Regular Series

Vol. 28 (1997), No. 11, pp. 2213 – 2545

Neutrino Masses

Acta Phys. Pol. B 28, 2213 (1997)

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67 years after neutrinos had been introduced into physics many of their properties remain unknown. An open question of whether neutrinos have masses is addressed in the present lecture. After reviewing briefly limits on neutrino masses obtained in direct experiments, indirect searches for neutrino masses are discussed. Particular attention is paid to the search for neutrino oscillations. The Sun is a particularly strong source of neutrinos and for this reason has been used for pertinent experiments. The different solar neutrino experiments are compared in the lecture.

On the Possibilities of Distinguishing Dirac from Majorana Neutrinos

Acta Phys. Pol. B 28, 2225 (1997)

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The problem if existing neutrinos are Dirac or Majorana particles is considered in a very pedagogical way. After a few historical remarks we recall the theoretical description of neutral spin 1/2 particles, emphasizing the difference between chirality and helicity which is important in our discussion. Next we describe the properties of neutrinos in the cases when their interactions are given by the standard model and by its extensions (massive neutrinos, right-handed currents, electromagnetic neutrino interaction, interaction with scalar particles). Various processes where the different nature of neutrinos could in principle be visible are reviewed. We clear up misunderstandings which have appeared in last suggestions how to distinguish both types of neutrinos.

The Kinematics and Dynamics of Flavor Mixing

Acta Phys. Pol. B 28, 2259 (1997)

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In view of the observed strong hierarchy of the quark and lepton masses and of the flavor mixing angles, it is argued that the description of flavor mixing must take this into account. One particularly interesting way to describe the flavor mixing, which, however, is not the one used today, emerges, which is particularly suited for models of quark mass matrices based on flavor symmetries. We conclude that the unitarity triangle important for \(B\) physics should be close to or identical to a rectangular triangle. CP violation is maximal in this sense.

Constrained Differential Renormalization

Acta Phys. Pol. B 28, 2279 (1997)

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We review the method of differential renormalization, paying special attention to a new constrained version for symmetric theories.

Electroweak Theory and the 1996/97 Precision Electroweak Data

Acta Phys. Pol. B 28, 2291 (1997)

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We review the empirical evidence for the validity of the Standard Electroweak Theory in Nature. The experimental data are interpreted in terms of an effective Lagrangian for Z physics, allowing for potential sources of SU(2) violation and containing the predictions of the Standard Electroweak Theory as a special case. Particular emphasis is put on discriminating loop corrections due to fermion-loop vector-boson propagator corrections on the one hand, from corrections depending on the non-Abelian structure and the Higgs sector on the other hand. Results from recently obtained fits of the Higgs-boson mass are reported, yielding \(M_{\rm H} \lesssim 430\) GeV [680 GeV] at 95% C.L. based on the input of \(s^{-2}_{\rm w}({\rm LEP} + {\rm SLD})_{'97} = 0.23152 \pm 0.00023\) \([s^{-2}_{\rm w}(LEP)_{'97} = 0.23196 \pm 0.00028]\). The LEP2 data provide first direct experimental evidence for non-zero non-Abelian couplings among the electroweak vector bosons.

The \(Z\) Boson Resonance and Radiative Corrections

Acta Phys. Pol. B 28, 2317 (1997)

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The \(Z\) line shape is measured at LEP with an accuracy at the per mill level. Usually it is described in the Standard Model of electroweak interactions with account of quantum corrections. Alternatively, one may attempt different model-independent approaches in order to extract quantities like mass and width of the \(Z\) boson. If a fit deviates from that in the standard approach, this may give hints for New Physics contributions. I describe two model-independent approaches and compare their applications to LEP data with the Standard Model approach.

Multi-Loop Calculations in the Standard Model: Techniques and Applications

Acta Phys. Pol. B 28, 2333 (1997)

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We present a review of the Bielefeld-Dubna activities on the multiloop calculations. In the first part, a C-program DIANA (DIagram ANAlyser) for the automation of Feynman diagram evaluations is presented, in the second part various techniques for the evaluation of scalar diagrams are described, based on the Taylor expansion method and large mass expansion.

Higher-Order Corrections to Precision Observables in the Standard Model and the MSSM

Acta Phys. Pol. B 28, 2351 (1997)

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A summary of recent results obtained for higher-order corrections to precision observables in the Standard Model and the Minimal Supersymmetric Standard Model is given. In the Standard Model, electroweak two-loop results valid for arbitrary values of the masses of the top quark, the Higgs boson and the gauge bosons are discussed. For the example of two specific diagrams the exact two-loop result is compared with the result of an expansion in the top-quark mass up to next-to-leading order. Furthermore the Higgs-mass dependence of the two-loop corrections to the relation between the gauge-boson masses is analyzed. In the MSSM, the gluonic corrections to \(\Delta r\) are derived. They are compared with the leading contribution entering via the \(p\) parameter.

Phenomenology of Supergravity Unified Models

Acta Phys. Pol. B 28, 2367 (1997)

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Recent developments in the phenomenology of supergravity grand unified models are reviewed. Two special topics are discussed: (i) the search for neutral Higgs bosons in the minimal supergravity model via their decays into muon pairs at the CERN LHC, and (ii) constraints from theoretical requirements and the relic density of neutralino dark matter on the supergravity parameter space.

Low-Energy Gravitino Interactions

Acta Phys. Pol. B 28, 2383 (1997)

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I discuss the low-energy limit of several processes involving only ordinary particles and gravitinos. Astrophysical and laboratory applications are briefly addressed.

One-Loop Weak Dipole Moments of Heavy Fermions in the MSSM

Acta Phys. Pol. B 28, 2389 (1997)

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The MSSM predictions at the one-loop level for the weak dipole moments of the \(\tau \) lepton and the \(b\) quark are presented. The imaginary part of the AWMDM is of the order of the SM contribution whereas the real part may be a factor 5 (20) larger for the \(\tau (b)\) in the high \(\tan \beta \) scenario, still a factor five below the QCD contribution in the \(b\) case. More interestingly, a contribution up to twelve orders of magnitude larger than in the SM may be obtained, already at the one-loop level, for the WEDM in a MSSM with complex parameters.

Angular and Energy Distribution in Neutralino Production and Decay with Complete Spin Correlations

Acta Phys. Pol. B 28, 2395 (1997)

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We study the process \(e^-e^+ \to \tilde \chi ^0_1 \tilde \chi ^0_2\) with the subsequent decay \(\tilde \chi ^0_2 \to \tilde \chi ^0_1 l^+ l^-\) taking into account the complete spin correlations between production and decay. We present numerical results for the lepton angular distribution and the distribution of the opening angle between the outgoing leptons for \(\sqrt {s} = 182\) GeV. We examine representative mixing scenarios in the MSSM and study the influence of the common scalar mass parameter \(m_0\). For the lepton angular distribution, the effect of the spin correlations amounts to up to 20%. The shape of the lepton angular distribution is very sensitive to the mixing in the gaugino sector and to the value of \(m_0\). We find that the opening angle distribution is suitable for distinguishing between Higgsino-like and gaugino-like neutralinos.

Associated Production and Decay of Neutralinos and Selectrons in \(e^-\gamma \) Collisions

Acta Phys. Pol. B 28, 2401 (1997)

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In the framework of the Minimal Supersymmetric Standard Model (MSSM) with \(R\)-parity conservation, angular distributions and total cross sections for the process \(e^-\gamma \to \tilde \chi ^0_1 \tilde e_{L/R} \to \tilde \chi ^0_1 \tilde \chi ^0_1 e^-\) are presented in the \(e^-\gamma \)-cms and the \(e^-e^+\)-cms of a photon linear collider (PLC) with CMS-energy \(\sqrt {s} = 500\) GeV.

Hera Data at High \(Q^2\): A Sign of New Physics?

Acta Phys. Pol. B 28, 2407 (1997)

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I review theoretical interpretations of the recently observed excess of high-\(Q^2\) events in deep-inelastic positron–proton scattering at HERA, concentrating on scenarios with leptoquarks or squarks with \(R\)-parity violating couplings.

Sleptons in \(R\)-Parity Violating SUSY

Acta Phys. Pol. B 28, 2423 (1997)

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In \(R\)-parity violating SUSY models, sleptons can be produced singly in \(e^+e^-\) and \(q \bar q\) collisions. The formation of slepton resonances at LEP2 or Tevatron at current energies is an exciting possibility. Existing LEP2 and Tevatron data can be exploited to look for sleptons and, if unsuccessful, to derive bounds on the Yukawa couplings of sleptons to quark and lepton pairs.

Physics Beyond the Standard Model at HERA

Acta Phys. Pol. B 28, 2439 (1997)

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This talk is divided in two parts. In the first one we discuss the signals of the Minimal Supersymmetric Standard Model through the production of \(\tilde e \tilde q\). The second part is devoted to contact terms. The bounds on the mass scale \(\mit \Lambda \) obtained from atomic parity violation experiments and from LEP are reviewed. Afterwards, we show that the excess of events at high \(Q^2\) observed at HERA could be explained in terms of these contact terms.

Low \(x\) Inelastic Electron Scattering from Generalized Vector Dominance

Acta Phys. Pol. B 28, 2453 (1997)

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It is shown that the HERA experimental data on deep inelastic scattering at low values of the scaling variable \(x \leq 0.05\) are in good agreement with predictions from Generalized Vector Dominance in the full kinematic range from \(Q^2 = 0\) (photoproduction) to \(Q^2 \simeq 350\) GeV.

Top Quark Pair Production and Decay Near Threshold in \(e^+e^-\) Collisions

Acta Phys. Pol. B 28, 2461 (1997)

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We review the physics involved in the production and decay of top quarks in \(e^+e^- \to t \bar t\) near threshold, with special emphasis on the recent theoretical study on the decay process of top quarks in the threshold region. The energy-angular distribution of \(l^+\) in semileptonic top decays is calculated including the full \(\mathcal {O}(\alpha _s)\) corrections. Various effects of the final-state interactions are elucidated. A new observable is defined near threshold, which depends only on the decay of free polarized top quarks, and thus it can be calculated without bound-state effects or the final-state interactions.

New Analysis of the \(\Delta I = 1/2\) Rule in the \(1/N_c\) Expansion for \(K \to \pi \pi \) Decays

Acta Phys. Pol. B 28, 2479 (1997)

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We analyze long-distance contributions to the \(K \to \pi \pi \) amplitudes relevant for the \(\Delta I = 1/2\) selection rule in the framework of the \(1/N_c\) expansion. We use a modified prescription for the identification of meson momenta in the chiral loop corrections to gain a consistent matching with the short-distance part. Our approach involves a separation of non-factorizable and factorizable \(1/N_c\) corrections. Along these lines we calculate the one-loop contributions from the lowest order Lagrangian. Our main result is an additional enhancement of the \(\Delta I = 1/2\) channel amplitude which we find in good agreement with experiment.

Probing the Helicity Structure of \(b \to s \gamma \) in \(\mit \Lambda _b \to \mit \Lambda _{\gamma }\)

Acta Phys. Pol. B 28, 2489 (1997)

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We investigate the rare decay \(\mit \Lambda _b \to \mit \Lambda _{\gamma }\) which receives both short and long distance contributions. We estimate the long distance contributions and find them very small. The form factors are obtained from \(\mit \Lambda _c \to \mit \Lambda \) \(\ell \bar \nu _{\ell }\) using heavy quark symmetry and a pole model. The short distance piece opens a window to new physics and we discuss the sensitivity of \(\mit \Lambda _b \to \mit \Lambda _{\gamma }\) to such effects.

Form Factors and Radiative Corrections in \(Z^\prime \) Physics

Acta Phys. Pol. B 28, 2495 (1997)

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This lecture contains a pedagogical approach to the description of \(Z^\prime \) physics in the formalism of form factors. Usually, only electroweak corrections are described by form factors, which modify the Weinberg angle and the overall normalization. It is demonstrated how this formalism can be extended to include different Born contributions. In the second part of the lecture, QCD and QED corrections are considered. The development and consequences of the radiative tail for a \(Z^\prime \) search are discussed in detail.

Search for SM Higgs Signals at LHC

Acta Phys. Pol. B 28, 2509 (1997)

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Both the ATLAS and CMS collaborations have developed search strategies (which are quite similar) to find a Standard Model Higgs boson at the LHC. This paper describes the basic concepts of them, it is mostly based on the Technical Proposals of the two experiments ATLAS (Technical Proposal CERN/LHC/94-43 (15.Dez 1994) and Technical Proposal CMS Collaboration CERN/LHC/94-38 (15.Dez 1994)). After combining the different channels both experiments will be able to see a SM Higgs boson in the range of 80 GeV/\(c^2 \gt m_H \gt 1000\) GeV/\(c^2\) with at least \(5\sigma \) significances after collecting an integrated luminosity of \(10^5\) pb\(^{-1}\).

Has the General Two-Higgs-Doublet Model Unnatural FCNC Suppression? An RGE Analysis

Acta Phys. Pol. B 28, 2515 (1997)

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There is a widespread belief that the general two-Higgs-doublet model (G2HDM) behaves unnaturally with respect to evolution of the flavor-changing neutral Yukawa coupling parameters (FCNYCP’s) — i.e. , that the latter, although being suppressed at low energies of probes, in general increase by a large factor as the energy of probes increases. We investigate this, by evolving Yukawa parameters by one-loop renormalization group equations and neglecting contributions of the first quark generation. For patterns of FCNYCP suppression at low energies suggested by existing quark mass hierarchies, FCNYCP’s remain remarkably stable (suppressed) up to energies very close to the Landau pole. This indicates that G2HDM preserves FCNYCP suppression, for reasonably chosen patterns of that suppression at low energies.

Dark Matter in the Universe

Acta Phys. Pol. B 28, 2525 (1997)

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The review of the dark matter problem is given from broad astrophysical perspective. The state of the art presentation of different methods of inference about the dark matter is provided together with recent observational suggestions concerning composition of the dark matter.

A Nonhomogeneous Inflation

Acta Phys. Pol. B 28, 2541 (1997)

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A nonhomogeneous inflation in the scalar field theory is studied. The nonhomogeneity of the Universe is used to determine the scalar field potential. Connection of the model with the elementary particles theory is suggested.


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