Effective Weak Interaction Research Articles

QED factorization of non-leptonic B decays

We show that the QCD factorization approach for B-meson decays to charmless hadronic two-body final states can be extended to include electromagnetic corrections. The presence of electrically charged final-state particles complicates the framework. Nevertheless, the factorization formula takes the same form as in QCD alone, with appropriate generalizations of the definitions of light-cone distribution amplitudes and form factors to include QED effects. More precisely, we factorize QED effects above the strong interaction scale ΛQCD for the non-radiative matrix elements leftlangle {M}_1{M}_2left|{Q}_iright|overline{B}rightrangle of the current-current operators from the effective weak interactions. The rates of the branching fractions for the infrared-finite observables overline{B}to {M}_1{M}_2left(gamma right) with photons of maximal energy ∆E ≪ ΛQCD is then obtained by multiplying with the soft-photon exponentiation factors. We provide first estimates for the various electromagnetic corrections, and in particular quantify their impact on the πK ratios and sum rules that are often used as diagnostics of New Physics.

Post-industrial university towns and the triple helix concept: case studies of Bristol, Sheffield, Novosibirsk and Tomsk

Abstract The paper examines the role of universities in city development under the Triple Helix model through case studies of Russian and British cities. The cases of Bristol and Sheffield illustrate that the implementation of the Triple Helix model can be achieved through different approaches. In Bristol, universities reached beyond their campuses to create a ground for cooperation with partners. In Sheffield, there was a platform for interaction with partners using the brand of a top university. Meanwhile, the examples of Tomsk and Novosibirsk provide some evidence for the growing importance of universities in the innovative urban economy. The comparative analysis provides recommendations for Russian universities, whose application of the Triple Helix model is prevented by the lack of experience in developing an effective marketing strategy and weak interactions between research and enterprises.

Внески векторних резонансів у CP-асиметрію розпаду нейтрального B-мезона на мюон-антимюонну пару та нейтральний K*-мезон

Contributions of the processes ¯ B0d → ¯ K*0(→ K−п+) V with vector mesons V = p(770), w(782), ф(1020), J/w, w(2S), and others decaying into the м+м− pair to the CP-asymmetry in the decay ¯ B0d → ¯ K*0(→ K−п+)м+м− induced by the flavor-changing neutral currents are calculated. For the description of the transition b → sм+м−, the most general form of the effective weak-interaction Hamiltonian is applied. Predictions are made for the CP-asymmetry of the decay ¯ B0d → ¯ K*0(→ K−п+)м+м− in the framework of the standard model, as well for two scenarios of new physics. The obtained results are compared with experimental data of the LHCb Collaboration.

Factorization at subleading power and irreducible uncertainties in $ \bar{B} \to {X_s}\gamma $ decay

Using methods from soft-collinear and heavy-quark effective theory, a systematic factorization analysis is performed for the $\bar B\to X_s\gamma$ photon spectrum in the endpoint region $m_b-2E_\gamma={\cal O}(\Lambda_{\rm QCD})$. It is proposed that, to all orders in $1/m_b$, the spectrum obeys a novel factorization formula, which besides terms with the structure $H\,J\otimes S$ familiar from inclusive $\bar B\to X_u l\,\bar\nu$ decay distributions contains "resolved photon" contributions of the form $H\,J\otimes S\otimes\bar J$ and $H\,J\otimes S\otimes\bar J\otimes\bar J$. Here $S$ and $\bar J$ are new soft and jet functions, whose form is derived. These contributions arise whenever the photon couples to light partons instead of coupling directly to the effective weak interaction. The new contributions appear first at order $1/m_b$ and are related to operators other than $Q_{7\gamma}$ in the effective weak Hamiltonian. They give rise to non-vanishing $1/m_b$ corrections to the total decay rate, which cannot be described using a local operator product expansion. A systematic analysis of these effects is performed at tree level in hard and hard-collinear interactions. The resulting uncertainty on the decay rate defined with a cut $E_\gamma>1.6$ GeV is estimated to be approximately $\pm 5%$. It could be reduced by an improved measurement of the isospin asymmetry $\Delta_{0-}$ to the level of $\pm 4%$. We see no possibility to reduce this uncertainty further using reliable theoretical methods.

QED Theory of Transition Probabilities and Line Profiles in Highly Charged Ions

A rigorous QED theory of the spectral line profiles is applied to transition probabilities in few-electron highly charged ions. Interelectron interaction corrections are included as well as radiative corrections. Parity nonconserving (PNC) amplitudes with effective weak interactions between the electrons and nucleus are also considered. QED and interelectron interaction corrections to the PNC amplitudes are derived.

Dimensional taming of mass singularities in QCD corrections to weak radiative decays of quarks

Lowest order QCD corrections to the rate of the b→sγ decay induced by effective weak-interaction dipole operators are calculated by using dimensional regularization. The existing calculations of the rate all appear to have had recourse to dimensional reduction as a way of regularization. It is shown that the rate does not depend on which one of the two methods of regularization is used as long as the s quark is considered massive, because both regularizations give rise to the same on-shell wave function renormalization and because of the validity of the Bloch–Nordsieck theorem. In the heavy b-quark limit, realized by treating the s quark as massless, however, the two regularization methods give different results. It is argued that only dimensional regularization leads to correct results unless some unconventional on-shell wave function renormalization of massless fermion fields is adopted.

Precision analysis of experiments studying the beta decay of the free neutron: Standard model and possibilities of its violation

The current status of experimental results on the beta decay of the free neutron is described. An analysis of these data shows that, within the present-day accuracy, the data are fully consistent with the Standard Model of electroweak interaction. At the same time, there exists the possibility of deviations from the Standard Model at a level of 1%. The possible violations due to the contributions of right-handed (WR) bosons, as well as of leptoquark mechanisms introducing anomalous scalar and tensor terms in the effective weak-interaction Hamiltonian, which include the right-handed neutrinos, are estimated. In the last case, the analysis is performed by an analytic method that makes it possible to take into account, for the first time, the possibility of CP violation.

Second-order corrections to correlations in muon capture

Muon capture by a nucleus with an arbitrary spin is considered. Second-order terms in 1/M in the effective weak-interaction Hamiltonian are taken into account. New terms in the Hamiltonian associated with the nucleon-nucleus potential are found. A general expression for the angular distribution of neutrinos (recoil nuclei) is derived for polarized muons and oriented target nuclei. Second-order contributions to the amplitudes M u (k) are obtained. This allows one to calculate second-order corrections to any integral and correlation characteristics in muon capture that are expressed in terms of M u (k).

Higgs boson mass constraints from precision data and direct searches

Two of the nine measurements of ${\mathrm{sin}}^{2}\ensuremath{\theta}{}_{\mathrm{eff}}^{\mathrm{lepton}},$ the effective weak interaction mixing angle, are found to be in significant conflict with the direct search limits for the standard model (SM) Higgs boson. Using a scale factor method, analogous to one used by the Particle Data Group, we assess the possible effect of these discrepancies on the SM fit of the Higgs boson mass. The scale factor fits increase the value of ${\mathrm{sin}}^{2}\ensuremath{\theta}{}_{\mathrm{eff}}^{\mathrm{lepton}}$ by as much as two standard deviations. The central value of the Higgs boson mass increases as much as a factor of 2, to $\ensuremath{\simeq}200 \mathrm{G}\mathrm{e}\mathrm{V},$ and the 95% confidence level upper limit increases to as much as 750 GeV. The scale factor is based not simply on the discrepant measurements, as was the case in a previous analysis, but on an aggregate goodness-of-fit confidence level for the nine measurements and the limit. The method is generally applicable to fits in which one or more of a collection of measurements are in conflict with a physical boundary or limit. In the present context, the results suggest caution in drawing conclusions about the Higgs boson mass from the existing data.

Parity violation in charged-particle resonance reactions.

Parity nonconservation (PNC) measurements utilizing charged-particle resonance reactions are proposed. PNC observables have been calculated for over 300 resonance pairs (with the same angular momentum and opposite parity) in five {ital s}-{ital d} shell nuclei. Detailed numerical results are presented for the longitudinal analyzing powers in the {sup 31}P({ital p}{searrow},{alpha}{sub 0}) reaction. There is strong dependence on energy, angle, and resonance parameters. A figure of merit that includes both the relative enhancement of the parity violation and the cross section is used to identify the most promising resonances for study. A proposed detector design and experimental procedure are described. These measurements should provide information on the weak spreading width (the effective nucleon-nucleus weak interaction) in light nuclei. {copyright} {ital 1996 The American Physical Society.}

Parity violation in charged particle resonances

Recent parity nonconservation (PNC) measurements in nuclei use the compound nucleus as a laboratory for the study of symmetry breaking, with the symmetry breaking matrix elements treated as random variables. This approach is made appealing by the observation of very large parity violation in neutron resonances. One key issue is the mass dependence of the effective nucleon-nucleus weak interaction. The neutron measurements do not appear feasible for light nuclei. We have calculated PNC observables for charged particle resonance reactions for over 100 states in five s-d shell nuclides using experimental values of the resonance parameters. Analyzing powers show strong dependence on energy and angle, and vary greatly from resonance to resonance. Proposed PNC experiments are discussed.

ANALYSIS OF NONLEPTONIC KAON DECAYS USING CHIRAL-LOOP EXPANSION

The amplitudes of the decays K→2π and K→3π have been calculated within the chiral Lagrangian approach including chiral loops. The phenomenological structure of the effective weak meson interaction has then been fixed by experimental data. We estimate the CP asymmetry for decay probabilities and slope parameters in K±→π±π±π∓ and K±→π0π0π± decays using data on Re(ε′/ε). The modification of the Li-Wolfenstein relation for the direct CP-violation parameter in [Formula: see text] decays is also discussed.

The K ∗ pole model of K → ππ decays and final-state interactions

It is shown that final-state interactions can enhance (suppress) substantially the ΔI = 1 2 (ΔI = 3 2 ) K → ππ parity-violating decay amplitude calculated from the K ∗ vector meson pole model. This enhancement (suppression) combined with short-distance QCD corrections to the effective weak interaction almost brings the K ∗ pole model into agreement with experiment.

Phenomenological Kähler sigma models: (II). Four-Fermi interactions in a realistic composite model

The formalism of phenomenological Kähler sigma models is applied to a semi-realistic supersymmetric composite model. The residual four-Fermi interactions, described geometrically in terms of the curvature tensor of the Kähler target manifold, are shown to have coupling strengths independent of the scale of the effective weak interactions, as is essential for the experimental viability of the model.

Role of [formula omitted] at the Z° peak

The possible role of the MSparameter sin 2 θ w(m z) in discussing physics at the Z° peak is outlined. A radiative correction Δ r ̂ (the analogue or Δr, which links directly sin 2 θ w(m> z) to m z , is introduced and evaluated in the standard model. Assuming 60 GeV × m t < 200 GeV, 10 GeV < m H < 1 TeV, employing Δ r ̂ and m z =91.12±0.16 GeV leads to an accurate determination sin 2 θ w(m z)=0.2328±0.0012±0.0022 (the first error is due to δm z and the second reflects the m t , m H uncertainty). It is interesting to note that this result is consistent with the simplest SUSY GUTs prediction. Accurate values for α i ( m z ) ( i=1,2) are also given. Constraints due to gauge invariance in defining effective weak interaction angles are discussed.

Supplementary evidence for T violation.

The only significant experimental evidence for T violation is based on the data on CP violation and other measured properties of the decay amplitudes of neutral K mesons and their combined use in an analysis based on the Bell-Steinberger unitarity relation or its equivalent. It has been pointed out by Kenny and Sachs that there is a technical possibility that this conclusion can be evaded because the argument depends on the assumption that the effective (phenomenological) weak-interaction Hamiltonian from which the decay amplitudes are derived is Hermitian. The purpose of this paper is to show that this assumption can be circumvented by making use of additional data on the unitarity of the decay amplitudes of both the neutral and charged K mesons to establish an upper limit on the magnitude of amplitudes associated with T-invariant anti-Hermitian interactions. It is assumed that the order of magnitude of such terms is in conformity with the values expected on the basis of the usual approximate isotopic spin selection rules for the weak interactions. Then it is found that if all the relevant weak interactions are T invariant, the data on unitarity would place an upper limit on the CP-violation parameter Vertical Bareta/sub +/-Verticalmore » Bar of Vertical Bareta/sub +/-Vertical Bar<0.34 x 10/sup -3/, which is an order of magnitude smaller than the observed value. It is therefore found that the possibility of including in the analysis a non-Hermitian effective weak Hamiltonian up to the limit permitted by the data on unitarity does not alter the conclusion that T invariance is violated.« less

A simple model of neutrinoless double beta decay

By modifying the properties of the neutrino, we formulate a simple model of effective weak interactions, which allows the neutrinoless double beta decay. The estimated upper bound for the neutrino mass is of the order of 10 eV.

Effective weak interaction theory with a possible new vector resonance from a strong higgs sector

We consider the effective lagrangian for electroweak interactions in the limit of a strong interacting Higgs sector ( m H → ∞). We assume that the appearing SU(2) v hidden local symmetry is realized through a new dynamical vector boson resonance V. We derive the physical admixtures and masses of W, Z and V bosons and calculate the couplings of the physical bosons to fermions. No physical Higgs remains in the spectrum. We find that the standard low energy phenomenology of weak interactions, as well as the W-, Z-masses and properties, may be rather closely reproduced in our effective theory, even for low values of the mass of the new vector resonance, within presently accessible energies.

Double Beta Decay and Majorana Neutrino

This review consists of three parts: Various properties of the quantized neutrino fields are summarized in part I from the viewpoint that a Dirac neutrino consists of two Majorana neutrinos with a degenerate mass but with opposite CP sings. It is shown why the Dirac neutrino has a freedom of the phase transformation to guarantee the lepton number conservation, while the Majorana neutrino does not. Part II is devoted to the theoretical investigation of the double beta decay and the analysis on the experimental data. Various corrections due to the vanishing terms in the closure approximation and the higher spherical waves of leptons are estimated. The constraints on the effective neutrino mass and the effective right-handed weak interaction parameters are derived from the present experimental data. In part III, the above bounds are compared with those from other processes like the 3H decay, the neutrino oscillation, the π-µ-e decay, etc. The possible mixing schemes of the neutrino system are explored.

Muon Decay and the Majorana Neutrino

Recently, the Berkeley group reported the precise and excellent experimental result on the e+ spectrum end point in /1+ decay.') In order to get the lower limit for the possible heavier (righthanded) gauge boson mass M( Wz»380 GeV, they have used the following assumptions made by Beg, Budny, Mohapatra and Sirlin;Z) (i) the manifest left-right symmetry in the charged current sector, (ii) no mirror leptons, (iii) the CP invariance, (iv) the smallness of all neutrino masses (Ll j =(mjlmp)4{.l), m" being the f.I. mass. In this note, we shall reinterpret this Berkeley result from the viewpoint of the massive Majorana neutrino, and show the information which we can draw from this result for the case where the right-handed Majorana neutrino (Nn+k) has a quite large mass mn+kl m,,~ 1. Namely, the fourth assumption (Ll j 4{.l) is reexamined by taking into account the effect due to the neutrino mixing. In order to be self-contained, we shall start from the effective lepton-hadron weak interaction Hamiltonian to treat the 7[+ decay;