Abstract
In the past, the axion-nucleon coupling has been calculated in the framework of SU(2) heavy baryon chiral perturbation theory up to third order in the chiral power counting. Here, we extend these earlier studies to the case of heavy baryon chiral perturbation theory with SU(3) flavor symmetry and derive the axion coupling to the full SU(3) baryon octet, showing that the axion also significantly couples to hyperons. As studies on dense nuclear matter suggest the possible existence of hyperons in stellar objects such as neutron stars, our results should have phenomenological implications related to the so-called axion window.
Highlights
Constant, Gμν the gluon field strength tensor, Gμν = μναβGαβ/2 its dual, and Tr denotes the trace in color space
We extend these earlier studies to the case of heavy baryon chiral perturbation theory with SU(3) flavor symmetry and derive the axion coupling to the full SU(3) baryon octet, showing that the axion significantly couples to hyperons
Such an analysis has been carried out up-to-and-including O(p3) in SU(2) heavy baryon chiral perturbation theory (HBCHPT) in our previous work [58], where p denotes a small parameter. We extend these previous studies using SU(3) HBCHPT in two regards: (i) we extend the calculations of the axion-nucleon couplings to the SU(3) case, up-to-andincluding O(p3), and (ii) we derive the couplings of the axion to the full ground state baryon octet
Summary
Consider the general QCD Lagrangian with axions below the electroweak symmetry breaking scale [32]. We assume the canonical scenario that the couplings are flavor conserving at tree-level, i.e. Xq = diag {Xq} is a diagonal 6 × 6 matrix acting in flavor space, where the Xq’s, q = {u, d, s, c, b, t}, are the coupling constants of the respective axion-quark interactions. Note that in contrast to usual chiral perturbation theory, it is necessary to add isosinglet axial-vector currents a(μs,)i in order to preserve the full QCD axion interaction This is possible here, as the subtleties that usually arise due to the U(1)A anomaly are absent, because the model is anomaly-free. If one considers flavor-changing axion-quark couplings at tree-level, Xq would be non-diagonal In this case, it is likewise appropriate to decompose Xq − Qa into traceless parts and parts with non-vanishing trace, such that aμ. We here stick to the most prevalent models excluding such flavor-changing axion-quark couplings at tree-level
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