The LPM effect in sequential bremsstrahlung

  • Peter Arnold
  • Shahin Iqbal
Open Access
Regular Article - Theoretical Physics


The splitting processes of bremsstrahlung and pair production in a medium are coherent over large distances in the very high energy limit, which leads to a suppression known as the Landau-Pomeranchuk-Migdal (LPM) effect. We analyze the case when the coherence lengths of two consecutive splitting processes overlap, which is important for understanding corrections to standard treatments of the LPM effect in QCD. Previous authors have analyzed this problem in the case of overlapping double bremsstrahlung where at least one of the bremsstrahlung gluons is soft. Here we show how to generalize to include the case where both splittings are hard. A number of techniques must be developed, and so in this paper we simplify by (i) restricting attention to a subset of the interference effects, which we call the “crossed” diagrams, and (ii) working in the large-Nc limit. We first develop some general formulas that could in principle be implemented numerically (with substantial difficulty). To make more analytic progress, we then focus on the case of a thick, homogeneous medium and make the multiple scattering approximation (also known as the \( \widehat{q} \) or harmonic approximation) appropriate at high energy. We show that the differential rate dΓ/dx dy for overlapping double bremsstrahlung of gluons with momentum fractions x and y can then be reduced to the calculation of a 1-dimensional integral, which we perform numerically.


Quark-Gluon Plasma QCD 


Open Access

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Copyright information

© The Author(s) 2015

Authors and Affiliations

  1. 1.Department of PhysicsUniversity of VirginiaCharlottesvilleUnited States
  2. 2.National Centre for PhysicsQuaid-i-Azam University CampusIslamabadPakistan

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