54 research outputs found
Enclothed Cognition and Controlled Attention during Insight Problem-Solving
Individual differences in working memory capacity (WMC) increase the ability, and tendency, to devote greater attentional control to a task—improving performance on a wide range of skills. In addition, recent research on enclothed cognition demonstrates that the situational influence of wearing a white lab coat increases controlled attention, due to the symbolic meaning and physical experience of wearing the coat. We examined whether these positive influences on attentional control lead to negative performance outcomes on insight problem-solving, a task thought to rely on associative processes that operate largely outside of explicit attentional control. Participants completed matchstick arithmetic problems while either wearing a white lab coat or in a no-coat control condition. Higher WMC was associated with lower insight problem-solving accuracy in the no-coat condition. In the coat condition, the insight problem-solving accuracy of lower WMC individuals dropped to the level of those higher in WMC. These results indicate that wearing a white lab coat led individuals to increase attentional control towards problem solving, hindering even lower WMC individuals from engaging in more diffuse, associative problem-solving processes, at which they otherwise excel. Trait and state factors known to increase controlled attention and improve performance on more attention-demanding tasks interact to hinder insight problem-solving
Closed timelike curves in asymmetrically warped brane universes
In asymmetrically warped spacetimes different warp factors are assigned to
space and to time. We discuss causality properties of these warped brane
universes and argue that scenarios with two extra dimensions may allow for
timelike curves which can be closed via paths in the extra-dimensional bulk. In
particular, necessary and sufficient conditions on the metric for the existence
of closed timelike curves are presented. We find a six-dimensional warped
metric which satisfies the CTC conditions, and where the null, weak and
dominant energy conditions are satisfied on the brane (although only the former
remains satisfied in the bulk). Such scenarios are interesting, since they open
the possibility of experimentally testing the chronology protection conjecture
by manipulating on our brane initial conditions of gravitons or hypothetical
gauge-singlet fermions (sterile neutrinos) which then propagate in the extra
dimensions.Comment: 24 pages, 2 figures; major corrections: CTC metric generalized from
5D to 6D, the new 6D metric satisfies the conclusions attributed
(incorrectly) to the 5D metric in v
Can a circulating light beam produce a time machine?
In a recent paper, Mallett found a solution of the Einstein equations in
which closed timelike curves (CTC's) are present in the empty space outside an
infinitely long cylinder of light moving in circular paths around an axis. Here
we show that, for physically realistic energy densities, the CTC's occur at
distances from the axis greater than the radius of the visible universe by an
immense factor. We then show that Mallett's solution has a curvature
singularity on the axis, even in the case where the intensity of the light
vanishes. Thus it is not the solution one would get by starting with Minkowski
space and establishing a cylinder of light.Comment: 5 pages, RevTe
Centrifugal force induced by relativistically rotating spheroids and cylinders
Starting from the gravitational potential of a Newtonian spheroidal shell we
discuss electrically charged rotating prolate spheroidal shells in the Maxwell
theory. In particular we consider two confocal charged shells which rotate
oppositely in such a way that there is no magnetic field outside the outer
shell. In the Einstein theory we solve the Ernst equations in the region where
the long prolate spheroids are almost cylindrical; in equatorial regions the
exact Lewis "rotating cylindrical" solution is so derived by a limiting
procedure from a spatially bound system. In the second part we analyze two
cylindrical shells rotating in opposite directions in such a way that the
static Levi-Civita metric is produced outside and no angular momentum flux
escapes to infinity. The rotation of the local inertial frames in flat space
inside the inner cylinder is thus exhibited without any approximation or
interpretational difficulties within this model.
A test particle within the inner cylinder kept at rest with respect to axes
that do not rotate as seen from infinity experiences a centrifugal force.
Although the spacetime there is Minkowskian out to the inner cylinder
nevertheless that space has been induced to rotate, so relative to the local
inertial frame the particle is traversing a circular orbit.Comment: 12 pages, 2 figure
Self-gravitating clouds of generalized Chaplygin and modified anti-Chaplygin Gases
The Chaplygin gas has been proposed as a possible dark energy, dark matter
candidate. As a working fluid in a Friedmann-Robertson-Walker universe, it
exhibits early behavior reminiscent of dark matter, but at later times is more
akin to a cosmological constant. In any such universe, however, one can expect
local perturbations to form. Here we obtain the general equations for a
self-gravitating relativistic Chaplygin gas. We solve these equations and
obtain the mass-radius relationship for such structures, showing that only in
the phantom regime is the mass-radius relationship large enough to be a serious
candidate for highly compact massive objects at the galaxy core. In addition,
we study the cosmology of a modified anti-Chaplygin gas. A self-gravitating
cloud of this matter is an exact solution to Einstein's equations.Comment: 16 page
Causality-Violating Higgs Singlets at the LHC
We construct a simple class of compactified five-dimensional metrics which
admits closed timelike curves (CTCs), and derive the resulting CTCs as analytic
solutions to the geodesic equations of motion. The associated Einstein tensor
satisfies all the null, weak, strong and dominant energy conditions. In
particular, no negative-energy "tachyonic" matter is required. In
extra-dimensional models where gauge charges are bound to our brane, it is the
Kaluza-Klein (KK) modes of gauge-singlets that may travel through the CTCs.
From our brane point of view, many of these KK modes would appear to travel
backward in time. We give a simple model in which time-traveling Higgs singlets
can be produced by the LHC, either from decay of the Standard Model (SM) Higgs
or through mixing with the SM Higgs. The signature of these time-traveling
singlets is a secondary decay vertex pre-appearing before the primary vertex
which produced them. The two vertices are correlated by momentum conservation.
We demonstrate that pre-appearing vertices in the Higgs singlet-doublet mixing
model may well be observable at the LHC.Comment: 55 pages, 5 figures, v4: Version updated to include in single
manuscript the contents of Erratum [Phys. Rev. D 88, 069901(E) (2013)], Reply
[Phys. Rev. D 88, 068702 (2013)], Comment [Phys. Rev. D 88, 068701 (2013),
arXiv:1302.1711], and original published article [Phys. Rev. D 87, 045004
(2013), arXiv:1103.1373]. Positive conclusions remain unchange
Old and new results for superenergy tensors from dimensionally dependent tensor identities
It is known that some results for spinors, and in particular for superenergy
spinors, are much less transparent and require a lot more effort to establish,
when considered from the tensor viewpoint. In this paper we demonstrate how the
use of dimensionally dependent tensor identities enables us to derive a number
of 4-dimensional identities by straightforward tensor methods in a signature
independent manner. In particular, we consider the quadratic identity for the
Bel-Robinson tensor and also the new conservation laws for the
Chevreton tensor, both of which have been obtained by spinor means; both of
these results are rederived by {\it tensor} means for 4-dimensional spaces of
any signature, using dimensionally dependent identities, and also we are able
to conclude that there are no {\it direct} higher dimensional analogues. In
addition we demonstrate a simple way to show non-existense of such identities
via counter examples; in particular we show that there is no non-trivial Bel
tensor analogue of this simple Bel-Robinson tensor quadratic identity. On the
other hand, as a sample of the power of generalising dimensionally dependent
tensor identities from four to higher dimensions, we show that the symmetry
structure, trace-free and divergence-free nature of the four dimensional
Bel-Robinson tensor does have an analogue for a class of tensors in higher
dimensions.Comment: 18 pages; TeX fil
On Properties of Vacuum Axial Symmetric Spacetime of Gravitomagnetic Monopole in Cylindrical Coordinates
We investigate general relativistic effects associated with the
gravitomagnetic monopole moment of gravitational source through the analysis of
the motion of test particles and electromagnetic fields distribution in the
spacetime around nonrotating cylindrical NUT source. We consider the circular
motion of test particles in NUT spacetime, their characteristics and the
dependence of effective potential on the radial coordinate for the different
values of NUT parameter and orbital momentum of test particles. It is shown
that the bounds of stability for circular orbits are displaced toward the event
horizon with the growth of monopole moment of the NUT object. In addition, we
obtain exact analytical solutions of Maxwell equations for magnetized and
charged cylindrical NUT stars.Comment: 16 pages, 3 figures, 1 tabl
Chronology protection in stationary three-dimensional spacetimes
We study chronology protection in stationary, rotationally symmetric
spacetimes in 2+1 dimensional gravity, focusing especially on the case of
negative cosmological constant. We show that in such spacetimes closed timelike
curves must either exist all the way to the boundary or, alternatively, the
matter stress tensor must violate the null energy condition in the bulk. We
also show that the matter in the closed timelike curve region gives a negative
contribution to the conformal weight from the point of view of the dual
conformal field theory. We illustrate these properties in a class of examples
involving rotating dust in anti-de Sitter space, and comment on the use of the
AdS/CFT correspondence to study chronology protection.Comment: 20 pages. V2: minor corrections, Outlook expanded, references added,
published versio
Supersymmetric Rotating Black Holes and Causality Violation
The geodesics of the rotating extreme black hole in five spacetime dimensions
found by Breckenridge, Myers, Peet and Vafa are Liouville integrable and may be
integrated by additively separating the Hamilton-Jacobi equation. This allows
us to obtain the St\"ackel-Killing tensor. We use these facts to give the
maximal analytic extension of the spacetime and discuss some aspects of its
causal structure. In particular, we exhibit a `repulson'-like behaviour
occuring when there are naked closed timelike curves. In this case we find that
the spacetime is geodesically complete (with respect to causal geodesics) and
free of singularities. When a partial Cauchy surface exists, we show, by
solving the Klein-Gordon equation, that the absorption cross-section for
massless waves at small frequencies is given by the area of the hole. At high
frequencies a dependence on the angular quantum numbers of the wave develops.
We comment on some aspects of `inertial time travel' and argue that such time
machines cannot be constructed by spinning up a black hole with no naked closed
timelike curves.Comment: 36 pages,LaTeX,8 figures;added 1 reference and a few comments;
formula (2.6) corrected; a few changes to section
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