Axial anomaly and magnetism of nuclear and quark matter
Oct, 200717 pages
Published in:
- Phys.Rev.D 77 (2008) 014021
e-Print:
- 0710.1084 [hep-ph]
Report number:
- INT-PUB-07-24
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Abstract: (arXiv)
We consider the response of the QCD ground state at finite baryon density to a strong magnetic field B. We point out the dominant role played by the coupling of neutral Goldstone bosons, such as pi^0, to the magnetic field via the axial triangle anomaly. We show that, in vacuum, above a value of B ~ m_pi^2/e, a metastable object appears - the pi^0 domain wall. Because of the axial anomaly, the wall carries a baryon number surface density proportional to B. As a result, for B ~ 10^{19} G a stack of parallel pi^0 domain walls is energetically more favorable than nuclear matter at the same density. Similarly, at higher densities, somewhat weaker magnetic fields of order B ~ 10^{17}-10^{18} G transform the color-superconducting ground state of QCD into new phases containing stacks of axial isoscalar (eta or eta') domain walls. We also show that a quark-matter state known as ``Goldstone current state,'' in which a gradient of a Goldstone field is spontaneously generated, is ferromagnetic due to the axial anomaly. We estimate the size of the fields created by such a state in a typical neutron star to be of order 10^{14}-10^{15} G.Note:
- 18 pages, v2: added a discussion of the energy cost of neutralizing the domain wall charge
- 12.38.Aw
- 26.60.-c
- quantum chromodynamics: ground state
- density: finite
- magnetic field: high
- pi0: coupling
- anomaly: axial
- pi0: domain wall
- baryon number: density
- nuclear matter
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