6,721 research outputs found
Early Science with the Karoo Array Telescope: a Mini-Halo Candidate in Galaxy Cluster Abell 3667
Abell 3667 is among the most well-studied galaxy clusters in the Southern
Hemisphere. It is known to host two giant radio relics and a head-tail radio
galaxy as the brightest cluster galaxy. Recent work has suggested the
additional presence of a bridge of diffuse synchrotron emission connecting the
North-Western radio relic with the cluster centre. In this work, we present
full-polarization observations of Abell 3667 conducted with the Karoo Array
Telescope at 1.33 and 1.82 GHz. Our results show both radio relics as well as
the brightest cluster galaxy. We use ancillary higher-resolution data to
subtract the emission from this galaxy, revealing a localised excess, which we
tentatively identify as a radio mini-halo. This mini-halo candidate has an
integrated flux density of mJy beam at 1.37 GHz,
corresponding to a radio power of P
W Hz, consistent with established trends in mini-halo power scaling.Comment: 17 pages, 10 figures, accepted MNRA
An Analysis of the Decay with Predictions from Heavy Quark and Chiral Symmetry
This paper considers the implications of the heavy quark and chiral
symmetries for the semi-leptonic decay . The general kinematic analysis for decays of the form {\sl
pseudoscalar meson vector meson pseudoscalar meson lepton
anti-lepton} is presented. This formalism is applied to the above exclusive
decay which allows the differential decay rate to be expressed in a form that
is ideally suited for the experimental determination of the different form
factors for the process through angular distribution measurements. Heavy quark
and chiral symmetry predictions for the form factors are presented, and the
differential decay rate is calculated in the kinematic region where chiral
perturbation theory is valid.Comment: 15 pages, uses jytex.tex and tables.tex; 3 figures not included but
available on reques
Realization of a semiconductor-based cavity soliton laser
The realization of a cavity soliton laser using a vertical-cavity
surface-emitting semiconductor gain structure coupled to an external cavity
with a frequency-selective element is reported. All-optical control of bistable
solitonic emission states representing small microlasers is demonstrated by
injection of an external beam. The control scheme is phase-insensitive and
hence expected to be robust for all-optical processing applications. The
motility of these structures is also demonstrated
Remark on Charm Quark Fragmentation to Mesons
The observed mesons have flavor quantum numbers and
spin-parity of the light degrees of freedom . In
the limit the spin of the charm quark is conserved and
the fragmentation process is characterized by the
probability for the charm quark to fragment to a meson with a given
helicity for the light degrees of freedom. We consider the calculated fragmentation functions in the limit as a qualitative model for the fragmentation
functions. We find that in this model charm quark fragmentation to
light degrees of freedom with helicities is favored over fragmentation to light
degrees of freedom with helicities .Comment: 6 pages, CALT-68-192
The Decay in the Context of Chiral Perturbation Theory
We study the decay , using
chiral perturbation theory for heavy charmed mesons
and vector mesons, in the kinematic regime where (here or ) is much smaller than the chiral symmetry breaking
scale, ( 1 GeV). We present the
leading diagrams and amplitude, and calculate the rate, in the region where, to
leading order in our calculations, the is at zero recoil in the
rest frame. The rate thus calculated is given in terms of a known form
factor and depends on the coupling constant of the heavy
(charmed) meson chiral perturbation theory Lagrangian. A measurement of the
above decay, in the aforementioned kinematic regime, can result in the
extraction of an experimental value for , accurate at the level of our
approximations, and give us a measure of the validity of approaches based on
chiral perturbation theory in studying similar processes.Comment: 17 pages, Latex, 2 embedded postscript figure
A Deep Chandra Observation of the AGN Outburst and Merger in Hickson Compact Group 62
We report on an analysis of new Chandra data of the galaxy group HCG 62, well
known for possessing cavities in its intragroup medium (IGM) that were inflated
by the radio lobes of its central active galactic nucleus (AGN). With the new
data, a factor of three deeper than previous Chandra data, we re-examine the
energetics of the cavities and determine new constraints on their contents. We
confirm that the ratio of radiative to mechanical power of the AGN outburst
that created the cavities is less than 10^-4, among the lowest of any known
cavity system, implying that the relativistic electrons in the lobes can supply
only a tiny fraction of the pressure required to support the cavities. This
finding implies additional pressure support in the lobes from heavy particles
(e.g., protons) or thermal gas. Using spectral fits to emission in the
cavities, we constrain any such volume-filling thermal gas to have a
temperature kT > 4.3 keV. For the first time, we detect X-ray emission from the
central AGN, with a luminosity of L(2-10 keV) = (1.1 +/- 0.4) x 10^39 erg s^-1
and properties typical of a low-luminosity AGN. Lastly, we report evidence for
a recent merger from the surface brightness, temperature, and metallicity
structure of the IGM.Comment: Accepted to MNRAS, 14 pages, 9 figure
First direct observation of the Van Hove singularity in the tunneling spectra of cuprates
In two-dimensional lattices the electronic levels are unevenly spaced, and
the density of states (DOS) displays a logarithmic divergence known as the Van
Hove singularity (VHS). This is the case in particular for the layered cuprate
superconductors. The scanning tunneling microscope (STM) probes the DOS, and is
therefore the ideal tool to observe the VHS. No STM study of cuprate
superconductors has reported such an observation so far giving rise to a debate
about the possibility of observing directly the normal state DOS in the
tunneling spectra. In this study, we show for the first time that the VHS is
unambiguously observed in STM measurements performed on the cuprate Bi-2201.
Beside closing the debate, our analysis proves the presence of the pseudogap in
the overdoped side of the phase diagram of Bi-2201 and discredits the scenario
of the pseudogap phase crossing the superconducting dome.Comment: 4 pages, 4 figure
- …