Vacuum decay constraints on a cosmological scalar field

If the potential of a scalar field phi which currently provides the "dark energy" of the Universe has a minimum at phi = -M(0)(4)<0, then quantum-mechanical fluctuations could nucleate a bubble of phi at a negative value of the potential. This bubble would then expand at the speed of light. Given that no such bubble enveloped us in the past, we find that any minimum in V(phi) must be separated from the current phi value by more than min[1.5M(0),0.21M(Pl)], where M(Pl) is the Planck mass. We also show that vacuum decay renders a cyclic or ekpyrotic universe with M(0)(4) > or approximately 10(-10)M(4)(Pl) untenable.     

Effective cosmological constant within the expanding axion universe

We show that the value of an effective cosmological constant, _Λeff${\Lambda }_{\mathit{eff}}$, is influenced by the dimensionality of the space. Results were obtained in the framework of the axion model describing expansion of the inhomogeneous universe. _Λeff${\Lambda }_{\mathit{eff}}$ determines the tension of the space (i.e. elasticity), and is relaxed when extra dimensions are accessible. We demonstrate that the effective value of the cosmological constant may be tuned to be consistent with experimental observation. Inhomogeneities considered are representative of temperature fluctuations observed within the cosmic microwave background radiation.     

Electromagnetic catalysis of the radiative decay of the axion

The radiative decay of the axion a → γγ is investigated in an external electromagnetic field in DFSZ model in which axion couples to both quarks and leptons at tree level. The decay probability is strongly catalyzed by the external field, namely, the field removes the main suppression caused by the smallness of the axion mass.     

Estimates of axion signal from positronium decay

Numerical values for axion decay channel branching ratio in positronium decays are presented. From the ³S₁ state the maximum is of the order of 10^?6. If the axion mass were to be in the vicinity of the positronium mass, the best way of observing the signal would be the decay from the 2¹P₁ state. The feasibility of attaining this by optical pumping is indicated.     

Magnetic-field influence on radiative axion decay into photons of the same polarization

The decays of a pseudoscalar particle, the axion, into two photons of the same polarization are studied in the model involving direct axion-electron coupling. These processes, which are forbidden in a vacuum because of a pseudoscalar nature of the axion, become possible in a magnetic field. It is shown that the kinematics of ultrarelativistic-axion decay substantially depends on photon polarizations. The probability of radiative axion decay in the limit of a strong magnetic field substantially exceeds the corresponding probability in a vacuum.     

Renormalization-group analysis of the cosmological constraint on the Higgs scalar mass

The standard Model Higgs scalar boson minimally coupled to gravity does not take part in the inflation of the early universe if its mass exceeds a threshold value, which is m _H ^min = 142 GeV in the tree approximation for the potential of the scalar. Two-loop corrections modify this estimate, which becomes m _H ^min = 150 ± 3 GeV. Therefore, higher order corrections of perturbation theory have quite a controllable moderate character, but they are numerically important for experiments.     

Production of scalar particles in cosmological models

The mean number of particles produced in a space-time with the metric ds²=dt²–t² (dx²+dy²)–Kt²dz²(=1/t², 1) is calculated. It is shown that the produced particles are described by a Bose-Einstein distribution with a certain temperature.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 3–6, July, 1980.I thank D. M. Gitman and V. P. Frolov for discussing a number of questions touched upon in the paper.     

Universal decay of scalar turbulence

The asymptotic decay of passive scalar fields is solved analytically for the Kraichnan model, where the velocity has a short correlation time. At long times, two universality classes are found, both characterized by a distribution of the scalar-generally non-Gaussian-with global self-similar evolution in time. Analogous behavior is found numerically with a more realistic flow resulting from an inverse energy cascade.     

Conformally coupled scalar field solutions and the cosmological constant

Solutions are presented for a scalar field coupled conformally to Einstein gravity with a nonvanishing cosmological constant, in the case that the spacetime metric is spatially homogeneous and isotropic. Since the cosmological constant destroys the conformal invariance of the action, these solutions cannot be obtained by solving the flat space wave equation for the scalar field. It turns out that the metric is determined entirely by the cosmological constant, while the scalar field acquires an apparent mass squared which is proportional to the cosmological constant. It is conjectured that the cosmological constant in the universe at present may thus be disguised as the mass of some scalar field.     

Nonsingular cosmological models: the massive scalar field case

The nonminimal coupling of a massive self-interacting scalar field with a gravitational field is studied. Spontaneous symmetry breaking occurs in the open universe even when the sign on the mass term is positive. In contrast to grand unified theories, symmetry breakdown is more important for the early universe and it is restored only in the limit of an infinite expansion. Symmetry breakdown is shown to occur in flat and closed universes when the mass term carries a wrong sign. The model has a naturally defined effective gravitational coupling coefficient which is rendered time-dependent due to the novel symmetry breakdown. It changes sign below a critical value of the cosmic scale factor indicating the onset of a repulsive field. The presence of the mass term severely alters the behaviour of ordinary matter and radiation in the early universe. The total energy density becomes negative in a certain domain. These features make possible a nonsingular cosmological model for an open universe. The model is also free from the horizon and the flatness problems.     

Neutrino decay of an axion in an external electromagnetic field

Switching on an external electromagnetic field opens a neutrino decay channel of a hypothetical pseudoscalar particle, an axion, which plays an important role in modern field theory. We obtain exact expressions in the one-loop approximation for the probability of the decay into a massless neutrino in a crossed fieldF and study the asymptotic behavior by the nature of the parameter . Moscow State Industrial University, Moscow. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 42, No. 2, pp. 8–12, February, 1999.     

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.