Resonant mechanism of axion photoproduction in a magnetized electron gas

It was shown that the contribution of diagrams with electron-positron vacuum excitation in a strong magnetic field B ? B ₀ = m ²/e = 4.41 × 10¹³ G in the Compton mechanism of axion production γe → ae at temperatures on the order of the axion mass exceeds the contribution of the “simple” Compton diagram and the contribution of the neutrino production γe → (ν\(\bar \nu \))e to the radiation power by many orders of magnitude. The conclusion is made on the probable axionic nature of the cold hidden mass of the Universe.     

The elusive axion

In view of the uncertainties attached to the interpretation of existing axion searches we consider the possibility of probing the direct axion-quark coupling in K and B decays.     

Inflation and axion cosmology

It is argued that the standard constraint ƒ⪷10¹²GeV in the axion theory and related constraints in the theories of other weakly interacting scalar fields do not apply in many versions of the inflationary universe scenario.     

A short-lived axion variant

It is argued that existing experiments do not preclude the existence of an axion with very small Peccei-Quinn scale, coupled preferentially to light fermions. Parameters are fixed for the 1.8 MeV particle suggested by recent heavy-ion experiments. Mechanisms for slowing down or binding the axion in a nuclear environment are suggested.     

Opening the axion window

In this paper I consider models where the strong CP problem is solved by means of a Peccei-Quinn symmetry carried by exotic colored fermions. An example is Kim's recently proposed composite invisible axion model. Axions from such models don't couple to electrons, and have model dependent photon couplings which may differ from the standard coupling by a factor of 10^?2 ? 10⁺¹. As a result, laboratory detection of relic axions may be very difficult, and astrophysical bounds on the axion mass are weakened. Pulsar observations place no strong bound on such an axion unless the core is known not to be superfluid. Normal fusion stars allow an axion mass as large as $\text{m}{}_{\mathrm{<mtext>a</mtext>}}\text{? 20}\text{eV}$ for certain models.     

Hypernuclear photoproduction

Calculations of the nuclear (γ, K⁺) reaction employing full Coulomb and optical distortions and a complete photoproduction vertex are reported. Hypernuclear excitations other than spin-flip modes are found to be significantly excited and distortion effects are found to strongly alter the magnitude of the cross sections.     

Wave propagation in axion electrodynamics

In this paper, the axion contribution to the electromagnetic wave propagation is studied. First we show how the axion electrodynamics model can be embedded into a premetric formalism of Maxwell electrodynamics. In this formalism, the axion field is not an arbitrary added Chern–Simon term of the Lagrangian, but emerges in a natural way as an irreducible part of a general constitutive tensor. We show that in order to represent the axion contribution to the wave propagation it is necessary to go beyond the geometric approximation, which is usually used in the premetric formalism. We derive a covariant dispersion relation for the axion modified electrodynamics. The wave propagation in this model is studied for an axion field with timelike, spacelike and null derivative covectors. The birefringence effect emerges in all these classes as a signal of Lorentz violation. This effect is however completely different from the ordinary birefringence appearing in classical optics and in premetric electrodynamics. The axion field does not simple double the ordinary light cone structure. In fact, it modifies the global topological structure of light cones surfaces. In CFJ-electrodynamics, such a modification results in violation of causality. In addition, the optical metrics in axion electrodynamics are not pseudo-Riemannian. In fact, for all types of the axion field, they are even non-Finslerian.     

Grand unification and heavy axion

We argue that sufficiently complex grand unified theories involving extra strong intractions that confine at very short distances may lead to a heavy axion solution of the CP problem of QCD. This axion may have a mass within the accessible energy range, and its low-energy interactions emerge through mixing with axial Higgs boson(s). Another signature of this scenario is softly broken Peccei-Quinn symmetry in the electroweak Higgs sector. We present a toy GUT exhibiting these features. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 590–593 (25 April 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Large non-gaussianity in axion inflation

The inflationary paradigm has enjoyed phenomenological success; however, a compelling particle physics realization is still lacking. Axions are among the best-motivated inflaton candidates, since the flatness of their potential is naturally protected by a shift symmetry. We reconsider the cosmological perturbations in axion inflation, consistently accounting for the coupling to gauge fields cΦFF, which is generically present in these models. This coupling leads to production of gauge quanta, which provide a new source of inflaton fluctuations, δΦ. For c≥10(2)M(p)(-1), these dominate over the vacuum fluctuations, and non-Gaussianity exceeds the current observational bound. This regime is typical for concrete realizations that admit a UV completion; hence, large non-Gaussianity is easily obtained in minimal and natural realizations of inflation.     

Superconducting strings in axion models

An SU(5) axion model is discussed in detail to show that axionic strings are superconducting.