64 research outputs found
Can Gravity Distinguish Between Dirac and Majorana Neutrinos?
We show that spin-gravity interaction can distinguish between Dirac and
Majorana neutrino wave packets propagating in a Lense-Thirring background.
Using time-independent perturbation theory and gravitational phase to generate
a perturbation Hamiltonian with spin-gravity coupling, we show that the
associated matrix element for the Majorana neutrino differs significantly from
its Dirac counterpart. This difference can be demonstrated through significant
gravitational corrections to the neutrino oscillation length for a two-flavour
system, as shown explicitly for SN1987A.Comment: 4 pages, 2 figures; minor changes of text; typo corrected; accepted
in Physical Review Letter
Tidal Dynamics in Cosmological Spacetimes
We study the relative motion of nearby free test particles in cosmological
spacetimes, such as the FLRW and LTB models. In particular, the influence of
spatial inhomogeneities on local tidal accelerations is investigated. The
implications of our results for the dynamics of the solar system are briefly
discussed. That is, on the basis of the models studied in this paper, we
estimate the tidal influence of the cosmic gravitational field on the orbit of
the Earth around the Sun and show that the corresponding temporal rate of
variation of the astronomical unit is negligibly small.Comment: 12 pages, no figures, REVTeX 4.0; appendix added, new references, and
minor changes throughout; to appear in Classical and Quantum Gravity; v4:
error in (A24) of Appendix A corrected, results and conclusions unchanged. We
thank L. Iorio for pointing out the erro
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
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
Effects of Space-Time Curvature on Spin-1/2 Particle Zitterbewegung
This paper investigates the properties of spin-1/2 particle Zitterbewegung in
the presence of a general curved space-time background described in terms of
Fermi normal co-ordinates, where the spatial part is expressed using general
curvilinear co-ordinates. Adopting the approach first introduced by Barut and
Bracken for Zitterbewegung in the local rest frame of the particle, it is shown
that non-trivial gravitational contributions to the relative position and
momentum operators appear due to the coupling of Zitterbewegung frequency terms
with the Ricci curvature tensor in the Fermi frame, indicating a formal
violation of the weak equivalence principle. Explicit expressions for these
contributions are shown for the case of quasi-circular orbital motion of a
spin-1/2 particle in a Vaidya background. Formal expressions also appear for
the time-derivative of the Pauli-Lubanski vector due to space-time curvature
effects coupled to the Zitterbewegung frequency. As well, the choice of
curvilinear co-ordinates results in non-inertial contributions in the time
evolution of the canonical momentum for the spin-1/2 particle, where
Zitterbewegung effects lead to stability considerations for its propagation,
based on the Floquet theory of differential equations.Comment: 22 pages, no figures; slight revisions; accepted for publication in
Classical and Quantum Gravit
Muon capture by a proton in heavy baryon chiral perturbation theory
The matrix element for muon capture by a proton is calculated to O(p^3)
within heavy baryon chiral perturbation theory using the new O(p^3) Lagrangian
of Ecker and Mojzis. External nucleon fields are renormalized using the
appropriate definition of the wave function renormalization factor Z_N. Our
expression for Z_N differs somewhat from that found in existing literature, but
is the one which is consistent with the Lagrangian we use and the one which
ensures, within our approach, the nonrenormalization of the vector coupling as
required by the conserved vector current. Expressions for the standard muon
capture form factors are derived and compared to experimental data and we
determine three of the coefficients of the Ecker - Mojzis Lagrangian, namely,
b_7, b_{19}, and b_{23}.Comment: 14 pages, LaTeX, using revte
Local Space-Time Curvature Effects on Quantum Orbital Angular Momentum
This paper claims that local space-time curvature can non-trivially
contribute to the properties of orbital angular momentum in quantum mechanics.
Of key importance is the demonstration that an extended orbital angular
momentum operator due to gravitation can identify the existence of orbital
states with half-integer projection quantum numbers "m" along the axis of
quantization, while still preserving integer-valued orbital quantum numbers "l"
for a simply connected topology. The consequences of this possibility are
explored in depth, noting that the half-integer "m" states vanish as required
when the locally curved space-time reduces to flat space-time, fully recovering
all established properties of orbital angular momentum in this limit. In
particular, it is shown that a minimum orbital number of "l = 2" is necessary
for the gravitational interaction to appear within this context, in perfect
correspondence with the spin-2 nature of linearized general relativity.Comment: 21 pages, 1 figure; references added; accepted for publication in
Classical and Quantum Gravit
Chiral perturbation theory calculation for pn -> dpipi at threshold
We investigate the reaction pn -> dpipi in the framework of Chiral
Perturbation Theory. For the first time a complete calculation of the leading
order contributions is presented. We identify various diagrams that are of
equal importance as compared to those recognized in earlier works. The diagrams
at leading order behave as expected by the power counting. Also for the first
time the nucleon-nucleon interaction in the initial, intermediate and final
state is included consistently and found to be very important. This study
provides a theoretical basis for a controlled evaluation of the non-resonant
contributions in two-pion production reactions in nucleon-nucleon collisions.Comment: 24 pages, 3 figures, 3 table
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