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.
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
Odprti dostop
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.
samurai
is a tool for the automated numerical evaluation of one-loop corrections to any scattering amplitudes within the dimensional-regularization scheme. It is based on the decomposition of the ...integrand according to the OPP -approach, extended to accommodate an implementation of the generalized
d
-dimensional unitarity-cuts technique, and uses a polynomial interpolation exploiting the Discrete Fourier Transform.
samurai
can process integrands written either as numerator of Feynman diagrams or as product of tree-level amplitudes. We discuss some applications, among which the 6-and 8-photon scattering in QED, and the 6-quark scattering in QCD.
samurai
has been implemented as a
Fortran90
library, publicly available, and it could be a useful module for the systematic evaluation of the virtual corrections oriented towards automating next-to-leading order calculations relevant for the LHC phenomenology.
We present the first fully analytic evaluation of the transition amplitude for the scattering of a massless into a massive pair of fermions at the two-loop level in quantum electrodynamics. Our ...result is an essential ingredient for the determination of the electromagnetic coupling within scattering reactions, beyond the currently known accuracy, which has a crucial impact on the evaluation of the anomalous magnetic moment of the muon. It will allow, in particular, for a precise determination of the leading hadronic contribution to the (g-2)_{μ} in the MUonE experiment at CERN, and therefore can be used to shed light on the current discrepancy between the standard model prediction and the experimental measurement for this important physical observable.
In this paper, we provide new rigidity results for four-dimensional Riemannian manifolds and their twistor spaces. In particular, using the moving frame method, we prove that
C
P
3
is the only ...twistor space whose Bochner tensor is parallel; moreover, we classify Hermitian Ricci-parallel and locally symmetric twistor spaces and we show the nonexistence of conformally flat twistor spaces. We also generalize a result due to Atiyah, Hitchin and Singer concerning the self-duality of a Riemannian four-manifold.
Elaborating on the four-dimensional helicity scheme, we propose a pure four-dimensional formulation (FDF) of the
d
-dimensional regularization of one-loop scattering amplitudes. In our formulation ...particles propagating inside the loop are represented by massive internal states regulating the divergences. The latter obey Feynman rules containing multiplicative selection rules which automatically account for the effects of the extra-dimensional regulating terms of the amplitude. We present explicit representations of the polarization and helicity states of the four-dimensional particles propagating in the loop. They allow for a complete, four-dimensional, unitarity-based construction of
d
-dimensional amplitudes. Generalized unitarity within the FDF does not require any higher-dimensional extension of the Clifford and the spinor algebra. Finally we show how the FDF allows for the recursive construction of
d
-dimensional one-loop integrands, generalizing the four-dimensional open-loop approach.
We report on the calculation of the cross section for Higgs boson production in association with three jets via gluon fusion, at next-to-leading-order (NLO) accuracy in QCD, in the infinite top-mass ...approximation. After including the complete NLO QCD corrections, we observe a strong reduction in the scale dependence of the result, and an increased steepness in the transverse momentum distributions of both the Higgs boson and the leading jets. The results are obtained with the combined use of GOSAM, SHERPA, and the MADDIPOLE-MADEVENT framework.
We investigate the triviality of compact Ricci solitons under general scalar conditions involving the Weyl tensor. More precisely, we show that a compact Ricci soliton is Einstein if a generic linear ...combination of divergences of the Weyl tensor contracted with suitable covariant derivatives of the potential function vanishes. In particular, we recover and improve all known related results. This paper can be thought as a first, preliminary step in a general program which aims at showing that Ricci solitons can be classified finding a “generic”
k
,
s
-vanishing condition on the Weyl tensor, for every
k
,
s
∈
N
, where
k
is the order of the covariant derivatives of Weyl and
s
is the type of the (covariant) tensor involved.
We present the full NLO QCD corrections to the production of a W+W− pair in association with two jets in hadronic collisions, which is an important background to New Physics and Higgs boson searches. ...We include leptonic decays of the W-bosons with full spin correlations. We find NLO corrections of the order of 10% for standard cuts at the LHC. The scale dependence is considerably reduced by the NLO corrections.
PDF
