4,518 research outputs found
Radiation reaction in strong field QED
We derive radiation reaction from QED in a strong background field. We
identify, in general, the diagrams and processes contributing to recoil effects
in the average momentum of a scattered electron, using perturbation theory in
the Furry picture: we work to lowest nontrivial order in the electromagnetic
coupling alpha. For the explicit example of scattering in a plane wave
background, we compare QED with classical electrodynamics in the limit h-bar
goes to zero, finding agreement with the Lorentz-Abraham-Dirac and
Landau-Lifshitz equations, and with Larmor's formula. The first quantum
corrections are also presented.Comment: Version2: 7 pages, 2 figures. Discussion of related results and
applications extended, references added. Matches version to appear in
Phys.Lett.
Radiation reaction from QED: lightfront perturbation theory in a plane wave background
We derive dynamical, real time radiation reaction effects from lightfront
QED. Combining the Hamiltonian formalism with a plane wave background field,
the calculation is performed in the Furry picture for which the background is
treated exactly while interactions between quantum fields are treated in
perturbation theory as normal. We work to a fixed order in perturbation theory,
but no other approximation is made. The literature contains many proposals for
the correct classical equation describing a radiating particle; we take the
classical limit of our results and identify which equations are consistent with
QED.Comment: 33 pages, 5 pdf figures. Version 3: corrected typographical mistakes
and presentation issues in equations 4.10--4.14 and accompanying discussion.
Results and conclusions unaffected and unchange
Critical Schwinger pair production
We investigate Schwinger pair production in spatially inhomogeneous electric
backgrounds. A critical point for the onset of pair production can be
approached by fields that marginally provide sufficient electrostatic energy
for an off-shell long-range electron-positron fluctuation to become a real
pair. Close to this critical point, we observe features of universality which
are analogous to continuous phase transitions in critical phenomena with the
pair-production rate serving as an order parameter: electric backgrounds can be
subdivided into universality classes and the onset of pair production exhibits
characteristic scaling laws. An appropriate design of the electric background
field can interpolate between power-law scaling, essential BKT-type scaling and
a power-law scaling with log corrections. The corresponding critical exponents
only depend on the large-scale features of the electric background, whereas the
microscopic details of the background play the role of irrelevant perturbations
not affecting criticality.Comment: 6 pages, 1 figur
Emergence of a common energy scale close to the orbital-selective Mott transition
We calculate the spectra and spin susceptibilities of a Hubbard model with
two bands having different bandwidths but the same on-site interaction, with
parameters close to the orbital-selective Mott transition, using dynamical
mean-field theory. If the Hund's rule coupling is sufficiently strong, one
common energy scale emerges which characterizes both the location of kinks in
the self-energy and extrema of the diagonal spin susceptibilities. A physical
explanation of this energy scale is derived from a Kondo-type model. We infer
that for multi-band systems local spin dynamics rather than spectral functions
determine the location of kinks in the effective band structure.Comment: 5 pages, 5 figure
Isosbestic Points: Theory and Applications
We analyze the sharpness of crossing ("isosbestic") points of a family of
curves which are observed in many quantities described by a function f(x,p),
where x is a variable (e.g., the frequency) and p a parameter (e.g., the
temperature). We show that if a narrow crossing region is observed near x* for
a range of parameters p, then f(x,p) can be approximated by a perturbative
expression in p for a wide range of x. This allows us, e.g., to extract the
temperature dependence of several experimentally obtained quantities, such as
the Raman response of HgBa2CuO4+delta, photoemission spectra of thin VO2 films,
and the reflectivity of CaCu3Ti4O12, all of which exhibit narrow crossing
regions near certain frequencies. We also explain the sharpness of isosbestic
points in the optical conductivity of the Falicov-Kimball model and the
spectral function of the Hubbard model.Comment: 12 pages, 11 figure
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