José María Román
Spanish National Research Council
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Featured researches published by José María Román.
Nuclear Physics | 2002
José María Román; Germán Sierra; J. Dukelsky
Abstract We have studied the numerical solutions of Richardson equations of the BCS model in the limit of large number of energy levels at half-filling, and compare them with the analytic results derived by Gaudin and Richardson, which in turn leads to the standard BCS solution. We focus on the location and density of the roots, the eigenvalues of the conserved quantities, and the scaling properties of the total energy for the equally spaced and the two-level models.
Physical Review B | 2004
André LeClair; José María Román; Germán Sierra
We show that a simple extension of the standard BCS Hamiltonian leads to an infinite number of BCS eigenstates with different energy gaps and self-similar properties, described by a cyclic renormalization group flow of the BCS coupling constant which returns to its original value after a finite renormalization group time.
Nuclear Physics | 2003
André LeClair; José María Román; Germán Sierra
We investigate the previously proposed cyclic regime of the Kosterlitz-Thouless renormalization group (RG) flows. The period of one cycle is computed in terms of the RG invariant. Using bosonization, we show that the theory has
Nuclear Physics | 2004
André LeClair; José María Román; Germán Sierra
U_q (\hat{sl(2)})
Physical Review B | 2003
José María Román; Germán Sierra; J. Dukelsky
quantum affine symmetry, with
Journal of Physics A | 1996
José María Román; R. Tarrach
q
Nuclear Physics | 2004
J. M. P. Carmelo; José María Román; Karlo Penc
{\it real}. Based on this symmetry, we study two possible S-matrices for the theory, differing only by overall scalar factors. We argue that one S-matrix corresponds to a continuum limit of the XXZ spin chain in the anti-ferromagnetic domain
International Journal of Modern Physics B | 1999
José María Román; Joan Soto
\Delta<-1
Journal of Physics A | 1998
José María Román; Germán Sierra; J. Dukelsky; M. A. Martin-Delgado
. The latter S-matrix has a periodicity in energy consistent with the cyclicity of the RG. We conjecture that this S-matrix describes the cyclic regime of the Kosterlitz-Thouless flows. The other S-matrix we investigate is an analytic continuation of the usual sine-Gordon one. It has an infinite number of resonances with masses that have a Russian doll scaling behavior that is also consistent with the period of the RG cycles computed from the beta-function. Closure of the bootstrap for this S-matrix leads to an infinite number of particles of higher spin with a mass formula suggestive of a string theory.
Physical Review B | 2002
José María Román; Germán Sierra; J. Dukelsky
Abstract We compute the finite size effects in the ground state energy, equivalently the effective central charge c eff , based on S-matrix theories recently conjectured to describe a cyclic regime of the Kosterlitz–Thouless renormalization group flows. The effective central charge has periodic properties consistent with renormalization group predictions. Whereas c eff for the massive case has a singularity in the very deep ultra-violet, we argue that the massless version is non-singular and periodic on all length scales.