Biomedical subjects

H Heiselberg

Publications and source records attributed to H Heiselberg.

17 recordsLinked to original sources

PubMed2004

Collective modes of trapped gases at the BEC-BCS crossover.

The collective mode frequencies in isotropic and deformed traps are calculated for general polytropic equation of states, P proportional n(gamma+1), and expressed in terms of gamma and the trap geometry. For molecular and standard Bose-Einstein condensates and Fermi gases near Feshbach resonances, the effective power gamma approximately 0.5-1.3 is calculated from Jastrow type wave-function ansatz, and from the crossover model of Leggett. The resulting mode frequencies are calculated for these phases around the BEC-BCS crossover.

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PubMed2002

Universal behavior of the energy of trapped few-boson systems with large scattering length.

We calculate energy levels of two and three bosons trapped in a harmonic oscillator potential with oscillator length a(osc). The atoms are assumed to interact through a short-range potential with a scattering length a, and the short-distance behavior of the three-body wave function is characterized by a parameter theta. For large positive a/a(osc), the energies of states that, in the absence of the trap, correspond to three free atoms approach values independent of a and theta. For other states, the theta dependence of the energy is strong, but the energy is independent of a for |a/a(osc)|>>1.

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PubMed2002

Cold bose gases with large scattering lengths.

We calculate the energy and condensate fraction for a dense system of bosons interacting through an attractive short range interaction with positive s-wave scattering length a. At high densities n>>a(-3), the energy per particle, chemical potential, and square of the sound speed are independent of the scattering length and proportional to n(2/3), as in Fermi systems. The condensate is quenched at densities na(3) approximately 1.

Journal Article↗

PubMed2000

Influence of induced interactions on the superfluid transition in dilute fermi gases

We calculate the effects of induced interactions on the transition temperature to the BCS state in dilute Fermi gases. For a pure Fermi system with two species having equal densities, the transition temperature is suppressed by a factor (4e)(1/3) approximately 2.2, and for nu fermion species, the transition temperature is increased by a factor (4e)(nu/3-1) approximately 2.2(nu-3). For mixtures of fermions and bosons the exchange of boson density fluctuations gives rise to an attractive interaction, and we estimate the increase of the transition temperature due to this effect.

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PubMed1999

Phase Transitions in Neutron Stars and Maximum Masses.

Using the most recent realistic effective interactions for nuclear matter with a smooth extrapolation to high densities including causality, we constrain the equation of state and calculate maximum masses of rotating neutron stars. First- and second-order phase transitions to, e.g., quark matter at high densities are included. If neutron star masses of approximately 2.3 M middle dot in circle from quasi-periodic oscillations in low-mass X-ray binaries are confirmed, a soft equation of state as well as strong phase transitions can be excluded in neutron star cores.

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PubMed1996