Biomedical subjects

R R Caldwell

Publications and source records attributed to R R Caldwell.

7 recordsLinked to original sources

PubMed2005

Limits of quintessence.

We present evidence that the simplest particle-physics scalar-field models of dynamical dark energy can be separated into distinct behaviors based on the acceleration or deceleration of the field as it evolves down its potential towards a zero minimum. We show that these models occupy narrow regions in the phase plane of w and w', the dark energy equation of state and its time derivative in units of the Hubble time. Restricting an energy scale of the dark energy microphysics limits how closely a scalar field can resemble a cosmological constant. These results, indicating a desired measurement resolution of order sigma(w') approximately = (1+w), define firm targets for observational tests of the physics of dark energy.

Journal Article↗

PubMed2002

Measuring the speed of sound of quintessence.

Quintessence, a time-varying energy component that may account for the accelerated expansion of the universe, can be characterized by its equation of state and sound speed. In this paper, we show that if the quintessence density is at least 1% of the critical density at the surface of last scattering the cosmic microwave background anisotropy can distinguish between models whose sound speed is near the speed of light versus near zero, which could be useful in distinguishing competing candidates for dark energy.

Journal Article↗

PubMed2001