1,053 research outputs found

    A Technique for generating Feynman Diagrams

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    We present a simple technique that allows to generate Feynman diagrams for vector models with interactions of order 2n2n and similar models (Gross-Neveu, Thirring model), using a bootstrap equation that uses only the free field value of the energy as an input. The method allows to find the diagrams to, in principle, arbitrarily high order and applies to both energy and correlation functions. It automatically generates the correct symmetry factor (as a function of the number of components of the field) and the correct sign for any diagram in the case of fermion loops. We briefly discuss the possibility of treating QED as a Thirring model with non-local interaction.Comment: 19 pages, LateX, To be published in Z. f. Phys.

    Stability domain of systems of three arbitrary charges

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    We present results on the stability of quantum systems consisting of a negative charge ‚ąíq1-q_1 with mass m1m_{1} and two positive charges q2q_2 and q3q_3, with masses m2m_{2} and m3m_{3}, respectively. We show that, for given masses mim_{i}, each instability domain is convex in the plane of the variables (q1/q2,q1/q3)(q_{1}/q_{2}, q_{1}/q_{3}). A new proof is given of the instability of muonic ions (őĪ,p,őľ‚ąí)(\alpha, p, \mu^-). We then study stability in some critical regimes where q3‚Č™q2q_3\ll q_2: stability is sometimes restricted to large values of some mass ratios; the behaviour of the stability frontier is established to leading order in q3/q2q_3/q_2. Finally we present some conjectures about the shape of the stability domain, both for given masses and varying charges, and for given charges and varying masses

    Hund's Rule for Composite Fermions

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    We consider the ``fractional quantum Hall atom" in the vanishing Zeeman energy limit, and investigate the validity of Hund's maximum-spin rule for interacting electrons in various Landau levels. While it is not valid for {\em electrons} in the lowest Landau level, there are regions of filling factors where it predicts the ground state spin correctly {\em provided it is applied to composite fermions}. The composite fermion theory also reveals a ``self-similar" structure in the filling factor range 4/3>őĹ>2/34/3>\nu>2/3.Comment: 10 pages, revte

    WHY THE REAL PART OF THE PROTON-PROTON FORWARD SCATTERING AMPLITUDE SHOULD BE MEASURED AT THE LHC

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    4p, 2figs, Contribution to EDS2005, Blois May 2005For the energy of 14 TeV, to be reached at the Large Hadron Collider (LHC), we have had for some time accurate predictions for both the real and imaginary parts of the forward proton-proton elastic scattering amplitude. LHC is now scheduled to start operating in two years, and it is timely to discuss some of the important consequences of the measurements of both the total cross-section and the ratio of the real to the imaginary part. We stress the importance of measuring the real part of the proton-proton forward scattering amplitude at LHC, because a deviation from existing theoretical predictions could be a strong sign for new physics

    CP Violation

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    Three possibilities for the origin of CP violation are discussed: (1) the Standard Model in which all CP violation is due to one parameter in the CKM matrix, (2) the superweak model in which all CP violation is due to new physics and (3) the Standard Model plus new physics. A major goal of B physics is to distinguish these possibilities. CP violation implies time reversal violation (TRV) but direct evidence for TRV is difficult to obtain.Comment: 13 pages, to be published in Lecture Notes of TASI-2000, edited by Jonathan L. Rosner, World Scientific, 200

    Exact Schwarzschild-Like Solution for Yang-Mills Theories

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    Drawing on the parallel between general relativity and Yang-Mills theory we obtain an exact Schwarzschild-like solution for SU(2) gauge fields coupled to a massless scalar field. Pushing the analogy further we speculate that this classical solution to the Yang-Mills equations shows confinement in the same way that particles become confined once they pass the event horizon of the Schwarzschild solution. Two special cases of the solution are considered.Comment: 11 pages LaTe

    Instantons of Type IIB Supergravity in Ten Dimensions

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    A family of SO(10) symmetric instanton solutions in Type IIB supergravity is developed. The instanton of least action is a candidate for the low-energy, semiclassical approximation to the {D=--1} brane. Unlike a previously published solution,[GGP] this admits an interpretation as a tunneling amplitude between perturbatively degenerate asymptotic states, but with action twice that found previously. A number of associated issues are discussed such as the relation between the magnetic and electric pictures, an inversion symmetry of the dilaton and the metric, the R√óS9R\times S^9 topology of the background, and some properties of the solution in an "instanton frame" corresponding to a Lagrangian in which the dilaton's kinetic energy vanishes.Comment: 15 pages, no figures; Version 2 has revised sections IV and V. Earlier equations are essentially unchanged, but interpretation changed, on advice of counse

    Fractional Quantum Hall States in Low-Zeeman-Energy Limit

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    We investigate the spectrum of interacting electrons at arbitrary filling factors in the limit of vanishing Zeeman splitting. The composite fermion theory successfully explains the low-energy spectrum {\em provided the composite fermions are treated as hard-core}.Comment: 12 pages, revte

    Renormalization Effects in a Dilute Bose Gas

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    The low-density expansion for a homogeneous interacting Bose gas at zero temperature can be formulated as an expansion in powers of ŌĀa3\sqrt{\rho a^3}, where ŌĀ\rho is the number density and aa is the S-wave scattering length. Logarithms of ŌĀa3\rho a^3 appear in the coefficients of the expansion. We show that these logarithms are determined by the renormalization properties of the effective field theory that describes the scattering of atoms at zero density. The leading logarithm is determined by the renormalization of the pointlike 3‚Üí33 \to 3 scattering amplitude.Comment: 10 pages, 1 postscript figure, LaTe

    Inconsistency of QED in the Presence of Dirac Monopoles

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    A precise formulation of U(1)U(1) local gauge invariance in QED is presented, which clearly shows that the gauge coupling associated with the unphysical longitudinal photon field is non-observable and actually has an arbitrary value. We then re-examine the Dirac quantization condition and find that its derivation involves solely the unphysical longitudinal coupling. Hence an inconsistency inevitably arises in the presence of Dirac monopoles and this can be considered as a theoretical evidence against their existence. An alternative, independent proof of this conclusion is also presented.Comment: Extended and combined version, refinements added; 20 LaTex pages, Published in Z. Phys. C65, pp.175-18
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