The relativistic Winther-Alder functions 9 .2 B-The total cross sections in the PWBA and in the semiclassical approximation. .. . 9 .3 C-Useful handy formulas 101 10 .0 Referenees vi EEectromagnetic Proeesses and they are equivalent to two pulses of plane polarized radiation incident on the target (see figure 1 .1b) : one in the beam direction (P1), and another perpendicular to it (P2). In the case of the pulse P, the equivalency is exact. Since the electric field in the z-direction is not accompanied by a corresponding magnetic field, the equivalency is not complete for the pulse P 2, but this will not where the z and Introduction Eleetromagnetic Proeesses Eiectromagnetic Proeesses The ionization of atomic electrons in RHI collisons has very large cross sections and is an extensively studied process, and we show in chapter 6 the main theoretical aspects of it. Chapter 7 is dedicated to the production of lepton pairs in RHI collisions. The consequences of the large cross sections for the production of electron-positron pairs are analysed. Of special interest for the development of relativistic heavy ion colliders is the case of electron-positron pair production with capture of the electron in an atomic orbit in the ions. Conclusions and an outlook are given in chapter B. n=-oo \\ j Then the integral over 0 in (2 .1 .8) leads to Wern (r, w) = et Zü eKm (W b!yv) 5rz sin 8 d8 e i (wiv) r cos 0 YYm (6,0) Im v sin. (2 .1 .10) 0 Writing Yein (8,0) in terms of the Gegenbauer polynomials C,(x) (see e .g. Ab-64, p. 771), and using the Gegenbauer integral (see e .g. Gr-65, p. 832, eq. 7 .333) one finds for m> 0 W,,,m(r,w)= ZVe .v 167t(2e+ 1) (t°+m)! ] 1f2 (2m-1)1r/ m (2 .L11) x (c/yv) m Km (wbI yv) j((xr) , 7 1 ey (2 .1 .4) (2 .1 .5)

229 Pages, 121 figuresWe discuss the physics of large impact parameter interactions at the LHC: ultraperipheral collisions (UPCs). The dominant processes in UPCs are photon-nucleon (nucleus) interactions. The current LHC detector configurations can explore small $x$ hard phenomena with nuclei and nucleons at photon-nucleon center-of-mass energies above 1 TeV, extending the $x$ range of HERA by a factor of ten. In particular, it will be possible to probe diffractive and inclusive parton densities in nuclei using several processes. The interaction of small dipoles with protons and nuclei can be investigated in elastic and quasi-elastic $J/\psi$ and $\Upsilon$ production as well as in high $t$ $\rho^0$ production accompanied by a rapidity gap. Several of these phenomena provide clean signatures of the onset of the new high gluon density QCD regime. The LHC is in the kinematic range where nonlinear effects are several times larger than at HERA. Two-photon processes in UPCs are also studied. In addition, while UPCs play a role in limiting the maximum beam luminosity, they can also be used a luminosity monitor by measuring mutual electromagnetic dissociation of the beam nuclei. We also review similar studies at HERA and RHIC as well as describe the potential use of the LHC detectors for UPC measurements

Due to coherence, there are strong electromagnetic fields of short duration in very peripheral collisions. They give rise to photon-photon and photon-nucleus collisions with a high flux up to an invariant mass region hitherto unexplored experimentally. After a general survey of the field equivalent photon numbers and photon-photon luminosities, especially for relativistic heavy ion collisions, are discussed. Special care needs to be taken to include the effects of the strong interaction and nuclear size in this case. Photon-photon and photon-hadron physics at various invariant mass scales are then discussed. The maximum equivalent photon energy in the lab-system (collider frame) are typically of the order of 3 GeV for RHIC and 100 GeV for LHC. Diffractive processes are an important background process. Lepton-pair, especially electron-positron pair production is copious. Due to the strong fields there will be new phenomena, like multiple e + e − pair production. The experimental techniques to select γγ-processes are finally discussed together with important background processes.

In central collisions at relativistic heavy ion colliders like the Relativistic Heavy Ion Collider RHIC/Brookhaven and the Large Hadron Collider LHC (in its heavy ion mode) at CERN/Geneva, one aims at detecting a new form of hadronic matter -the Quark Gluon Plasma. It is the purpose of this review to discuss a complementary aspect of these collisions, the very peripheral ones. Due to coherence, there are strong electromagnetic fields of short duration in such collisions. They give rise to photon-photon and photon-nucleus collisions with high flux up to an invariant mass region hitherto unexplored experimentally. After a general survey photon-photon luminosities in relativistic heavy ion collisions are discussed. Special care is taken to include the effects of strong interactions and nuclear size. Then photon-photon physics at various γγ-invariant mass scales is discussed. The region of several GeV, relevant for RHIC is dominated by QCD phenomena (meson and vector meson pair production). Invariant masses of up to about 100 GeV can be reached at LHC, and the potential for new physics is discussed. Photonuclear reactions and other important background effects, especially diffractive processes are also discussed. A special chapter is devoted to lepton-pair production, especially electron-positron pair production; due to the strong fields new phenomena, especially multiple e + e − pair production, will occur there.