25,854 research outputs found
Quantum Quenches in Free Field Theory: Universal Scaling at Any Rate
Quantum quenches display universal scaling in several regimes. For quenches
which start from a gapped phase and cross a critical point, with a rate slow
compared to the initial gap, many systems obey Kibble-Zurek scaling. More
recently, a different scaling behaviour has been shown to occur when the quench
rate is fast compared to all other physical scales, but still slow compared to
the UV cutoff. We investigate the passage from fast to slow quenches in scalar
and fermionic free field theories with time dependent masses for which the
dynamics can be solved exactly for all quench rates. We find that renormalized
one point functions smoothly cross over between the regimes.Comment: 40 pages; v2: a bit late, but it includes minor modifications to
match published versio
Electron spin interferometry using a semiconductor ring structure
A ring structure fabricated from GaAs is used to achieve interference of the
net spin polarization of conduction band electrons. Optically polarized spins
are split into two packets by passing through two arms of the ring in the
diffusive transport regime. Optical pumping with circularly polarized light on
one arm establishes dynamic nuclear polarization which acts as a local
effective magnetic field on electron spins due to the hyperfine interaction.
This local field causes one spin packet to precess faster than the other,
thereby controlling the spin interference when the two packets are combined.Comment: 4 pages, 2 figure
An Improved Measurement of the Hubble Constant from the Sunyaev-Zeldovich Effect
We present a determination of the Hubble constant from measurements of the
Sunyaev-Zeldovich Effect (SZE) in an orientation-unbiased sample of 7 z < 0.1
galaxy clusters. With improved X-ray models and a more accurate 32-GHz
calibration, we obtain H_O = 64+14-11 +/- 14_sys km/s/Mpc. for a standard CDM
cosmology, or 66+14-11 +/- 15_sys km/s/Mpc for a flat LambdaCDM cosmology. In
combination with X-ray cluster measurements and the BBN value for Omega_B, we
find Omega_M = 0.32 +/- 0.05.Comment: 5 pp., Accepted for publication in ApJ
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