34,379 research outputs found
Contributions to Pion Decay from Lorentz Violation in the Weak Sector
Lorentz violation in the weak sector would affect the beta-decay lifetimes of
pions. The decay amplitude may be rendered anisotropic, but only an isotropic
violation of boost invariance can affect the net lifetime in the center of mass
frame. However, since the rest frames of the pions that produce the NuMI
neutrino beam at Fermilab vary with the rotation of the Earth, it is possible
to constrain anisotropic Lorentz violation using prior analyses of sidereal
variations in the event rate at the MINOS near detector. The resulting bounds
on weak-sector Lorentz violation are at the 10^(-4) level, a substantial
improvement over previous results. The highly relativistic character of the
pions involved is responsible for the improvement.Comment: 16 page
Absence of Long-Wavelength Cerenkov Radiation With Isotropic Lorentz and CPT Violation
Modified theories of electrodynamics that include violations of Lorentz
symmetry often allow for the possibility of vacuum Cerenkov radiation. This
phenomenon has previously been studied in a number of Lorentz-violating
theories, but none of the methods that have previously been developed are
sufficient to study a theory with a timelike Chern-Simons term ,
because such a term may generate exponentially growing solutions to the field
equations. Searching for vacuum Cerenkov radiation in a theory with a purely
timelike Chern-Simons term using only elementary methods, we find that, despite
the presence of the runaway modes, a charge in uniform nonrelativistic motion
does not radiate energy, up to second order in the velocity.Comment: 9 page
Lorentz Violation in Fermion-Antifermion Decays of Spinless Particles
If Lorentz and CPT violation exist, they could affect the decays of scalar
and pseudoscalar particles. For a decay into a fermion and an antifermion (not
necessarily of the same mass), both the total decay rate and the outgoing
particle distribution may be modified, through interference between the
conventional decay mechanism and a separate Lorentz-violating mechanism. The
modifications are sensitive to forms of Lorentz violation that are otherwise
rather difficult to study, since at tree level they do not affect particle
propagation, but only interaction vertices. Using existing experimental data on
charged pion decay, it is possible to constrain three parameters in the
modified pion-muon-neutrino coupling at better than the level; these
are the first bounds on these quantities.Comment: 16 page
Consequences of Neutrino Lorentz Violation For Leptonic Meson Decays
If the observation by OPERA of apparently superluminal neutrinos is correct,
the Lagrangian for second-generation leptons must break Lorentz invariance. We
calculate the effects of an energy-independent change in the neutrino speed on
another observable, the charged pion decay rate. The rate decreases by an
factor [1 - 3/(1 - (m_mu)^2 / (m_pi) ^ 2) ( - 1)], where
is the (directionally averaged) neutrino speed in the pion's rest frame. This
provides a completely independent experimental observable that is sensitive to
the same forms of Lorentz violation as a neutrino time of flight measurement.Comment: 10 page
There is No Ambiguity in the Radiatively Induced Gravitational Chern-Simons Term
Quantum corrections to Lorentz- and CPT-violating QED in flat spacetime
produce unusual radiative corrections, which can be finite but of undetermined
magnitude. The corresponding radiative corrections in a gravitational theory
are even stranger, since the term in the fermion action involving a preferred
axial vector would give rise to a gravitational Chern-Simons term
that is proportional , yet which actually does not break Lorentz
invariance. Initially, the coefficient of this gravitational Chern-Simons term
appears to have the same ambiguity as the coefficient for the analogous term in
QED. However, this puzzle is resolved by the fact that the gravitational theory
has more stringent gauge invariance requirements. Lorentz symmetry in a metric
theory of gravity can only be broken spontaneously, and when the vector
arises from spontaneous symmetry breaking, these specific radiative
corrections are no longer ambiguous but instead must vanish identically.Comment: 16 page
Coupling Right- and Left-Handed Photons Differently to Charged Matter
We consider a modification of electrodynamics in which right- and
left-circularly polarized photons are coupled to charged sources differently.
Even though photon helicity is a Lorentz invariant quantity, such a
modification breaks Lorentz symmetry, as well as locality. The modified theory
includes novel magnetic forces between perpendicular currents. Existing data
can be used to constrain the modification at approximately a 2 x 10^(-3) level.Comment: 12 page
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