arXiv subjects

S. Ronen

Publications and source records attributed to S. Ronen.

6 recordsLinked to original sources

arXiv2010

Bilayer superfluidity of fermionic polar molecules: many body effects

We study the BCS superfluid transition in a single-component fermionic gas of dipolar particles loaded in a tight bilayer trap, with the electric dipole moments polarized perpendicular to the layers. Based on the detailed analysis of the interlayer scattering, we calculate the critical temperature of the interlayer superfluid pairing transition when the layer separation is both smaller (dilute regime) and of the order or larger (dense regime) than the mean interparticle separation in each layer. Our calculations go beyond the standard BCS approach and include the many-body contributions resulting in the mass renormalization, as well as additional contributions to the pairing interaction. We find that the many-body effects have a pronounced effect on the critical temperature, and can either decrease (in the very dilute limit) or increase (in the dense and moderately dilute limits) the transition temperature as compared to the BCS approach.

cond-mat.quant-gas↗

arXiv2008

How Does a Dipolar Bose-Einstein Condensate Collapse?

We emphasize that the macroscopic collapse of a dipolar Bose-Einstein condensate in a pancake-shaped trap occurs through local density fluctuations, rather than through a global collapse to the trap center. This hypothesis is supported by a recent experiment in a chromium condensate.

physics.atom-ph↗

arXiv2008

Bragg spectroscopy of a strongly interacting 85Rb Bose-Einstein condensate

We report on measurements of the excitation spectrum of a strongly interacting Bose-Einstein condensate (BEC). A magnetic-field Feshbach resonance is used to tune atom-atom interactions in the condensate and to reach a regime where quantum depletion and beyond mean-field corrections to the condensate chemical potential are significant. We use two-photon Bragg spectroscopy to probe the condensate excitation spectrum; our results demonstrate the onset of beyond mean-field effects in a gaseous BEC.

cond-mat.other↗

arXiv2006

Dipolar Bose gases: Many-body versus mean-field description

We characterize zero-temperature dipolar Bose gases under external spherical confinement as a function of the dipole strength using the essentially exact many-body diffusion Monte Carlo (DMC) technique. We show that the DMC energies are reproduced accurately within a mean-field framework if the variation of the s-wave scattering length with the dipole strength is accounted for properly. Our calculations suggest stability diagrams and collapse mechanisms of dipolar Bose gases that differ significantly from those previously proposed in the literature.

cond-mat.stat-mech↗

arXiv1999

The 2dF Galaxy Redshift Survey: Spectral Types and Luminosity Functions

We describe the 2dF Galaxy Redshift Survey (2dFGRS), and the current status of the observations. In this exploratory paper, we apply a Principal Component Analysis to a preliminary sample of 5869 galaxy spectra and use the two most significant components to split the sample into five spectral classes. These classes are defined by considering visual classifications of a subset of the 2dF spectra, and also by comparing to high quality spectra of local galaxies. We calculate a luminosity function for each of the different classes and find that later-type galaxies have a fainter characteristic magnitude, and a steeper faint-end slope. For the whole sample we find M*=-19.7 (for Omega=1, H_0=100 km/sec/Mpc), alpha=-1.3, phi*=0.017. For class 1 (`early-type') we find M*=-19.6, alpha=-0.7, while for class 5 (`late-type') we find M*=-19.0, alpha=-1.7. The derived 2dF luminosity functions agree well with other recent luminosity function estimates.

astro-ph↗

arXiv1998

Principal Component Analysis Of Synthetic Galaxy Spectra

We analyse synthetic galaxy spectra from the evolutionary models of Bruzual&Charlot and Fioc&Rocca-Volmerange using the method of Principal Component Analysis (PCA). We explore synthetic spectra with different ages, star formation histories and metalicities, and identify the Principal Components (PCs) of variance in the spectra due to these different model parameters. The PCA provides a more objective and informative alternative to diagnostics by individual spectral lines. We discuss how the PCs can be used to estimate the input model parameters and explore the impact of noise in this inverse problem. We also discuss how changing the sampling of the ages and other model parameters affects the resulting PCs. Our first two synthetic PCs agree with a similar analysis on observed spectra obtained by Kennicutt and the 2dF redshift survey. We conclude that with a good enough signal-to-noise (S/N>> 10) it is possible to derive age, star formation history and metallicity from observed galaxy spectra using PCA.

astro-ph↗