Ruiz Ruiz, Fernando

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Ruiz Ruiz
Universidad Complutense de Madrid
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Ciencias Físicas
Física Teórica
Física Teórica
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Now showing 1 - 10 of 34
  • Publication
    Thermal-energy in robertson-walker universes
    (Elsevier Science Bv, 1989-03-23) Ruiz Ruiz, Fernando
    The covariant functional Schrödinger formalism is used to study thermal equilibrium for a scalar field in Robertson Walker spacetimes. It is found that thermal equilibrium can be maintained for field masses, coupling constants and geometries satisfying a given differential equation, of which the massless conformally coupled case is a solution, but not the only one. The thermal energy is computed; it contains a term which for particular geometries, such as de Sitter spacetime, grows in time.
  • Publication
    Geometric construction of D-branes in WZW models
    (Springer, 2011-09) Ruiz Ruiz, Fernando; Horcajada Reales, Guillermo
    The geometric description of D-branes inWZWmodels is pushed forward. Our starting point is a gluing condition J+ = FJ− that matches the model’s chiral currents at the worldsheet boundary through a linear map F acting on the WZW Lie algebra. The equivalence of boundary and gluing conditions of this type is studied in detail. The analysis involves a thorough discussion of Frobenius integrability, shows that F must be an isometry, and applies to both metrically degenerate and nondegenerate D-branes. The isometry F need not be a Lie algebra automorphism nor constantly defined over the brane. This approach, when applied to isometries of the form F = R with R a constant Lie algebra automorphism, validates metrically degenerate R-twined conjugacy classes as D-branes. It also shows that no D branes exist in semisimple WZW models for constant F = −R.
  • Publication
    Seiberg-Witten maps for SO(1,3) gauge invariance and deformations of gravity
    (The American Physical Society, 2009-01) Ruiz Ruiz, Fernando; Marculescu, S
    A family of diffeomorphism-invariant Seiberg-Witten deformations of gravity is constructed. In a first step Seiberg-Witten maps for an SO(1,3) gauge symmetry are obtained for constant deformation parameters. This includes maps for the vierbein, the spin connection, and the Einstein-Hilbert Lagrangian. In a second step the vierbein postulate is imposed in normal coordinates and the deformation parameters are identified with the components theta(mu nu)(x) of a covariantly constant bivector. This procedure gives for the classical action a power series in the bivector components which by construction is diffeomorphism invariant. Explicit contributions up to second order are obtained. For completeness a cosmological constant term is included in the analysis. Covariant constancy of theta(mu nu)(x), together with the field equations, imply that, up to second order, only four dimensional metrics which are direct sums of two two dimensional metrics are admissible, the two-dimensional curvatures being expressed in terms of theta(mu nu). These four-dimensional metrics can be viewed as a family of deformed emergent gravities.
  • Publication
    Anomaly freedom in Seiberg-Witten noncommutative gauge theories
    (Springer, 2003-07) Ruiz Ruiz, Fernando; Pérez Martín, Carmelo
    We show that noncommutative gauge theories with arbitrary compact gauge group defined by means of the Seiberg-Witten map have the same one-loop anomalies as their commutative counterparts. This is done in two steps. By explicitly calculating the epsilon(mu1mu2mu3mu4) part of the renormalized effective action, we first find the would-be one-loop anomaly of the theory to all orders in the noncommutativity parameter theta(munu). And secondly we isolate in the would-be anomaly radiative corrections which are not BRS trivial. This gives as the only true anomaly occurring in the theory the standard Bardeen anomaly of commutative spacetime, which is set to zero by the usual anomaly cancellation condition.
  • Publication
    Semilocal strings and monopoles
    (Elsevier Science BV, 1992-10-19) Ruiz Ruiz, Fernando; Samols, T.M.; Ortiz, M.E.; Gibbons, G.W.
    A variation on the abelian Higgs model, with SU(2)global x U(1)local symmetry broken to U(1)global, was recently shown by Vachaspati and Achucarro to admit stable, finite-energy cosmic string solutions, even though the manifold of minima of the potential energy does not have non-contractible loops. This new and unexpected feature motivates a full investigation of the properties of the model. Here we exploit the existence of first-order Bogomol'nyi equations to classify all static finite-energy vortex solutions in the Bogomol'nyi limit. We find a 4n-dimensional moduli space for the nth topological (n-vortex) sector. Single-vortex configurations depend on a position coordinate and on an additional complex parameter and may be regarded as hybrids of Nielsen-Olesen vortices and CP1 lumps. The model is also shown to obey Bogomol'nyi equations in curved space, and these allow a simple calculation of the gravitational field of the above configurations. Finally, monopole-like solutions interpolating between a Dirac monopole and a global monopole are found. These must be surrounded by an event horizon as isolated solutions, but may also arise as unstable end points of semi-local strings.
  • Publication
    Perturbative quantization of Yang-Mills theory with classical double as gauge algebra.
    (Springer, 2016-02-22) Ruiz Ruiz, Fernando
    Perturbative quantization of Yang-Mills theory with a gauge algebra given by the classical double of a semisimple Lie algebra is considered. The classical double of a real Lie algebra is a nonsemisimple real Lie algebra that admits a nonpositive definite invariant metric, the indefiniteness of the metric suggesting an apparent lack of unitarity. It is shown that the theory is UV divergent at one loop and that there are no radiative corrections at higher loops. One-loop UV divergences are removed through renormalization of the coupling constant, thus introducing a renormalization scale. The terms in the classical action that would spoil unitarity are proved to be cohomologically trivial with respect to the Slavnov-Taylor operator that controls gauge invariance for the quantum theory. Hence they do not contribute gauge invariant radiative corrections to the quantum effective action and the theory is unitary.
  • Publication
    A family of exact-solutions for the thirring model at nonzero temperature
    (Elsevier Science Bv, 1986-12-25) Ruiz Ruiz, Fernando; Álvarez Estrada, Ramón F.
    It is shown that thermo-field dynamics permits the extension of the path integral methods used to solve the Thirring model at zero temperature to the finite temperature case. A family of exact solutions for the propagator and their dependence with temperature is given.
  • Publication
    The universality of the shift of the Chern-Simons parameter for a general class of BRS invariant regularizations
    (Elsevier Science Bv, 1993-09-23) Ruiz Ruiz, Fernando; Martin, C. P.; Giavarini, G.
    We consider a biparametric family of BRS invariant regularization methods of SU (N) Chem-Simons theory (the parameters defining the family taking arbitrary values in R2) and show that the one-loop shift k --> k + sign(k) N of the Chern-Simons parameter k occurs for arbitrary values of the family defining parameters. This strongly supports the conjecture that the shift of k is universal for BRS invariant regulators
  • Publication
    Physically meaningful and not so meaningful symmetries in Chern-Simons theory
    (American Physical Soc, 1993-06-15) Ruiz Ruiz, Fernando; Martin, C.P.; Giavarini, G;
    We explicitly show that the Landau gauge supersymmetry of Chem-Simons theory does not have any physical significance. In fact, the difference between an effective action that is both Becchi-Rouet-Stora (BRS) invariant and Landau supersymmetric and an effective action that is only BRS invariant is a finite field redefinition. Having established this, we use a BRS-invariant regulator that defines CS theory as the large mass limit of topologically massive Yang-Mills theory to discuss the shift k-->k+c(v) of the bare Chern-Simons parameter k in connection with the Landau supersymmetry. Finally, to convince ourselves that the shift above is not an accident of our regularization method, we comment on the fact that all BRS-invariant regulators used as yet yield the same value for the shift.
  • Publication
    BRS symmetry versus supersymmetry in Yang-Mills-Chern Simons theory
    (Elsevier Science Bv, 1997-02-17) Ruiz Ruiz, Fernando; van Nieuwenhuizen, P.
    We prove that three-dimensional N=1 supersymmetric Yang Mills-Chem-Simons theory is finite to all loop orders, In general this leaves open the possibility that different regularization methods lead to different finite effective actions. We show that in this model dimensional regularization and regularization by dimensional reduction yield the same effective action. Consequently, the superfield approach preserves BRS invariance for this model.