14,725 research outputs found
Evaluating `elliptic' master integrals at special kinematic values: using differential equations and their solutions via expansions near singular points
This is a sequel of our previous paper where we described an algorithm to
find a solution of differential equations for master integrals in the form of
an -expansion series with numerical coefficients. The algorithm is
based on using generalized power series expansions near singular points of the
differential system, solving difference equations for the corresponding
coefficients in these expansions and using matching to connect series
expansions at two neighboring points. Here we use our algorithm and the
corresponding code for our example of four-loop generalized sunset diagrams
with three massive and two massless propagators, in order to obtain new
analytical results. We analytically evaluate the master integrals at threshold,
, in an expansion in up to . With the help of
our code, we obtain numerical results for the threshold master integrals in an
-expansion with the accuracy of 6000 digits and then use the PSLQ
algorithm to arrive at analytical values. Our basis of constants is build from
bases of multiple polylogarithm values at sixth roots of unity.Comment: Discussion extende
Four-loop quark form factor with quartic fundamental colour factor
We analytically compute the four-loop QCD corrections for the colour
structure to the massless non-singlet quark form factor. The
computation involves non-trivial non-planar integral families which have master
integrals in the top sector. We compute the master integrals by introducing a
second mass scale and solving differential equations with respect to the ratio
of the two scales. We present details of our calculational procedure.
Analytical results for the cusp and collinear anomalous dimensions, and the
finite part of the form factor are presented. We also provide analytic results
for all master integrals expanded up to weight eight.Comment: 16 pages, 2 figure
Three-loop massive form factors: complete light-fermion and large- corrections for vector, axial-vector, scalar and pseudo-scalar currents
We compute the three-loop QCD corrections to the massive quark form factors
with external vector, axial-vector, scalar and pseudo-scalar currents. All
corrections with closed loops of massless fermions are included. The
non-fermionic part is computed in the large- limit, where only planar
Feynman diagrams contribute.Comment: 33 page
Core formation on Mars and differentiated asteroids
Meteorite chronometry based on the Hf-182-W-182 system can provide powerful constraints on the timing of planetary accretion and differentiation(1-4), although the full potential of this method has yet to be realized. For example, no measurements have been made on the silicate-rich portions of planets and planetesimals other than the Earth and Moon. Here we report tungsten isotope compositions for two eucrites, thought to be derived from asteroid 4 Vesta, and from eight other basaltic achondritic meteorites that are widely considered to be from Mars. The eucrites, which are among the oldest differentiated meteorites, yield exceedingly radiogenic tungsten, indicating rapid accretion, differentiation and core formation on Vesta within the first 5-15 Myr of Solar System history, whereas the range of radiogenic tungsten measurements on the martian meteorites points towards tungsten depletion via melting and core formation within the first 30 Myr of the Solar System. The survival of tungsten isotope heterogeneity in the martian upper mantle implies that no giant impacts or large-scale convective mixing took place since this time, These results contrast with those obtained for the Earth-Moon system(2,3) for which accretion and core formation related to giant impacts appears to have continued for at least an additional 20 Myr.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62720/1/388854a0.pd
Behavioral interventions for asthma self-management in South Asian populations: a systematic review
Objective: Asthma outcomes are significantly worse for minority groups, including South Asians (SAs), in high-income settings. Despite this, comparatively few existing studies have focused on SAs when studying the effectiveness of behavioral interventions on asthma self-management, and no prior study has synthesized these findings. We review the effectiveness of behavioral interventions on asthma management in adults and children of SA origin across low- (LICs), middle- (MICs), and high-income countries (HICs). //
Methods: Data sources included EMBASE, MEDLINE, Cochrane Library and Trial registries: WHO, ICTRP and ClinicalTrials.gov. Eligibility criteria: randomized controlled trials (RCTs), quasi-RCTs and non-RCTs (controlled before-after [CBA] studies), published in English, with no publication year or country restrictions in adults and children of South Asian origin. Exclusion criteria: those focusing solely on pharmacological interventions. Search terms were “asthma” and “South Asian”. //
Results: We included 33 studies, 27 from MICs and 6 from HICs (education [n = 10], self-management plans [n = 6], yoga/breathing exercises [n = 10]) organizational interventions [n =1], diet therapy [n = 1] and combined interventions [n = 5]). Outcome measures included: blood biochemistry, lung function, healthcare utilization and quality of life. A meta-analysis was not performed due to significant study heterogeneity. //
Conclusion: Behavioral interventions for asthma management in SAs are effective. Educational interventions that aim to optimize asthma knowledge, control, and inhaler technique, and yoga/breathing exercises are most effective for improved long-term outcomes in adults and children across LICs and MICs. Further research is needed to evaluate the effectiveness of all behavioral interventions for SAs in HICs to better inform current guidance by policy makers and health care providers
Inelastic scattering of photon pairs in qubit arrays with subradiant states
We develop a rigorous theoretical approach for analyzing inelastic scattering
of photon pairs in arrays of two-level qubits embedded in a waveguide. Our
analysis reveals strong enhancement of the scattering when the energy of
incoming photons resonates with the double-excited subradiant states. We
identify the role of different double-excited states in the scattering such as
superradiant, subradiant, and twilight states, being a product of
single-excitation bright and subradiant states. Importantly, the N-excitation
subradiant states can be engineered only if the number of qubits exceeds 2N.
Both the subradiant and twilight states can generate long-lived photon-photon
correlations, paving the way to a storage and processing of quantum
information
Pressure dependence of upper critical fields in FeSe single crystals
We investigate the pressure dependence of the upper critical fields
({\mu}) for FeSe single crystals with pressure up to 2.57 GPa.
The superconducting (SC) properties show a disparate behavior across a critical
pressure where the pressure-induced antiferromagnetic phase coexists with
superconductivity. The magnetoresistance for and is very
different: for , magnetic field induces and enhances a hump in the
resistivity close to the for pressures higher than 1.2 GPa, while it is
absent for . Since the measured {\mu} for FeSe samples is
smaller than the orbital limited upper critical field ()
estimated by the Werthamer Helfand and Hohenberg (WHH) model, the Maki
parameter ({\alpha}) related to Pauli spin-paramagnetic effects is additionally
considered to describe the temperature dependence of {\mu}().
Interestingly, the {\alpha} value is hardly affected by pressure for ,
while it strongly increases with pressure for . The pressure evolution of
the {\mu}(0)s for the FeSe single crystals is found to be almost
similar to that of (), suggesting that the pressure-induced magnetic
order adversely affects the upper critical fields as well as the SC transition
temperature.Comment: 23 pages, 6 figures, 1 tabl
Dimensional recurrence relations: an easy way to evaluate higher orders of expansion in
Applications of a method recently suggested by one of the authors (R.L.) are
presented. This method is based on the use of dimensional recurrence relations
and analytic properties of Feynman integrals as functions of the parameter of
dimensional regularization, . The method was used to obtain analytical
expressions for two missing constants in the -expansion of the most
complicated master integrals contributing to the three-loop massless quark and
gluon form factors and thereby present the form factors in a completely
analytic form. To illustrate its power we present, at transcendentality weight
seven, the next order of the -expansion of one of the corresponding
most complicated master integrals. As a further application, we present three
previously unknown terms of the expansion in of the three-loop
non-planar massless propagator diagram. Only multiple values at integer
points are present in our result.Comment: Talk given at the International Workshop `Loops and Legs in Quantum
Field Theory' (April 25--30, 2010, W\"orlitz, Germany)
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