9,364 research outputs found
Role of resonances in rho^0 -> pi^+ pi^- gamma
We study the effect of the sigma(600) and a_1(1260) resonances in the rho^0
-> pi^+ pi^- gamma decay, within the meson dominance model. Major effects are
driven by the mass and width parameters of the sigma(600), and the usually
neglected contribution of the a_1(1260), although small by itself, may become
sizable through its interference with pion bremsstrahlung, and the proper
relative sign can favor the central value of the experimental branching ratio.
We present a procedure, using the gauge invariant structure of the resonant
amplitudes, to kinematically enhance the resonant effects in the angular and
energy distribution of the photon. We also elaborate on the coupling constants
involved.Comment: 5 pages, 5 figures, accepted for publication in PR
Swift observations of the 2015 outburst of AG Peg -- from slow nova to classical symbiotic outburst
Symbiotic stars often contain white dwarfs with quasi-steady shell burning on
their surfaces. However, in most symbiotics, the origin of this burning is
unclear. In symbiotic slow novae, however, it is linked to a past thermonuclear
runaway. In June 2015, the symbiotic slow nova AG Peg was seen in only its
second optical outburst since 1850. This recent outburst was of much shorter
duration and lower amplitude than the earlier eruption, and it contained
multiple peaks -- like outbursts in classical symbiotic stars such as Z And. We
report Swift X-ray and UV observations of AG Peg made between June 2015 and
January 2016. The X-ray flux was markedly variable on a time scale of days,
particularly during four days near optical maximum, when the X-rays became
bright and soft. This strong X-ray variability continued for another month,
after which the X-rays hardened as the optical flux declined. The UV flux was
high throughout the outburst, consistent with quasi-steady shell burning on the
white dwarf. Given that accretion disks around white dwarfs with shell burning
do not generally produce detectable X-rays (due to Compton-cooling of the
boundary layer), the X-rays probably originated via shocks in the ejecta. As
the X-ray photo-electric absorption did not vary significantly, the X-ray
variability may directly link to the properties of the shocked material. AG
Peg's transition from a slow symbiotic nova (which drove the 1850 outburst) to
a classical symbiotic star suggests that shell burning in at least some
symbiotic stars is residual burning from prior novae.Comment: Accepted by MNRAS 23 June 2016. Manuscript submitted in original form
5 April 201
Symbiotic stars in X-rays III: Suzaku observations
We describe the X-ray emission as observed with Suzaku from five symbiotic
stars that we selected for deep Suzaku observations after their initial
detection with ROSAT, ASCA and Swift. We find that the X-ray spectra of all
five sources can be adequately fit with absorbed, optically thin thermal plasma
models, with either single- or multi-temperature plasmas. These models are
compatible with the X-ray emission originating in the boundary layer between an
accretion disk and a white dwarf. The high plasma temperatures of kT keV
for all five targets were greater than expected for colliding winds. Based on
these high temperatures, as well as previous measurements of UV variability and
UV luminosity, and the large amplitude of X-ray flickering in 4 Dra, we
conclude that all five sources are accretion-powered through predominantly
optically thick boundary layers. Our X-ray data allow us to observe a small,
optically thin portion of the emission from these boundary layers. Given the
time between previous observations and these observations, we find that the
intrinsic X-ray flux and the intervening absorbing column can vary by factors
of three or more on a time scale of years. However, the location of the
absorber and the relationship between changes in accretion rate and absorption
are still elusive.Comment: 14 pages, 3 figures and 3 tables. Accepted to published 04/15/2016.
arXiv admin note: substantial text overlap with arXiv:1505.0063
Periodic Chaotic Billiards: Quantum-Classical Correspondence in Energy Space
We investigate the properties of eigenstates and local density of states
(LDOS) for a periodic 2D rippled billiard, focusing on their quantum-classical
correspondence in energy representation. To construct the classical
counterparts of LDOS and the structure of eigenstates (SES), the effects of the
boundary are first incorporated (via a canonical transformation) into an
effective potential, rendering the one-particle motion in the 2D rippled
billiard equivalent to that of two-interacting particles in 1D geometry. We
show that classical counterparts of SES and LDOS in the case of strong chaotic
motion reveal quite a good correspondence with the quantum quantities. We also
show that the main features of the SES and LDOS can be explained in terms of
the underlying classical dynamics, in particular of certain periodic orbits. On
the other hand, statistical properties of eigenstates and LDOS turn out to be
different from those prescribed by random matrix theory. We discuss the quantum
effects responsible for the non-ergodic character of the eigenstates and
individual LDOS that seem to be generic for this type of billiards with a large
number of transverse channels.Comment: 13 pages, 18 figure
X-ray and UV emission from the recurrent nova RS Ophiuchi in quiescence: Signatures of accretion and shocked gas
RS Ophiuchi is a recurrent nova system that experiences outbursts every ~20
years, implying accretion at a high rate onto a massive white dwarf. However,
previous X-ray observations of the system in quiescence have detected only
faint emission that is difficult to reconcile with the high accretion rate
predicted by nova theory for such frequent outbursts. Here, we use new Chandra
and XMM-Newton observations obtained 537 and 744 days after the 2006 outburst
to constrain both the accretion rate onto the white dwarf and the properties of
the nova ejecta at these times. We detect low level UV variability with the
XMM-Newton Optical Monitor on day 744 that is consistent with accretion disk
flickering, and use this to place a lower limit on the accretion rate. The
X-ray spectra in both observations are well described by a two component
thermal plasma model. The first component originates in the nova shell, which
can emit X-rays for up to a decade after the outburst. The other component
likely arises in the accretion disk boundary layer, and can be equally well fit
by a single temperature plasma or a cooling flow model. Although the flux of
the single temperature model implies an accretion rate that is 40 times lower
than theoretical predictions for RS Oph, the best fit cooling flow model
implies Mdot < 1.2x10^-8 M_sol/yr 537 days after the outburst, which is within
a factor of 2 of the theoretical accretion rate required to power an outburst
every 20 years. Furthermore, we place an upper limit on the accretion rate
through an optically thick region of the boundary layer of 2.0x10^-8 M_sol/yr.
Thus, the X-ray emission in quiescence is consistent with the accretion rate
expectations of nova theory. Finally, we discuss the possible origins of the
low temperature associated with the accretion component, which is a factor of
10 lower than in T CrB, an otherwise similar recurrent nova.Comment: 16 pages, 6 figures, accepted for publication in Ap
Chaotic Waveguide-Based Resonators for Microlasers
We propose the construction of highly directional emission microlasers using
two-dimensional high-index semiconductor waveguides as {\it open} resonators.
The prototype waveguide is formed by two collinear leads connected to a cavity
of certain shape. The proposed lasing mechanism requires that the shape of the
cavity yield mixed chaotic ray dynamics so as to have the appropiate (phase
space) resonance islands. These islands allow, via Heisenberg's uncertainty
principle, the appearance of quasi bound states (QBS) which, in turn,
propitiate the lasing mechanism. The energy values of the QBS are found through
the solution of the Helmholtz equation. We use classical ray dynamics to
predict the direction and intensity of the lasing produced by such open
resonators for typical values of the index of refraction.Comment: 5 pages, 5 figure
Effect of electroacupuncture (EA) on gastrointestinal peristaltism in dogs
The article has no abstract
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