Constraining axion by polarized prompt emission from gamma ray bursts.pdf
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arXiv: 0708.2646 [hep-ph]
CERN-TH/2007-146
August 2007
Constraining axion by polarized prompt emission
from gamma ray bursts
A. Rubbiaa and A.S. Sakharova,b
Abstract
A polarized gamma ray emission spread over a sufficiently wide energy band from a strongly
magnetized astrophysical object like gamma ray bursts (GRBs) offers an opportunity to test
the hypothesis of invisible axion. The axionic induced dichroism of gamma rays at different
energies should cause a misalignment of the polarization plane for higher energy events relative
to that one for lower energies events resulting in the loss of statistics needed to form a pattern
of the polarization signal to be recognized in a detector. According to this, any evidence of
polarized gamma rays coming from an object with extended magnetic field could be interpreted
as a constraint on the existence of the invisible axion for a certain parameter range. Based
on reports of polarized MeV emission detected in several GRBs we derive a constraint on the
axion-photon coupling. This constraint gaγγ ≤ 2.2 · 10?11 GeV?1 calculated for the axion mass
ma = 10
?3 eV is competitive with the sensitivity of CAST and becomes even stronger for lower
masses.
CERN-TH/2007-146
August 2007
a Swiss Institute of Technology, ETH-Zu?rich, 8093 Zu?rich, Switzerland
b TH Division, PH Department, CERN, 1211 Geneva 23, Switzerland
1
The Peccei-Quinn (PQ) mechanism [1] remains perhaps the most natural solution to
the CP problem in QCD. A new chiral UPQ(1) symmetry being spontaneously broken at
some large energy scale, fa, and explicitly broken by the color anomaly at QCD scale
would allow for the dynamical vanishing of the θ term and thus the restoration of the CP
symmetry in strong interactions. The pseudo-scalar field, which drives the relaxation of
the θ term to zero is called axion. The most important phenomenological property of this
axion is its two-photon vertex interact
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