The first version of quantum theory, developed in the mid 1920's, is what is called nonrelativistic quantum theory; it is based on a form of relativity which, in a previous volume, was called Newton relativity. But quickly after this first development, it was realized that, in order to account for high energy phenomena such as particle creation, it was necessary to develop a quantum theory based on Einstein relativity. This in turn led to the development of relativistic quantum field theory, which is an intrinsically many-body theory. But this is not the only possibility for a relativistic quantum theory. In this book we take the point of view of a particle theory, based on the irreducible representations of the Poincare group, the group that expresses the symmetry of Einstein relativity. There are several ways of formulating such a theory; we develop what is called relativistic point form quantum mechanics, which, unlike quantum field theory, deals with a fixed number of particles in a relativistically invariant way. A central issue in any relativistic quantum theory is how to introduce interactions without spoiling relativistic invariance. We show that interactions can be incorporated in a mass operator, in such a way that relativistic invariance is maintained. Surprisingly for a relativistic theory, such a construction allows for instantaneous interactions; in addition, dynamical particle exchange and particle production can be included in a multichannel formulation of the mass operator. For systems of more than two particles, however, straightforward application of such a construction leads to the undesirable property that clusters of widely separated particles continue to interact with one another, even if the interactions between the individual particles are of short range. A significant part of this volume deals with the solution of this problem. Since relativistic quantum mechanics is not as well-known as relativistic quantum field theory, a chapter is devoted to applications of point form quantum mechanics to nuclear physics; in particular we show how constituent quark models can be used to derive electromagnetic and other properties of hadrons.

Thisvolumecontainsthewrittenversionsofinvitedlecturespresentedat the"39. InternationaleUniversitatswochenfur .. Kern-undTeilchenphysik"in Schladming, Austria, which took place from February 26th to March 4th, 2000. The title of the school was "Methods of Quantization". This is, of course,averybroad?eld,soonlysomeofthenewandinterestingdevel- mentscouldbecoveredwithinthescopeoftheschool. About75yearsagoSchrodingerpresentedhisfamouswaveequationand Heisenbergcameupwithhisalgebraicapproachtothequantum-theoretical treatmentofatoms. Aimingmainlyatanappropriatedescriptionofatomic systems, these original developments did not take into consideration E- stein'stheoryofspecialrelativity. WiththeworkofDirac,Heisenberg,and Pauliitsoonbecameobviousthatauni?edtreatmentofrelativisticandqu- tume?ectsisachievedbymeansoflocalquantum?eldtheory,i. e. anintrinsic many-particletheory. Mostofourpresentunderstandingoftheelementary buildingblocksofmatterandtheforcesbetweenthemisbasedonthequ- tizedversionof?eldtheorieswhicharelocallysymmetricundergaugetra- formations. Nowadays,theprevailingtoolsforquantum-?eldtheoreticalc- culationsarecovariantperturbationtheoryandfunctional-integralmethods. Beingnotmanifestlycovariant,theHamiltonianapproachtoquantum-?eld theorieslagssomewhatbehind,althoughitresemblesverymuchthefamiliar nonrelativisticquantummechanicsofpointparticles. Aparticularlyintere- ingHamiltonianformulationofquantum-?eldtheoriesisobtainedbyqu- tizingthe?eldsonhypersurfacesoftheMinkowsispacewhicharetangential tothelightcone. The"timeevolution"ofthesystemisthenconsideredin + "light-conetime"x =t+z/c. Theappealingfeaturesof"light-conequ- tization",whicharethereasonsfortherenewedinterestinthisformulation ofquantum?eldtheories,werehighlightedinthelecturesofBernardBakker andThomasHeinzl. Oneoftheopenproblemsoflight-conequantizationis theissueofspontaneoussymmetrybreaking. Thiscanbetracedbacktozero modeswhich,ingeneral,aresubjecttocomplicatedconstraintequations. A generalformalismforthequantizationofphysicalsystemswithconstraints waspresentedbyJohnKlauder. Theperturbativede?nitionofquantum?eld theoriesisingenerala?ictedbysingularitieswhichareovercomebyare- larizationandrenormalizationprocedure. Structuralaspectsoftherenormal- VI Preface izationprobleminthecaseofgaugeinvariant?eldtheorieswerediscussed inthelectureofKlausSibold. Areviewofthemathematicsunderlyingthe functional-integralquantizationwasgivenbyLudwigStreit. Apartfromthetopicsincludedinthisvolumetherewerealsolectures ontheKaluza-odingerpresentedhisfamouswaveequationand Heisenbergcameupwithhisalgebraicapproachtothequantum-theoretical treatmentofatoms. Aimingmainlyatanappropriatedescriptionofatomic systems, these original developments did not take into consideration E- stein'stheoryofspecialrelativity. WiththeworkofDirac,Heisenberg,and Pauliitsoonbecameobviousthatauni?edtreatmentofrelativisticandqu- tume?ectsisachievedbymeansoflocalquantum?eldtheory,i. e. anintrinsic many-particletheory. Mostofourpresentunderstandingoftheelementary buildingblocksofmatterandtheforcesbetweenthemisbasedonthequ- tizedversionof?eldtheorieswhicharelocallysymmetricundergaugetra- formations. Nowadays,theprevailingtoolsforquantum-?eldtheoreticalc- culationsarecovariantperturbationtheoryandfunctional-integralmethods. Beingnotmanifestlycovariant,theHamiltonianapproachtoquantum-?eld theorieslagssomewhatbehind,althoughitresemblesverymuchthefamiliar nonrelativisticquantummechanicsofpointparticles. Aparticularlyintere- ingHamiltonianformulationofquantum-?eldtheoriesisobtainedbyqu- tizingthe? eldsonhypersurfacesoftheMinkowsispacewhicharetangential tothelightcone. The"timeevolution"ofthesystemisthenconsideredin + "light-conetime"x =t+z/c. Theappealingfeaturesof"light-conequ- tization",whicharethereasonsfortherenewedinterestinthisformulation ofquantum?eldtheories,werehighlightedinthelecturesofBernardBakker andThomasHeinzl. Oneoftheopenproblemsoflight-conequantizationis theissueofspontaneoussymmetrybreaking. Thiscanbetracedbacktozero modeswhich,ingeneral,aresubjecttocomplicatedconstraintequations. A generalformalismforthequantizationofphysicalsystemswithconstraints waspresentedbyJohnKlauder. Theperturbativede?nitionofquantum?eld theoriesisingenerala?ictedbysingularitieswhichareovercomebyare- larizationandrenormalizationprocedure. Structuralaspectsoftherenormal- VI Preface izationprobleminthecaseofgaugeinvariant?eldtheorieswerediscussed inthelectureofKlausSibold. Areviewofthemathematicsunderlyingthe functional-integralquantizationwasgivenbyLudwigStreit. Apartfromthetopicsincludedinthisvolumetherewerealsolectures ontheKaluza-Kleinprogramforsupergravity(P. vanNieuwenhuizen),on dynamicalr-matricesandquantization(A. Alekseev),andonthequantum Liouvillemodelasaninstructiveexampleofquantumintegrablemodels(L. Faddeev). Inaddition,theschoolwascomplementedbymanyexcellents- inars. Thelistofseminarspeakersandthetopicsaddressedbythemcanbe foundattheendofthisvolume. Theinterestedreaderisrequestedtocontact thespeakersdirectlyfordetailedinformationorpertinentmaterial. Finally,wewouldliketoexpressourgratitudetothelecturersforalltheir e?ortsandtothemainsponsorsoftheschool,theAustrianMinistryofE- cation,Science,andCultureandtheGovernmentofStyria,forprovidingg- eroussupport. Wealsoappreciatethevaluableorganizationalandtechnical assistanceofthetownofSchladming,theSteyr-Daimler-PuchFahrzeugte- nik, Ricoh Austria, Styria Online, and the Hornig company. Furthermore, wethankoursecretaries,S. FuchsandE. Monschein,anumberofgra- atestudentsfromourinstitute,and,lastbutnotleast,ourcolleaguesfrom theorganizingcommitteefortheirassistanceinpreparingandrunningthe school. Graz, HeimoLatal March2001 WolfgangSchweiger Contents FormsofRelativisticDynamics BernardL. G. Bakker...1 1 Introduction...1 2 ThePoincar'eGroup...3 3 FormsofRelativisticDynamics...4 3. 1 ComparisonofInstantForm,FrontForm,andPointForm...6 4 Light-FrontDynamics...9 4. 1 RelativeMomentum,InvariantMass...9 4. 2 TheBoxDiagram...14 5 Poincar'eGeneratorsinFieldTheory...19 5. 1 FermionsInteractingwithaScalarField...20 5. 2 InstantForm...20 5. 3 FrontForm(LF)...21 5. 4 InteractingandNon-interactingGeneratorsonanInstant andontheLightFront...22 6 Light-FrontPerturbationTheory...23 6. 1 ConnectionofCovariantAmplitudes toLight-FrontAmplitudes...24 6. 2 Regularization...26 6. 3 MinusRegularization...26 7 TriangleDiagraminYukawaTheory...27 7. 1 CovariantCalculation ...28 7. 2 ConstructionoftheCurrentinLFD...30 7. 3 NumericalResults...37 3 8 FourVariationsonaThemein? Theory...37 8. 1 CovariantCalculation...39 8. 2 Instant-FormCalculation...42 8. 3 CalculationinLight-FrontCoordinates...47 8. 4 Front-FormCalculation...49 9 DimensionalRegularization:BasicFormulae...51 10 Four-DimensionalIntegration...52 11 SomeUsefulIntegrals...53 References...53 VIII Contents Light-ConeQuantization:FoundationsandApplications ThomasHeinzl...

In this volume seven leading theoreticians and experimenters review the origin of the asymmetry of matter and antimatter in the Big Bang, solar neutrinos, the physics of enormous densities and temperatures in stars and of immense magnetic fields around collapsed stars, strong electric fields in heavy ion collisions, and the extreme conditions in quark-gluon plasmas. The articles address nuclear and particle physicists, especially graduate students, but also astrophysicists and cosmologists, since they have to deal with events under the extreme physical conditions discussed here.

Thisvolumecontainsthewrittenversionsofinvitedlecturespresentedat the"39. InternationaleUniversitatswochenfur .. Kern-undTeilchenphysik"in Schladming, Austria, which took place from February 26th to March 4th, 2000. The title of the school was "Methods of Quantization". This is, of course,averybroad?eld,soonlysomeofthenewandinterestingdevel- mentscouldbecoveredwithinthescopeoftheschool. About75yearsagoSchrodingerpresentedhisfamouswaveequationand Heisenbergcameupwithhisalgebraicapproachtothequantum-theoretical treatmentofatoms. Aimingmainlyatanappropriatedescriptionofatomic systems, these original developments did not take into consideration E- stein'stheoryofspecialrelativity. WiththeworkofDirac,Heisenberg,and Pauliitsoonbecameobviousthatauni?edtreatmentofrelativisticandqu- tume?ectsisachievedbymeansoflocalquantum?eldtheory,i. e. anintrinsic many-particletheory. Mostofourpresentunderstandingoftheelementary buildingblocksofmatterandtheforcesbetweenthemisbasedonthequ- tizedversionof?eldtheorieswhicharelocallysymmetricundergaugetra- formations. Nowadays,theprevailingtoolsforquantum-?eldtheoreticalc- culationsarecovariantperturbationtheoryandfunctional-integralmethods. Beingnotmanifestlycovariant,theHamiltonianapproachtoquantum-?eld theorieslagssomewhatbehind,althoughitresemblesverymuchthefamiliar nonrelativisticquantummechanicsofpointparticles. Aparticularlyintere- ingHamiltonianformulationofquantum-?eldtheoriesisobtainedbyqu- tizingthe?eldsonhypersurfacesoftheMinkowsispacewhicharetangential tothelightcone. The"timeevolution"ofthesystemisthenconsideredin + "light-conetime"x =t+z/c. Theappealingfeaturesof"light-conequ- tization",whicharethereasonsfortherenewedinterestinthisformulation ofquantum?eldtheories,werehighlightedinthelecturesofBernardBakker andThomasHeinzl. Oneoftheopenproblemsoflight-conequantizationis theissueofspontaneoussymmetrybreaking. Thiscanbetracedbacktozero modeswhich,ingeneral,aresubjecttocomplicatedconstraintequations. A generalformalismforthequantizationofphysicalsystemswithconstraints waspresentedbyJohnKlauder. Theperturbativede?nitionofquantum?eld theoriesisingenerala?ictedbysingularitieswhichareovercomebyare- larizationandrenormalizationprocedure. Structuralaspectsoftherenormal- VI Preface izationprobleminthecaseofgaugeinvariant?eldtheorieswerediscussed inthelectureofKlausSibold. Areviewofthemathematicsunderlyingthe functional-integralquantizationwasgivenbyLudwigStreit. Apartfromthetopicsincludedinthisvolumetherewerealsolectures ontheKaluza-odingerpresentedhisfamouswaveequationand Heisenbergcameupwithhisalgebraicapproachtothequantum-theoretical treatmentofatoms. Aimingmainlyatanappropriatedescriptionofatomic systems, these original developments did not take into consideration E- stein'stheoryofspecialrelativity. WiththeworkofDirac,Heisenberg,and Pauliitsoonbecameobviousthatauni?edtreatmentofrelativisticandqu- tume?ectsisachievedbymeansoflocalquantum?eldtheory,i. e. anintrinsic many-particletheory. Mostofourpresentunderstandingoftheelementary buildingblocksofmatterandtheforcesbetweenthemisbasedonthequ- tizedversionof?eldtheorieswhicharelocallysymmetricundergaugetra- formations. Nowadays,theprevailingtoolsforquantum-?eldtheoreticalc- culationsarecovariantperturbationtheoryandfunctional-integralmethods. Beingnotmanifestlycovariant,theHamiltonianapproachtoquantum-?eld theorieslagssomewhatbehind,althoughitresemblesverymuchthefamiliar nonrelativisticquantummechanicsofpointparticles. Aparticularlyintere- ingHamiltonianformulationofquantum-?eldtheoriesisobtainedbyqu- tizingthe? eldsonhypersurfacesoftheMinkowsispacewhicharetangential tothelightcone. The"timeevolution"ofthesystemisthenconsideredin + "light-conetime"x =t+z/c. Theappealingfeaturesof"light-conequ- tization",whicharethereasonsfortherenewedinterestinthisformulation ofquantum?eldtheories,werehighlightedinthelecturesofBernardBakker andThomasHeinzl. Oneoftheopenproblemsoflight-conequantizationis theissueofspontaneoussymmetrybreaking. Thiscanbetracedbacktozero modeswhich,ingeneral,aresubjecttocomplicatedconstraintequations. A generalformalismforthequantizationofphysicalsystemswithconstraints waspresentedbyJohnKlauder. Theperturbativede?nitionofquantum?eld theoriesisingenerala?ictedbysingularitieswhichareovercomebyare- larizationandrenormalizationprocedure. Structuralaspectsoftherenormal- VI Preface izationprobleminthecaseofgaugeinvariant?eldtheorieswerediscussed inthelectureofKlausSibold. Areviewofthemathematicsunderlyingthe functional-integralquantizationwasgivenbyLudwigStreit. Apartfromthetopicsincludedinthisvolumetherewerealsolectures ontheKaluza-Kleinprogramforsupergravity(P. vanNieuwenhuizen),on dynamicalr-matricesandquantization(A. Alekseev),andonthequantum Liouvillemodelasaninstructiveexampleofquantumintegrablemodels(L. Faddeev). Inaddition,theschoolwascomplementedbymanyexcellents- inars. Thelistofseminarspeakersandthetopicsaddressedbythemcanbe foundattheendofthisvolume. Theinterestedreaderisrequestedtocontact thespeakersdirectlyfordetailedinformationorpertinentmaterial. Finally,wewouldliketoexpressourgratitudetothelecturersforalltheir e?ortsandtothemainsponsorsoftheschool,theAustrianMinistryofE- cation,Science,andCultureandtheGovernmentofStyria,forprovidingg- eroussupport. Wealsoappreciatethevaluableorganizationalandtechnical assistanceofthetownofSchladming,theSteyr-Daimler-PuchFahrzeugte- nik, Ricoh Austria, Styria Online, and the Hornig company. Furthermore, wethankoursecretaries,S. FuchsandE. Monschein,anumberofgra- atestudentsfromourinstitute,and,lastbutnotleast,ourcolleaguesfrom theorganizingcommitteefortheirassistanceinpreparingandrunningthe school. Graz, HeimoLatal March2001 WolfgangSchweiger Contents FormsofRelativisticDynamics BernardL. G. Bakker...1 1 Introduction...1 2 ThePoincar'eGroup...3 3 FormsofRelativisticDynamics...4 3. 1 ComparisonofInstantForm,FrontForm,andPointForm...6 4 Light-FrontDynamics...9 4. 1 RelativeMomentum,InvariantMass...9 4. 2 TheBoxDiagram...14 5 Poincar'eGeneratorsinFieldTheory...19 5. 1 FermionsInteractingwithaScalarField...20 5. 2 InstantForm...20 5. 3 FrontForm(LF)...21 5. 4 InteractingandNon-interactingGeneratorsonanInstant andontheLightFront...22 6 Light-FrontPerturbationTheory...23 6. 1 ConnectionofCovariantAmplitudes toLight-FrontAmplitudes...24 6. 2 Regularization...26 6. 3 MinusRegularization...26 7 TriangleDiagraminYukawaTheory...27 7. 1 CovariantCalculation ...28 7. 2 ConstructionoftheCurrentinLFD...30 7. 3 NumericalResults...37 3 8 FourVariationsonaThemein? Theory...37 8. 1 CovariantCalculation...39 8. 2 Instant-FormCalculation...42 8. 3 CalculationinLight-FrontCoordinates...47 8. 4 Front-FormCalculation...49 9 DimensionalRegularization:BasicFormulae...51 10 Four-DimensionalIntegration...52 11 SomeUsefulIntegrals...53 References...53 VIII Contents Light-ConeQuantization:FoundationsandApplications ThomasHeinzl...

This volume contains the written versions of invited lectures presented at the 29th "Internationale Universitatswochen fiir Kernphysik" in Schladming, Aus tria, in March 1990. The generous support of our sponsors, the Austrian Ministry of Science and Research, the Government of Styria, and others, made it possible to invite expert lecturers. In choosing the topics of the course we have tried to select some of the currently most fiercely debated aspects of quantum field theory. It is a pleasure for us to thank all the speakers for their excellent presentations and their efforts in preparing the lecture notes. After the school the lecture notes were revised by the authors and partly rewritten ~n '!EX. We are also indebted to Mrs. Neuhold for the careful typing of those notes which we did not receive in '!EX. Graz, Austria H. Mitter July 1990 W. Schweiger Contents An Introduction to Integrable Models and Conformal Field Theory By H. Grosse (With 6 Figures) .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1 1. Introduction ............................................. . 1 1.1 Continuous Integrable Models .......................... . 1 1.2 "Solvable" Models of Statistical Physics ................. . 2 1.3 The Yang-Baxter Relation ............................. . 3 1.4 Braids and I(nots .................................... . 3 1.5 Confonnal Field Theory d = 2 ......................... . 3 2. Integrable Continuum Models - The Inverse Scattering Method - Solitons .................... . 4 2.1 A General Scheme for Solving (Linear) Problems ......... . 4 2.2 The Direct Step ...................................... . 6 2.3 The Inverse Step ..................................... .

Fuhren die sozialen Medien zu einer einseitigen Pseudo-Informiertheit von Burgern und verstarken damit die Polarisierung der Gesellschaft? Der Nachrichten- und Informationskosmos im Internet befindet sich im Umbruch - mit beunruhigenden Folgen fur die Demokratie. Lange waren journalistische Medien, alternative Angebote und die oeffentliche Kommunikation unter Burgern getrennt. In Facebook, YouTube, Google und Co. vermischen sie sich. Nachrichten, Verschwoerungstheorien und Hasskommentare stehen direkt nebeneinander. Das uberfordert die Medienkompetenz vieler Burger. Obwohl sie das Nachrichtengeschehen kaum uberblicken, fuhlen sie sich gut informiert. Gleichzeitig bleiben die Meinungslager unter sich (Filterblase) und schaukeln sich gegenseitig auf (Echokammer). Das tragt zur verzerrten Wahrnehmung der oeffentlichen Meinung durch den Einzelnen bei, verandert die Meinungsbildung und verscharft die Polarisierung der Gesellschaft. Indizien sprechen dafur, dass besonders die politisierte Bildungsmitte betroffen ist.

Das Handbuch gibt in zahlreichen Beitragen einschlagiger FachautorInnen einen umfassenden und systematischen UEberblick des aktuellen Forschungsstandes kommunikationswissenschaftlicher Online-Forschung. Einfuhrend werden die zentralen Fragestellungen, theoretischen Ansatze und empirischen Befunde dargestellt. Das Themenspektrum reicht von den Grundlagen computervermittelter Kommunikation (interpersonale, Gruppen- und oeffentliche Kommunikation), uber oekonomische, ethische und politische Fragen wie Regulierung und Kontrolle des Internets, sowie seine Verbreitung, Nutzung und Wirkung. Weitere Beitrage befassen sich mit OEffentlichkeit und Journalismus online, kulturellen und sozialpsychologischen Aspekten, Online-Werbung und -PR, Gesundheitskommunikation, E-Learning und Wissensmanagement sowie Online-Spielen. Ein UEberblick uber Methoden der Online-Forschung sowie die wichtigsten Datenquellen und Standarduntersuchungen rundet das Werk ab.

Inzwischen hat das Internet eine neue Entwicklungsphase erreicht: Mit dem Schlagwort "Web 2.0" werden partizipative Formate wie Weblogs und kollaborative Websites gelabelt, die den Nutzern die aktive Teilnahme an der Offentlichkeit in der Kommunikatorrolle ermoglichen. Haufig ist in diesem Zusammenhang auch von "partizipativem Journalismus," "Burgerjournalismus" oder "Open-Source-Journalismus" die Rede. Machen normale Burger den professionellen Online-Journalismus uberflussig oder erlebt der Online-Journalismus eine neue Blute?
In diesem Band werden Akteure, Strukturen, Prozesse und Leistungen neuer Formen der aktuellen Internetoffentlichkeit facettenreich diskutiert. Neben deutschsprachigen Kommunikationswissenschaftlern kommentieren auch internationale Experten und anerkannte Praxisvertreter neueste Entwicklungen.

Massenmedien sind aus modernen Gesellschaften nicht wegzudenken. Nicht umsonst hat die herrschende Rechtsprechung in Deutschland dem Fernsehgerat den Status einer nicht pfand- ren Sache des persoenlichen Gebrauchs gegeben. Jeder erwachsene Deutsche nutzte 2005 taglich zehn Stunden Medien, davon achteinhalb Stunden Fernsehen, Radio, Zeitung und das Internet (van Eimeren & Ridder 2005). Eine knappe Stunde davon werden zwei oder mehrere Medien gleichzeitig genutzt, so dass die netto mit Medien verbrachte Zeit etwas kurzer ist. Ein Vergleich mit 1980 zeigt schliesslich, dass die Bedeutung der Massenmedien in den vergangenen 25 Jahren erheblich gestiegen sein muss: Damals lag das Brutto-Zeitbudget bei weniger als sechs Stunden. Dabei wurde Mediennutzung schon immer ambivalent gesehen. Bereits im ausgehenden 17. Jahrhundert zog die 'Zeitungslust' mancher Zeitgenossen Kritik auf sich (Stieler 1695). Heute ist die Rede von ubergewichtigen und sozial isolierten Kindern und Jugendlichen, die den g- zen Tag vor dem Fernseher, Computer oder der Spielkonsole sitzen, von einer zunehmenden Aggressivitat auf Schulhoefen, von Politikverdrossenheit unter Erwachsenen durch anspruchslose Politikberichterstattung im Fernsehen oder von der generellen Verdummung der Gesellschaft durch verantwortungslose Medienmacher, die lediglich die primitivsten Bedurfnisse ihres Pub- kums befriedigen. Auf der anderen Seite befeuert besonders das Internet weitreichende Ho- nungen. Man musse nur dafur sorgen, so die Annahme, dass alle Menschen weltweit Anschluss ans Internet haben und die noetige Medienkompetenz erwerben. Dann wurde die allgegenwartige Verfugbarkeit von Informationen zu einem gesamtgesellschaftlichen Wissens- und Bildun- schub fuhren, die volkswirtschaftliche Leistungsfahigkeit erhoehen und sogar die Bedingungen der gelebten Demokratie - Stichworte sind E-Government und E-Democracy - verbessern.

Wie fugt sich das Internet in die Alltagshandlungen seiner Nutzer ein? Welche Veranderungen ergeben sich fur Journalisten? Nach welchen Kriterien entscheiden sich Nutzer fur ein bestimmtes Internetangebot? Diese Fragen beruhren einen zentralen Aspekt der Kommunikationsforschung: die Selektion. Dieser Band setzt sich aus empirischer Sicht mit dem Thema auseinander."

The first version of quantum theory, developed in the mid 1920's, is what is called nonrelativistic quantum theory; it is based on a form of relativity which, in a previous volume, was called Newton relativity. But quickly after this first development, it was realized that, in order to account for high energy phenomena such as particle creation, it was necessary to develop a quantum theory based on Einstein relativity. This in turn led to the development of relativistic quantum field theory, which is an intrinsically many-body theory. But this is not the only possibility for a relativistic quantum theory. In this book we take the point of view of a particle theory, based on the irreducible representations of the Poincare group, the group that expresses the symmetry of Einstein relativity. There are several ways of formulating such a theory; we develop what is called relativistic point form quantum mechanics, which, unlike quantum field theory, deals with a fixed number of particles in a relativistically invariant way. A central issue in any relativistic quantum theory is how to introduce interactions without spoiling relativistic invariance. We show that interactions can be incorporated in a mass operator, in such a way that relativistic invariance is maintained. Surprisingly for a relativistic theory, such a construction allows for instantaneous interactions; in addition, dynamical particle exchange and particle production can be included in a multichannel formulation of the mass operator. For systems of more than two particles, however, straightforward application of such a construction leads to the undesirable property that clusters of widely separated particles continue to interact with one another, even if the interactions between the individual particles are of short range. A significant part of this volume deals with the solution of this problem. Since relativistic quantum mechanics is not as well-known as relativistic quantum field theory, a chapter is devoted to applications of point form quantum mechanics to nuclear physics; in particular we show how constituent quark models can be used to derive electromagnetic and other properties of hadrons.

Das Handbuch gibt in zahlreichen Beitragen einschlagiger FachautorInnen einen umfassenden und systematischen Uberblick des aktuellen Forschungsstandes kommunikationswissenschaftlicher Online-Forschung. Einfuhrend werden die zentralen Fragestellungen, theoretischen Ansatze und empirischen Befunde dargestellt.
Das Themenspektrum reicht von den Grundlagen computervermittelter Kommunikation (interpersonale, Gruppen- und offentliche Kommunikation), uber okonomische, ethische und politische Fragen wie Regulierung und Kontrolle des Internets, sowie seine Verbreitung, Nutzung und Wirkung. Weitere Beitrage befassen sich mit Offentlichkeit und Journalismus online, kulturellen und sozialpsychologischen Aspekten, Online-Werbung und PR, Gesundheitskommunikation, E-Learning und Wissensmanagement sowie Online-Spielen. Ein Uberblick uber Methoden der Online-Forschung und die wichtigsten Datenquellen und Standarduntersuchungen rundet das Werk ab.
"