Konjunkturprognosen und wissenschaftlich-technischer Fortschritt

Wissenschaftliche Prognosen unterscheiden sich von sonstigen Vorhersagen nicht zuletzt dadurch, daß mit ihnen der Anspruch auf systematische Verbesserbarkeit verknüpft wird. Hat sich die Treffsicherheit von Konjunkturprognosen als Folge des wissenschaftlich-technischen Fortschritts verbessert? --

Counting statistics of collective photon transmissions

We theoretically study cooperative effects in the steady-state transmission of photons through a medium of $N$ radiators. Using methods from quantum transport, we find a cross-over in scaling from $N$ to $N^2$ in the current and even higher powers of $N$ in the higher cumulants of the photon counting statistics as a function of the tunable source occupation. The effect should be observable for atoms confined within a nano-cell with a pumped optical cavity as photon source.Comment: extended results, 9 pages, 2 figures, to appear in Annals of Physic

The flatness problem and Λ\Lambda

By way of a complete integration of the Friedmann equations, in terms of observables, it is shown that for the cosmological constant $\Lambda > 0$ there exist non-flat FLRW models for which the total density parameter $\Omega$ remains $\sim 1$ throughout the entire history of the universe. Further, it is shown that in a precise quantitative sense these models are not finely tuned. When observations are brought to bear on the theory, and in particular the WMAP observations, they confirm that we live in just such a universe. The conclusion holds when the classical notion of $\Lambda$ is extended to dark energy.Comment: Final form to appear in Physical Review Letters. Further information at http://grtensor.org/Robertson

The Polarization of the Cosmic Microwave Background Due to Primordial Gravitational Waves

We review current observational constraints on the polarization of the Cosmic Microwave Background (CMB), with a particular emphasis on detecting the signature of primordial gravitational waves. We present an analytic solution to the Polanarev approximation for CMB polarization produced by primordial gravitational waves. This simplifies the calculation of the curl, or B-mode power spectrum associated with gravitational waves during the epoch of cosmological inflation. We compare our analytic method to existing numerical methods and also make predictions for the sensitivity of upcoming CMB polarization observations to the inflationary gravitational wave background. We show that upcoming experiments should be able either detect the relic gravitational wave background or completely rule out whole classes of inflationary models.Comment: 25 pages, 4 figures, review published in IJMP

Theory of superradiant scattering of laser light from Bose-Einstein condensates

In a recent MIT experiment, a new form of superradiant Rayleigh scattering was observed in Bose-Einstein condensates. We present a detailed theory of this phenomena in which the directional dependence of the scattering rate and condensate depletion lead to mode competition which is ultimately responsible for superradiance. The nonlinear response of the system is highly sensitive to initial quantum fluctuations which cause large run to run variations in the observed superradiant pulses.Comment: Updated version with new figures,a numerical simulation with realistic experimental parameters is now included. Featured in September 1999 Physics Today, in Search and Discovery sectio

Optically controlled spin-glasses in multi-qubit cavity systems

Recent advances in nanostructure fabrication and optical control, suggest that it will soon be possible to prepare collections of interacting two-level systems (i.e. qubits) within an optical cavity. Here we show theoretically that such systems could exhibit novel phase transition phenomena involving spin-glass phases. By contrast with traditional realizations using magnetic solids, these phase transition phenomena are associated with both matter and radiation subsystems. Moreover the various phase transitions should be tunable simply by varying the matter-radiation coupling strength.Comment: 4 pages, 3 figure

Generation of scalar-tensor gravity effects in equilibrium state boson stars

Boson stars in zero-, one-, and two-node equilibrium states are modeled numerically within the framework of Scalar-Tensor Gravity. The complex scalar field is taken to be both massive and self-interacting. Configurations are formed in the case of a linear gravitational scalar coupling (the Brans-Dicke case) and a quadratic coupling which has been used previously in a cosmological context. The coupling parameters and asymptotic value for the gravitational scalar field are chosen so that the known observational constraints on Scalar-Tensor Gravity are satisfied. It is found that the constraints are so restrictive that the field equations of General Relativity and Scalar-Tensor gravity yield virtually identical solutions. We then use catastrophe theory to determine the dynamically stable configurations. It is found that the maximum mass allowed for a stable state in Scalar-Tensor gravity in the present cosmological era is essentially unchanged from that of General Relativity. We also construct boson star configurations appropriate to earlier cosmological eras and find that the maximum mass for stable states is smaller than that predicted by General Relativity, and the more so for earlier eras. However, our results also show that if the cosmological era is early enough then only states with positive binding energy can be constructed.Comment: 20 pages, RevTeX, 11 figures, to appear in Class. Quantum Grav., comments added, refs update

Coherent states and global entanglement in an N qubit system

We consider an $N$ qubit system and show that in the symmetric subspace, $\mathbb{S}$ a state is not globally entangled, iff it is a coherent state. It is also proven that in the orthogonal complement $\mathbb{S}_{\bot}$ all states are globally entangled

Singularity Free (Homogeneous Isotropic) Universe in Graviton-Dilaton Models

We present a class of graviton-dilaton models in which a homogeneous isotropic universe, such as our observed one, evolves with no singularity at any time. Such models may stand on their own as interesting models for singularity free cosmology, and may be studied further accordingly. They may also arise from string theory. We discuss critically a few such possibilities.Comment: 11 pages. Latex file. Revised in response to referees' Comments. Results remain same. To appear in Phys. Rev. Let