85,727 research outputs found
Thick Braneworlds and the Gibbons-Kallosh-Linde No-go Theorem in the Gauss-Bonnet Framework
The sum rules related to thick braneworlds are constructed, in order to
encompass Gauss-Bonnet terms. The generation of thick branes is hence proposed
in a periodic extra dimension scenario, what circumvents the
Gibbons-Kallosh-Linde no-go theorem in this context.Comment: 6 pages, to appear in the EPL. arXiv admin note: text overlap with
arXiv:1406.632
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
ELKO, flagpole and flag-dipole spinor fields, and the instanton Hopf fibration
In a previous paper we explicitly constructed a mapping that leads Dirac
spinor fields to the dual-helicity eigenspinors of the charge conjugation
operator (ELKO spinor fields). ELKO spinor fields are prime candidates for
describing dark matter, and belong to a wider class of spinor fields, the
so-called flagpole spinor fields, corresponding to the class-(5), according to
Lounesto spinor field classification, based on the relations and values taken
by their associated bilinear covariants. Such a mapping between Dirac and ELKO
spinor fields was obtained in an attempt to extend the Standard Model in order
to encompass dark matter. Now we prove that such a mapping, analogous to the
instanton Hopf fibration map , prevents ELKO to describe the
instanton, giving a suitable physical interpretation to ELKO. We review ELKO
spinor fields as type-(5) spinor fields under the Lounesto spinor field
classification, explicitly computing the associated bilinear covariants. This
paper is also devoted to investigate some formal aspects of the flag-dipole
spinor fields, which correspond to the class-(4) under the Lounesto spinor
field classification. In addition, we prove that type-(4) spinor fields
(corresponding to flag-dipoles) and ELKO spinor fields (corresponding to
flagpoles) can also be entirely described in terms of the Majorana and Weyl
spinor fields. After all, by choosing a projection endomorphism of the
spacetime algebra Cl(1,3) it is shown how to obtain ELKO, flagpole, Majorana
and Weyl spinor fields, respectively corresponding to type-(5) and -(6) spinor
fields, uniquely from limiting cases of a type-(4) (flag-dipole) spinor field,
in a similar result obtained by Lounesto.Comment: 17 Pages, RevTeX, accepted for publication in Adv. Appl. Clifford Al
Schwarzschild generalized black hole horizon and the embedding space
By performing a Taylor expansion along the extra dimension of a metric
describing a black hole on a brane, we explore the influence of the embedding
space on the black hole horizon. In particular, it is shown that the existence
of a Kottler correction of the black hole on the brane, in a viable braneworld
scenario, might represent the radius of the black string collapsing to zero,
for some point(s) on the black string axis of symmetry along the extra
dimension. Further scrutiny on such black hole corrections by braneworld
effects is elicited, the well-known results in the literature are recovered as
limiting cases, and we assert and show that when the radius of the black string
transversal section is zero, as one moves away from the brane into the bulk, is
indeed a singularity.Comment: 7 pages, to appear in European Phys. J.
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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