9,753 research outputs found

    The Evolution of Quantum Field Theory, From QED to Grand Unification

    Full text link
    In the early 1970s, after a slow start, and lots of hurdles, Quantum Field Theory emerged as the superior doctrine for understanding the interactions between relativistic sub-atomic particles. After the conditions for a relativistic field theoretical model to be renormalizable were established, there were two other developments that quickly accelerated acceptance of this approach: first the Brout-Englert-Higgs mechanism, and then asymptotic freedom. Together, these gave us a complete understanding of the perturbative sector of the theory, enough to give us a detailed picture of what is now usually called the Standard Model. Crucial for this understanding were the strong indications and encouragements provided by numerous experimental findings. Subsequently, non-perturbative features of the quantum field theories were addressed, and the first proposals for completely unified quantum field theories were launched. Since the use of continuous symmetries of all sorts, together with other topics of advanced mathematics, were recognised to be of crucial importance, many new predictions were pointed out, such as the Higgs particle, supersymmetry and baryon number violation. There are still many challenges ahead.Comment: 25 pages in total. A contribution to: The Standard Theory up to the Higgs discovery - 60 years of CERN - L. Maiani and G. Rolandi, ed

    Minimal Gauge Invariant Classes of Tree Diagrams in Gauge Theories

    Get PDF
    We describe the explicit construction of groves, the smallest gauge invariant classes of tree Feynman diagrams in gauge theories. The construction is valid for gauge theories with any number of group factors which may be mixed. It requires no summation over a complete gauge group multiplet of external matter fields. The method is therefore suitable for defining gauge invariant classes of Feynman diagrams for processes with many observed final state particles in the standard model and its extensions.Comment: 13 pages, RevTeX (EPS figures

    Colored Resonant Signals at the LHC: Largest Rate and Simplest Topology

    Get PDF
    We study the colored resonance production at the LHC in a most general approach. We classify the possible colored resonances based on group theory decomposition, and construct their effective interactions with light partons. The production cross section from annihilation of valence quarks or gluons may be on the order of 400 - 1000 pb at LHC energies for a mass of 1 TeV with nominal couplings, leading to the largest production rates for new physics at the TeV scale, and simplest event topology with dijet final states. We apply the new dijet data from the LHC experiments to put bounds on various possible colored resonant states. The current bounds range from 0.9 to 2.7 TeV. The formulation is readily applicable for future searches including other decay modes.Comment: 29 pages, 9 figures. References updated and additional K-factors include

    The U(1)A anomaly in noncommutative SU(N) theories

    Full text link
    We work out the one-loop U(1)AU(1)_A anomaly for noncommutative SU(N) gauge theories up to second order in the noncommutative parameter ΞΌΜ\theta^{\mu\nu}. We set Ξ0i=0\theta^{0i}=0 and conclude that there is no breaking of the classical U(1)AU(1)_A symmetry of the theory coming from the contributions that are either linear or quadratic in ΞΌΜ\theta^{\mu\nu}. Of course, the ordinary anomalous contributions will be still with us. We also show that the one-loop conservation of the nonsinglet currents holds at least up to second order in ΞΌΜ\theta^{\mu\nu}. We adapt our results to noncommutative gauge theories with SO(N) and U(1) gauge groups.Comment: 50 pages, 5 figures in eps files. Some comments and references adde

    Limitations on the superposition principle: superselection rules in non-relativistic quantum mechanics

    Get PDF
    The superposition principle is a very basic ingredient of quantum theory. What may come as a surprise to many students, and even to many practitioners of the quantum craft, is tha superposition has limitations imposed by certain requirements of the theory. The discussion of such limitations arising from the so-called superselection rules is the main purpose of this paper. Some of their principal consequences are also discussed. The univalence, mass and particle number superselection rules of non-relativistic quantum mechanics are also derived using rather simple methods.Comment: 22 pages, no figure

    History of Supersymmetric Extensions of the Standard Model

    Full text link
    We recall the many obstacles which seemed, long ago, to prevent supersymmetry from possibly being a fundamental symmetry of Nature. We also present their solutions, leading to the construction of the supersymmetric extensions of the Standard Model. Finally we discuss briefly the early experimental searches for Supersymmetry.Comment: 40 pages, 10 figures, 3 Table

    Quantum field theory with varying couplings

    Get PDF
    A quantum scalar field theory with spacetime-dependent coupling is studied. Surprisingly, while translation invariance is explicitly broken in the classical theory, momentum conservation is recovered at the quantum level for some specific choice of the coupling's profile for any finite-order perturbative expansion. For one of these cases, some tree and one-loop diagrams are calculated. This is an example of a theory where violation of Lorentz symmetry is not enhanced at the quantum level. We draw some consequences for the renormalization properties of certain classes of fractional field theories.Comment: 12 pages. v2: discussion improved, minor typos correcte

    The Glorious Days of Physics - Renormalization of Gauge theories

    Get PDF
    This is an account of the author's recollections of the turbulent days preceding the establishment of the Standard Model as an accurate description of all known elementary particles and forces.Comment: 21 pages plain TeX, 4 figures PostScript. Small cosmetic - yet important - changes were made in the original manuscrip
    • 

    corecore