abstract

Overview is given of the theoretical issues of the physics which can be addressed with nuclear beams circulating in HERA. It is shown that such experiments widen considerably the horizon for probing QCD compared to that from free nucleon targets. They would allow to study nonlinear QCD phenomena at small \(x\), understand dynamics of nuclear shadowing, as well as the origin of diffraction in deep inelastic scattering. Interplay between the physics to be studied at HERA and in \(AA\) collisions at RHIC and LHC is also discussed.

abstract

The QCD expectations for the behaviour of the deep inelastic scattering structure functions in the region of small values of the Bjorken parameter \(x\) are summarized. The Balitzkij, Lipatov, Fadin, Kuraev (BFKL) equation which sums the leading powers of \(\alpha _s\) ln(1/\(x\)) is described and confronted with the “conventional” formalism based on the leading order QCD evolution equations. The small \(x\) behaviour of the spin dependent structure function \(g_1\) is also discussed. The dedicated measurements of the hadronic final state in deep inelastic scattering at small \(x\) probing the QCD pomeron are described. This includes discussion of the deep inelastic scattering accompanied by forward jets as well as production of forward prompt photons and \(\pi ^0-s\). Finally the basic facts concerning the deep inelastic diffraction are briefly summarized.

abstract

The first part of my talk is a very brief review of the Pomeron and how it is described in perturbative QCD by the BFKL equation. The BFKL Pomeron differs from that observed in total cross sections, but there is some hope that it may be observed in perturbative high energy processes. A particular application of the BFKL equation is to the evolution of the gluon at low \(x\) and the consequences that this has on the structure functions, \(F_2\) and \(F_L\). Finally I discuss the CCFM equation which contains both the BFKL and more traditional DGLAP forms of gluon evolution.

abstract

We describe recent perturbative QCD calculations of diffractive \(J/\psi \) and open \(c \bar c\) production at HERA and show that they offer a sensitive probe of the gluon density at small \(x\). We discuss briefly the \(Q^2\) and \(\beta \) dependence of the cross section and show that estimates of the higher order corrections indicate a strong enhancement of the open charm production.

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The perturbative QCD approach to multiparticle production assuming Local Parton Hadron Duality (LPHD) and some recent results are discussed. Finite asymptotic scaling limits are obtained for various observables, after an appropriate rescaling, in the Double Logarithmic Approximation (DLA). Non-asymptotic corrections are also known in some eases. The DLA applies also to very soft particle production where energy conservation constraints can be neglected. In this region the particle density follows rather well a scaling behaviour over the full energy range explored so far in \(e^+e^-\) annihilation.

abstract

The new approach to decays of heavy quarkonia, based on factorization and expansions in powers of the relative velocity of the valence quarks is reviewed.

abstract

These lectures review some of the progress made in the quantitative understanding of \(B\) decays. The emphasis here is on applications of QCD using perturbative and non-perturbative techniques. In some cases, however, phenomenological models must at present be invoked to make meaningful comparison with data. The resulting picture is consistent with the standard model (SM) and this agreement is quantified in terms of the branching ratios, mixing probabilities, and lifetimes which measure the charge current and effective flavour changing neutral current transitions involving \(B\) hadrons. This, in turn, enables a determination of five of the nine elements of the quark mixing matrix. We discuss several proposals on improving the precision on the parameters of this matrix in forthcoming experiments. Issues intimately related to the quark mixing matrix such as the profile of the unitarity triangle and CP-violating asymmetries in \(B\) decays are discussed. In particular, we emphasize the role of rare \(B\) decays and \(B^0\)–\(\overline {B^0}\) mixings in testing the SM quantitatively and in searching for physics beyond the SM.

abstract

Perturbative corrections of the order of \(\alpha _s\) to inclusive double differential lepton distribution from \(b\) quark decay are considered. A perturbative correction to the charged lepton energy spectrum has been calculated for an arbitrary charged lepton mass. The perturbative contribution suppresses the partial rate but almost does not change the shape of energy distribution. Applications of our result to semileptonic \(B\) meson decays are briefly discussed.

abstract

Weak hyperon decays present us with a couple of interesting problems. After discussing hyperon nonleptonic decays to set a reliable reference basis, we review the status of the long-standing puzzle of weak radiative hyperon decays and the question of validity of Hara’s theorem. The conflict between expectations based on Hara’s theorem and experiment as well as the violation of that theorem in the quark and vector meson dominance models are briefly discussed. The importance of upcoming experiments as tests of Hara’s theorem is stressed. Significant role of hyperon nonleptonic decays in search for direct CP violation is also pointed out.

abstract

These lecture notes give a pedagogical introduction to the use of dispersion relations in loop calculations. We first derive dispersion relations which allow us to recover the real part of a physical amplitude from the knowledge of its absorptive part along the branch cut. In perturbative calculations, the latter may be constructed by means of Cutkosky’s rule, which is briefly discussed. For illustration, we apply this procedure at one loop to the photon vacuum-polarization function induced by leptons as well as to the \(\gamma f \bar f\) vertex form factor generated by the exchange of a massive vector boson between the two fermion legs. We also show how the hadronic contribution to the photon vacuum polarization may be extracted from the total cross section of hadron production in \(e^+e^-\) annihilation measured as a function of energy. Finally, we outline the application of dispersive techniques at the two-loop level, considering as an example the bosonic decay width of a high-mass Higgs boson.

abstract

The application of the background-field method to the electroweak Standard Model and its virtues are reviewed. Special emphasis is directed to the Ward identities that follow from the gauge invariance of the background-field effective action. They are compatible with on-shell renormalization and imply a decent behavior of the background-field vertex functions. Via the usual construction of connected Green functions they transfer to Ward identities for connected Green functions which, in distinction to the conventional formalism, remain exactly valid in finite orders of perturbation theory even if a Dyson summation of self-energies (within a systematic use of one-particle irreducible building blocks) is performed. Finally, we comment on the interplay between gauge invariance and gauge-parameter (in-)dependence of vertex and Green functions and the uniqueness of resummation procedures.

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This lecture reviews various Higgs-sector amplitudes which have been calculated to two loops in the Higgs quartic coupling. After explaining the framework of these calculations, the perturbative behaviour of these amplitudes is discussed, and perturbative upper bounds on the Higgs boson mass are given.

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The radiative corrections involved in the precise determination of the electroweak mixing angle measured at the \(Z^0\) peak are reviewed in detail, with particular emphasis on the new calculation of two-loop heavy top effects. This example serves as a brief pedagogical introduction to the problems and techniques of higher order electroweak calculations.

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The status of the standard model predictions for electroweak precision observables is summarized and the status of the standard model and of the MSSM is discussed in view of the most recent data.

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Comparisons are presented of the ability of RHIC experiments to perform hadronic studies at high energy densities. Emphasis is placed on the “common” physics topics that all four experiments will study. As expected, the two “large” experiments at RHTC will provide rich data sets. However, the two “small” RHIC experiments will also contribute significantly to many of the studies.

abstract

Among various projects for future high-energy colliders a special place is occupied by the muon collider (for a review see Ref. [1]). It is interesting to note that if this machine is ever built, this will be the first place where collisions of unstable particles can be investigated. It turns out that even though the muon is only slightly unstable, this instability, as a matter of principle, brings in a new interesting effect. We name this effect a linear beam size effect because it predicts that certain scattering cross sections must be proportional to the transverse sizes of the colliding muon beams [2,3,4]. This paper is devoted to the detailed presentation of this effect.

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A study on the effective anomalous interactions, up to dimension 5, of the top quark with the electroweak gauge bosons is made in the non-linear Chiral Lagrangian approach. Bounds on the anomalous dimension four terms are obtained from their contribution to low energy data. Also, the potential contribution to the production of top quarks at hadron colliders (the Tevatron and the LHC) and the electron Linear Collider from both dimension 4 and 5 operators is analyzed.

abstract

Top quark pair production close to threshold at a next linear collider is discussed, with special focus on the influence of rescattering corrections. Numerical results are shown for the differential cross-section, i.e. the momentum distribution and the forward backward asymmetry, and for moments of the angular distribution of leptons arising from the semileptonic top quark decay.

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This article presents a brief overview of the potential of the ATLAS detector at LHC for the detectability of the Higgs boson of the Minimal Supersymmetric Standard Model. The expected rates, backgrounds and significances are discussed channel by channel with the realistic assumptions for the detector performance. As final results the range of the MSSM parameter space where expected significances exceed 5\(\sigma \) value is shown on the \((m_A\),tan\(\beta \)) plane for the ATLAS detector alone and for combined results from ATLAS and CMS detectors. It is concluded, that potential of combined both LHC detectors will allow for the full coverage in the Higgs sector of the studied region of the MSSM parameter space. The direct impact of the SUSY particles sector on the Higgs observability is neglected so far.

abstract

I briefly review the Higgs sector in the Standard Model and in its minimal supersymmetric extension. After summarizing the properties of the Higgs bosons, I will discuss the prospects for discovering these particles at the present colliders LEP2 and Tevatron, and at the next generation colliders LHC and a high-energy \(e^+e^-\) linear collider. The possibilities of studying the properties of the Higgs bosons will be then summarized.

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We present the techniques of the calculations of the 1-loop radiative corrections to the neutral MSSM Higgs boson masses and production cross sections in the on-shell renormalization scheme. We discuss possible applications to the analysis of experimental results from LEP1 and the expected physics potential of LEP2 and the NLC.

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A short description is given of the perspectives for the detection of supersymmetric particles at the LHC. The first part of the lecture is on inclusive searches addressing the Minimal Supersymmetric Standard Model. Some results are then given of ongoing work on a model based on minimal supergravity (SUGRA).

abstract

Experimental aspects of SUSY at future linear \(e^+e^-\) colliders are discussed. In particular, the procedures to determine the masses and mixings of SUSY particles are explained with emphasis put on the crucial role of polarized electron beam. These measurements constrain the SUSY breaking parameters and guide us to conduct systematic searches. The implications of the so determined SUSY breaking parameters are discussed also in relation to the GUT scale physics.

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I briefly review some recent work on the flavour dependence of supersymmetrice theories. Attempts to solve the flavour puzzle based on horizontal — or vertical — symmetries predict flavour structures in the supersymmetric sector that could serve to constrain and even to test such theories in present and future experiments.

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Gauge–Yukawa Unification (GYU) is a renormalization group invariant functional relation among gauge and Yukawa couplings which holds beyond the unification point in Grand Unified Theories (GUTs). We present here various models where GYU is obtained by requiring the principles of finiteness and reduction of couplings. We examine the consequences of these requirements for the low energy parameters, especially for the top quark mass. The predictions are such that they clearly distinguish already GYU from ordinary GUTs. It is expected that it will be possible to discriminate among the various GYUs when more accurate measurements of the top quark mass are available.

abstract

The renormalization of supersymmetric gauge theories requires solution of either the problem of handling canonical fields of vanishing dimensions or the problem of non-linear symmetry transformations. Since the supersymmetric extension of the standard model has become a realistic option the use of the respective supersymmetry Ward identity represents a relevant issue in phenomenology.

abstract

These two lectures give a pedagogical introduction to the “string-inspired” worldline technique for perturbative calculations in quantum field theory. This includes an overview over the present range of its applications. Several examples are calculated in detail, up to the three-loop level. The emphasis is on photon scattering in quantum electrodynamics.