545 research outputs found
Local cosmic strings in Brans-Dicke theory with a cosmological constant
It is known that Vilenkin's phenomenological equation of state for static
straight cosmic strings is inconsistent with Brans-Dicke theory. We will prove
that, in the presence of a cosmological constant, this equation of state is
consistent with Brans-Dicke theory. The general solution of the full nonlinear
field equations, representing the interior of a cosmic string with a
cosmological constant is also presented.Comment: 5 pages, Revte
Multi-Scalar-Tensor Equivalents for Modified Gravitational Actions
A general scheme of constructing scalar-tensor equivalents to modified
gravitational actions are studied using the algebra of exterior differential
forms and the first order formalism that allows an independent connection and
coframe. By introducing appropriate constraints on the connection,
pseudo-Riemannian cases as well as non-Riemannian cases are discussed for
various gravitational models. The issue of the dynamical degree of freedom for
the resulting scalar fields is discussed at the level of the field equations.
Explicit scalar-tensor equivalents for gravitational models based on
models, the quadratic curvature lagrangians and the models involving the
gradients of the scalar curvature are presented. In particular, explicit ST
equivalence for gravitational lagrangians popular in some cosmological models
are constructed.Comment: V1:17 pages in two column format, revtex; V2: 19 pages, an appendix
and references added, published versio
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Catalogue Note on Taner Ceylan's 1879 (2011)
In this recent piece from his Lost Painting Series, following 1881 (2010) and 1923 (2010), the photorealist painter Taner Ceylan engages with the questions of history and Orientalism by creating yet another visual allegory. The mischievous gaze of the smoking Ottoman boy in 1881 and the homoerotic farewell scene in 1923 are followed this time by an ingenious montage of Pascal Sébah's photograph from the 1880s and Gustave Courbet's L'Origine du monde (The Origin of the World, 1866). In this intricately crafted oil painting, Ceylan juxtaposes different yet related histories of artistic style and connoisseurship to trigger a rethinking of Orientalism, femininity, the veil and the gaze. Recovering and drawing together forgotten legacies and silenced voices in a brilliantly imagined new setting, Ceylan invites the viewer to look behind the veil of Orientalism and the politics of representation. Rather than offering a corrective, the artist amalgamates irony, playfulness and realism to recast Orientalism as heterogeneous and susceptible to negotiation, contestation and even subversion
On Stationary Axially Symmetric Solutions in Brans-Dicke Theory
Stationary, axially symmetric Brans-Dicke-Maxwell solutions are reexamined in
the framework of the Brans-Dicke (BD) theory. We see that, employing a
particular parametrization of the standard axially symmetric metric simplifies
the procedure of obtaining the Ernst equations for axially symmetric
electrovacuum space-times for this theory. This analysis also permits us to
construct a two parameter extension in both Jordan and Einstein frames of an
old solution generating technique frequently used to construct axially
symmetric solutions for BD theory from a seed solution of general relativity.
As applications of this technique, several known and new solutions are
constructed including a general axially symmetric BD-Maxwell solution of
Plebanski-Demianski with vanishing cosmological constant, i.e. the Kinnersley
solution and general magnetized Kerr-Newman--type solutions. Some physical
properties and the circular motion of test particles for a particular subclass
of Kinnersley solution, i.e., a Kerr-Newman-NUT--type solution for BD theory,
are also investigated in some detail.Comment: V2: 18 pages, published version; some references and section VI is
added. V1:17 pages, Revte
Linearized modified gravity theories with a cosmological term: advance of perihelion and deflection of light
Two different ways of generalizing Einstein's general theory of relativity
with a cosmological constant to Brans-Dicke type scalar-tensor theories are
investigated in the linearized field approximation. In the first case a
cosmological constant term is coupled to a scalar field linearly whereas in the
second case an arbitrary potential plays the role of a variable cosmological
term. We see that the former configuration leads to a massless scalar field
whereas the latter leads to a massive scalar field. General solutions of these
linearized field equations for both cases are obtained corresponding to a
static point mass. Geodesics of these solutions are also presented and solar
system effects such as the advance of the perihelion, deflection of light rays
and gravitational redshift were discussed. In general relativity cosmological
constant has no role on these phenomena. We see that for the Brans-Dicke theory
the cosmological constant has also no effect on these phenomena. This is
because solar system observations require very large values of the Brans-Dicke
parameter and the correction terms to these phenomena becomes identical to GR
for these large values of this parameter. This result is also observed for the
theory with arbitrary potential if the mass of the scalar field is very light.
For a very heavy scalar field, however, there is no such limit on the value of
this parameter and there are ranges of this parameter where these contributions
may become relevant in these scales. Galactic and intergalactic dynamics is
also discussed for these theories at the latter part of the paper with similar
conclusions.Comment: 25 pages, Revtex. V2: two new sections discussing galactic and
intergalactic phenomena are added, discussion is extended, references added,
Published version
Brans-Dicke-Maxwell Solutions for Higher Dimensional Static Cylindrical Symmetric Spacetime
In this paper, Brans-Dicke-Maxwell type vacuum solutions are considered for a
static cylindrically symmetric spacetime in arbitrary dimensions. Exact
solutions are obtained by directly solving the field equations for the case
where an azimuthal magnetic field is present. Other configurations such as
axial magnetic field case can be obtained by suitably relabeling the
coordinates. We have also considered conformally related "Einstein frame" to
relate the solutions we have obtained with the dilaton-Maxwell type solutions
that exist in the literature. We see that for a special case the general
solution we present reduces to Dilaton-Melvin spacetime. The General
Relativistic limit of these solutions are also discussed and we found that this
limit is different from the four dimensional case.Comment: 9 Pages, articl
Antropoloji Penceresinden Hukuk : Basit Toplumlarda Akrabalık İktidar ve Çıkar İlişkileri
Antropoloji çalışmaları, insan topluluklarının tamamına yakınının çatışma ve ihtilaf içinde yaşadıklarını göstermektedir. Tüm toplumlarda gözlemlenmesi nedeniyle bazı yazarlar olgunun insan kültürü için en az cinsiyet kadar temel bir unsur olduğu iddiasını dile getirmiştir. Bizler ihtilaf ve çatışmanın olmadığı hiçbir toplumu bilmiyoruz. Çünkü kültürel örüntüler aracılığıyla işleyen kontrol şekilleri dışında toplumsal ahlaka ya da yasalara itaati temin edecek herhangi bir içgüdü yoktur. Hukuk, evrensel niteliğe sahip bu olgunun yok edilemeyeceği gerçeği üzerine inşa edilmiştir. İnsan toplulukları çatışmalardan arınmanın imkansız olduğu gerçeğiyle yüz yüze kaldığında çatışmaları denetim altına alma ve yönlendirme yolunu seçer
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