Search results for "Deceleration parameter"

showing 2 items of 2 documents

Cosmology with self-adjusting vacuum energy density from a renormalization group fixed point

2001

Cosmologies with a time dependent Newton constant and cosmological constant are investigated. The scale dependence of $G$ and $\Lambda$ is governed by a set of renormalization group equations which is coupled to Einstein's equation in a consistent way. The existence of an infrared attractive renormalization group fixed point is postulated, and the cosmological implications of this assumption are explored. It turns out that in the late Universe the vacuum energy density is automatically adjusted so as to equal precisely the matter energy density, and that the deceleration parameter approaches $q = -1/4$. This scenario might explain the data from recent observations of high redshift type Ia S…

High Energy Physics - TheoryPhysicsNuclear and High Energy PhysicsDeceleration parametermedia_common.quotation_subjectCosmic microwave backgroundAstrophysics (astro-ph)FOS: Physical sciencesAstrophysicsCosmological constantGeneral Relativity and Quantum Cosmology (gr-qc)Astrophysics::Cosmology and Extragalactic AstrophysicsRenormalization groupAstrophysicsGeneral Relativity and Quantum CosmologyCosmologyUniverseHigh Energy Physics - PhenomenologyGeneral Relativity and Quantum CosmologyHigh Energy Physics - Phenomenology (hep-ph)Vacuum energyHigh Energy Physics - Theory (hep-th)Mathematical physicsmedia_commonQuintessencePhysics Letters B
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Imaging of SN 1993J

2005

SN 1993J has been imaged with VLBI, and its angular expansion monitored, for almost ten years. The images show shell-like radio structures with almost circular symmetry. SN 1993J expands according to models of shock excited emission. The angular expansion has a changing deceleration rate and is best modeled with two different slopes. The swept-up mass estimate at an age of 3159 days (∼0.4 M⨀), comparable to the low-mass envelope, favors a binary scenario. The observed spectral index of SN 1993J has slowly flattened since age 1000 days onward (α has changed from −1 to −0.67 at an age of 2820 days).

PhysicsSpectral indexDeceleration parameterShock (fluid dynamics)Excited stateVery-long-baseline interferometryAstrophysicsCircular symmetryEnvelope (waves)
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