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Sommerfeld enhancement: general results from field theory diagrams
No full textAssuming that two incoming annihilating particles interact by exchanging a generally massive attractive vector (or scalar) boson, we find, by taking the non-relativistic limit of the field theory ladder diagrams, that the complete annihilation amplitude A is equal to: the convolution of a solution of the Schroedinger equation (including the attractive potential) with the Fourier transform of the bare (i.e. ignoring the attraction) annihilation amplitude A0. The main novelty is that A0 can be completely arbitrary. For a Coulomb potential we find analytically the enhancement for the l-partial-wave cross-section, e.g. the P wave enhancement 2π(α/v)3 (v relative velocity), for a Yukawa potential we describe a simple algorithm and give numerical results showing an important P wave enhancement with a resonant pattern
Massless radiation from strings: Quantum spectrum average statistics and cusp-kink configurations
No full textA simple UV completion of QED in 5 dimensions
No full textWe construct a Lifshitz-like version of five-dimensional (5D) QED which is UV - completed and reduces at low energies to ordinary 5D QED. The UV quantum behaviour of this theory is very smooth. In particular, the gauge coupling constant is finite at all energy scales and at all orders in perturbation theory. We study the IR properties of this theory, when compactified on a circle, and compare the one-loop energy dependence of the coupling in the Lifshitz theory with that coming from the standard 5D QED effective field theory. The range of validity of the 5D effective field theory is found to agree with the more conservative version of Naive Dimensional Analysis
Supercurrent Decay by Vortex Nucleation in the Presence of an Array of Pinning Centres: a Renormalization Group Approach
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Philosophical Magazine B: Physics of Condensed Matter; Statistical Mechanics, Electronic, Optical and Magnetic Properties
Volume 80, Issue 7, July 2000, Pages 1311-1316
Supercurrent decay by vortex nucleation in the presence of an array of pinning centres: A renormalization group approach (Article)
Iengo, R.a, Jug, G.bc
a International School for Advanced Studies, Via Beirut 4, 34014 Trieste, Italy
b Istituto Nazionale per la Fisica della Materia, Dipartimento di Scienze, Università dell'Insubria, Via Lucini 3, 22100 Como, Italy
c Max-Planck-Institut für Physik Komplexer Systeme, Nöthnitzer Strasse 38, D-01187 Dresden, Germany
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Abstract
We study the phenomenon of decay of a supercurrent in a superconducting thin film due to the spontaneous homogeneous nucleation of quantized vortex-antivortex pairs in the absence of an external magnetic field and in the presence of a periodic pinning potential. We describe the vortex nucleation by means of a Schwinger-type path-integral calculation including the effects of quantum dissipation. The overdamped case is treated exactly, while the case in which a periodic array of pinning centres is present is dealt with by means of a renormalization group (RG) approach in frequency space. This yields an approximate but very appealing analytic result for the dependence of the vortex nucleation rate on the externally driven supercurrent. In this formula the rate dependence displays oscillations which are connected to the pinning periodicity and correspond to the vortex nucleation length probing over the pinning sites as the current density is varied. Our RG treatment describes the vortex nucleation process in both the confined and the mobile phases of the dissipation-driven localization transition characterizing the motion of dissipating quantum particles in a periodic potential
Long lived large type-II strings: decay within compactification
No full textMotivated also by recent revival of interest about metastable string states (as cosmic strings or in accelerator physics), we study the decay, in presence of dimensional compactification, of a particular superstring state, which was proven to be remarkably long-lived in the flat uncompactified scenario. We compute the decay rate by an exact numerical evaluation of the imaginary part of the one-loop propagator. For large radii of compactification, the result tends to the fully uncompactified one (lifetime Tequivalent toconst. g(s)(-2) M-5), as expected, the string mainly decaying by massless radiation. For small radii, the features of the decay (emitted states, initial mass dependence,...) change, depending on how the string wraps on the compact dimensions
SCHWARZSCHILD-LIKE CORRECTIONS TO GRAVITY FROM SUPERSTRINGS AT ONE LOOP
No full textWe examine the scattering between a scalar massive particle and a graviton at one loop in a four-dimensional type-II superstring model. The absence of a non-renormalization theorem for this case allows a one-particle reducible contribution to the amplitude containing a non-vanishing one-loop three-point function. Using the hyperelliptic language we compute its asymptotic behavior for s → ∞ and t → 0. We find a contribution to the amplitude which can be interpreted as a long-range correction to Newton's potential like the first-order expansion of the Schwarzschild metric. We compare also our results with ordinary one-loop Feynman diagrams. © 1990
EXACT RESULTS FOR ANYONS ON A TORUS
No full textWe analyse the quantum mechanics of a system of non-relativistic anyons on a torus, the statistics of which is described by an abelian Chern-Simons field theory with an arbitrary rational coupling constant. We construct the hamiltonian and the momentum operator, and show that by properly taking into account the topological components of the field they satisfy usual commutation relations. The structure of the Hilbert space for the general case is then described and we determine also exact eigenfunctions in some cases. By introducing a constant external magnetic field orthogonal to the surface and an electric field tangent to it, we are able to study the Hall effect for the anyons and their resulting motion on the torus, and we derive the exact eigenfunctions for the ground state at a given momentum for those configurations relevant to the fractional Hall effect hierarchy. © 1991
Quantum entanglement of charges in bound states with finite-size dyons
No full textWe show that the presence of finite-size monopoles can lead to a number of interesting physical processes involving quantum entanglement of charges. Taking as a model the classical solution of the N = 2 SU(2) Yang-Mills theory, we study interaction between dyons and scalar particles in the adjoint and fundamental representation. We find that there are bound states of scalars and dyons, which, remarkably, are always an entangled configuration of the form vertical bar psi> = verical bar dyon(+)i>vertical bar scalar_>+/- vertical bar dyon_>vertical bar scalar(+)>. We determine the energy levels and the wave functions and also discuss their stability
Quantum Field Theory Approach to Vortex Pair Nucleation in a Thin Superconductor: Role of Dissipation and Periodic Pinning
No full textANYON MEAN FIELD AS A CRITICAL-FIELD THEORY
No full textWe discuss an abelian gauge theory in 2+1 dimensions, the gauge field being coupled to nonrelativistic fermions. The action for the gauge field is a combination of the Maxwell term and a Chern-Simons (CS) term. We study the limit of vanishing fermion' charge, keeping fixed the gauge-field mass induced by the CS term. By considering a closed surface, in particular a torus to keep translational invariance, we show that the fermions do not decouple completely from the gauge field, and in fact we find that they behave as anyons treated in the - translationally invariant formulation of the - mean-field approximation. © 1992
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