166 research outputs found
Spectropolarimetry of PKS 0040-005 and the Orientation of Broad Absorption Line Quasars
We have used the Very Large Telescope (VLT) to obtain spectropolarimetry of
the radio-loud, double-lobed broad absorption line (BAL) quasar PKS 0040-005.
We find that the optical continuum of PKS 0040-005 is intrinsically polarized
at 0.7% with an electric vector position angle nearly parallel to that of the
large-scale radio axis. This result is naturally explained in terms of an
equatorial scattering region seen at a small inclination, building a strong
case that the BAL outflow is not equatorial. In conjunction with other recent
results concerning radio-loud BAL quasars, the era of simply characterizing
these sources as ``edge-on'' is over.Comment: 5 Pages, including 2 PostScript figures. Accepted for publication in
MNRAS letter
Susceptibilities near the QCD (tri)critical point
Based on the proper-time renormalization group approach, the scalar and the
quark number susceptibilities in the vicinity of possible critical end points
of the hadronic phase diagram are investigated in the two-flavor quark-meson
model. After discussing the quark-mass dependence of the location of such
points, the critical behavior of the in-medium meson masses and quark number
density are calculated. The universality classes of the end points are
determined by calculating the critical exponents of the susceptibilities. In
order to numerically estimate the influence of fluctuations we compare all
quantities with results from a mean-field approximation. It is concluded that
the region in the phase diagram where the susceptibilities are enhanced is more
compressed around the critical end point if fluctuations are included.Comment: 14 pages, 19 figures; v3 typos and minor changes, references adde
Coupled Cluster Externally Corrected by Adaptive Configuration Interaction
An externally corrected coupled cluster (CC) method, where an adaptive
configuration interaction (ACI) wave function provides the external cluster
amplitudes, named ACI-CC, is presented. By exploiting the connection between
configuration interaction and coupled cluster through cluster analysis, the
higher-order T3 and T4 terms obtained from ACI are used to augment the T1 and
T2 amplitude equations from traditional coupled cluster. These higher-order
contributions are kept frozen during the coupled cluster iterations and do not
contribute to an increased cost with respect to CCSD. We have benchmarked this
method on three closed-shell systems: beryllium dimer, carbonyl oxide, and
cyclobutadiene, with good results compared to other corrected coupled cluster
methods. In all cases, the inclusion of these external corrections improved
upon the "gold standard" CCSD(T) results, indicating that ACI-CCSD(T) can be
used to assess strong correlation effects in a system and as an inexpensive
starting point for more complex external corrections
Lattice QCD without topology barriers
As the continuum limit is approached, lattice QCD simulations tend to get
trapped in the topological charge sectors of field space and may consequently
give biased results in practice. We propose to bypass this problem by imposing
open (Neumann) boundary conditions on the gauge field in the time direction.
The topological charge can then flow in and out of the lattice, while many
properties of the theory (the hadron spectrum, for example) are not affected.
Extensive simulations of the SU(3) gauge theory, using the HMC and the closely
related SMD algorithm, confirm the absence of topology barriers if these
boundary conditions are chosen. Moreover, the calculated autocorrelation times
are found to scale approximately like the square of the inverse lattice
spacing, thus supporting the conjecture that the HMC algorithm is in the
universality class of the Langevin equation.Comment: Plain TeX source, 26 pages, 4 figures include
Non-renormalizability of the HMC algorithm
In lattice field theory, renormalizable simulation algorithms are attractive,
because their scaling behaviour as a function of the lattice spacing is
predictable. Algorithms implementing the Langevin equation, for example, are
known to be renormalizable if the simulated theory is. In this paper we show
that the situation is different in the case of the molecular-dynamics evolution
on which the HMC algorithm is based. More precisely, studying the phi^4 theory,
we find that the hyperbolic character of the molecular-dynamics equations leads
to non-local (and thus non-removable) ultraviolet singularities already at
one-loop order of perturbation theory.Comment: Plain TeX source, 23 pages, 3 figures included; v2: typos corrected,
agrees with published versio
The Mid-Infrared Emission of M87
We discuss Subaru and Spitzer Space Telescope imaging and spectroscopy of M87
in the mid-infrared from 5-35 um. These observations allow us to investigate
mid-IR emission mechanisms in the core of M87 and to establish that the
flaring, variable jet component HST-1 is not a major contributor to the mid-IR
flux. The Spitzer data include a high signal-to-noise 15-35 m spectrum of
the knot A/B complex in the jet, which is consistent with synchrotron emission.
However, a synchrotron model cannot account for the observed {\it nuclear}
spectrum, even when contributions from the jet, necessary due to the degrading
of resolution with wavelength, are included. The Spitzer data show a clear
excess in the spectrum of the nucleus at wavelengths longer than 25 um, which
we model as thermal emission from cool dust at a characteristic temperature of
55 \pm 10 K, with an IR luminosity \sim 10^{39} {\rm ~erg ~s^{-1}}. Given
Spitzer's few-arcsecond angular resolution, the dust seen in the nuclear
spectrum could be located anywhere within ~5'' (390 pc) of the nucleus. In any
case, the ratio of AGN thermal to bolometric luminosity indicates that M87 does
not contain the IR-bright torus that classical unified AGN schemes invoke.
However, this result is consistent with theoretical predictions for
low-luminosity AGNsComment: 9 pages, 7 figures, ApJ, in pres
On the Convergence of the Expansion of Renormalization Group Flow Equation
We compare and discuss the dependence of a polynomial truncation of the
effective potential used to solve exact renormalization group flow equation for
a model with fermionic interaction (linear sigma model) with a grid solution.
The sensitivity of the results on the underlying cutoff function is discussed.
We explore the validity of the expansion method for second and first-order
phase transitions.Comment: 12 pages with 10 EPS figures included; revised versio
XMM-Newton Detection of the Rare FR II BAL Quasar FIRST J101614.3+520916
We have detected FIRST J101614.3+520916 with the XMM-Newton X-ray
Observatory. FIRST J101614.3+520916, one of the most extreme radio-loud, broad
absorption line (BAL) quasars so far discovered, is also a Fanaroff-Riley type
II (FR II) radio source. We find that, compared to its estimated intrinsic
X-ray flux, the observed X-rays are likely suppressed, and that the observed
hardness ratio indicates significant soft X-ray photons. This is inconsistent
with the simplest model, a normal quasar spectrum absorbed by a large neutral
HI column density, which would primarily absorb the softer photons. More
complex models, involving partial covering, an ionized absorber, ionized mirror
reflection, or jet contributions need to be invoked to explain this source. The
suppressed but soft X-ray emission in this radio-loud BAL quasar is consistent
with the behavior displayed by other BAL quasars, both radio-loud and
radio-quiet.Comment: 5 pages, 2 figures. Accepted in AJ. (Typos corrected.
XMM-Newton detection of the rare Fanaroff-Riley type II broad absorption line quasar first J101614.3+520916
We have detected FIRST J101614.3+520916 with the XMM-Newton X-ray observatory. FIRST J101614.3+520916, one of the most extreme radio-loud, broad absorption line (BAL) quasars so far discovered, is also a Fanaroff-Riley type II radio source. We find that, compared to its estimated intrinsic X-ray flux, the observed X-rays are likely suppressed and that the observed hardness ratio indicates significant soft X-ray photons. This is inconsistent with the simplest model, a normal quasar spectrum absorbed by a large neutral H I column density, which would primarily absorb the softer photons. More complex models, involving partial covering, an ionized absorber, ionized mirror reflection, or jet contributions need to be invoked to explain this source. The suppressed but soft X-ray emission in this radio-loud BAL quasar is consistent with the behavior displayed by other BAL quasars, both radio-loud and radio-quiet
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