24 research outputs found
Exact renormalisation group flow for ultracold Fermi gases in unitary limit
We study the exact renormalisation group flow for ultracold Fermi-gases in
unitary regime. We introduce a pairing field to describe the formation of the
Cooper pairs, and take a simple ansatz for the effective action. Set of
approximate flow equations for the effective couplings including boson and
fermionic fluctuations is derived. At some value of the running scale, the
system undergoes a phase transition to a gapped phase. The values of the energy
density, chemical potential, pairing gap and the corresponding proportionality
constants relating the interacting and non-interacting Fermi gases are
calculated. Standard mean field results are recovered if we omit the boson
loops.Comment: 11 pages, Revtex, misprints corrected, references and comments adde
Chiral symmetry and mixing of axial and vector correlators in matter
The effect of mixing of the vector and axial vector correlation functions in
the nuclear medium arising from the interaction of nuclear pions with
corresponding interpolating currents is considered. It is shown that the mass
difference between and meson gets smaller with the increase of the
nuclear density reflecting the phenomena of partial restoration of chiral
symmetry whereas the absolute values of meson masses may both decrease and
increase in nuclear medium depending on the model used for the phenomenological
spectral density.Comment: 9 pages, 2 figures, Late
Superfluidity within Exact Renormalisation Group approach
The application of the exact renormalisation group to a many-fermion system
with a short-range attractive force is studied. We assume a simple ansatz for
the effective action with effective bosons, describing pairing effects and
derive a set of approximate flow equations for the effective coupling including
boson and fermionic fluctuations.
The phase transition to a phase with broken symmetry is found at a critical
value of the running scale. The mean-field results are recovered if boson-loop
effects are omitted. The calculations with two different forms of the regulator
was shown to lead to similar results.Comment: 17 pages, 3 figures, to appear in the proceedings of Renormalization
Group 2005 (RG 2005), Helsinki, Finland, 30 Aug - 3 Sep 200
Renormalization group, dimer-dimer scattering, and three-body forces
We study the ratio between the fermion-fermion scattering length and the
dimer-dimer scattering length for systems of nonrelativistic fermions, using
the same functional renormalisation technique as previously applied to
fermionic matter. We find a strong dependence on the cutoff function used in
the renormalisation flow for a two-body truncation of the action. Adding a
simple three-body term substantially reduces this dependence.Comment: 5 pages, 2 picture
Off-shell effects and consistency of many-body treatments of dense matter
Effective field theory requires all observables to be independent of the
representation used for the quantum field operators. It means that off-shell
properties of the interactions should not lead to any observable effects. We
analyse this issue in the context of many-body approaches to nuclear matter,
where it should be possible to shift the contributions of lowest order in
purely off-shell two-body interactions into three-body forces. We show that
none of the commonly used truncations of the two-body scattering amplitude such
as the ladder, Brueckner-Hartree-Fock or parquet approximations respect this
requirement.Comment: 5 pages, RevTeX, 6 figure