Dennis W. Sciama

SONOLUMINESCENCE : BOGOLUBOV COEFFICIENTS FOR THE QED VACUUM OF A TIME-DEPENDENT DIELECTRIC BUBBLE

We extend Schwingers ideas regarding sonoluminescence by explicitly calculating the Bogolubov coefficients relating the QED vacuum states associated with changes in a dielectric bubble. Sudden (non-adiabatic) changes in the refractive index lead to an efficient production of real photons with a broadband spectrum, and a high-frequency cutoff that arises from the asymptotic behaviour of the dielectric constant.

Sonoluminescence as a QED vacuum effect. I. The physical scenario

Several years ago Schwinger proposed a physical mechanism for sonoluminescence in terms of changes in the properties of the quantum-electrodynamic vacuum state during collapse of the bubble. This mechanism is most often phrased in terms of changes in the Casimir energy (i.e., changes in the distribution of zero-point energies) and has recently been the subject of considerable controversy. The present paper further develops this quantum-vacuum approach to sonoluminescence: We calculate Bogolubov coefficients relating the QED vacuum states in the presence of a homogeneous medium of changing dielectric constant. In this way we derive an estimate for the spectrum, number of photons, and total energy emitted. We emphasize the importance of rapid spatio-temporal changes in refractive indices and the delicate sensitivity of the emitted radiation to the precise dependence of the refractive index as a function of wave number, pressure, temperature, and noble gas admixture. Although the basic physics of the dynamical Casimir effect is a universal phenomenon of QED, specific and particular experimental features are encoded in the condensed matter physics controlling the details of the refractive index. This calculation places rather tight constraints on the possibility of using the dynamical Casimir effect as an explanation for sonoluminescence, and wemorexa0» are hopeful that this scenario will soon be amenable to direct experimental probes. In the following paper we discuss the technical complications due to finite-size effects, but for reasons of clarity in this paper we confine our attention to bulk effects. (c) 2000 The American Physical Society.«xa0less

Sonoluminescence as a QED vacuum effect. II. Finite volume effects

In a companion paper [quant-ph/9904013] we have investigated several variations of Schwingers proposed mechanism for sonoluminescence. We demonstrated that any realistic version of Schwingers mechanism must depend on extremely rapid (femtosecond) changes in refractive index, and discussed ways in which this might be physically plausible. To keep that discussion tractable, the technical computations in that paper were limited to the case of a homogeneous dielectric medium. In this paper we investigate the additional complications introduced by finite-volume effects. The basic physical scenario remains the same, but we now deal with finite spherical bubbles, and so must decompose the electromagnetic field into Spherical Harmonics and Bessel functions. We demonstrate how to set up the formalism for calculating Bogolubov coefficients in the sudden approximation, and show that we qualitatively retain the results previously obtained using the homogeneous-dielectric (infinite volume) approximation.

On an Einstein-de Sitter universe of radiating massive photinos

Abstract Photons emitted by massive photinos ( γ ) formed in the hot big bang could ionise the intergalactic medium and galactic halos to the observed extent if m γ ∼ 100 eV and the radiative lifetime τ ∼ 10 27 s. These photinos could have the critical Einstein-de Sitter density if they decoupled at T ∼ 200 MeV. Supersymmetric theories then indicate that the order parameter d is roughly 10 8 GeV 2 . This estimate would be numerically consitent with particle-physics estimates or limits on the grand unification scale, the boson-fermion mass splitting, and the mass of the gravitino, and would lead to a value of τ comparable to the astronomical one.

Sonoluminescence: two-photon correlations as a test of thermality

Abstract In this Letter we propose a fundamental test for probing the thermal nature of the spectrum emitted by sonoluminescence. We show that two-photon correlations can in principle discriminate between real thermal light and the pseudo-thermal squeezed-state photons typical of models based on the dynamic Casimir effect. Two-photon correlations provide a powerful experimental test for various classes of sonoluminescence models.

Cosmological constraints on broken supersymmetry

The present cosmological constraint on the number of allowed particle types and the particle physics constraint on broken supersymmetric theories which solve the hierarchy problem work in opposite directions and can both just be satisfied, but only if egd ≈ 107 GeV2, in the usual notation. This extreme value suggests that both the symmetry breaking of the electroweak theory and the masses of the associated Higgs particles are radiatively induced. The cosmological constraint requires in addition that d ⩾ 108 GeV2. If photinos (∼γ) have the critical density then m∼γ ≈ 100 eV, and possibly d ≈ 108GeV2, implying that eg ≈ e. These values would lead to the photino mass and radiative lifetime required by our hypothesis that ionising photons emitted by photinos dominating the galactic halo are responsible for the SiIV and CIV observed by IUE to exist in the halo. We conclude that broken supersymmetry may be a physical reality.

On the production of N V and O VI in galactic halos by photons emitted by massive photinos

Abstract Photinos dominating galactic halos would emit photons energetic enough to produce the recently observed N V and O VI if their rest mass ∼250 eV. Such photinos would have the critical density if they are ten times less abundant than neutrinos. This suppression would require a photino decoupling temperature ∼200 MeV and so a supersymmetry breaking parameter d∼108 GeV2. The theoretical radiative lifetime of the photino then ∼1026 s, which is short enough for the halo photon flux to be adequate to produce the observed abundances of N V and O VI as well as the previously discussed Si IV and C IV.

Decaying Neutrinos and the Flattening of the Galactic Halo

The recently constructed Dehnen-Binney set of mass models for the Galaxy is used to show that the decaying neutrino theory for the ionisation of the interstellar medium (Sciama 1990a, 1993) requires the neutrino halo of the Galaxy to be as flattened as is observationally permitted (axial ratio q=0.2 or shape E8). The argument involves an evaluation of the contribution of red-shifted decay photons from the cosmological distribution of neutrinos to the extragalactic diffuse background at 1500 Angstroms. This contribution must be as large as is observationally permitted. These two requirements depend on the decay lifetime in potentially conflicting ways. For consistency to be achieved the lifetime must lie within 30 per cent of 10^23 seconds.

Sterile neutrinos and CMB

Sterile neutrinos have been invoked in attempts to use neutrino oscillations to account for several experimental anomalies, the most recently confirmed being the atmospheric anomaly announced by the SuperKamiokande collaboration. In this talk I describe the development and its relevance for both big bang nucleosynthesis and the CMB.

Cosmological Implications of the 3 K Background

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