336 research outputs found
Complex structures in galaxy cluster fields: implications for gravitational lensing mass models
The distribution of mass on galaxy cluster scales is an important test of
structure formation scenarios, providing constraints on the nature of dark
matter itself. Several techniques have been used to probe the mass
distributions of clusters, sometimes yielding results which are discrepant, or
at odds with clusters formed in simulations - for example giving NFW
concentration parameters much higher than expected in the standard CDM model.
In addition, the velocity fields of some well studied galaxy clusters reveal
the presence of several structures close to the line-of-sight, often not
dynamically bound to the cluster itself. We investigate what impact such
neighbouring but unbound massive structures would have on the determination of
cluster profiles using weak gravitational lensing. Depending on its
concentration and mass ratio to the primary halo, one secondary halo close to
the line-of-sight can cause the estimated NFW concentration parameter to be
significantly higher than that of the primary halo, and also cause the
estimated mass to be biased high. Although it is difficult to envisage how this
mechanism alone could yield concentrations as high as reported for some
clusters, multiple haloes close to the line-of-sight, such as in the case of
Abell 1689, can substantially increase the concentration parameter estimate.
Together with the fact that clusters are triaxial, and that including baryonic
physics also leads to an increase in the concentration of a dark matter halo,
the tension between observations and the standard CDM model is eased. If the
alignment with the secondary structure is imprecise, then the estimated
concentration parameter can also be even lower than that of the primary halo,
reinforcing the importance of identifying structures in cluster fields.Comment: To appear in MNRAS letters, 5 pages, 3 figure
Renorm-group, Causality and Non-power Perturbation Expansion in QFT
The structure of the QFT expansion is studied in the framework of a new
"Invariant analytic" version of the perturbative QCD. Here, an invariant
(running) coupling is transformed
into a "--analytized" invariant coupling which, by constuction, is free of ghost singularities due to
incorporating some nonperturbative structures.
Meanwhile, the "analytized" perturbation expansion for an observable , in
contrast with the usual case, may contain specific functions , the "n-th power of analytized as a whole", instead
of . In other words, the pertubation series for , due to
analyticity imperative, may change its form turning into an {\it asymptotic
expansion \`a la Erd\'elyi over a nonpower set} .
We analyse sets of functions and discuss properties of
non-power expansion arising with their relations to feeble loop and scheme
dependence of observables.
The issue of ambiguity of the invariant analytization procedure and of
possible inconsistency of some of its versions with the RG structure is also
discussed.Comment: 12 pages, LaTeX To appear in Teor. Mat. Fizika 119 (1999) No.
On the infrared freezing of perturbative QCD in the Minkowskian region
The infrared freezing of observables is known to hold at fixed orders of
perturbative QCD if the Minkowskian quantities are defined through the analytic
continuation from the Euclidean region. In a recent paper [1] it is claimed
that infrared freezing can be proved also for Borel resummed all-orders
quantities in perturbative QCD. In the present paper we obtain the Minkowskian
quantities by the analytic continuation of the all-orders Euclidean amplitudes
expressed in terms of the inverse Mellin transform of the corresponding Borel
functions [2]. Our result shows that if the principle of analytic continuation
is preserved in Borel-type resummations, the Minkowskian quantities exhibit a
divergent increase in the infrared regime, which contradicts the claim made in
[1]. We discuss the arguments given in [1] and show that the special
redefinition of Borel summation at low energies adopted there does not
reproduce the lowest order result obtained by analytic continuation.Comment: 19 pages, 1 figur
A novel series solution to the renormalization group equation in QCD
Recently, the QCD renormalization group (RG) equation at higher orders in
MS-like renormalization schemes has been solved for the running coupling as a
series expansion in powers of the exact 2-loop order coupling. In this work, we
prove that the power series converges to all orders in perturbation theory.
Solving the RG equation at higher orders, we determine the running coupling as
an implicit function of the 2-loop order running coupling. Then we analyze the
singularity structure of the higher order coupling in the complex 2-loop
coupling plane. This enables us to calculate the radii of convergence of the
series solutions at the 3- and 4-loop orders as a function of the number of
quark flavours . In parallel, we discuss in some detail the
singularity structure of the coupling at the 3- and 4-loops in
the complex momentum squared plane for . The
correspondence between the singularity structure of the running coupling in the
complex momentum squared plane and the convergence radius of the series
solution is established. For sufficiently large values, we find
that the series converges for all values of the momentum squared variable
. For lower values of , in the scheme,
we determine the minimal value of the momentum squared above
which the series converges. We study properties of the non-power series
corresponding to the presented power series solution in the QCD Analytic
Perturbation Theory approach of Shirkov and Solovtsov. The Euclidean and
Minkowskian versions of the non-power series are found to be uniformly
convergent over whole ranges of the corresponding momentum squared variables.Comment: 29 pages,LateX file, uses IOP LateX class file, 2 figures, 13 Tables.
Formulas (4)-(7) and Table 1 were relegated to Appendix 1, some notations
changed, 2 footnotes added. Clarifying discussion added at the end of Sect.
3, more references and acknowledgments added. Accepted for publication in
Few-Body System
Vacuum polarization of massive scalar fields in the spacetime of the electrically charged nonlinear black hole
The approximate renormalized stress-energy tensor of the quantized massive
conformally coupled scalar field in the spacetime of electrically charged
nonlinear black hole is constructed. It is achieved by functional
differentiation of the lowest order of the DeWitt-Schwinger effective action
involving coincidence limit of the Hadamard-Minakshisundaram-DeWitt-Seely
coefficient The result is compared with the analogous result derived
for the Reissner-Nordstr\"om black hole. It is shown that the most important
differences occur in the vicinity of the event horizon of the black hole near
the extremality limit. The structure of the nonlinear black hole is briefly
studied by means of the Lambert functions.Comment: 22 pages, 10 figure
Bubble Growth in Superfluid 3-He: The Dynamics of the Curved A-B Interface
We study the hydrodynamics of the A-B interface with finite curvature. The
interface tension is shown to enhance both the transition velocity and the
amplitudes of second sound. In addition, the magnetic signals emitted by the
growing bubble are calculated, and the interaction between many growing bubbles
is considered.Comment: 20 pages, 3 figures, LaTeX, ITP-UH 11/9
The Hubble constant from galaxy lenses: impacts of triaxiality and model degeneracies
The Hubble constant can be constrained using the time delays between multiple
images of gravitationally lensed sources. In some notable cases, typical
lensing analyses assuming isothermal galaxy density profiles produce low values
for the Hubble constant, inconsistent with the result of the HST Key Project
(72 +- 8 km/s/Mpc). Possible systematics in the values of the Hubble constant
derived from galaxy lensing systems can result from a number of factors, e.g.
neglect of environmental effects, assumption of isothermality, or contamination
by line-of-sight structures. One additional potentially important factor is the
triaxial structure of the lensing galaxy halo; most lens models account for
halo shape simply by perturbing the projected spherical lensing potential, an
approximation that is often necessary but that is inadequate at the levels of
triaxiality predicted in the CDM paradigm. To quantify the potential error
introduced by this assumption in estimates of the Hubble parameter, we strongly
lens a distant galaxy through a sample of triaxial softened isothermal halos
and use an MCMC method to constrain the lensing halo profile and the Hubble
parameter from the resulting multiple image systems. We explore the major
degeneracies between the Hubble parameter and several parameters of the lensing
model, finding that without a way to accurately break these degeneracies
accurate estimates of the Hubble parameter are not possible. Crucially, we find
that triaxiality does not significantly bias estimates of the Hubble constant,
and offer an analytic explanation for this behaviour in the case of isothermal
profiles. Neglected triaxial halo shape cannot contribute to the low Hubble
constant values derived in a number of galaxy lens systems.Comment: Minor revisions to match version published in MNRAS. 13 pages, 11
figure
Real world challenges in delivering person centred care: A community based case study
Community nurses face many challenges when trying to practice evidence-based, person-centred care. Ongoing concerns regarding the impact of the 2013 Francis Report (Ford and Lintern, 2017) suggest that individualised and holistic care is an impossible dream, one made harder when the client appears uncooperative. This paper presents a case study that sets out how some of these challenges were met in a potentially difficult situation experienced by a student nurse and her mentor in practice, in which the student was supported to further examine and explore issues that may have influenced the situation. In this instance, the solution came with the recognition that the client had expertise and knowledge that needed to be taken into account, alongside that of the nurses looking after him. His care became a partnership, not an imposition of expertise; a principle which is transferable to many other situations. Underpinning it was the recognition of our shared humanity, wherein lies the essence of truly holistic care, and student nurses learning this, through the guidance and support of their mentor.
Minimum Length Cutoff in Inflation and Uniqueness of the Action
According to most inflationary models, fluctuations that are of cosmological
size today started out much smaller than any plausible cutoff length such as
the string or Planck lengths. It has been shown that this could open an
experimental window for testing models of the short-scale structure of
space-time. The observability of effects hinges crucially, however, on the
initial conditions imposed on the new comoving modes which are continually
being created at the cutoff length scale. Here, we address this question while
modelling spacetime as obeying the string and quantum gravity inspired minimum
length uncertainty principle. We find that the usual strategy for determining
the initial conditions faces an unexpected difficulty because it involves
reformulating the action and discarding a boundary term: we find that actions
that normally differ merely by a boundary term can differ significantly when
the minimum length is introduced. This is possible because the introduction of
a minimum length comes with an ordering ambiguity much like the ordering
ambiguity that arises with the introduction of hbar in the process of
quantization.Comment: 18 pages, 1 figur
Registration and analysis of multispectral images acquired during uterine transplantation surgery
Organ transplant success is dependent on blood supply health. A multispectral imaging laparoscope has been used to monitor tissue oxygenation changes during a rabbit uterine transplant. A feature tracking algorithm was used to compensate for movement. © OSA 2012
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