68 research outputs found
Robust Limits on Lorentz Violation from Gamma-Ray Bursts
We constrain the possibility of a non-trivial refractive index in free space
corresponding to an energy-dependent velocity of light: c(E) \simeq c_0 (1 -
E/M), where M is a mass scale that might represent effect of
quantum-gravitational space-time foam, using the arrival times of sharp
features observed in the intensities of radiation with different energies from
a large sample of gamma-ray bursters (GRBs) with known redshifts. We use
wavelet techniques to identify genuine features, which we confirm in
simulations with artificial added noise. Using the weighted averages of the
time-lags calculated using correlated features in all the GRB light curves, we
find a systematic tendency for more energetic photons to arrive earlier.
However, there is a very strong correlation between the parameters
characterizing an intrinsic time-lag at the source and a distance-dependent
propagation effect. Moreover, the significance of the earlier arrival times is
less evident for a subsample of more robust spectral structures. Allowing for
intrinsic stochastic time-lags in these features, we establish a statistically
robust lower limit: M > 0.9x10^{16} GeV on the scale of violation of Lorentz
invariance.Comment: 18 pages, 4 eps figure
Low-Temperature Specific Heat of an Extreme-Type-II Superconductor at High Magnetic Fields
We present a detailed study of the quasiparticle contribution to the
low-temperature specific heat of an extreme type-II superconductor at high
magnetic fields. Within a T-matrix approximation for the self-energies in the
mixed state of a homogeneous superconductor, the electronic specific heat is a
linear function of temperature with a linear- coefficient
being a nonlinear function of magnetic field . In the range of magnetic
fields H\agt (0.15-0.2)H_{c2} where our theory is applicable, the calculated
closely resembles the experimental data for the borocarbide
superconductor YNiBC.Comment: 7 pages, 2 figures, to appear in Physical Review
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