4,231 research outputs found

    One-particle reducible contribution to the one-loop scalar propagator in a constant field

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    Recently, Gies and Karbstein showed that the two-loop Euler-Heisenberg Lagrangian receives a finite one-particle reducible contribution in addition to the well-known one-particle irreducible one. Here, we demonstrate that a similar contribution exists for the propagator in a constant field already at the one-loop level, and we calculate this contribution for the scalar QED case. We also present an independent derivation of the Gies-Karbstein result using the worldline formalism, treating the scalar and spinor QED cases in a unified manner.Comment: 13 pages, 4 figures. Minor corrections mad

    Mixed symmetry tensors in the worldline formalism

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    We consider the first quantised approach to quantum field theory coupled to a non-Abelian gauge field. Representing the colour degrees of freedom with a single family of auxiliary variables the matter field transforms in a reducible representation of the gauge group which - by adding a suitable Chern-Simons term to the particle action - can be projected onto a chosen fully (anti-)symmetric representation. By considering F families of auxiliary variables, we describe how to extend the model to arbitrary tensor products of F reducible representations, which realises a U(F) "flavour" symmetry on the worldline particle model. Gauging this symmetry allows the introduction of constraints on the Hilbert space of the colour fields which can be used to project onto an arbitrary irreducible representation, specified by a certain Young Tableau. In particular the occupation numbers of the wavefunction - i.e. the lengths of the columns (rows) of the Young Tableau - are fixed through the introduction of Chern-Simons terms. We verify this projection by calculating the number of colour degrees of freedom associated to the matter field. We suggest that, using the worldline approach to quantum field theory, this mechanism will allow the calculation of one-loop scattering amplitudes with the virtual particle in an arbitrary representation of the gauge group.Comment: 1+32 page

    Coherent spin control by electrical manipulation of the magnetic anisotropy

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    High-spin paramagnetic manganese defects in polar piezoelectric zinc oxide exhibit a simple almost axial anisotropy and phase coherence times of the order of a millisecond at low temperatures. The anisotropy energy is tunable using an externally applied electric field. This can be used to control electrically the phase of spin superpositions and to drive spin transitions with resonant microwave electric fields

    Unified theory in the worldline approach

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    We explore unified field theories based on the gauge groups SU(5)SU(5) and SO(10)SO(10) using the worldline approach for chiral fermions with a Wilson loop coupling to a background gauge field. Representing path ordering and chiral projection operators with functional integrals has previously reproduced the sum over the chiralities and representations of standard model particles in a compact way. This paper shows that for SU(5)SU(5) the 5ˉ\bar{\mathbf{5}} and 10\mathbf{10} representations -- into which the Georgi-Glashow model places the left-handed fermionic content of the standard model -- appear naturally and with the familiar chirality. We carry out the same analysis for flipped SU(5)SU(5) and uncover a link to SO(10)SO(10) unified theory. We pursue this by exploring the SO(10)SO(10) theory in the same framework, the less established unified theory based on SU(6)SU(6) and briefly consider the Pati-Salam model using SU(4) ⁣× ⁣SU(2) ⁣× ⁣SU(2)SU(4) \!\times \!SU(2)\! \times\! SU(2).Comment: 10 Pages. Published versio

    QED as the tensionless limit of the spinning string with contact interaction

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    QED with spinor matter is argued to correspond to the tensionless limit of spinning strings with contact interactions. The strings represent electric lines of force with charges at their ends. The interaction is constructed from a delta-function on the world-sheet which, although off-shell, decouples from the world-sheet metric. Integrating out the string degrees of freedom with fixed boundary generates the super-Wilson loop that couples spinor matter to electromagnetism in the world-line formalism. World-sheet and world-line, but not spacetime, supersymmetry underpin the model
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