60,851 research outputs found
Simplicial minisuperspace models in the presence of a massive scalar field with arbitrary scalar coupling
We extend previous simplicial minisuperspace models to account for arbitrary
scalar coupling \eta R\phi^2.Comment: 24 pages and 9 figures. Accepted for publication by Classical and
Quantum Gravit
Anisotropic simplicial minisuperspace model
The computation of the simplicial minisuperspace wavefunction in the case of
anisotropic universes with a scalar matter field predicts the existence of a
large classical Lorentzian universe like our own at late timesComment: 19 pages, Latex, 6 figure
Unfolding Physics from the Algebraic Classification of Spinor Fields
After reviewing the Lounesto spinor field classification, according to the
bilinear covariants associated to a spinor field, we call attention and unravel
some prominent features involving unexpected properties about spinor fields
under such classification. In particular, we pithily focus on the new aspects
--- as well as current concrete possibilities. They mainly arise when we deal
with some non-standard spinor fields concerning, in particular, their
applications in physics.Comment: 6 pages, accepted for publication in PL
Gravitational constraints of dS branes in AdS Einstein-Brans-Dicke bulk
We derive the full projected Einstein-Brans-Dicke gravitational equations
associated with a n-dimensional brane embedded in a (n+1)-dimensional bulk. By
making use of general conditions, as the positivity of the Brans-Dicke
parameter and the effective Newton gravitational constant as well, we are able
to constrain the brane cosmological constant in terms of the brane tension, the
Brans-Dicke scalar field, and the trace of the stress tensor on the brane, in
order to achieve a brane. Applying these constraints to a specific
five-dimensional model, a lower bound for the scalar field on the brane is
elicited without solving the full equations. It is shown under which conditions
the brane effective cosmological constant can be ignored in the brane projected
gravitational field equations, suggesting a different fine tuning between the
brane tension and the bulk cosmological.Comment: 9 pages, revTe
Braneworld Remarks in Riemann-Cartan Manifolds
We analyze the projected effective Einstein equation in a 4-dimensional
arbitrary manifold embedded in a 5-dimensional Riemann-Cartan manifold. The
Israel-Darmois matching conditions are investigated, in the context where the
torsion discontinuity is orthogonal to the brane. Unexpectedly, the presence of
torsion terms in the connection does not modify such conditions whatsoever,
despite of the modification in the extrinsic curvature and in the connection.
Then, by imposing the Z_2-symmetry, the Einstein equation obtained via
Gauss-Codazzi formalism is extended, in order to now encompass the torsion
terms. We also show that the factors involving contorsion change drastically
the effective Einstein equation on the brane, as well as the effective
cosmological constant.Comment: 7 pages. A corrected misprint in def.(18), and the respective terms
in Eqs.(20-23). All physical consequences remain unchange
Hawking Radiation from Elko Particles Tunnelling across Black Strings Horizon
We apply the tunnelling method for the emission and absorption of Elko
particles in the event horizon of a black string solution. We show that Elko
particles are emitted at the expected Hawking temperature from black strings,
but with a quite different signature with respect to the Dirac particles. We
employ the Hamilton-Jacobi technique to black hole tunnelling, by applying the
WKB approximation to the coupled system of Dirac-like equations governing the
Elko particle dynamics. As a typical signature, different Elko particles are
shown to produce the same standard Hawking temperature for black strings.
However we prove that they present the same probability irrespective of
outgoing or ingoing the black hole horizon. It provides a typical signature for
mass dimension one fermions, that is different from the mass dimension three
halves fermions inherent to Dirac particles, as different Dirac spinor fields
have distinct inward and outward probability of tunnelling.Comment: 5 pages, notation for the event horizon changed, 4 lines removed, to
appear in Europhys. Let
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