R. Barbieri's research while affiliated with Scuola Normale Superiore di Pisa and other places

Publications (81)

Article
In 1990, a study group was formed, to provide the INFN Executive Board with an independent evaluation of the physics potential of DAPHNE, a high luminosity \\Phi-factory, besides that of measuring the direct CP-violation parameter, \\epsilon'/ \\epsilon. The study group conclusions appeared, in italian, as an internal report of the Frascati Nationa...
Article
We consider supersymmetric models with low-energy baryon number (and R-parity) violation through renormalizable interactions. We find that: (i) the most stringent limit on superpartner masses from nucleon instability comes from the reaction NN → KK + X requiring squark masses in the TeV range; (ii) the lightest supersymmetric particle, which can be...
Article
Within the framework of supergravity models without grand unified steps, we analyse in detail the consequences of the hypothesis that gauginos have no bare masses due to supergravity interactions. To this purpose we have made a one-loop calculation of wino, zino, and photino masses and a renormalization group improved two-loop calculation of the gl...
Article
We show that the reaction any is an important experimental test for a possible composite nature of the Z0-boson. In the standard model this process is dominated by q̄q annihilations. In a composite-Z scheme the subprocess g + g → Z0 + γ may yield cross sections which are substantially larger than those of the standard model, especially at large pTγ...
Article
We compute the renormalization of the neutral-to-charged current Fermi constant ratio, arising from the new particles required in supersymmetric schemeś.We find that ϱ is insensitive to the scale of the supersymmetry mass-splitting. For a t-quark mass mt greater than this scale, the scalar-t and scalar-b contribution increases proportionally to mt2...
Article
Scalar electrons and scalar neutrinos may appear among the decay products of the W produced in p− collisions. Under the assumption that: (se) → e + photino and (sνe) → undetected neutrals, we compute the contribution of the decay: W → (se) + (sνe) to the process + missing energy + hadrons. A numerical analysis, performed in the case m se = 20 GeV a...
Article
We analyze all possible sources of radiative gaugino masses in a class of SU(3) ⊗ SU(2) ⊗ U(1) locally supersymmetric models. Barring direct gaugino masses and radiative contributions from superheavy particles of grand unified theories, we find that: (i) consistently with the present bounds, gluinos with a mass of 1-1.5 GeV and relatively long live...
Article
The combined effect of chirality and supersymmetry (through Goldstone partnership) can generate a variety of light mass scales for spin composites. The general ideas are illustrated in a one-family example with technicolour-type breaking of the standard low energy group.
Article
The phenomenological value of the weak mixing angle, sin2θW, puts dynamical constraints on composite models of the weak vector bosons with mass comparable to the scale of the binding force. These constraints are studied by making use of the asymptotic freedom sum rules (AFSR). In models where the sum over the squared preonic electric charges exceed...
Chapter
We briefly describe how a general unified theory can account for the observed hierarchical pattern of fermion masses. An explicit SU(5) model predicts at the unification mass mb = mτ and, necessarily, mS = mµ/3. It also incorporates a Peccei-Quinn symmetry broken at superlarge energies.
Article
An effective low-energy lagrangian for gauge theories based on local supersymmetry spontaneously broken at an intermediate energy between the weak interaction and the Planck scale is obtained. The derivation uses the general coupling of the Yang-Mills matter system to n = 1 supergravity. As illustrative examples of this framework we exhibit realist...
Article
We consider the one-loop corrections to the muon anomalous magnetic moment in a class of spontaneously broken supersymmetric gauge theories. We add to the well known contributions from photon, W and Z exchange the effects of the corresponding fermionic superpartners, photino, w-ino and z-ino, and that of the massless goldstino. We reobtain the boun...
Article
We reconsider a realistic model of electroweak and strong interactions with calculable mass spectrum at the tree level in which supersymmetry and an extra gauge group factor Ũ(1) beyond SU(3) × SU(2) × U(1) are both broken at very high energies: , . In spite of these high-energy scales, especially the large scale of supersymmetry breaking, the low...
Article
We derive the general formula for the supertrace of the quartic mass matrix in a general supersymmetric gauge theory, with arbitrary representations for the chiral multiplets. This formula clarifies the non-renormalization theorems in presence of gauge interactions and gives “extended renormalization theorems” for N = 2 and N = 4 supersymmetric Yan...
Article
We describe a supersymmetric model of strong and electroweak interactions based on the gauge groupSU(3)SU(2)U(1)(1). We concentrate on the pattern of the spontaneous symmetry breaking by the tree level scalar potential. It is possible to break the(1) factor at superlarge energies relative to the simultaneous breaking scale ofSU(2)U(1) and supersymm...
Article
Full-text available
We show that in order for a U(1) gauge theory with a Fayet-Illiopoulos term to be consistently coupled to supergravity, preserving gauge invariance, the superpotential must be R invariant. A supersymmetric cosmological term and therefore an explicit mass-like term for the gravitino is forbidden by gauge invariance. This result severely constrains t...
Article
We study a previously developed composite model for quarks, leptons, and weak bosons without broken gauge interactions. The conjectured pattern of symmetry breaking is discussed, paying special attention to the 't Hooft anomaly conservation requirement, which is fulfilled. Using techniques similar to those earlier used by Hung and Sakurai, we study...
Article
We study the diagonalization of the general mass matrix for quarks and their scalar superpartners in models based on a gauge group SU(3) × SU(2) × U(1) × with spontaneous breakdown of supersymmetry. We characterize a class of models where the Cabibbo-Kobayashi-Maskawa unitary matrices occuring in the mass-eigenstate basis are the same in the gaugin...
Article
We discuss the implications of a recently proposed minimally extended SU(5) model that incorporates the superlight axion mechanism to solve the strong CP problem. We prove that in the absence of instanton effects, the pseudoscalar nature of the axion coupling to fermionic matter is not modified by higher order weak radiative corrections including C...
Article
We propose a scheme of hierarchical supersymmetry breaking in the framework of N = 8 supergravity with dynamical SU(8) gauge symmetry. This scheme naturally explains the existence of a light gravitino with mass O(m2/Mp), where m is the spontaneous breaking scale of both SU(2) × U(1) and supersymmetry. This mass for the gravitino is consistent with...
Article
We give a detailed account of the calculation of the one-loop QCD corrections to the annihilation widths into hadrons and into two photons of P wave quarkonium states of JPC = 0++, 2++.
Article
We calculate the leading radiative corrections in QCD to ΔE(1−−−0−+) in quarkonium. We also present a summary of present knowledge of quarkonium rates together with numerical estimates for charmonium and bottonium.
Article
We present an SU(5) model with hierarchical fermion structure and without strong CP violation. The Peccei-Quinn U(1) symmetry we need is tied to the symmetry needed to produce the observed fermion mass spectrum. It is spontaneously broken at 1015 GeV which makes the axion almost unobservable.
Article
We present a composite model of quarks and lepton satisfying 't Hooft's anomaly conditions, where the electroweak interactions are left-right symmetric and are not associated with broken local flavour symmetries. The scales of left- and right-handed weak interactions are associated with the scale ΛH of hypercolour interactions responsible for preon...
Article
A recent proposal for getting hierarchical fermion masses in GUTs is realized by using E6 as a prototype model. The existence of superheavy fermions is crucial. An interesting consequence a is possible explanation of mc > mmu.
Article
Rediative masses are generated for the first and the second fermion families by exploiting the idea that their chirality is a symmetry of the “low-energy” SU(3) × SU(2) × U(1) approximation of SU(5), broken only by including the effects of superheavy particles. With only 5's of Higgs coupled to fermions and getting a non-zero vacuum expectation val...
Article
In a class of four-dimensional, non-linear fermionic lagrangians, a classical gauge symmetry induces dynamical gauge fields at the quantum level. The construction requires flavour (or families) as well as the “unification” of all gauge couplings at the common Landau pole mass.
Article
We study the possibility that theU(1) B global symmetry associated with baryon number is spontaneously broken. We present realistic examples implemented in the context of a suitably extended standardSU(2) LU(1)SU(3)c model and of a composite model of quarks and leptons. The globalU(1) B symmetry in both cases is spontaneously broken at a relatively...
Article
We explore the possibility that quarks and leptons are composite states of preons, bound by an O(n) gauge force. Solutions to the consistency conditions proposed by 't Hooft are found. The simplest solution consists in precisely n families of quarks and leptons, which can be interpreted as composite states of one preon and O(n) glue. The breaking o...
Article
A mechanism is presented for generating fermion masses as a reflection of the superheavy fermions existing in a class of grand unified theories. By means of it we propose a way of understanding how, giving a driving mass term for the top-generation, the charm-generation mass results as a relative first-order perturbation in the unified gauge coupli...
Article
We have calculated one-loop QCD corrections to the annihilation widths of P-wave quarkonium states into hadrons and into two photons. Comparison with accurate experimental data may lead to a clear test of perturbative QCD if alphaS turns out to be small enough for reasonable convergence.
Article
A unified model of strong and electro-weak interactions based on the exceptional group E6 is presented, with three generations of fermions and all the symmetry breaking obtained from the fermion-fermion operator. A small mass for the neutrinos is obtained in a way which may be natural. The asymptotic SU(5) relations mb = mτ, mS = mμ, md = me, as we...
Article
Various models proposed in the context of a SO(10) grand unified theory to keep the neutrino masses “naturally” small are discussed. Their connection with the breaking scheme of BL as a local symmetry is emphasized. Finite and naturally small one-loop radiative corrections to zeroth order neutrino masses arise. The very existence of these correcti...
Article
A detailed analysis is made within perturbative QCD of the decays into gluon jets of P-wave and S-wave quarkonia (JPC = 0++, 1++, 2++, 1+− and 0−+, 1−−). For all those states we compute to leading non-trivial order in αs the conventional fraction f(ϵ, δ) of the jet-like hadronic final states, characterized by the back-to-back cone of half angle δ,...
Article
Cosmological effects of superheavy fermions present in a wide class of grand unified models are discussed. An interesting outcome is that long-lived superweakly interacting fermions may be the only source of surviving baryon asymmetry generated at temperatures possibly as low as 1 TeV.
Article
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 αs, as defined in the min...
Article
The fraction of hadronic final states in the heavy quarkonium decays (e.g. Upsilon(9.4) or the related P-waves) containing heavy quark flavours (e.g. DD, psi (3.1)) is calculated in detail according to the QCD theoretical model as function of the ratio between the mass of the produced heavy quark and the mass of the heavier constituent quark.
Article
We try to understand the meaning of the recent data on scaling violations of the moments of the structure function F3 measured in nu and nu deep inelastic scattering, and their relevance as a test of QCD. We do this by reducing to the minimum the theoretical machinery and prejudices and stressing the perturbative nature of the problem. We are led t...
Article
The present status of the calculation of the (alpha/pi)3 term for the anomalous magnetic moment of the electron in QED is reviewed. Exact results for two sets of graphs contributing to this order are presented. An outline of the method used, which is based on a new invariant decomposition of the vertex amplitude and dispersion relations, is given....
Article
We propose a Coulomb-like kernel for the relativistic two-fermion Bethe-Salpeter equation, to be used as the lowest-order approximation in systematic perturbative calculation of bound-state energy levels in QED. The kernel is symmetric in the two fermions and for the exchange of in and out momenta. The resulting equation is exactly soluble, unlike...
Article
We point out that QCD contains the prediction that, to a good approximation, no interference should occur, between direct and virtual photon channels, in the inclusive hadronic annihilation of a heavy quark-antiquark 1-- bound state (but not necessarily so for an exclusive channel). Quantitative predictions are made for upsilo-decays. We also comme...
Article
We show that in the SU(2) × U(1) model with an arbitrary number of quarks there exists no set of discrete symmetries which may determine the Cabibbo angle in terms of quark masses. An enlargement of the ``minimal'' group is therefore crucial for the success of the discrete symmetry approach to this problem.
Article
A general expression is derived for the radiative corrections to the one-photon decay rates of hydrogen-like ions. Our approach is based on the evaluation of the imaginary part of the fourth-order Lamb shift for excited states. We thereby avoid the ambiguities connected with electron wave function renormalization. The result may be cast in a form w...
Article
An analysis is given of the mixing of the axial vector kaon resonances by use of new data from SLAC. Mass values, decay widths and branching ratios of the SLAC work may be compatible with SU(3) and/or “pair creation model” classifications for a mixing angle λ ≈ −35° ± 10°. The mass values and coupling strengths proposed by Basdevant and Berger, fro...
Article
In view of forthcoming experiments of greater statistics and accurate particle identification we have calculated the complete angular correlation in reactions of charmed particle (pseudo-scalar, vector, axial-vector) production from e+e- and their subsequenc sequential decays, including possible photonic transitions. On leave from Istituto di Fisic...
Article
Withibn color gauge-theory we adopt renormalization prescription which introduces a scale-dependent quark mass to analyse tau(e+e--->hadrons). We obtain a satisfactory fit with four flavors (u, s, d, c) and one heavy lepton. Within such model one can conclude that a scale-dependent effective quark mass is more suitable to describe the experiments t...
Article
We reconsider the calculation of the contribution to the positronium ground state splitting from the iteration of one-photon direct and exchange diagrams. New alpha61galpha terms are found besides the previously known vacuum polarization contribution. The present situation in the comparison of theory and experiment is summarized.
Article
The annihilation rates into hadrons of P-wave heavy quark-antiquark bound states are calculated within SU(3) colour gauge theory (in particular for the charm scheme). An interesting feature we find is a logarithmic divergence for small binding for the states 1++ and 1+−. Implications for the asymptotic freedom approach to the decay rates of the new...
Article
A linear binding potential with one-gluon exchange corrections, within a colour gauge field theory including four types of quarks, is applied to the description of the meson masses and leptonic widths (both for light and heavy mesons). First order relativistic corrections are calculated by means of the Breit-Fermi Hamiltonian. Mixing effects and th...
Article
We present the calculation in quantum electro-dynamics of the transition probability for the inverse bremsstrahlung process. The expected number of events is also given for an experiment which was recently proposed to study the inverse bremsstrahlung reaction.
Article
In the framework of the gauge theory of strong interactions (in particular for the charm scheme) we calculate the annihilation rates of P wave quark-antiquark bound states of JPC = 0++, 2++. Applications can be made to the decays of the C = +1 states lying between ψ and ψ′, to their gluonic production, and to f′ decay. Annihilations into 2γ and the...
Chapter
The present theoretical knowledge of electron and muon anomalous magnetic moments is reviewed, discussing in particular recent progresses in the analytic evaluation of sixth order quantum electrodynamical corrections.
Article
We introduce a new method of calculating the lepton anomalous magnetic moment, combining the features of the dispersive and the mass operator approach. We apply it to the study of the contributions to the electron and muon anomalies coming from QED vertex graphs containing vacuum polarization insertions. Complete analytic results up to sixth order...
Article
The 3S-1S mass separations of the bound quark-antiquark systems, as arising from one-gluon exchange, in the charm color quartet scheme, are discussed for the ground mesons and their first radial excitations expecially in connection to leptonic decay rates. Overall consistency requires large modifications for the positronium-like formulae for annihi...
Article
We evaluate analytically the contribution to the anomalous magnetic moment of the electron due to a set of sixth order graphs with two crossed photon lines. The dimensional regularization is used to parametrize the spurious infrared divergences. Laboratoire propre du C.N.R.S. associé à l'Ecole Normale Supérieure et à l'Université de Paris Sud. Post...
Article
The existence of a weakly-coupled scalar boson, recently proposed to explain the apparent discrepancy in X-rays from muonic atoms is shown to be inconsistent with the angular distribution measurements in low energy neutron-nucleus scattering. Other negative evidence from various different physical situatiions is also briefly reviewed.
Article
The relationship between the renormalization group and the muon anomalous magnetic moment calculation in QED is reconsidered. A very simple analysis shows that the contribution to the muon anomaly from muon vertex graphs with electron loop insertions in the photon propagators is function of only one dimensionless effective coupling constant alphamu...
Article
A firsr exploratory attempt is made of quantitatively describing in the charm scheme the behaviour of sigma (e+e- --> hadrons) in the region above charm threshold. Indications are given for the important role of psi'' and possibly of psi ''', second and third radial excitations of psi.
Article
The possible existence of non-perturbative vacuum polarization modifications and the possible existence of a weakly-coupled light scalar boson have been recently proposed to explain the apparent mu-mesic atom X-ray discrepancy. Their effects are shown to introduce in the separation of the 2P3/2 and 2S1/2 levels of the (mu4He)+ system a discrepancy...
Article
We complete the analytic evaluation of sixth order contributions to electron and muon anomalous magnetic moments coming from second order vacuum polarization insertions into all the fourth order graphs.
Article
The value of vacuum-polarization amplitude is investigated in the region of positronium bound-state poles, where the naive Feynman-graph expansion fails. The corresponding contribution to positronium-ground-state splitting is explicitly evaluated up to order α6. The previously given result for the α6 lnα-1 term coming from fourth-order vacuum-polar...
Article
The contribution to the triplet-singlet splitting of positronium ground state arising from fourth-order vacuum polarization in the annihilation channel is reported. It is found to be ].
Article
The method, developed in a previous work, is extended to the evaluation of second-order radiative corrections to the Coulomb scattering differential cross-section. Virtual and real photons are always given exactly zero mass and are described in terms of the same integration variable, avoiding the usual artificial distinction between « elastic » and...
Article
It is shown, discussing the explicit case of further order vacuum polarization, that the adiabatic switching procedure allows a proper treatment of infra-red divergences, without introducing any fictitious photon mass. The new approach suggests a method of carrying out explicitly the calculation, which does not create dishomogeneity in evaluating t...
Article
The explicit results of the analytic evaluation of the discontinuities of the electron form factors and of their zero-momentum-transfer values, up to the fourth order of the perturbative expansion of QED in the electric charge, are presented. Asymptotic and threshold behaviours are discussed. The related form of the dispersion relations for the rea...
Article
Summary The methods and the techniques developed and used in a foregoing paper for the evaluation of the radiative corrections to the electron form factors up to fourth order in the electric charge (two internal loops) in QED are presented in this paper.
Article
The slope of the charge form factor of the electron is analytically evaluated in fourth-order perturbation theory of QED and found to bem 2F′1(0)=(α/π)2[−4819/5184−(49/72)ζ(2)+3ζ(2) log 2−(3/4)ζ(3)]==(α/π)2·0.470. Correspondingly the theoretical Lamb-shift value for the hydrogen atom is Δν(2S 1/2−2P 1/2)=(1057.90±0.09) MHz, in agreement with experi...

Citations

... Finally, the EFT analysis shows that the modeling of hadronic light-by-light scattering by a constituent quark loop, as suggested in Refs. [301,302] (see also [303]), is not consistent with QCD. 32 The latter has a priori nothing to do with the full "quark loop" in QCD which is dual to the corresponding contribution in terms of hadronic degrees of freedom. ...
Reference: The muon g-2
... Early attempts to obtain the two-loop logarithmic corrections, starting in 1970, were incorrect or incomplete because of awkward bound state formalisms and because the origins of the logs were not at first understood. Many groups contributed to the successful calculation of C 21 [27][28][29][30][31][32][33][34]. The correct result, C 21 = 5 24 , was obtained by Lepage in 1977 and was quickly confirmed [35][36][37]. ...
... Our goal is to perform as many integrations of the 8-dimensional integral over x, y in Eq. (13) as possible (semi-) analytically to have full control over the QED kernel function L [ρ,σ];µνλ (p, x, y). To achieve this, we will rewrite the function I(p, x, y) IR reg. in Eq. (11) in terms of position-space propagators [57,58] and use the method of Gegenbauer polynomials [59][60][61][62][63] to perform the angular integrals and average over the direction of the muon momentum [64] (see also Ref. [63,65]). We will show the details of this calculation in the next sections, but present here first the structure of the final result, our master formula for a HLbL µ in position space. ...
... Similar estimates have been performed in refs. [88][89][90][91] and are closely related to spurion arguments in refs. [54,92]. ...
... The earliest calculations of inclusive charm (ccX) production from bottomonia focused on Υ → ggg decays, giving estimates of a few percent [5]. It was soon pointed out that while production of ccX is predicted to be suppressed in gg hadronization, it is not expected to be suppressed in qqg hadronization [6]. Since the gg process is absent for the χ b1 (nP ) states, they should have higher branching fractions to ccX. ...
... We will put some emphasis on those aspects that are immediately relevant to the Odderon. For more detailed accounts of the BFKL approach we refer the reader to [53, 54, 55]. ...
... Other approaches contain those proposals that do not impose conditions (7) but impose the suppression of the FCNC either by some popular ansatz, like in the case of the Cheng-Sher ansatz [13] or even by imposing this suppression with symmetries, like is the case of the Branco Grimus Lavoura (BGL) 2HDM and its generalizations [14][15][16][17][18]. An incomplete part of the long list of relevant contributions to the subject can be found here [19][20][21][22][23][24][25][26][27]. ...
... A numerical value of A ð6Þ 1 is given in [18], and after work spanning several decades in calculating the various diagrams that constitute A ð6Þ 1 (e.g. [19][20][21][22][23][24][25]), the calculation was finalized and the exact close form analytic result was presented in [26]. Purely numerical calculations for A can be found in [27][28][29][30][31][32][33], and a result to 1100 digit precision, accompanied by a semianalytic fit to the result, is presented in [34]. ...
... Equation (13) defines the factor C which we will use later. The value of O 1 V is solved from the NLO expression for the vector-meson leptonic decay width [30,[81][82][83], ...
... 2. Extraction of the contribution to A 4 from the amplitude of each diagram by using projectors [18,19] with a FORM program [20,21]. ...