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laboratoire de physique statistique

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2010
Normal state of highly polarized Fermi gases: The bound state - Combescot, R. and Giraud, S. and Leyronas, X.
LASER PHYSICS 20678-682 (2010)

Abstract : We consider a highly polarized Fermi gas with a single a dagger'' atom within a Fermi sea of a dagger atoms. We extend a preceding many-body analysis to the case where a bound state is formed between the a dagger'' atom and an a dagger atom.
 
2009
Superfluid equation of state of dilute composite bosons or how to include 3-and 4-body problems in the many body problem - Leyronas, X. and Combescot, R.
LASER PHYSICS 19599-601 (2009)

Abstract : We show how the 3 and 4-body problems emerge in the BEC limit of the BEC-BCS crossover, where we treat explicitly dimers as made of two fermions. We give the argument leading, at zero temperature, to the calculation of the equation of state. We find that, when expanding the chemical potential in powers of the density n up to the Lee-Huang-Yang order, proportional to n (3/2), the result is identical to the one of elementary bosons in terms of the dimer-dimer scattering length a (M) , the composite nature of the dimers appearing only in the next order term proportional to n (2).
Normal state of highly polarized Fermi gases: Full many-body treatment - Giraud, S. and Combescot, R.
LASER PHYSICS 19583-587 (2009)

Abstract : We present a full many-body analysis of the problem of a single a dagger'' atom resonantly interacting with a Fermi sea of a dagger atoms. A series of successive approximations permits us to clarify the quite mysterious agreement between Monte Carlo results and approximate calculations taking only into account single particle-hole excitations. We show that it results from a nearly perfect destructive interference of the contributions of states with more than one particle-hole pair. Our treatment provides, at the same time, an essentially exact solution to this problem.
 
2007
Four-particle problem using Feynman diagrams - Brodsky, I. V. and Kagan, M. Yu. and Klaptsov, A. V. and Combescot, R. and Leyronas, X.
LASER PHYSICS 17523-526 (2007)

Abstract : We present an exact diagrammatic approach for the problem of dimer-dimer scattering in 3D for dimers being a resonant bound state of two fermions in a spin singlet state, with corresponding scattering length a. We recover exactly the previously known result a(B) = 0.60a, where a(B) is the dimer-dimer scattering length. A detailed discussion of how one can ``sum all the diagrams'' in this case is presented. Applications to the study of 4-particle bound states of various complexes in 2D are briefly presented.