22,299 research outputs found
Beltrami-like fields created by baroclinic effect in two-fluid plasmas
A theory of two-dimensional plasma evolution with Beltrami-like flow and
field due to baroclinic effect has been presented. Particular solution of the
nonlinear two-fluid equations is obtained. This simple model can explain the
generation of magnetic field without assuming the presence of a seed in the
system. Coupled field and flow naturally grow together. The theory has been
applied to estimate B-field in laser-induced plasmas and the result is in good
agreement with experimental values.Comment: 3 page
Quasinormal modes of a massless charged scalar field on a small Reissner-Nordstr\"om-anti-de Sitter black hole
We investigate quasinormal modes of a massless charged scalar field on a
small Reissner-Nordstr\"om-anti-de Sitter (RN-AdS) black hole both with
analytical and numerical approaches. In the analytical approach, by using the
small black hole approximation (r_+ << L), we obtain the quasinormal mode
frequencies in the limit of r_+/L -> 0, where r_+ and L stand for the black
hole event horizon radius and the AdS scale, respectively. We then show that
the small RN-AdS black hole is unstable if its quasinormal modes satisfy the
superradiance condition and that the instability condition of the RN-AdS black
hole in the limit of r_+/L -> 0 is given by Q>(3/eL)Q_c, where Q, Q_c, and e
are the charge of the black hole, the critical (maximum) charge of the black
hole, and the charge of the scalar field, respectively. In the numerical
approach, we calculate the quasinormal modes for the small RN-AdS black holes
with r_+ << L and confirm that the RN-AdS black hole is unstable if its
quasinormal modes satisfy the superradiance condition. Our numerical results
show that the RN-AdS black holes with r_+ =0.2L, 0.1L, and 0.01L become
unstable against scalar perturbations with eL=4 when the charge of the black
hole satisfies Q > 0.8Q_c, 0.78Q_c, and 0.76Q_c, respectively.Comment: 13 pages, 11 figure
A search for x-ray counterparts of gamma-ray bursts with the ROSAT PSPC
We search for faint X-ray bursts with duration 10--300 seconds in the ROSAT
PSPC pointed observations with a total exposure of 1.6e7 seconds. We do not
detect any events shorter than ~100s, i.e. those that could be related to the
classic gamma-ray bursts. At the same time, we detect a number of long flares
with durations of several hundred seconds. Most, but not all, of the long
flares are associated with stars. If even a small number of those long flares,
that cannot identified with stars, are X-ray afterglows of GRB, the number of
X-ray afterglows greatly exceeds the number of BATSE GRB. This would imply that
the beaming factor of gamma-rays from the burst should be >100. The
non-detection of any short bursts in our data constrains the GRB counts at the
fluences 1--2.5 orders of magnitude below the BATSE limit. The constrained
burst counts are consistent with the extrapolation of the BATSE log N - log S
relation. Finally, our results do not confirm a reality of short X-ray flashes
found in the Einstein IPC data by Gotthelf, Hamilton and Helfand.Comment: Accepted to ApJ Letters. 4 pages with 3 figures, LaTeX2
Dense Molecular Gas In A Young Cluster Around MWC 1080 -- Rule Of The Massive Star
We present CS , CO , and CO , observations with the 10-element Berkeley Illinois Maryland Association
(BIMA) Array toward the young cluster around the Be star MWC 1080. These
observations reveal a biconical outflow cavity with size 0.3 and 0.05 pc
for the semimajor and semiminor axis and 45\arcdeg position angle.
These transitions trace the dense gas, which is likely the swept-up gas of the
outflow cavity, rather than the remaining natal gas or the outflow gas. The gas
is clumpy; thirty-two clumps are identified. The identified clumps are
approximately gravitationally bound and consistent with a standard isothermal
sphere density, which suggests that they are likely collapsing protostellar
cores. The gas kinematics suggests that there exists velocity gradients
implying effects from the inclination of the cavity and MWC 1080. The
kinematics of dense gas has also been affected by either outflows or stellar
winds from MWC 1080, and lower-mass clumps are possibly under stronger effects
from MWC 1080 than higher-mass clumps. In addition, low-mass cluster members
tend to be formed in the denser and more turbulent cores, compared to isolated
low-mass star-forming cores. This results from contributions of nearby forming
massive stars, such as outflows or stellar winds. Therefore, we conclude that
in clusters like the MWC 1080 system, effects from massive stars dominate the
star-forming environment in both the kinematics and dynamics of the natal cloud
and the formation of low-mass cluster members. This study provides insights
into the effects of MWC 1080 on its natal cloud, and suggests a different
low-mass star forming environment in clusters compared to isolated star
formation.Comment: 42 pages, 5 tables, and 13 figures, accepted for publication in Ap
Invariants of Collective Neutrino Oscillations
We consider the flavor evolution of a dense neutrino gas by taking into
account both vacuum oscillations and self interactions of neutrinos. We examine
the system from a many-body perspective as well as from the point of view of an
effective one-body description formulated in terms of the neutrino polarization
vectors. We show that, in the single angle approximation, both the many-body
picture and the effective one-particle picture possess several constants of
motion. We write down these constants of motion explicitly in terms of the
neutrino isospin operators for the many-body case and in terms of the
polarization vectors for the effective one-body case. The existence of these
constants of motion is a direct consequence of the fact that the collective
neutrino oscillation Hamiltonian belongs to the class of Gaudin Hamiltonians.
This class of Hamiltonians also includes the (reduced) BCS pairing Hamiltonian
describing superconductivity. We point out the similarity between the
collective neutrino oscillation Hamiltonian and the BCS pairing Hamiltonian.
The constants of motion manifest the exact solvability of the system. Borrowing
the well established techniques of calculating the exact BCS spectrum, we
present exact eigenstates and eigenvalues of both the many-body and the
effective one-particle Hamiltonians describing the collective neutrino
oscillations. For the effective one-body case, we show that spectral splits of
neutrinos can be understood in terms of the adiabatic evolution of some
quasi-particle degrees of freedom from a high density region where they
coincide with flavor eigenstates to the vacuum where they coincide with mass
eigenstates. We write down the most general consistency equations which should
be satisfied by the effective one-body eigenstates and show that they reduce to
the spectral split consistency equations for the appropriate initial
conditions.Comment: 26 pages with one figure. Published versio
Open Semiclassical Strings and Long Defect Operators in AdS/dCFT Correspondence
We consider defect composite operators in a defect superconformal field
theory obtained by inserting an AdS_4 x S^2-brane in the AdS_5 x S^5
background. The one-loop dilatation operator for the scalar sector is
represented by an integrable open spin chain. We give a description to
construct coherent states for the open spin chain. Then, by evaluating the
expectation value of the Hamiltonian with the coherent states in a long
operator limit, a Landau-Lifshitz type of sigma model action is obtained. This
action is also derived from the string action and hence we find a complete
agreement in both SYM and string sides. We see that an SO(3)_H pulsating string
solution is included in the action and its energy completely agrees with the
result calculated in a different method. In addition, we argue that our
procedure would be applicable to other AdS-brane cases.Comment: 22 pages, 1 figure, LaTeX, minor corrections and references added.
v3) some new results added. shortened and accepted version in PR
Stable Neutral Fermi Ball
Fermi Ball is a kind of nontopological soliton with fermions trapped in its
domain wall, and is suggested to arises from the spontaneous symmetry breaking
of the approximate symmetry in the early universe. We find that the
neutral thin-wall Fermi Ball is stable in the limited region of the scalar
self-coupling constant and the Yukawa coupling constant . We find
that the Fermi Ball is stabilized due to the curvature effect of the domain
wall caused by the fermion sector. We also discuss whether such stable Fermi
Balls may contribute to the cold dark matter.Comment: 18 pages in RevTeX, 5 figure
Ultralong-Range Rydberg Molecules in a Divalent-Atomic System
We report the creation of ultralong-range Sr molecules comprising one
ground-state atom and one atom in a Rydberg state
for ranging from 29 to 36. Molecules are created in a trapped ultracold
atomic gas using two-photon excitation near resonant with the
intermediate state, and their formation is detected through ground-state atom
loss from the trap. The observed molecular binding energies are fit with the
aid of first-order perturbation theory that utilizes a Fermi pseudopotential
with effective -wave and -wave scattering lengths to describe the
interaction between an excited Rydberg electron and a ground-state Sr atom.Comment: 5 pages, 2 figure
General Relativistic Rossby-Haurwitz waves of a slowly and differentially rotating fluid shell
We show that, at first order in the angular velocity, the general
relativistic description of Rossby-Haurwitz waves (the analogues of r-waves on
a thin shell) can be obtained from the corresponding Newtonian one after a
coordinate transformation. As an application, we show that the results recently
obtained by Rezzolla and Yoshida (2001) in the analysis of Newtonian
Rossby-Haurwitz waves of a slowly and differentially rotating, fluid shell
apply also in General Relativity, at first order in the angular velocity.Comment: 4 pages. Comment to Class. Quantum Grav. 18(2001)L8
- …