8,984 research outputs found
Position and Momentum Uncertainties of the Normal and Inverted Harmonic Oscillators under the Minimal Length Uncertainty Relation
We analyze the position and momentum uncertainties of the energy eigenstates
of the harmonic oscillator in the context of a deformed quantum mechanics,
namely, that in which the commutator between the position and momentum
operators is given by [x,p]=i\hbar(1+\beta p^2). This deformed commutation
relation leads to the minimal length uncertainty relation \Delta x >
(\hbar/2)(1/\Delta p +\beta\Delta p), which implies that \Delta x ~ 1/\Delta p
at small \Delta p while \Delta x ~ \Delta p at large \Delta p. We find that the
uncertainties of the energy eigenstates of the normal harmonic oscillator
(m>0), derived in Ref. [1], only populate the \Delta x ~ 1/\Delta p branch. The
other branch, \Delta x ~ \Delta p, is found to be populated by the energy
eigenstates of the `inverted' harmonic oscillator (m<0). The Hilbert space in
the 'inverted' case admits an infinite ladder of positive energy eigenstates
provided that \Delta x_{min} = \hbar\sqrt{\beta} > \sqrt{2}
[\hbar^2/k|m|]^{1/4}. Correspondence with the classical limit is also
discussed.Comment: 16 pages, 31 eps figure
Lambda(1405) as a Resonance in the Baryon-Meson Scattering Coupled to the q^3 State in a Quark Model
In order to describe Lambda(1405) as a resonance in the baryon-meson
scattering, we have investigated q^3-q qbar scattering system with the
flavor-singlet q^3 (0s)^2(0p) state (the Lambda^1 pole). The scattering is
treated by the quark cluster model (QCM). The Lambda^1 pole is treated as a
bound state embedded in the continuum. We found that the peak appears below the
N Kbar threshold in the spin one half, isospin 0 channel even if the mass of
the Lambda^1 pole is above the threshold. This peak disappears when the
coupling to the Lambda^1 pole is switched off. To use the observed hadron mass
in the kinetic part of QCM is also found to be important to reproduce a peak
just below the N Kbar threshold.Comment: 16 pages and 7 figure
Diffusive versus local spin currents in dynamic spin pumping systems
Using microscopic theory, we investigate the properties of a spin current
driven by magnetization dynamics. In the limit of smooth magnetization texture,
the dominant spin current induced by the spin pumping effect is shown to be the
diffusive spin current, i.e., the one arising from only a diffusion associated
with spin accumulation. That is to say, there is no effective field that
locally drives the spin current. We also investigate the conversion mechanism
of the pumped spin current into a charge current by spin-orbit interactions,
specifically the inverse spin Hall effect. We show that the spin-charge
conversion does not always occur and that it depends strongly on the type of
spin-orbit interaction. In a Rashba spin-orbit system, the local part of the
charge current is proportional to the spin relaxation torque, and the local
spin current, which does not arise from the spin accumulation, does not play
any role in the conversion. In contrast, the diffusive spin current contributes
to the diffusive charge current. Alternatively, for spin-orbit interactions
arising from random impurities, the local charge current is proportional to the
local spin current that constitutes only a small fraction of the total spin
current. Clearly, the dominant spin current (diffusive spin current) is not
converted into a charge current. Therefore, the nature of the spin current is
fundamentally different depending on its origin and thus the spin transport and
the spin-charge conversion behavior need to be discussed together along with
spin current generation
Prospects for measuring coherent neutrino-nucleus elastic scattering at a stopped-pion neutrino source
Rates of coherent neutrino-nucleus elastic scattering at a high-intensity
stopped-pion neutrino source in various detector materials (relevant for novel
low-threshold detectors) are calculated. Sensitivity of a coherent
neutrino-nucleus elastic scattering experiment to new physics is also explored.Comment: 9 pages, 14 figures; minor modifications for publicatio
P-wave Pentaquark and its Decay in the Quark Model with Instanton Induced Interaction
P-wave pentaquarks with strangeness +1, I=0 and J^P=1/2^+ are studied in the
non-relativistic quark model with instanton induced interaction (III). We
present their mass splittings and orbital-spin-isospin-color structures. It is
found that decompositions of the wave functions are sensitive to III, while the
mass splittings are insensitive. The decay of the lowest energy pentaquark,
\Theta^+, is found to be suppressed when the contribution of III is increased.
Its wave function is dominated by Jaffe-Wilczek-type configuration at large
III.Comment: 9 pages, 5 figure
Effects of Instanton Induced Interaction on the Pentaquarks
Roles of instanton induced interactions (III) in the masses of pentaquark
baryons, Theta^+ (J=1/2 and 3/2) and Xi^{--}, and a dibaryon, H, are discussed
using the MIT bag model in the negative parity case. It is shown that the
two-body terms in III give a strong attraction mainly due to the increase of
the number of pairs in multi-quark systems. In contrast, the three-body u-d-s
interaction is repulsive. It is found that III lowers the mass of Theta^+ as
much as 100 MeV from the mass predicted by the bag model without III.Comment: 11 pages, 3 figure
X-Ray Fluctuations from Locally Unstable Advection-Dominated Disks
The response of advection-dominated accretion disks to local disturbances is
examined by one-dimensional numerical simulations. It is generally believed
that advection-dominated disks are thermally stable. We, however, find that any
disurbance added onto accretion flow at large radii does not decay so rapidly
that it can move inward with roughly the free-fall velocity. Although
disturbances continue to be present, the global disk structure will not be
modified largely. This can account for persistent hard X-ray emission with
substantial variations observed in active galactic nuclei and stellar black
hole candidates during the hard state. Moreover, when the disturbance reaches
the innermost parts, an acoustic wave emerges, propagating outward as a shock
wave. The resultant light variation is roughly (time) symmetric and is quite
reminiscent of the observed X-ray shots of Cygnus X-1.Comment: plain TeX, 11 pages, without figures; to be published in ApJ Lette
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