11,321 research outputs found
Initial state maximizing the nonexponentially decaying survival probability for unstable multilevel systems
The long-time behavior of the survival probability for unstable multilevel
systems that follows the power-decay law is studied based on the N-level
Friedrichs model, and is shown to depend on the initial population in unstable
states. A special initial state maximizing the asymptote of the survival
probability at long times is found and examined by considering the spontaneous
emission process for the hydrogen atom interacting with the electromagnetic
field.Comment: 5 pages, 1 table. Accepted for publication in Phys. Rev.
Zero energy resonance and the logarithmically slow decay of unstable multilevel systems
The long time behavior of the reduced time evolution operator for unstable
multilevel systems is studied based on the N-level Friedrichs model in the
presence of a zero energy resonance.The latter means the divergence of the
resolvent at zero energy. Resorting to the technique developed by Jensen and
Kato [Duke Math. J. 46, 583 (1979)], the zero energy resonance of this model is
characterized by the zero energy eigenstate that does not belong to the Hilbert
space. It is then shown that for some kinds of the rational form factors the
logarithmically slow decay of the reduced time evolution operator can be
realized.Comment: 31 pages, no figure
Outgassing measurement of the aluminum alloy UHV chamber
A large vacuum chamber (580 mm diameter) was fabricated from an aluminum alloy surface treated by a special process normally used on small chambers. The chamber was tested unbaked and baked at various temperatures, pressures, and holding periods. The chamber was filled with N2 gas, and the outgassing rate was measured after one hour. Then the ultimate pressure was measured. Outgassing rates for baked and unbaked groups were compared. It is concluded that the same surface treatment technique can be used on both large and small chambers produced by the same special extrusion process
Generic features of Einstein-Aether black holes
We reconsider spherically symmetric black hole solutions in Einstein-Aether
theory with the condition that this theory has identical PPN parameters as
those for general relativity, which is the main difference from the previous
research. In contrast with previous study, we allow superluminal propagation of
a spin-0 Aether-gravity wave mode. As a result, we obtain black holes having a
spin-0 "horizon" inside an event horizon. We allow a singularity at a spin-0
"horizon" since it is concealed by the event horizon. If we allow such a
configuration, the kinetic term of the Aether field can be large enough for
black holes to be significantly different from Schwarzschild black holes with
respect to ADM mass, innermost stable circular orbit, Hawking temperature, and
so on. We also discuss whether or not the above features can be seen in more
generic vector-tensor theories.Comment: 9 pages, 9 figures, basic equations and their analytic arguments are
adde
Constraining global properties of the Draco dwarf spheroidal galaxy
By fitting a flexible stellar anisotropy model to the observed surface
brightness and line-of-sight velocity dispersion profiles of Draco we derive a
sequence of cosmologically plausible two-component (stars + dark matter) models
for this galaxy. The models are consistent with all the available observations
and can have either cuspy Navarro-Frenk-White or flat-cored dark matter density
profiles. The dark matter halos either formed relatively recently (at z~2...7)
and are massive (up to ~5x10^9 M_Sun), or formed before the end of the
reionization of the universe (z~7...11) and are less massive (down to ~7x10^7
M_Sun). Our results thus support either of the two popular solutions of the
"missing satellites" problem of Lambda cold dark matter cosmology - that dwarf
spheroidals are either very massive, or very old. We carry out high-resolution
simulations of the tidal evolution of our two-component Draco models in the
potential of the Milky Way. The results of our simulations suggest that the
observable properties of Draco have not been appreciably affected by the
Galactic tides after 10 Gyr of evolution. We rule out Draco being a "tidal
dwarf" - a tidally disrupted dwarf galaxy. Almost radial Draco orbits (with the
pericentric distance <15 kpc) are also ruled out by our analysis. The case of a
harmonic dark matter core can be consistent with observations only for a very
limited choice of Draco orbits (with the apocentric-to-pericentric distances
ratio of <2.5).Comment: 18 pages, 14 figures; accepted by Ap
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