DSpace Community:
http://hdl.handle.net/10261/14181
Tue, 16 Sep 2014 15:34:59 GMT
20140916T15:34:59Z
The Channel Image
http://digital.csic.es:80/retrieve/56934/iff.jpg
http://hdl.handle.net/10261/14181

Dwarf galaxies with gentle star formation and the counts of galaxies from the Hubble Deep Field
http://hdl.handle.net/10261/100781
Title: Dwarf galaxies with gentle star formation and the counts of galaxies from the Hubble Deep Field
Authors: Campos, Ana
Abstract: In this paper the counts and colors of the faint galaxies observed in the Hubble Deep Field are fitted by means of simple luminosity evolution models that incorporate a numerous population of fading dwarfs. The observed color distribution of the very faint galaxies now allows us to put constraints on the star formation history in dwarfs. It is shown that the starforming activity in these small systems has to proceed in a gentle way, i.e., through episodes where each one lasts much longer than a simple instantaneous burst of star formation. By allowing dwarfs to form stars in this gentle way, the number of predicted red remnants is severely reduced, in good agreement with the observations. Then, if the faint counts are to be fitted by means of dwarfs, the simple model for dwarfs forming stars in single, very short episodes is challenged, and a more complex star formation history has to be invoked. Recent observational evidence supporting this new dwarf model is also discussed. © 1997. The American Astronomical Society. All rights reserved.
Mon, 11 Aug 2014 08:15:14 GMT
http://hdl.handle.net/10261/100781
20140811T08:15:14Z

Conformal and nonconformal symmetries in 2D dilaton gravity
http://hdl.handle.net/10261/100780
Title: Conformal and nonconformal symmetries in 2D dilaton gravity
Authors: Cruz, J.; NavarroSalas, José; Navarro, M.; Talavera, C.F.
Abstract: We introduce new extra symmetry transformations for generic 2D dilatongravity models. These symmetries are nonconformal but special linear combinations of them turn out to be the extra (conformal) symmetries of the CGHS model and the model with an exponential potential. We show that one of the nonconformal extra symmetries can be converted into a conformal one by means of adequate field redefinitions involving the metric and the derivatives of the dilaton. Finally, by expressing the PolyakovLiouville effective action in terms of an auxiliary invariant metric, we construct oneloop models which maintain the extra symmetry of the classical action. © 1997 Elsevier Science B.V.
Mon, 11 Aug 2014 08:10:46 GMT
http://hdl.handle.net/10261/100780
20140811T08:10:46Z

Coisotropic and LegendreLagrangian submanifolds and conformal Jacobi morphisms
http://hdl.handle.net/10261/100779
Title: Coisotropic and LegendreLagrangian submanifolds and conformal Jacobi morphisms
Authors: Ibáñez, Raul; León, Manuel de; Marrero, Juan Carlos; Martín de Diego, David
Abstract: The notion of a coisotropic and LegendreLagrangian submanifold of a Jacobi manifold is given. A characterization of conformal Jacobi morphisms and conformal Jacobi infinitesimal transformations is obtained as coisotropic and LegendreLagrangian submanifolds of Jacobi manifolds.
Mon, 11 Aug 2014 08:05:07 GMT
http://hdl.handle.net/10261/100779
20140811T08:05:07Z

Circular strings, wormholes, and minimum size
http://hdl.handle.net/10261/100778
Title: Circular strings, wormholes, and minimum size
Authors: Garay, Luís Javier; González Díaz, Pedro F.; Mena Marugán, Guillermo A.; Raya, José M.
Abstract: The quantization of circular strings in an antide Sitter background spacetime is performed, obtaining a discrete spectrum for the string mass. A comparison with a fourdimensional homogeneous and isotropic spacetime coupled to a conformal scalar field shows that the string radius and the scale factor have the same classical solutions and that the quantum theories of these two models are formally equivalent. However, the physically relevant observables of these two systems have different spectra, although they are related to each other by a specific onetoone transformation. We finally obtain a discrete spectrum for the spacetime size of both systems, which presents a nonvanishing lower bound. © 1997 The American Physical Society
Mon, 11 Aug 2014 07:58:48 GMT
http://hdl.handle.net/10261/100778
20140811T07:58:48Z

Chiral determinant formulae and subsingular vectors for the N = 2 superconformal algebras
http://hdl.handle.net/10261/100777
Title: Chiral determinant formulae and subsingular vectors for the N = 2 superconformal algebras
Authors: Gato Rivera, Beatriz; Rosado, Jose Ignacio
Abstract: We derive conjectures for the N = 2 >chiral> determinant formulae of the topological algebra, the antiperiodic NS algebra, and the periodic Ralgebra, corresponding to incomplete Verma modules built on chiral topological primaries, chiral and antichiral NS primaries, and Ramond ground states, respectively. Our method is based on the analysis of the singular vectors in chiral Verma modules and their spectral flow symmetries, together with some computer exploration and some consistency checks. In addition, and as a consequence, we uncover the existence of subsingular vectors in these algebras, giving examples (subsingular vectors are nonhighestweight null vectors which are not descendants of any highestweight singular vectors). © 1997 Elsevier Science B.V.
Mon, 11 Aug 2014 07:48:51 GMT
http://hdl.handle.net/10261/100777
20140811T07:48:51Z

Canonical quantization of the Gowdy model
http://hdl.handle.net/10261/100776
Title: Canonical quantization of the Gowdy model
Authors: Mena Marugán, Guillermo A.
Abstract: The family of Gowdy universes with the spatial topology of a threetorus is studied both classically and quantum mechanically. Starting with the Ashtekar formulation of Lorentzian general relativity, we introduce a gaugefixing procedure to remove almost all of the nonphysical degrees of freedom. In this way, we arrive at a reduced model that is subject only to one homogeneous constraint. The phase space of this model is described by means of a canonical set of elementary variables. These are two real, homogeneous variables and the Fourier coefficients for four real fields that are periodic in the angular coordinate which does not correspond to a Killing field of the Gowdy spacetimes. We also obtain the explicit expressions for the line element and reduced Hamiltonian. We then proceed to quantize the system by representing the elementary variables as linear operators acting on a vector space of analytic functionals. The inner product on that space is selected by imposing Lorentzian reality conditions. We find the quantum states annihilated by the operator that represents the homogeneous constraint of the model and construct with them the Hilbert space of physical states. Finally, we derive the general form of the quantum observables of the model. © 1997 The American Physical Society
Mon, 11 Aug 2014 07:38:52 GMT
http://hdl.handle.net/10261/100776
20140811T07:38:52Z

A Nomizu's theorem for the coeffective cohomology
http://hdl.handle.net/10261/100775
Title: A Nomizu's theorem for the coeffective cohomology
Authors: Fernández, Marisa; Ibáñez, Raul; León, Manuel de
Mon, 11 Aug 2014 07:35:16 GMT
http://hdl.handle.net/10261/100775
20140811T07:35:16Z

An interpolating ansatz for the ground state of the spinless fermion hamiltonian in D = 1 and 2
http://hdl.handle.net/10261/100774
Title: An interpolating ansatz for the ground state of the spinless fermion hamiltonian in D = 1 and 2
Authors: MartínDelgado, Miguel Ángel; Sierra, Germán
Abstract: We propose an interpolating ansatz between the strong coupling and weak coupling regimes of a system of spinless interacting fermions in 1D and 2D lattices at halffilling. We address relevant issues such as the existence of Long Range Order, quantum phase transitions and the evaluation of ground state energy. In 1D our method is capable of unveiling the existence of a critical point in the coupling constant at (t/U)c = 0.7483 as in fact occurs in the exact solution at a value of 0.5. In our approach this phase transition is described as an example of Bifurcation Phenomena in the variational computation of the ground state energy. In 2D the van Hove singularity plays an essential role in changing the asymptotic behaviour of the system for large values of t/U. In particular, the staggered magnetization for large t/U does not display the HartreeFock law (t/U)e2π√t/U but instead we find the law (t/U)eπ2/3 t/U. Moreover, the system does not exhibit bifurcation phenomena and thus we do not find a critical point separating a CDW state from a fermion >liquid> state.
Mon, 11 Aug 2014 07:30:16 GMT
http://hdl.handle.net/10261/100774
20140811T07:30:16Z

A constraint algorithm for singular Lagrangians subjected to nonholonomic constraints
http://hdl.handle.net/10261/100773
Title: A constraint algorithm for singular Lagrangians subjected to nonholonomic constraints
Authors: León, Manuel de; Martín de Diego, David
Abstract: We construct a constraint algorithm for singular Lagrangian systems subjected to nonholonomic constraints which generalizes that of Dirac for constrained Hamiltonian systems. © 1997 American Institute of Physics.
Mon, 11 Aug 2014 07:23:43 GMT
http://hdl.handle.net/10261/100773
20140811T07:23:43Z

Study of the total and partial fragmentation dynamics of ArHCl after UV photodissociation
http://hdl.handle.net/10261/100765
Title: Study of the total and partial fragmentation dynamics of ArHCl after UV photodissociation
Authors: García Vela, Alberto
Abstract: The uv photolysis of the Ar–HCl cluster is studied applying an exact timedependent wave packet method in three dimensions, assuming zerototal angular momentum. The photodissociation process is found to occur via two different fragmentation mechanisms, depending on the initial excitation energy of the cluster. One mechanism leads to total dissociation of the complex, producing three fragments, Ar–HCl+hν→H+Ar+Cl. The fragmentation dynamics in this case is governed by resonance states at relatively low energies of the cluster, in which the H atom collides a number of times with Ar and Cl before dissociating. Manifestations of these collisions are found in the final kinetic energy distribution of the photofragments, which is redshifted in the case of the H fragment, and blueshifted in the Ar and Cl cases. The second type of mechanism consists of a fast and direct photodissociation of the hydrogen, leading to a partial fragmentation of Ar–HCl into hot H fragments and bound Ar–Cl radical molecules. This mechanism dominates at higher energies, which are those mostly populated by the wave packet initially prepared in the present calculations. The experimental implications of the results are discussed. . © 1998 American Institute of Physics.
Fri, 08 Aug 2014 08:47:11 GMT
http://hdl.handle.net/10261/100765
20140808T08:47:11Z