Searcharxiv⌕ Search

arXiv subjects

Alberto Sirlin

Publications and source records attributed to Alberto Sirlin.

At least 37 records · Page 2Linked to original sources
arXiv2004

Precision Measurements and CKM Unitarity

Determinations of $\vud$ and $\vus$ along with their implications for the unitarity test $\vud^2+\vus^2+\vub^2=1$ are discussed. The leading two loop radiative corrections to neutron $β$-decay are evaluated and used to derive a refined relationship $\vud^2 τ_n (1+3g_A^2)=4908(4)$sec. Employing $\vud =0.9740(5)$ from superallowed nuclear decays and the measured neutron lifetime $τ_n = 885.7(7)$sec, leads to the precise prediction $g_A=1.2703(8)$ which is compared with current direct experimental values. Various extractions of $\vus$ are described and updated. The long accepted Particle Data Group value of $\vus$ from fitted $K_{e3}$ decay rates suggests a deviation from CKM unitarity but it is contradicted by more recent experimental results which confirm unitarity with good precision. An outlook for possible future advances is given.

hep-ph↗
arXiv2003

Radiative Corrections and the Standard Model of Elementary Particles

This presentation includes an introductory discussion of the unification of fundamental forces, properties of the elementary particles, Quantum Electrodynamics, the transition from Quantum Electrodynamics and Weak Interactions to Electroweak Physics, Radiative Corrections in the Standard Model of Particle Physics, and some critical unsolved problems.

hep-ph↗
arXiv2003

Considerations Concerning the Contributions of Fundamental Particles to the Vacuum Energy Density

The covariant regularization of the contributions of fundamental particles to the vacuum energy density is implemented in the Pauli-Villars, dimensional regularization, and Feynman regulator frameworks. Rules of correspondence between dimensional regularization and cutoff calculations are discussed. Invoking the scale invariance of free field theories in the massless limit, as well as consistency with the rules of correspondence, it is argued that quartic divergencies are absent in the case of free fields, while it is shown that they arise when interactions are present.

hep-ph↗
arXiv2002

Thirty Years of Precision Electroweak Physics

We discuss the development of the theory of electroweak radiative corrections and its role in testing the Standard Model, predicting the top quark mass, constraining the Higgs boson mass, and searching for deviations that may signal the presence of new physics.

hep-ph↗
arXiv2002

Elimination of Threshold Singularities in the Relation Between On-Shell and Pole Widths

In a previous communication by two of us, Phys. Rev. Lett. 81, 1373 (1998), the gauge-dependent deviations of the on-shell mass and total decay width from their gauge-independent pole counterparts were investigated at leading order for the Higgs boson of the Standard Model. In the case of the widths, the deviation was found to diverge at unphysical thresholds, m_H = 2 root{xi_V} m_V (V = W,Z), in the R_xi gauge. In this Brief Report, we demonstrate that these unphysical threshold singularities are properly eliminated if a recently proposed definition of wave-function renormalization for unstable particles is invoked.

hep-ph↗
arXiv2002

Width and Partial Widths of Unstable Particles in the Light of the Nielsen Identities

Fundamental properties of unstable particles, including mass, width, and partial widths, are examined on the basis of the Nielsen identities (NI) that describe the gauge dependence of Green functions. In particular, we prove that the pole residues and associated definitions of branching ratios and partial widths are gauge independent to all orders. A simpler, previously discussed definition of branching ratios and partial widths is found to be gauge independent through next-to-next-to-leading order. It is then explained how it may be modified in order to extend the gauge independence to all orders. We also show that the physical scattering amplitude is the most general combination of self-energy, vertex, and box contributions that is gauge independent for arbitrary s, discuss the analytical properties of the NI functions, and exhibit explicitly their one-loop expressions in the Z-gamma sector of the Standard Model.

hep-ph↗
arXiv2001

On the Field Renormalization Constant for Unstable Particles

A recently proposed normalization condition for the imaginary part of the self-energy of an unstable particle is shown to lead to a closed expression for the field renormalization constant Z. In turn, the exact expression for Z is necessary, in some important cases, in order to avoid power-like infrared divergences in high orders of perturbation theory. In the same examples, the width plays the rôle of an infrared cutoff and, consequently, Z is not an analytic function of the coupling constant.

hep-ph↗
arXiv2000

Higgs-Boson Production and Decay Close to Thresholds

At one loop in the conventional on-mass-shell renormalization scheme, the production and decay rates of the Higgs boson H exhibit singularities proportional to (2 M_V - M)^{-1/2} as the Higgs-boson mass M approaches from below the pair-production threshold of a vector boson V with mass M_V. This problem is of phenomenological interest because the values 2 M_W and 2 M_Z, corresponding to the W- and Z-boson thresholds, lie within the M range presently favoured by electroweak precision data. We demonstrate how these threshold singularities are eliminated when the definitions of mass and total decay width of the Higgs boson are based on the complex-valued pole of its propagator. We illustrate the phenomenological implications of this modification for the partial width of the H -> W^+ W^- decay.

hep-ph↗
arXiv1999

Ten Years of Precision Electroweak Physics

We review a number of theoretical developments in Precision Electroweak Physics that are closely connected with the interpretation of experiments. The emphasis is on the test of the Standard Model at the level of its quantum corrections, the search for the Higgs boson, and constraints on new physics.

hep-ph↗
arXiv1995

Application of the Pinch Technique to Neutral Current Amplitudes and the Concept of the Z Mass

The pinch technique (PT) is applied to neutral current amplitudes, focusing on the mixing problem. Extending recent arguments due to Papavassiliou and Pilaftsis, it is shown that the use of the PT self-energies does not shift the complex-valued position of the pole through order {\cal O}($g^4$). This leads (to the same accuracy) to a simple interpretation of $M_Z$, the mass measured at LEP, in terms of the PT self-energies. It is pointed out that the PT approach provides a convenient and rather elegant formalism to discuss important neutral current amplitudes, such as those relevant to four-fermion processes and LEP2.

hep-ph↗
arXiv1995

Renormalon contributions to δρ

Leading QCD vacuum polarization contributions to the electroweak parameter $δρ$ are evaluated numerically using several different prescriptions for the gluon self-energy. Simple theoretical estimates of the asymptotic behavior are given. The results show a significant contribution from the leading infrared renormalons when $δρ$ is expressed in terms of the top-quark pole mass and its absence when the $\msbar$ running mass is employed. The calculations are applied to estimate higher order QCD contributions to $δρ$.

hep-ph↗
arXiv1995

EVIDENCE FOR ELECTROWEAK CORRECTIONS IN THE STANDARD MODEL

The phenomenological evidence for electroweak corrections in the Standard Model, both at very low energies and the $Z^0$ scale, is discussed. In particular, we review a simple but sharp argument for the presence of Electroweak Bosonic Corrections.

hep-ph↗
arXiv1995

Solar Neutrinos: Radiative Corrections in Neutrino-Electron Scattering Experiments

Radiative corrections to the electron recoil-energy spectra and to total cross sections are computed for neutrino-electron scattering by solar neutrinos. Radiative corrections change monotonically the electron recoil spectrum for incident \b8 neutrinos, with the relative probability of observing recoil electrons being reduced by about 4 \% at the highest electron energies. For $p-p$ and $\be7$ neutrinos, the recoil spectra are not affected significantly. Total cross sections for solar neutrino-electron scattering are reduced by about 2 \% compared to previously computed values. We also calculate the recoil spectra from $^{13}$N and $^{15}$O neutrinos including radiative corrections.

astro-ph↗
arXiv1994

On the QCD corrections to $Δρ$

We discuss some recent developments in the evaluation of the QCD corrections to $Δρ$, their interpretation, an estimate of the theoretical error, and its effect on electroweak physics.

hep-ph↗
arXiv1994

Considerations Concerning the QCD Corrections to $Δρ$

Using recent results of Avdeev et al. and an expansion for $μ_t/\mms$ ($M_t$ is the pole mass and $μ_t\equiv \hat{m_t}(μ_t)$ ), it is shown that when deltarho is expressed in terms of $\hat{m_t}^2(M_t)$, the QCD correction is only $(2-3)\times 10^{-3}$ in the NLO approximation. As a consequence, in terms of $M_t^2$ the correction to $\dr$ is almost entirely contained in $\mmss/M_t^2$, a pure QCD effect. The latter is studied using various optimization procedures, and the results compared with the expansion proposed by Avdeev et al.. Implications for \ew physics are discussed. Threshold effects are analyzed on the basis of a simple sum rule.

hep-ph↗
arXiv1994

Renormalizable W Self-Energy in the Unitary Gauge via the Pinch Technique

We use the S-matrix pinch technique to derive to one loop order an effective renormalizable self-energy for the W gauge boson, when the theory is quantized in the unitary gauge. We then show that this amplitude is identical to the $ξ$-independent W self-energy previously constructed by applying the pinch technique in the context of the renormalizable $R_ξ$ gauges.}

hep-ph↗