4,231 research outputs found
One-particle reducible contribution to the one-loop scalar propagator in a constant field
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
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
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
We explore unified field theories based on the gauge groups and
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 the and
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
and uncover a link to unified theory. We pursue this by exploring the
theory in the same framework, the less established unified theory
based on and briefly consider the Pati-Salam model using .Comment: 10 Pages. Published versio
QED as the tensionless limit of the spinning string with contact interaction
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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