Strong Radiative Corrections Research Articles

Ft values of the mirror β transitions and the weak-magnetism-induced current in allowed nuclear β decay

The precision of correlation measurements in neutron and nuclear $\ensuremath{\beta}$ decay has now reached the level of about 1% and better. At this level of precision, higher-order corrections such as recoil-order corrections induced by the strong interaction and radiative corrections cannot necessarily be neglected anymore. We provide here an update of the $\mathcal{F}t$ values of the isospin $T=1/2$ mirror $\ensuremath{\beta}$ decays including the neutron, of interest to determine the ${V}_{\mathrm{ud}}$ quark-mixing matrix element. We also provide an overview of current experimental and theoretical knowledge of the most important recoil term, weak magnetism, for both these mirror $\ensuremath{\beta}$ decays and a large set of $\ensuremath{\beta}$ decays in higher isospin multiplets. The matrix elements determining weak magnetism were calculated in the nuclear shell model and cross-checked against experimental data, showing overall good agreement. We show that the neutron and the mirror nuclei now effectively contribute to the value of ${V}_{\mathrm{ud}}$, but we also stress the need for further work on the radiative correction ${\mathrm{\ensuremath{\Delta}}}_{R}^{V}$. Our results provide new insight into the size of weak magnetism, extending the available information to nuclei with masses up to $A=$ 75. This provides important guidance for planning and improved sensitivity for interpreting correlation measurements in searches for new physics or to extract ${V}_{\mathrm{ud}}$ in mirror $\ensuremath{\beta}$ decays. It can also be of interest for further theoretical work related to the reactor neutrino problem.

Gravitational waves from double hybrid inflation

We present a two stage hybrid inflationary scenario in non-minimal supergravity which can predict values of the tensor-to-scalar ratio of the order of few times 0.01. For the parameters considered, the underlying supersymmetric particle physics model possesses two inflationary paths, the trivial and the semi-shifted one. The trivial path is stabilized by supergravity corrections and supports a first stage of inflation with a limited number of e-foldings. The tensor-to-scalar ratio can become appreciable while the value of the scalar spectral index remains acceptable as a result of the competition between the relatively mild supergravity corrections and the strong radiative corrections to the inflationary potential. The additional number of e-foldings required for solving the puzzles of hot big bang cosmology are generated by a second stage of inflation taking place along the semi-shifted path. This is possible only because the semi-shifted path is almost perpendicular to the trivial one and, thus, not affected by the strong radiative corrections along the trivial path and also because the supergravity effects remain mild. The requirement that the running of the scalar spectral index remains acceptable limits the possible values of the tensor-to-scalar ratio not to exceed about 0.05. Our model predicts the formation of an unstable string-monopole network, which may lead to detectable gravity wave signatures in future space-based laser interferometer observations.

Neutral-current Drell–Yan with combined QCD and electroweak corrections in the POWHEG BOX

Following recent work on the combination of electroweak and strong radiative corrections to single W-boson hadroproduction in the POWHEG BOX framework, we generalize the above treatment to cover the neutral-current Drell–Yan process. According to the POWHEG method, we combine both the next-to-leading order (NLO) electroweak and the QED multiple photon corrections with the native NLO and Parton Shower QCD contributions. We show comparisons with the predictions of the electroweak generator HORACE, to validate the reliability and accuracy of the approach. We also present phenomenological results obtained with the new tool for physics studies at the LHC.

Implementation of electroweak corrections in the POWHEG BOX: single W production

Abstract We present a fully consistent implementation of electroweak and strong radiative corrections to single W hadroproduction in the POWHEG BOX framework, treating soft and collinear photon emissions on the same ground as coloured parton emissions. This framework can be easily extended to more complex electroweak processes. We describe how next-to-leading order (NLO) electroweak corrections are combined with the NLO QCD calculation, and show how they are interfaced to QCD and QED shower Monte Carlo. The resulting tool fills a gap in the literature and allows to study comprehensively the interplay of QCD and electroweak effects to W production using a single computational framework. Numerical comparisons with the predictions of the electroweak generator HORACE, as well as with existing results on the combination of electroweak and QCD corrections to W production, are shown for the LHC energies, to validate the reliability and accuracy of the approach.

The left–right asymmetry of top quarks in associated top-charged Higgs bosons at the LHC as a probe of the [formula omitted] parameter

Many extensions of the Standard Model involve two Higgs doublet fields to break the electroweak symmetry, leading to the existence of three neutral and two charged Higgs particles. In particular, this is the case of the Minimal Supersymmetric extension of the Standard Model, the MSSM. A very important parameter is tanβ defined as the ratio of the vacuum expectation value of the two Higgs doublets. In this Letter we focus on the left–right asymmetry in the production of polarised top quarks in association with charged Higgs bosons at the LHC. This quantity allows for a theoretically clean determination of tanβ. In the MSSM, the asymmetry remains sensitive to the strong and electroweak radiative corrections and, thus, to the superparticle spectrum. Some possible implications of these results are discussed.

High‐Intensity Scattering Processes of Relativistic Electrons in Vacuum and Their Relevance to High‐Energy Astrophysics

The recent advent of ultra-short pulse, high-intensity lasers, together with advances in other novel technologies, such as high-gradient radiofrequency photoinjectors, have afforded researchers the possibility to simulate astrophysical conditions in the laboratory. Laser-produced plasmas have been successfully used to simulate astrophysical plasmas and supernovae in the laboratory for several years. Now, femtosecond laser systems operating in the terawatt to petawatt range are available, as are synchronized relativistic electron bunches with subpicosecond durations and terahertz bandwidths. With these tools, experiments have been conducted to study phenomena related to supernova explosions, stellar winds, solar coronae, cosmic rays, planetary and celestial matter, and interstellar plasmas. Other experiments have been proposed to investigate Unruh radiation, as well as ponderomotive scattering, which can accelerate electrons in vacuum to relativistic energies using the extremely high gradients in a three-dimensional laser focus. The nonlinear Doppler shift induced by ultrarelativistic radiation pressure is shown to yield complex nonlinear Compton backscattered spectra. Finally, strong radiative corrections are expected when the Doppler-upshifted laser wavelength approaches the Compton scale. These are discussed within the context of high-field classical electrodynamics, a new discipline borne out of the aforementioned innovations.

QCD corrections to at Lep 2 and the Next Linear Collider: CC11 at

QCD one-loop corrections to the full gauge invariant set of electroweak diagrams describing the hadronic process $e^+ e^- \to u~\bar d~s~\bar c$ are computed. Four-jet shape variables for $WW$ events are studied at next-to-leading order and the effects of QCD corrections on the determination of the $W$--mass in the hadronic channel at Lep 2 and NLC is discussed. We compare the exact calculation with a ``naive''approach to strong radiative corrections which has been widely used in the literature.

High-intensity scattering processes of relativistic electrons in vacuum

Recent advances in novel technologies such as chirped pulse amplification and high gradient rf photoinjectors make it possible to study experimentally the interaction of relativistic electrons with ultrahigh intensity photon fields. Femtosecond laser systems operating in the TW–PW range are now available, as well as synchronized relativistic electron bunches with subpicosecond durations and THz bandwidths. Ponderomotive scattering can accelerate these electrons with extremely high gradients in a three-dimensional vacuum laser focus. The nonlinear Doppler shift induced by relativistic radiation pressure in Compton backscattering is shown to yield complex nonlinear spectra which can be modified by using temporal laser pulse shaping techniques. Colliding lasers pulses, where ponderomotive acceleration and Compton backscattering are combined, could also yield extremely short wavelength photons. Finally, strong radiative corrections are expected when the Doppler-upshifted laser wavelength approaches the Compton scale. These are discussed within the context of high field classical electrodynamics, a new discipline borne out of the aforementioned innovations.

QCD corrections to [formula omitted] at LEP2 and the next linear collider: CC10 at O( αs)

QCD one-loop corrections to the semileptonic process e +e − → μ − ν μ u d are computed. We compare the exact calculation with a “naive” approach to strong radiative corrections which has been widely used in the literature and discuss the phenomenological relevance of QCD contributions for LEP2 and NLC physics.

The interplay between electroweak and strong radiative corrections in [formula omitted

The one-loop weak corrections for e + e −→ b b have been computed. The QED contribution to the process has been taken into account by using the radiator approach in a totally inclusive setup and all available QCD corrections have been included. The agreement between our results and other existing calculations is shown and discussions are made on the interplay between electroweak and QCD corrections.

Strong radiative corrections to strangeness-changing processes in the presence of right-handed currents

In the presence of weak right-handed currents the GIM suppression becomes less efficient in the effective ΔS=2 operator. Therefore new features arise and have to be taken into account when applying strong radiative corrections. We determine these QCD corrections to the ΔS=2 operator on the leading log level and (in contrast to the standard model) find a sizeable enhancement. If one ascribes CP violation to the presence of right-handed currents, then the parameter ϵ will enjoy the same enhancement. We show however that ϵ′ is increased in a similar way; the ratio ϵ′ ϵ is therefore not significantly affected.

Strong radiative corrections to annihilations of quarkonia in QCD

The significance of the lowest-order QCD prediction for the annihilations of heavy quark-antiquark bound states is analyzed. The calculation of the leading strong radiative corrections to the hadronic versus electromagnetic annihilation rate ratio R of pseudoscalar quarkonium is presented. In terms of the coupling constant α s, as defined in the minimal subtraction scheme, we find R = R (0)(1 + 22.14 α s/ π). The physical significance of this result is discussed by comparing it with the calculation of the non-leading effects in α s on the scaling violations in deep inelastic scattering. A bad convergence of the relative perturbative expansion is found, demanding for its safe application a value of the relevant momentum definitely higher than that of charmonium physics.