Electromagnetic Radiative Corrections Research Articles

Effects of Electromagnetic Radiative Corrections in the Production of Lepton Pairs in Photon–Photon Fusion at LHC

Effects of Electromagnetic Radiative Corrections in the Production of Lepton Pairs in Photon–Photon Fusion at LHC

Complete theory of radiative corrections to Kℓ3 decays and the Vus update

We fill up the missing piece in our own re-analysis of the long-distance electromagnetic radiative corrections to semileptonic kaon decays by performing a rigorous study in the K → πμ+νμ(γ) channels. With appropriate experimental and lattice inputs, we achieve a precision level of 10−4 in these channels. This is comparable to our previous analysis in the K → πe+νe(γ) channels. With this new result, we present an updated global analysis to extract the Standard Model parameter |Vus| from semileptonic kaon decays. We obtain |Vus| = 0.22308(55) and 0.22356(73), using the lattice average of the K0→ π− transition form factor at Nf = 2 + 1 + 1 and Nf = 2 + 1, respectively.

Flavor-dependent radiative corrections in coherent elastic neutrino-nucleus scattering

We calculate coherent elastic neutrino-nucleus scattering cross sections on spin-0 nuclei (e.g. 40Ar and 28Si) at energies below 100 MeV within the Standard Model and account for all effects of permille size. We provide a complete error budget including uncertainties at nuclear, nucleon, hadronic, and quark levels separately as well as perturbative error. Our calculation starts from the four-fermion effective field theory to explicitly separate heavy-particle mediated corrections (which are absorbed by Wilson coefficients) from light-particle contributions. Electrons and muons running in loops introduce a non- trivial dependence on the momentum transfer due to their relatively light masses. These same loops, and those mediated by tau leptons, break the flavor universality because of mass-dependent electromagnetic radiative corrections. Nuclear physics uncertainties significantly cancel in flavor asymmetries resulting in subpercent relative errors. We find that for low neutrino energies, the cross section can be predicted with a relative precision that is competitive with neutrino-electron scattering. We highlight potentially useful applications of such a precise cross section prediction ranging from precision tests of the Standard Model, to searches for new physics and to the monitoring of nuclear reactors.

Final-State Two-Loop Radiative Corrections to the Drell-Yan Process at the LHC in the Soft-Photon Approximation

In the soft-photon approximation, compact expressions for two-loop final-state electromagnetic radiative corrections to the four-fermion process in the s channel are obtained on the basis of the on-shell renormalization scheme. As applied to the Drell—Yan process, an efficient procedure for numerically estimating final-state radiative effects is proposed for experiments at the LHC for high invariant masses.

Soft-photon corrections to the Bethe-Heitler process in the γp→l+l−p reaction

We report on the calculation of first-order QED corrections for the $\gamma p\rightarrow l^+l^-p^{\prime}$ process. An upcoming experiment at MAMI (Mainz) aims to compare the cross sections of muon- and electron-pair production in this reaction to test lepton universality. Precise knowledge of the electromagnetic radiative corrections is needed for these measurements. As a first step, we present the leading QED radiative corrections in the soft-photon approximation when accounting for the finite lepton mass. For the kinematics at MAMI, we find corrections of the percent level for muons, and of order $10\%$ for electrons.

Decays of neutral pions: Electromagnetic transition form factor and radiative corrections

We briefly summarize experimental and theoretical results on the rare decay π 0 → e + e − . The notorious 3.3σ discrepancy between the Standard Model prediction and the experimental value provided by KTeV collaboration is discussed in the view of a complete set of next-to-leading-order QED radiative corrections. We also present the Two-Hadron Saturation (THS) scenario for the PVV correlator and apply it to the decay under discussion. The discrepancy under discussion then reduces down to 1.8σ. Finally, we turn our attention the the Dalitz decay π 0 → e + e − γ . We have recalculated the Mikaelian and Smith radiative corrections beyond the soft-photon approximation, i.e. over the whole range of the Dalitz plot and with no restrictions on the radiative photon. In contrast to the previous calculations, we also included the one-photon irreducible contribution at one-loop level. Our results can be also used for a further treatment of the processes with heavier particles in the final state.

Electromagnetic corrections to B― → V0 semileptonic transitions

We evaluate the O(α) electromagnetic radiative corrections to the B― → V0ℓ- v̄ℓ (V is a vector meson and ℓ = e, μ decay rates. Intermediate resonance states in the real- photon amplitude are considered in order to extend the region of validity of the soft-photon approximation. The virtual corrections are regularized by the cutoff scale Λ, which is used to match the long- and short-distance regimes. The radiative corrections to the integrated decay rate are presented and we discuss its impact in the precise determination of the b quark mixing parameters.

Radiative corrections of $$O(\alpha )$$ O ( α ) to $$B^{-} \rightarrow V^{0} \ell ^{-} \bar{\nu }_{\ell }$$ B - → V 0 ℓ - ν ¯ ℓ decays

The $O(\alpha)$ electromagnetic radiative corrections to the $B^- \rightarrow V^0 \ell^- \bar{\nu}_{\ell}$ ($V$ is a vector meson and $\ell$ a charged lepton) decay rates are evaluated using the cutoff method to regularize virtual corrections and incorporating intermediate resonance states in the real-photon amplitude to extend the region of validity of the soft-photon approximation. The electromagnetic and weak form factors of hadrons are assumed to vary smoothly over the energies of virtual and real photons under consideration. The cutoff dependence of radiative corrections upon the scale $\Lambda$ that separates the long- and short-distance regimes is found to be mild and is considered as an uncertainty of the calculation. Owing to partial cancellations of electromagnetic corrections evaluated over the three- and four-body regions of phase space, the photon-inclusive corrected rates are found to be dominated by the short-distance contribution. These corrections will be relevant for a precise determination of the $b$ quark mixing angles by testing isospin symmetry when measurements of semileptonic rates of charged and neutral $B$ mesons at the few percent level become available. For completeness, we also provide numerical values of radiative corrections in the three-body region of the Dalitz plot distributions of these decays.

Electromagnetic transition form factor and radiative corrections in decays of neutral pions

We briefly summarize experimental and theoretical results on the rare decay π 0 → e + e − . The notorious 3.3σ discrepancy between the SM prediction and the experimental value provided by KTeV collaboration is discussed in the view of a complete set of NLO QED radiative corrections. We also present the Two-Hadron Saturation (THS) scenario for the PVV correlator and apply it to the decay under discussion. The discrepancy then reduces down to 1.8σ.

Yu. V. Novozhilov: Creative path

The scientific activity of Yu. V. Novozhilov started under the influence of two outstanding physicists of that time: Corresponding Member of the Academy Ya. I. Frenkel and Academician V. A. Fock. From these two leading scientists, so different from each other, Novozhilov inherited a devotion to science, a taste for research at the frontier, a true understanding of the relevance of the studied questions, and a rigorous mathematical approach combined with physical intuition. The initial stage of Novozhilov’s scientific work coincided with the period of explosive development of quantum field theory and the theory of elementary particles in the 1940s and 1950s, with the creation of renormalization theory and relativistic scattering theory. The plenitude of new ideas and methods and the extremely rapid pace of research characteristic of that period determined Novozhilov’s direction and style of work. At this time, Novozhilov published papers on the functional method in quantum field theory. In them, he developed the theory of renormalization in the framework of Fock’s functional method and studied the problem of the variation of functionals in Fermi fields. The keen interest of Novozhilov in the functional method was somewhat ahead of its time: later, in the 1970s, this method became the base for analyzing gauge fields, which underlie the modern theory of fundamental interactions. The review paper “Functional method in quantum field theory” [1] by Novozhilov and A. V. Tulub, published as a separate book in the USA, was long the only handbook on the functional method and is still relevant today. In 1953, Novozhilov was awarded a first-degree university prize for the paper “Application of Fock’s functional method to the problem of self-energy” [2]. We briefly discuss this first paper by Novozhilov. In the abstract, he wrote: “Fock’s functional method is used to obtain the Dirac equation with electromagnetic mass and radiative corrections.” In the functional method, a state is described by an analytic functional Ω{α(x)} of the complex function α(x). The creation and annihilation operators a † (x )a nda(x) correspond to multiplication by α(x )a nd the functional derivative of that function. In application to the Dirac equation in quantum electrodynamics, we start from the equation for the state functional [ ˆ

Slavnov-Taylor and ward identities in the electroweak theory

In the framework of the Electroweak Theory we discuss a class of gauge fixing choices suitable for the calculation of electromagnetic processes. We show in particular that, with our choices, beyond the basic Slavnov-Taylor identities guaranteeing the independence of the physical results of the particular gauge fixing, one also has the standard QED Ward identities which play a well known crucial role in the calculation of electromagnetic processes and, in particular, in the analysis of the electromagnetic radiative corrections.

Electromagnetic Radiative Corrections in e/p Scattering for Q$_{\mathrm{weak}}$'s Measurement of a Parity-Violating Asymmetry in Elastic e/p Scattering

Electromagnetic Radiative Corrections in e/p Scattering for Q$_{\mathrm{weak}}$'s Measurement of a Parity-Violating Asymmetry in Elastic e/p Scattering

New Precision Limit on the Strange Vector Form Factors of the Proton

The parity-violating cross-section asymmetry in the elastic scattering of polarized electrons from unpolarized protons has been measured at a four-momentum transfer squared Q2 = 0.624 GeV2 and beam energy E(b) = 3.48 GeV to be A(PV) = -23.80 ± 0.78(stat) ± 0.36(syst) parts per million. This result is consistent with zero contribution of strange quarks to the combination of electric and magnetic form factors G(E)(s) + 0.517G(M)(s) = 0.003 ± 0.010(stat) ± 0.004(syst) ± 0.009(ff), where the third error is due to the limits of precision on the electromagnetic form factors and radiative corrections. With this measurement, the world data on strange contributions to nucleon form factors are seen to be consistent with zero and not more than a few percent of the proton form factors.

New positron spectral features from supersymmetric dark matter: A way to explain the PAMELA data?

The space-borne antimatter experiment PAMELA has recently reported a surprising rise in the positron to electron ratio at high energies. It has also recently been found that electromagnetic radiative corrections in some cases may boost the gamma-ray yield from supersymmetric dark-matter annihilations in the galactic halo by up to 3 or 4 orders of magnitude, providing distinct spectral signatures for indirect dark matter searches to look for. Here, we investigate whether the same type of corrections can also lead to sizeable enhancements in the positron yield. We find that this is indeed the case, albeit for a smaller region of parameter space than for gamma rays; selecting models with a small mass difference between the neutralino and sleptons, like in the stau-coannihilation region in mSUGRA, the effect becomes more pronounced. The resulting, rather hard positron spectrum with a relatively sharp cutoff may potentially fit the rising positron ratio measured by the PAMELA satellite. To do so, however, very large ``boost factors'' have to be invoked that are not expected in current models of halo structure. If the predicted cutoff would also be confirmed by later PAMELA data or upcoming experiments, one could either assume nonthermal production in the early universe or nonstandard halo formation to explain such a spectral feature as an effect of dark-matter annihilation. At the end of the paper, we briefly comment on the impact of radiative corrections on other annihilation channels, in particular, antiprotons and neutrinos.

Structure-dependent radiative corrections toϕ→K+K−/KLKSdecays

Current predictions for the ratio of $\ensuremath{\phi}\ensuremath{\rightarrow}{K}^{+}{K}^{\ensuremath{-}}/{K}_{L}{K}_{S}$ decay rates exceed the corresponding experimental value in about 5 standard deviations. By far, the dominant sources of isospin breaking to this ratio are the phase-space (52%) and the electromagnetic radiative (4.3%, computed within scalar QED) corrections. Here we estimate the effects of the electromagnetic structure of kaons and other model-dependent contributions into the radiative corrections.

New gamma-ray contributions to supersymmetric dark matter annihilation

We compute the electromagnetic radiative corrections to all leading annihilation processes which may occur in the Galactic dark matter halo, for dark matter in the framework of supersymmetric extensions of the Standard Model (MSSM and mSUGRA), and present the results of scans over the parameter space that is consistent with present observational bounds on the dark matter density of the Universe. Although these processes have previously been considered in some special cases by various authors, our new general analysis shows novel interesting results with large corrections that may be of importance, e.g., for searches at the soon to be launched GLAST gamma-ray space telescope. In particular, it is pointed out that regions of parameter space where there is a near degeneracy between the dark matter neutralino and the tau sleptons, radiative corrections may boost the gamma-ray yield by up to three or four orders of magnitude, even for neutralino masses considerably below the TeV scale, and will enhance the very characteristic signature of dark matter annihilations, namely a sharp step at the mass of the dark matter particle. Since this is a particularly interesting region for more constrained mSUGRA models of supersymmetry, we use an extensive scan over this parameter space to verify the significance of our findings. We also re-visit the direct annihilation of neutralinos into photons and point out that, for a considerable part of the parameter space, internal bremsstrahlung is more important for indirect dark matter searches than line signals.

Model-dependent radiative corrections to [formula omitted] revisited

The long-distance electromagnetic radiative corrections to τ − → π − π 0 ν τ are re-evaluated. A meson dominance model is used to describe the emission of real photons in this decay. Results obtained for the hadronic spectrum and the decay rate in photon inclusive reactions are compared with previous calculations based on the chiral resonance theory. Independent tests in τ → π π ν γ that can help to validate the predictions of one of the two models are briefly discussed.

Electromagnetic radiative corrections in parity-violating electron-proton scattering

QED radiative corrections have been calculated for leptonic and hadronic variables in parity-violating elastic ep scattering. For the first time, the calculation of the asymmetry in the elastic radiative tail is performed without the peaking-approximation assumption in hadronic variables configuration. A comparison with the PV-A4 data validates our approach. This method has been also used to evaluate the radiative corrections to the parity-violating asymmetry measured in the G0 experiment. The results obtained are here presented.

Lowest order QED radiative corrections to longitudinally polarized Møller scattering

The total lowest-order electromagnetic radiative corrections to the observables in Moeller scattering of longitudinally polarized electrons have been calculated. The final expressions obtained by the covariant method for the infrared divergency cancellation are free from any unphysical cut-off parameters. Since the calculation is carried out within the ultrarelativistic approximation our result has a compact form that is convenient for computing. Basing on these expressions the FORTRAN code MERA has been developed. Using this code the detailed numerical analysis performed under SLAC (E-158) and JLab kinematic conditions has shown that the radiative corrections are significant and rather sensitive to the value of the missing mass (inelasticity) cuts.

Gamma-Ray Constraint on Galactic Positron Production by MeV Dark Matter

The Galactic positrons, as observed by their annihilation gamma-ray line at 0.511 MeV, are difficult to account for with astrophysical sources. It has been proposed that they are produced instead by dark matter annihilation or decay in the inner Galactic halo. To avoid other constraints, these processes are required to occur "invisibly," such that the eventual positron annihilation is the only detectable signal. However, electromagnetic radiative corrections to these processes inevitably produce real gamma rays ("internal bremsstrahlung"); this emission violates COMPTEL and EGRET constraints unless the dark matter mass is less than about 20 MeV.