Astron. Astrophys. 360, 549-558 (2000)

Neutrino-pair emission in a strong magnetic field

E.N.E. van Dalen, A.E.L. Dieperink, A. Sedrakian and R.G.E. Timmermans

Kernfysisch Versneller Instituut, 9747 AA Groningen, The Netherlands (vandalen,dieperink,sedrakian,timmermans@kvi.nl)

Received 16 February 2000 / Accepted 9 May 2000

Abstract

We study the neutrino emissivity of strongly magnetized neutron stars due to the charged and neutral current couplings of neutrinos to baryons in strong magnetic fields. The leading order neutral current process is the one-body neutrino-pair bremsstrahlung, which does not have an analogue in the zero field limit. The leading order charged current reaction is the known generalization of the direct Urca processes to strong magnetic fields. While for superstrong magnetic fields in excess of G the direct Urca process dominates the one-body bremsstrahlung, we find that for fields on the order G and temperatures a few times  K the one-body bremsstrahlung is the dominant process. Numerical computation of the resulting emissivity, based on a simple parametrization of the equation of state of the npe-matter in a strong magnetic field, shows that the emissivity of this reaction is of the same order of magnitude as that of the modified Urca process in the zero field limit.

Key words: stars: neutron stars: evolution stars: magnetic fields

Send offprint requests to: A.E.L. Dieperink (dieperink@kvi.nl)

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Contents

• 1. Introduction
• 2. The bremsstrahlung emissivity
• 3. Neutrino-pair bremsstrahlung from neutrons ()
  • 3.1. Polarization function
  • 3.2. Emissivity
• 4. Neutrino-pair bremsstrahlung from protons ()
  • 4.1. Emissivity
• 5. Direct Urca process (; )
  • 5.1. Emissivity
    • 5.1.1. Superstrong magnetic fields
    • 5.1.2. Weak magnetic fields
• 6. Equation of state (EoS)
• 7. Results
• 8. Conclusion
• Acknowledgements
• Appendices
  • A: electrons, protons and neutrons in a magnetic field
    • A.1. Electron
    • A.2. Proton
    • A.3. Neutron
  • B: the weak interaction matrix elements
    • B.1. Neutrino-neutron interaction (neutral current)
    • B.2. Neutrino-proton interaction (neutral current)
    • B.3. Direct Urca process (charged current)
• References

© European Southern Observatory (ESO) 2000

Online publication: August 17, 2000
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