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Blobrana


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Vacuum birefringence
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First Signs of Weird Quantum Property of Empty Space?

By studying the light emitted from an extraordinarily dense and strongly magnetised neutron star using ESO's Very Large Telescope, astronomers may have found the first observational indications of a strange quantum effect, first predicted in the 1930s. The polarisation of the observed light suggests that the empty space around the neutron star is subject to a quantum effect known as vacuum birefringence.
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Blobrana


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RE: Quantum vacuum
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Cosmos may be 'inherently unstable'

Scientists say they may be able to determine the eventual fate of the cosmos as they probe the properties of the Higgs boson.
A concept known as vacuum instability could result, billions of years from now, in a new universe opening up in the present one and replacing it.
It all depends on some precise numbers related to the Higgs that researchers are currently trying to pin down.
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Blobrana


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Title: Inhomogeneous vacuum energy
Authors: David Wands, Josue De-Santiago, Yuting Wang

Vacuum energy remains the simplest model of dark energy which could drive the accelerated expansion of the Universe without necessarily introducing any new degrees of freedom. Inhomogeneous vacuum energy is necessarily interacting in general relativity. Although the four-velocity of vacuum energy is undefined, an interacting vacuum has an energy transfer and the vacuum energy defines a particular foliation of spacetime with spatially homogeneous vacuum energy in cosmological solutions. It is possible to give a consistent description of vacuum dynamics and in particular the relativistic equations of motion for inhomogeneous perturbations given a covariant prescription for the vacuum energy, or equivalently the energy transfer four-vector, and we construct gauge-invariant vacuum perturbations. We show that any dark energy cosmology can be decomposed into an interacting vacuum+matter cosmology whose inhomogeneous perturbations obey simple first-order equations.

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Blobrana


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Title: Zero-point quantum fluctuations in cosmology
Authors: Lukas Hollenstein, Maud Jaccard, Michele Maggiore, Ermis Mitsou

We re-examine the classic problem of the renormalization of zero-point quantum fluctuations in a Friedmann-Robertson-Walker background. We discuss a number of issues that arise when regularising the theory with a momentum-space cutoff, and show explicitly how introducing non-covariant counter-terms allows to obtain covariant results for the renormalized vacuum energy-momentum tensor. We clarify some confusion in the literature concerning the equation of state of vacuum fluctuations. Further, we point out that the general structure of the effective action becomes richer if the theory contains a scalar field phi with mass m smaller than the Hubble parameter H(t). Such an ultra-light particle cannot be integrated out completely to get the effective action. Apart from the volume term and the Einstein-Hilbert term, that are reabsorbed into renormalizations of the cosmological constant and Newton's constant, the effective action in general also has a term proportional to F(phi)R, for some function F(phi). As a result, vacuum fluctuations of ultra-light scalar fields naturally lead to models where the dark energy density has the form rho_{DE}(t)=rho_X(t)+rho_Z(t), where rho_X is the component that accelerates the Hubble expansion at late times and rho_Z(t) is an extra contribution proportional to H^2(t). We perform a detailed comparison of such models with CMB, SNIa and BAO data.

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Blobrana


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Posts: 131433
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Fluctuating quantum fields
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Quantum space monster leaps from a gravity well

Gravity may have the power to create quantum monsters. A strong gravitational field can induce a runaway effect in quantum fluctuations in apparently empty space, resulting in a burgeoning concentration of energy that may explode stars or create black holes. So say Daniel Vanzella and William Lima at the University of São Paulo in Brazil.
Quantum phenomena are not thought to have any significant influence over processes on the astrophysical scale, such as the compression of gas clouds into stars. That's the domain of gravity, which in turn is not supposed to be much affected by quantum events, like an elephant unaware of the microbes on its skin. In only a few exotic cases, such as singularities inside black holes, do gravity and quantum-level forces influence the same processes.
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Blobrana


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Posts: 131433
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Quantum vacuum
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Title: A magneto-electric quantum wheel
Authors: Alexander Feigel

Here we show that self-propulsion in quantum vacuum may be achieved by rotating or aggregating magneto-electric nano-particles. The back-action follows from changes in momentum of electro-magnetic zero-point fluctuations, generated in magneto-electric materials. This effect may provide new tools for investigation of the quantum nature of our world. It might also serve in the future as a "quantum wheel" to correct satellite orientation in space.

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