679 research outputs found
Inflation driven by scalar field with non-minimal kinetic coupling with Higgs and quadratic potentials
We study a scalar field with non-minimal kinetic coupling to itself and to
the curvature. The slow rolling conditions allowing an inflationary background
have been found. The quadratic and Higgs type potentials have been considered,
and the corresponding values for the scalar fields at the end of inflation
allows to recover the connection with particle physics.Comment: 16 pages, to appear in JCA
Exact solutions in a scalar-tensor model of dark energy
We consider a model of scalar field with non minimal kinetic and Gauss Bonnet
couplings as a source of dark energy. Based on asymptotic limits of the
generalized Friedmann equation, we impose restrictions on the kinetic an
Gauss-Bonnet couplings. This restrictions considerable simplify the equations,
allowing for exact solutions unifying early time matter dominance with
transitions to late time quintessence and phantom phases. The stability of the
solutions in absence of matter has been studied.Comment: 30 pages, 2 figures, to appear in JCA
Dark energy from scalar field with Gauss Bonnet and non-minimal kinetic coupling
We study a model of scalar field with a general non-minimal kinetic coupling
to itself and to the curvature, and additional coupling to the Gauss Bonnet
4-dimensional invariant. The model presents rich cosmological dynamics and some
of its solutions are analyzed. A variety of scalar fields and potentials giving
rise to power-law expansion have been found. The dynamical equation of state is
studied for two cases, with and without free kinetic term . In both cases
phenomenologically acceptable solutions have been found. Some solutions
describe essentially dark energy behavior, and and some solutions contain the
decelerated and accelerated phases.Comment: 21 page
On the Ricci dark energy model
We study the Ricci dark energy model (RDE) which was introduced as an
alternative to the holographic dark energy model. We point out that an
accelerating phase of the RDE is that of a constant dark energy model. This
implies that the RDE may not be a new model of explaining the present
accelerating universe.Comment: 8 page
Renormalization Group Flow of Quantum Gravity in the Einstein-Hilbert Truncation
The exact renormalization group equation for pure quantum gravity is used to
derive the non-perturbative \Fbeta-functions for the dimensionless Newton
constant and cosmological constant on the theory space spanned by the
Einstein-Hilbert truncation. The resulting coupled differential equations are
evaluated for a sharp cutoff function. The features of these flow equations are
compared to those found when using a smooth cutoff. The system of equations
with sharp cutoff is then solved numerically, deriving the complete
renormalization group flow of the Einstein-Hilbert truncation in . The
resulting renormalization group trajectories are classified and their physical
relevance is discussed. The non-trivial fixed point which, if present in the
exact theory, might render Quantum Einstein Gravity nonperturbatively
renormalizable is investigated for various spacetime dimensionalities.Comment: 58 pages, latex, 24 figure
E-pSylon: una herramienta para la teleenseñanza síncrona
Muchas de las herramientas de teleenseñanza actuales corresponden al modelo asíncrono, donde instructor y alumnos interactúan desde espacios y tiempos diferentes. El modelo de teleenseñanza síncrona permite incorporar estrategias probadas con éxito en la enseñanza presencial, donde el apoyo visual del instructor a las explicaciones facilita la comprensión por parte de los alumnos. Se consigue así una enseñanza guiada y una realimentación inmediata de los alumnos. En este trabajo se propone una herramienta
de teleenseñanza síncrona de sencillo manejo que permite el desarrollo de clases virtuales donde instructor y alumnos interactúan en tiempo real. También
se presenta la experiencia con el uso de la herramienta en asignaturas relacionadas con la Ingeniería Informática y algunas conclusiones al respecto.Peer Reviewe
Scalar wormholes with nonminimal derivative coupling
We consider static spherically symmetric wormhole configurations in a
gravitational theory of a scalar field with a potential and
nonminimal derivative coupling to the curvature describing by the term
in the
action. We show that the flare-out conditions providing the geometry of a
wormhole throat could fulfilled both if (phantom scalar) and
(ordinary scalar). Supposing additionally a traversability, we
construct numerical solutions describing traversable wormholes in the model
with arbitrary , and (no potential). The
traversability assumes that the wormhole possesses two asymptotically flat
regions with corresponding Schwarzschild masses. We find that asymptotical
masses of a wormhole with nonminimal derivative coupling could be positive
and/or negative depending on . In particular, both masses are positive
only provided , otherwise one or both wormhole masses are
negative. In conclusion, we give qualitative arguments that a wormhole
configuration with positive masses could be stable.Comment: 17 pages, 8 figure
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