neutron. This in
turn provides a limit on a P-odd/T-odd pion-nucleon coupling constant which is
10^-4 times the weak interaction strength. Limits on a P-even/T-odd interaction
are much less stringent. The better constraint stems also from the measurement
of the electric dipole moment of the neutron. Of all the other tests,
measurements of charge-symmetry breaking in neutron-proton elastic scattering
provide the next better constraint. The latter experiments were performed at
TRIUMF (at 477 and 347 MeV) and at IUCF (at 183 MeV). Weak decay experiments
(the transverse polarization of the muon in K+ -> pi0 mu+ nu and the transverse
polarization of the positrons in polarized muon decay) have the potential to
provide comparable or possibly better constraints.Comment: 7 Pages LaTeX, 2 PostScript figures, uses aipproc.sty. Written
version of Invited Paper presented at the 3rd International Symposium on
Symmetries in Subatomic Physics, Adelaide, SA, Australia, March 13-17, 200
Symmetries and Symmetry Breaking
Several new proton-proton parity violation experiments are presently either
being performed or are being prepared for execution in the near future.
Similarly, a new measurement of the parity-violating gamma-ray asymmetry in
polarized neutron capture on the proton is being developed with a ten-fold
improvement over previous measurements. These experiments are intended to
provide stringent constraints on the set of seven effective weak meson-nucleon
coupling constants. Time-reversal-invariance non-conservation has now been
unequivocally demonstrated in a direct measurement at CPLEAR. Tests may also be
made of time-reversal-invariance non-conservation in systems other than the
kaon system. There exist two classes of time-reversal invariance breaking
interactions: P-odd/T-odd and P-even/T-odd interactions. Constraints on the
first ones stem from measurements of the electric dipole moment of the neutron,
while constraints on the second ones stem from the same and measurements of
charge symmetry breaking in neutron-proton elastic scattering and from
semi-leptonic decays. A series of precision experiments, either ongoing or
being prepared, will determine the neutral weak current of the proton by
measuring the parity-violating normalized asymmetry in electron-proton elastic
scattering. A direct comparison between the electromagnetic and neutral weak
ground state currents of the nucleon will allow a delineation of the
contributions to these currents of the various quark flavours, including quarks
which belong exclusively to the nucleon sea. An extension of these precision
experiments to very low momentum transfer would permit stringent limits to be
placed on physics beyond the standard model.Comment: 11 Pages LaTeX, including 5 PostScript figures. Uses esprc1.sty.
Invited Paper presented at 16th International Conference on Few-Body Problems
in Physics, Taipei, March 6-10, 200
Interactions between Behaviour and Genetics in Wild and Domestic Bird Populations
Personality traits can be favoured by both natural and artificial selection, if they result in increased fitness or productivity, and therefore play an important role in both wild and domestic populations. Here, we review how personality traits affect and are affected by natural and artificial selection by focusing on studies from both wild and domestic bird populations. Further, we will also explore how artificial selection affects personality and fitness traits in a domestic population. We will use the great tit (Parus major) and the laying hen (Gallus gallus domesticus) as our model species. When comparing the studies on behaviour genetics in great tits and laying hens, it is fascinating to see that two fields of study that seem quite far apart have so much in common
Smelling out predators is innate in birds
The role of olfaction for predation risk assessment remains barely explored in birds, although predator chemical cues could be useful in predator detection under low visibility conditions for many bird species. We examine whether Great Tits Parus major are able to use the odour of mustelids to assess predation risk when selecting cavities for roosting. We analysed whether the response to predator chemical cues is innate and assessed whether the antipredatory response is associated with exploratory behaviour, a proxy for the personality of birds. In a choice experiment in aviaries, we offered naïve adult Great Tits of known personality two nest-boxes, one control and one experimental. The experimental nest-box had the odour of a mustelid predator or a strong new odour without biological significance, the control nest-box contained no odour. When one of the cavities contained the odour of a predator, birds avoided the use of either of the two offered nest-boxes, whereas there was no avoidance of boxes when one of the nest-boxes contained a control odour. There was no relationship with exploratory behaviour. We show that the ability to use the chemical cues of predators is innate in birds, but individual differences in the response to predator chemical cues cannot be explained by the personality of the bird.
Charge Independence and Charge Symmetry
Charge independence and charge symmetry are approximate symmetries of nature,
violated by the perturbing effects of the mass difference between up and down
quarks and by electromagnetic interactions. The observations of the symmetry
breaking effects in nuclear and particle physics and the implications of those
effects are reviewed.Comment: 41 pages, report # DOE/ER/40427-17-N94, Chapter for a book titled
"Symmetries and Fundamental Interactions in Nuclei" eds. E.M. Henley and W.
Haxton, to be published by World Scientifi
Baculovirus Per Os Infectivity Factors Form a Complex on the Surface of Occlusion-Derived Virus
Five highly conserved per os infectivity factors, PIF1, PIF2, PIF3, PIF4, and P74, have been reported to be essential for oral infectivity of baculovirus occlusion-derived virus (ODV) in insect larvae. Three of these proteins, P74, PIF1, and PIF2, were thought to function in virus binding to insect midgut cells. In this paper evidence is provided that PIF1, PIF2, and PIF3 form a stable complex on the surface of ODV particles of the baculovirus Autographa californica multinucleocapsid nucleopolyhedrovirus (AcMNPV). The complex could withstand 2% SDS-5% ß-mercaptoethanol with heating at 50°C for 5 min. The complex was not formed when any of the genes for PIF1, PIF2, or PIF3 was deleted, while reinsertion of these genes into AcMNPV restored the complex. Coimmunoprecipitation analysis independently confirmed the interactions of the three PIF proteins and revealed in addition that P74 is also associated with this complex. However, deletion of the p74 gene did not affect formation of the PIF1-PIF2-PIF3 complex. Electron microscopy analysis showed that PIF1 and PIF2 are localized on the surface of the ODV with a scattered distribution. This distribution did not change for PIF1 or PIF2 when the gene for PIF2 or PIF1 protein was deleted. We propose that PIF1, PIF2, PIF3, and P74 form an evolutionarily conserved complex on the ODV surface, which has an essential function in the initial stages of baculovirus oral infectio
The Three-Nucleon System at Next-To-Next-To-Leading Order
We calculate higher order corrections for the three-nucleon system up to
next-to-next-to-leading within an effective field theory with contact
interactions alone. We employ a subtraction formalism previously developed and
for which it has been shown that no new three-body force counterterm is needed
for complete renormalization up to this order. We give results for the
neutron-deuteron phaseshifts and the triton binding energy. Our results are in
very good agreement with experimental results and calculations using realistic
nucleon-nucleon potentials.Comment: 4 pages, 2 eps figures, revised version to appear in PR
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