46 research outputs found
The implications of noninertial motion on covariant quantum spin
It is shown that the Pauli-Lubanski spin vector defined in terms of
curvilinear co-ordinates does not satisfy Lorentz invariance for spin-1/2
particles in noninertial motion along a curved trajectory. The possibility of
detecting this violation in muon decay experiments is explored, where the
noninertial contribution to the decay rate becomes large for muon beams with
large momenta and trajectories with radius of curvature approaching the muon's
Compton wavelength scale. A new spacelike spin vector is derived from the
Pauli-Lubanski vector that satisfies Lorentz invariance for both inertial and
noninertial motion. In addition, this spin vector suggests a generalization for
the classification of spin-1/2 particles, and has interesting properties that
are applicable for both massive and massless particles.Comment: REVTeX file; 7 pages; 2 figures; slightly revised with new abstract;
accepted for publication in Classical and Quantum Gravit
Isospin violation and the proton's neutral weak magnetic form factor
The effects of isospin violation on the neutral weak magnetic form factor of
the proton are studied using two-flavour chiral perturbation theory. The first
nonzero contributions appear at O(p^4) in the small-momentum expansion, and the
O(p^5) corrections are also calculated. The leading contributions from an
explicit Delta(1232) isomultiplet are included as well. At such a high order in
the chiral expansion, one might have expected a large number of unknown
parameters to contribute. However, it is found that no unknown parameters can
appear within loop diagrams, and a single tree-level counterterm at O(p^4) is
sufficient to absorb all divergences. The momentum dependence of the neutral
weak magnetic form factor is not affected by this counterterm.Comment: 26 pages including 9 figure
Is There an Observable Limit to Lorentz Invariance at the Compton Wavelength Scale?
The possibility of a frame-induced violation of Lorentz invariance due to
non-inertial spin-1/2 particle motion is explored in detail for muon decay
while in orbit near the event horizon of a microscopic Kerr black hole. It is
explicitly shown that kinematic and curvature contributions to the muon's decay
spectrum--in the absence of any unforeseen processes due to quantum
gravity--lead to its stabilization at the muon's Compton wavelength scale. This
example is emblematic of the search for unambiguous indicators to critically
assess current and future approaches to quantum gravity research.Comment: 9 pages, 1 figure; 2009 Gravity Research Foundation essay competition
submission; accepted for publication in General Relativity and Gravitatio