A
bstract
We present two novel results about the universal structure of radiative QED amplitudes in the soft and in the collinear limit. On the one hand, we extend the well-known Low-Burnett-Kroll ...theorem to the one-loop level and give the explicit relation between the radiative and non-radiative amplitude at subleading power in the soft limit. On the other hand, we consider a factorisation formula at leading power in the limit where the emitted photon becomes collinear to a light fermion and provide the corresponding one-loop splitting function. In addition to being interesting in their own right these findings are particularly relevant in the context of fully-differential higher-order QED calculations. One of the main challenges in this regard is the numerical stability of radiative contributions in the soft and collinear regions. The results presented here allow for a stabilisation of realvirtual amplitudes in these delicate phase-space regions by switching to the corresponding approximation without the need of explicit computations.
A subtraction scheme for massive QED Engel, T.; Signer, A.; Ulrich, Y.
The journal of high energy physics,
01/2020, Letnik:
2020, Številka:
1
Journal Article
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Odprti dostop
A
bstract
We present an extension of the FKS subtraction scheme beyond next-to-leading order to deal with soft singularities in fully differential calculations within QED with mas- sive fermions. ...After a detailed discussion of the next-to-next-to-leading order case, we show how to extend the scheme to even higher orders in perturbation theory. As an application we discuss the computation of the next-to-next-to-leading order QED corrections to the muon decay and present differential results with full electron mass dependence.
A
bstract
We present the heavy-to-light form factors with two different non-vanishing masses at next-to-next-to-leading order and study its expansion in the small mass. The leading term of this ...small-mass expansion leads to a factorized expression for the form factor. The presence of a second mass results in a new feature, in that the soft contribution develops a factorization anomaly. This cancels with the corresponding anomaly in the collinear contribution. With the generalized factorization presented here, it is possible to obtain the leading small-mass terms for processes with large masses, such as muon-electron scattering, from the corresponding massless amplitude and the soft contribution.
We give an introduction to several regularization schemes that deal with ultraviolet and infrared singularities appearing in higher-order computations in quantum field theories. Comparing the ...computation of simple quantities in the various schemes, we point out similarities and differences between them.
Using the automation program GoSam, fully differential NLO corrections were obtained for the rare decay of the muon μ→eνν¯ee. This process is an important Standard Model background to searches of the ...Mu3e Collaboration for lepton-flavor violation, as it becomes indistinguishable from the signal μ→3e if the neutrinos carry little energy. With our NLO program we are able to compute the branching ratio as well as custom-tailored observables for the experiment. With minor modifications, related decays of the tau can also be computed.
Muon-electron scattering at NNLO Broggio, A.; Engel, T.; Ferroglia, A. ...
The journal of high energy physics,
01/2023, Letnik:
2023, Številka:
1
Journal Article
Recenzirano
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A
bstract
We present the first calculation of the complete set of NNLO QED corrections for muon-electron scattering. This includes leptonic, non-perturbative hadronic, and photonic contributions. All ...fermionic corrections as well as the photonic subset that only corrects the electron or the muon line are included with full mass dependence. The genuine four-point two-loop topologies are computed as an expansion in the small electron mass, taking into account both, logarithmically enhanced as well as constant mass effects using massification. A fast and stable implementation of the numerically delicate real-virtual contribution is achieved by combining O
pen
L
oops
with next-to-soft stabilisation. All matrix elements are implemented in the M
c
M
ule
framework, which allows for the fully-differential calculation of any infrared-safe observable. This calculation is to be viewed in the context of the MUonE experiment requiring a background prediction at the level of 10 ppm. Our results thus represent a major milestone towards this ambitious precision goal.
We present a general purpose Monte Carlo program for the calculation of the radiative muon decay μ→eνν¯γ and the radiative decays τ→eνν¯γ and τ→μνν¯γ at next-to-leading order in the Fermi theory. The ...full dependence on the lepton masses and polarization of the initial-sate lepton are kept. We study the branching ratios for these processes and show that fully-differential next-to-leading order corrections are important for addressing a tension between BaBar's recent measurement of the branching ratio B(τ→eνν¯γ) and the Standard Model prediction. In addition, we study various distributions of the process μ→eνν¯γ and obtain precise predictions for the irreducible background to μ→eγ searches, tailored to the geometry of the MEG detector.
The initial fitness benefits of group living are considered to be the greatest hurdle to the evolution of sociality
, and evolutionary theory predicts that these benefits need to arise at very small ...group sizes
. Such benefits are thought to emerge partly from scaling effects that increase efficiency as group size increases
. In social insects and other taxa, the benefits of group living have been proposed to stem from division of labour
, which is characterized by between-individual variability and within-individual consistency (specialization) in task performance. However, at the onset of sociality groups were probably small and composed of similar individuals with potentially redundant-rather than complementary-function
. Self-organization theory suggests that division of labour can emerge even in relatively small, simple groups
. However, empirical data on the effects of group size on division of labour and on fitness remain equivocal
. Here we use long-term automated behavioural tracking in clonal ant colonies, combined with mathematical modelling, to show that increases in the size of social groups can generate division of labour among extremely similar workers, in groups as small as six individuals. These early effects on behaviour were associated with large increases in homeostasis-the maintenance of stable conditions in the colony
-and per capita fitness. Our model suggests that increases in homeostasis are primarily driven by increases in group size itself, and to a smaller extent by a higher division of labour. Our results indicate that division of labour, increased homeostasis and higher fitness can emerge naturally in social groups that are small and homogeneous, and that scaling effects associated with increasing group size can thus promote social cohesion at the incipient stages of group living.
Centrifugal "lab on a disk" microfluidics is a promising avenue for developing portable, low-cost, automated immunoassays. However, the necessity of incorporating multiple wash steps results in ...complicated designs that increase the time and sample/reagent volumes needed to run assays and raises the probability of errors. We present proof of principle for a disk-based microfluidic immunoassay technique that processes blood samples without conventional wash steps.
Microfluidic disks were fabricated from layers of patterned, double-sided tape and polymer sheets. Sample was mixed on-disk with assay capture beads and labeling antibodies. Following incubation, the assay beads were physically separated from the blood cells, plasma, and unbound label by centrifugation through a density medium. A signal-laden pellet formed at the periphery of the disk was analyzed to quantify concentration of the target analyte.
To demonstrate this technique, the inflammation biomarkers C-reactive protein and interleukin-6 were measured from spiked mouse plasma and human whole blood samples. On-disk processing (mixing, labeling, and separation) facilitated direct assays on 1-μL samples with a 15-min sample-to-answer time, <100 pmol/L limit of detection, and 10% CV. We also used a unique single-channel multiplexing technique based on the sedimentation rate of different size or density bead populations.
This portable microfluidic system is a promising method for rapid, inexpensive, and automated detection of multiple analytes directly from a drop of blood in a point-of-care setting.
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