Studying invisible axion models at high temperature

During the thermal evolution of the universe, symmetry of the vacuum state in the presence of quantum fields should have changed at various stages. A possible indication of this effect on the DFSZ invisible axion model of the Peccei-Quinn CP conserving mechanism is presented here. To start with, the background theory of this mechanism in the cosmic evolution has been fully reviewed, as well as the leading cosmological arguments setting limits on the mass and coupling of such a particle. The CP conserving lagrangian of the invisible axion model also includes instanton gauge field configurations. In our opinion, these configurations could behave non trivially while decreasing the temperature as a consequence of the vacuum symmetry modifications. The interplay between symmetry modifications and cosmic evolution may thus lead to yet unclear effects. In fact, the model considered here is really quite a baby version of the real world, so that only preliminary indications and bare consistency arguments have been done from it. Nevertheless, the underlying idea, a possible neutral Higgs fields approximate resonance condition, seems to survive even in more sophisticated models.     

Radiative photino decay in models with an invisible axion

In models with an invisible axion, the lightest supersymmetric particle is likely to be the fermion superpartner of the axion, the axino. The photino decay rate into axino and photon is calculated, taking into account supersymetry-breaking effects. The resulting value of the photino lifetime can be larger by a factor ∼10³ than the value calculated in the supersymmetric limit by Kim, Masiero and Nanopoulos, which has interesting and potentially important consequences.     

Seeing an invisible axion in the supersymmetric particle spectrum

I describe how under favorable circumstances, the existence of an invisible axion could correlate with a distinctive CERN Large Hadron Collider sparticle spectrum, in particular, through a gluino approximately ln(M(P)/m(3/2)) times heavier than other gauginos.     

An invisible axion with a single Higgs isodoublet

We propose an SU(3) SU(2) U(1) gauge model with an invisible axion and a single Higgs isodoublet. The main peculiarity of the model is the use of non-renormalizable effective interactions left over from whatever theory combines SU(3) SU(2) U(1) with gravity. We also discuss the SU(5) extensions of the proposed model.     

Constraints on couplings of a fast decaying axion

Constraints are imposed on the couplings of an axion-like pseudoscalar particle φ that decays into e⁺e⁻ and γγ. The electron g−2 sets a severe bound not only on the φe⁺e⁻ coupling but also on the φγγ coupling. The most reliable bound on the φ coupling to the light quarks comes from the decay ∑⁺ → pe⁺e⁻ which was measured in a hydrogen bubble-chamber experiment with good sensitivity and resolution covering the entire range of e⁺e⁻ mass practically down to 2m_e. These upper bounds, together with a constraint from the decay K⁺→π⁺γγ, reinforce arguments against the particle-physics interpretation of the anomalous positrons in heavy-ion collisions, since the couplings are by orders of magnitude smaller than needed to produce e⁺e⁻ pairs at the observed level by known mechanisms.     

Families,the invisible axion,and domain walls

We consider models in which the unbroken discrete subgroup of a Peccei-Quinn symmetry may be effectively embedded in the rest of the continuous symmetry group to avoid the formation of domain walls. In this context we may gain insight into the family question. We note that instantons in an unbroken “hypercolor” group might be used to reduce the size of the discrete symmetry or to eliminate it altogether.     

Superconducting strings in axion models

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

Non-Gaussianity in axion N-flation models

We study perturbations in the multifield axion N-flation model, taking account of the full cosine potential. We find significant differences from previous analyses which made a quadratic approximation to the potential. The tensor-to-scalar ratio and the scalar spectral index move to lower values, which nevertheless provide an acceptable fit to observation. Most significantly, we find that the bispectrum non-Gaussianity parameter f{NL} may be large, typically of order 10 for moderate values of the axion decay constant, increasing to of order 100 for decay constants slightly smaller than the Planck scale. Such a non-Gaussian fraction is detectable. We argue that this property is generic in multifield models of hilltop inflation.     

SupersymmetricSU (11), the invisible axion,and proton decay

We supersymmetrize the very attractive flavour unification modelSU (11). As with other supersymmetric GUTs the gauge hierarchy problem is simplified, but we may also have observable (τ _p ≈10³³ yrs) proton decay. The required split multiplets are obtained by making the adjoint take a particular direction. Supersymmetry is broken softly at the TeV scale. There is a uniqueU(1) _A symmetry, and hence there are no true Nambu-Goldstone bosons. TheU(1) _A is broken at the GUT scale and there result an invisible axion and neutrino masses.     

Search for the invisible axion emitted in the M1 transition in 125m Te

A method of searching for the invisible axion emitted in M transitions of isomeric nuclei is proposed. It is determined experimentally that the probability of emission of an axion in the M1 transition in ^125m Te is ⩽1.3⋅10⁻⁵ (90% confidence level). Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 576–580 (25 April 1997)     

Goldstone fermion couplings and supersymmetry breaking in superstring models

We re-examine supersymmetry breaking in the observable sectors of superstring-inspired supergravity models by computing Goldstone fermion couplings at the one-loop level. We find that a single global U (1) phase invariance is sufficient to forbid masses for gauge non-singlet chiral scalar bosons, and that Heisenberg symmetry is not necessary.     

Relation between effective couplings for asymptotically free models

For asymptotically free models with two independent couplings asymptotic expansions are constructed which express one effective coupling in terms of the other. The expansions involve powers (including fractional or irrational exponents) and logarithms. All orders of the-functions are taken into account. The expansions found are complete in the sense that they represent solutions (exact to any order) which generalize all the solutions obtained with the-functions approximated to second order. It is shown that higher orders are relevant since it is not possible in general to reparametrize the system such that the-functions become polynomials of the coupling parameters. The simplifications in case of supersymmetric models are discussed.