It is postulated in Einstein's relativity that the speed of light in vacuum
is a constant for all observers. However, the effect of quantum gravity could
bring an energy dependence of light speed. Even a tiny speed variation, when
amplified by the cosmological distance, may be revealed by the observed time
lags between photons with different energies from astrophysical sources. From
the newly detected long gamma ray burst GRB~160509A, we find evidence to
support the prediction for a linear form modification of light speed in
cosmological space.Comment: 5 latex pages, 2 figures, final version for publicatio
The effect of quantum gravity can bring a tiny light speed variation which is
detectable through energetic photons propagating from gamma ray bursts (GRBs)
to an observer such as the space observatory. Through an analysis of the
energetic photon data of the GRBs observed by the Fermi Gamma-ray Space
Telescope (FGST), we reveal a surprising regularity of the observed time lags
between photons of different energies with respect to the Lorentz violation
factor due to the light speed energy dependence. Such regularity suggests a
linear form correction of the light speed $v(E)=c(1-E/E_{\rm LV})$, where $E$
is the photon energy and $E_{\rm LV}=(3.60 \pm 0.26) \times 10^{17}~ \rm GeV$
is the Lorentz violation scale measured by the energetic photon data of GRBs.
The results support an energy dependence of the light speed in cosmological
space.Comment: 7 pages, 3 figures, final version for publication with typos
correcte
Single-spin asymmetries for pions and charged kaons are measured in semi-inclusive deep-inelastic scattering of positrons and electrons off a transversely nuclear-polarized hydrogen target. The dependence of the cross section on the azimuthal angles of the target polarization ([phi]S) and the produced hadron ([phi]) is found to have a substantial sin([phi]+[phi]S) modulation for the production of [pi]+, [pi]- and K+. This Fourier component can be interpreted in terms of non-zero transversity distribution functions and non-zero favored and disfavored Collins fragmentation functions with opposite sign. For [pi]0 and K- production the amplitude of this Fourier component is consistent with zero
Single-spin asymmetries for semi-inclusive electroproduction of charged pions in deep-inelastic scattering of positrons are measured for the first time with transverse target polarization. The asymmetry depends on the azimuthal angles of both the pion (phi) and the target spin axis (phi(S)) about the virtual-photon direction and relative to the lepton scattering plane. The extracted Fourier component sin((phi+phi(S))(pi)(UT) is a signal of the previously unmeasured quark transversity distribution, in conjunction with the Collins fragmentation function, also unknown. The component sin((phi-phi(S)(pi)(UT) arises from a correlation between the transverse polarization of the target nucleon and the intrinsic transverse momentum of quarks, as represented by the previously unmeasured Sivers distribution function. Evidence for both signals is observed, but the Sivers asymmetry may be affected by exclusive vector meson production.
It is shown that the observed small value of the integrated spin structure function for protons could be naturally understood within the naive quark model by considering the effect from Melosh rotation. The key to this problem lies in the fact that the deep inelastic process probes the light-cone quarks rather than the instantform quarks, and that the spin of the proton is the sum of the Melosh rotated light-cone spin of the individual quarks rather than simply the sum of the light-cone spin of the quarks directly.
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