3,743,045 research outputs found
On Schwarzschild's Topology in Brane-Worlds
The topological structure of Schwarzschild's space-time and its maximal
analytic extension are investigated in context of brane-worlds. Using the
embedding coordinates, these geometries are seen as different states of the
evolution of a single brane-world. Comparing the topologies and the embeddings
it is shown that this evolution must be followed by a signature change in the
bulk.Comment: 6 page
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A database and challenge for acoustic scene classification and event detection
Functional integral over velocities for a spinning particle with and without anomalous magnetic moment in a constant electromagnetic field
The technique of functional integration over velocities is applied to the
calculation of the propagator of a spinning particle with and without anomalous
magnetic moment. A representation for the spin factor is obtained in this
context for the particle in a constant electromagnetic field. As a by-product,
we also obtain a Schwinger representation for the first case.Comment: latex, 19 page
The Infrared Jet In 3C66B
We present images of infrared emission from the radio jet in 3C66B. Data at
three wavelengths (4.5, 6.75 and 14.5 microns) were obtained using the Infrared
Space Observatory. The 6.75 micron image clearly shows an extension aligned
with the radio structure. The jet was also detected in the 14.5 micron image,
but not at 4.5 micron. The radio-infrared-optical spectrum of the jet can be
interpreted as synchrotron emission from a population of electrons with a
high-energy break of 4e11 eV. We place upper limits on the IR flux from the
radio counter-jet. A symmetrical, relativistically beamed twin-jet structure is
consistent with our results if the jets consist of multiple components.Comment: 7 pages, 4 figure
Multifluid, Magnetohydrodynamic Shock Waves with Grain Dynamics II. Dust and the Critical Speed for C Shocks
This is the second in a series of papers on the effects of dust on
multifluid, MHD shock waves in weakly ionized molecular gas. We investigate the
influence of dust on the critical shock speed, v_crit, above which C shocks
cease to exist. Chernoff showed that v_crit cannot exceed the grain
magnetosound speed, v_gms, if dust grains are dynamically well coupled to the
magnetic field. We present numerical simulations of steady shocks where the
grains may be well- or poorly coupled to the field. We use a time-dependent,
multifluid MHD code that models the plasma as a system of interacting fluids:
neutral particles, ions, electrons, and various ``dust fluids'' comprised of
grains with different sizes and charges. Our simulations include grain inertia
and grain charge fluctuations but to highlight the essential physics we assume
adiabatic flow, single-size grains, and neglect the effects of chemistry. We
show that the existence of a phase speed v_phi does not necessarily mean that C
shocks will form for all shock speeds v_s less than v_phi. When the grains are
weakly coupled to the field, steady, adiabatic shocks resemble shocks with no
dust: the transition to J type flow occurs at v_crit = 2.76 v_nA, where v_nA is
the neutral Alfven speed, and steady shocks with v_s > 2.76 v_nA are J shocks
with magnetic precursors in the ion-electron fluid. When the grains are
strongly coupled to the field, v_crit = min(2.76 v_nA, v_gms). Shocks with
v_crit < v_s < v_gms have magnetic precursors in the ion-electron-dust fluid.
Shocks with v_s > v_gms have no magnetic precursor in any fluid. We present
time-dependent calculations to study the formation of steady multifluid shocks.
The dynamics differ qualitatively depending on whether or not the grains and
field are well coupled.Comment: 43 pages with 17 figures, aastex, accepted by The Astrophysical
Journa
Decoupling of Heavy Kaluza-Klein Modes In Models With Five-Dimensional Scalar Fields
We investigate the decoupling of heavy Kaluza-Klein modes in
theory and scalar QED with space-time topology .
We calculate the effective action due to integrating out heavy KK modes. We
construct generalized RGE's for the couplings with respect to the
compactification scale . With the solutions to the RGE's we find the
-scale dependence of the effective theory due to higher dimensional quantum
effects. We find that the heavy modes decouple in theory, but do not
decouple in scalar QED. This is due to the zero mode of the 5-th component
of the 5-d gauge field. Because is a scalar under 4-d Lorentz
transformations, there is no gauge symmetry protecting it from getting mass and
interaction terms after loop corrections. In light of these
unpleasant features, we explore compactifications, which
eliminate , allowing for the heavy modes to decouple at low energies. We
also explore the possibility of decoupling by including higher dimensional
operators. It is found that this is possible, but a high degree of fine tuning
is required.Comment: 9 pages, no figures; sign error on equations 20, 36, 37; Added
additional reference
Nonlocality effects on spin-one pairing patterns in two-flavor color superconducting quark matter and compact stars applications
We study the influence of nonlocality in the interaction on two spin one
pairing patterns of two-flavor quark matter: the anisotropic blue color paring
besides the usual two color superconducting matter (2SCb), in which red and
green colors are paired, and the color spin locking phase (CSL). The effect of
nonlocality on the gaps is rather large and the pairings exhibit a strong
dependence on the form factor of the interaction, especially in the low density
region. The application of these small spin-one condensates for compact stars
is analyzed: the early onset of quark matter in the nonlocal models may help to
stabilize hybrid star configurations. While the anisotropic blue quark pairing
does not survive a big asymmetry in flavor space as imposed by the charge
neutrality condition, the CSL phase as a flavor independent pairing can be
realized as neutral matter in compact star cores. However, smooth form factors
and the missmatch between the flavor chemical potential in neutral matter make
the effective gaps of the order of magnitude keV, and a more
systematic analysis is needed to decide whether such small gaps could be
consistent with the cooling phenomenology.Comment: 18 pages, 7 figures, corrected version with revised parameterizatio
Analysis of electric-field-induced spin splitting in wide modulation-doped quantum wells
We analyze the proper inclusion of electric-field-induced spin splittings in
the framework of the envelope function approximation. We argue that the Rashba
effect should be included in the form of a macroscopic potential as diagonal
terms in a multiband approach rather than the commonly used Rashba term
dependent on k and electric field. It is pointed out that the expectation value
of the electric field in a subband is sometimes not unique because the
expectation values can even have opposite signs for the spin-split subband
components. Symmetric quantum wells with Dresselhaus terms and the influence of
the interfaces on the spin splitting are also discussed. We apply a well
established multiband approach to wide modulation-doped InGaSb quantum wells
with strong built-in electric fields in the interface regions. We demonstrate
an efficient mechanism for switching on and off the Rashba splitting with an
electric field being an order of magnitude smaller than the local built-in
field that determines the Rashba splitting. The implications of our findings
for spintronic devices, in particular the Datta-Das spin transistor and
proposed modifications of it, are discussed.Comment: Modified version, now published. 10 pages, 3 figures, 2 table
Canonical quantization of the relativistic particle in static spacetimes
We perform the canonical quantization of a relativistic spinless particle
moving in a curved and static spacetime. We show that the classical theory
already describes at the same time both particle and antiparticle. The analyses
involves time-depending constraints and we are able to construct the
two-particle Hilbert space. The requirement of a static spacetime is necessary
in order to have a well defined Schr\"odinger equation and to avoid problems
with vacuum instabilities. The severe ordering ambiguities we found are in
essence the same ones of the well known non-relativistic case.Comment: Revtex, 9 page
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