9,825 research outputs found

    Spatial and spin symmetry breaking in semidefinite-programming-based Hartree-Fock theory

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    The Hartree-Fock problem was recently recast as a semidefinite optimization over the space of rank-constrained two-body reduced-density matrices (RDMs) [Phys. Rev. A 89, 010502(R) (2014)]. This formulation of the problem transfers the non-convexity of the Hartree-Fock energy functional to the rank constraint on the two-body RDM. We consider an equivalent optimization over the space of positive semidefinite one-electron RDMs (1-RDMs) that retains the non-convexity of the Hartree-Fock energy expression. The optimized 1-RDM satisfies ensemble NN-representability conditions, and ensemble spin-state conditions may be imposed as well. The spin-state conditions place additional linear and nonlinear constraints on the 1-RDM. We apply this RDM-based approach to several molecular systems and explore its spatial (point group) and spin (S2S^2 and S3S_3) symmetry breaking properties. When imposing S2S^2 and S3S_3 symmetry but relaxing point group symmetry, the procedure often locates spatial-symmetry-broken solutions that are difficult to identify using standard algorithms. For example, the RDM-based approach yields a smooth, spatial-symmetry-broken potential energy curve for the well-known Be--H2_2 insertion pathway. We also demonstrate numerically that, upon relaxation of S2S^2 and S3S_3 symmetry constraints, the RDM-based approach is equivalent to real-valued generalized Hartree-Fock theory.Comment: 9 pages, 6 figure

    A coherent state approach to effective potential in noncommutative D=(2+1) models

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    In this work we study the effective potential in noncommutative three-dimensional models where the noncommutativity is introduced through the coherent state approach. We discuss some important characteristics that seem to be typical to this approach, specially the behavior of the quantum corrections in the small noncommutativity limit.Comment: revtex4, 8 pages, 2 figures

    On the Adler-Bell-Jackiw anomaly in a Horava-Lifshitz-like QED

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    We show the absence of the ABJ anomaly for the Horava-Lifshitz-like QED with any even zz. Besides of this, we study the graph contributing to the ABJ anomaly at non-zero temperature and extend the Fujikawa's methodology of studying the integral measure for our model.Comment: 9 pages, version accepted to EP

    On the perturbative generation of the higher-derivative Lorentz-breaking terms

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    In this paper, we describe the perturbative generation of the higher-derivative Lorentz-breaking terms for the gauge field, that is, the Myers-Pospelov term and the higher-derivative Carroll-Field-Jackiw term. These terms are explicitly calculated in the one-loop approximation and shown to be finite and ambiguous.Comment: 12 pages, version accepted to PR
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