284 research outputs found
Static wormholes on the brane inspired by Kaluza-Klein gravity
We use static solutions of 5-dimensional Kaluza-Klein gravity to generate
several classes of static, spherically symmetric spacetimes which are analytic
solutions to the equation , where is the
four-dimensional Ricci scalar. In the Randall & Sundrum scenario they can be
interpreted as vacuum solutions on the brane. The solutions contain the
Schwarzschild black hole, and generate new families of traversable Lorenzian
wormholes as well as nakedly singular spacetimes. They generalize a number of
previously known solutions in the literature, e.g., the temporal and spatial
Schwarzschild solutions of braneworld theory as well as the class of self-dual
Lorenzian wormholes. A major departure of our solutions from Lorenzian
wormholes {\it a la} Morris and Thorne is that, for certain values of the
parameters of the solutions, they contain three spherical surfaces (instead of
one) which are extremal and have finite area. Two of them have the same size,
meet the "flare-out" requirements, and show the typical violation of the energy
conditions that characterizes a wormhole throat. The other extremal sphere is
"flaring-in" in the sense that its sectional area is a local maximum and the
weak, null and dominant energy conditions are satisfied in its neighborhood.
After bouncing back at this second surface a traveler crosses into another
space which is the double of the one she/he started in. Another interesting
feature is that the size of the throat can be less than the Schwarzschild
radius , which no longer defines the horizon, i.e., to a distant observer
a particle or light falling down crosses the Schwarzschild radius in a finite
time
Scalar GW detection with a hollow spherical antenna
We study the response and cross sections for the absorption of GW energy in a
Jordan-Brans-Dicke theory by a resonant mass detector shaped as a hollow
sphere.Comment: latex file, 9 page
The detection of Gravitational Waves
This chapter is concerned with the question: how do gravitational waves (GWs)
interact with their detectors? It is intended to be a theory review of the
fundamental concepts involved in interferometric and acoustic (Weber bar) GW
antennas. In particular, the type of signal the GW deposits in the detector in
each case will be assessed, as well as its intensity and deconvolution. Brief
reference will also be made to detector sensitivity characterisation, including
very summary data on current state of the art GW detectors.Comment: 33 pages, 12 figures, LaTeX2e, Springer style files --included. For
Proceedings of the ERE-2001 Conference (Madrid, September 2001
How to reach a few percent level in determining the Lense-Thirring effect?
In this paper we discuss and compare a node-only LAGEOS-LAGEOS II combination
and a node-only LAGEOS-LAGEOS II-Ajisai-Jason1 combination for the
determination of the Lense-Thirring effect. The new combined EIGEN-CG01C Earth
gravity model has been adopted. The second combination cancels the first three
even zonal harmonics along with their secular variations but introduces the
non-gravitational perturbations of Jason1. The first combination is less
sensitive to the non-conservative forces but is sensitive to the secular
variations of the uncancelled even zonal harmonics of low degree J4 and J6
whose impact grows linearly in time.Comment: Latex2e, 22 pag. 1 table, 2 figures, 45 references. Changes in the
Abstract, Introduction and Conclusions. Discussion on the non-gravitational
perturbations on Ajisai and on the impact of the secular rates of the even
zonal harmonics added. EIGEN-CG01C CHAMP+GRACE+terrestrial
gravimetry/altimetry Earth gravity model used. Reference adde
General Relativity as an Attractor in Scalar-Tensor Stochastic Inflation
Quantum fluctuations of scalar fields during inflation could determine the
very large-scale structure of the universe. In the case of general
scalar-tensor gravity theories these fluctuations lead to the diffusion of
fundamental constants like the Planck mass and the effective Brans--Dicke
parameter, . In the particular case of Brans--Dicke gravity, where
is constant, this leads to runaway solutions with infinitely large
values of the Planck mass. However, in a theory with variable we find
stationary probability distributions with a finite value of the Planck mass
peaked at exponentially large values of after inflation. We conclude
that general relativity is an attractor during the quantum diffusion of the
fields.Comment: LaTeX (with RevTex) 11 pages, 2 uuencoded figures appended, also
available on WWW via http://star.maps.susx.ac.uk/index.htm
Value-based decision-making of cigarette and nondrug rewards in dependent and occasional cigarette smokers:An FMRI study
Little is known about the neural functioning that underpins drug valuation and choice in addiction, including nicotine dependence. Following ad libitum smoking, 19 dependent smokers (smokedâ„10/day) and 19 occasional smokers (smoked 0.5â5/week) completed a decisionâmaking task. First, participants stated how much they were willingâtoâpay for various amounts of cigarettes and shop vouchers. Second, during functional magnetic resonance imaging, participants decided if they wanted to buy these cigarettes and vouchers for a set amount of money. We examined decisionâmaking behaviour and brain activity when faced with cigarette and voucher decisions, purchasing (vs not purchasing) cigarettes and vouchers, and âvalue signalsâ where brain activity correlated with cigarette and voucher value. Dependent smokers had a higher willingnessâtoâpay for cigarettes and greater activity in the bilateral middle temporal gyrus when faced with cigarette decisions than occasional smokers. Across both groups, the decision to buy cigarettes was associated with activity in the left paracingulate gyrus, right nucleus accumbens, and left amygdala. The decision to buy vouchers was associated with activity in the left superior frontal gyrus, but dependent smokers showed weaker activity in the left posterior cingulate gyrus than occasional smokers. Across both groups, cigarette value signals were observed in the left striatum and ventromedial prefrontal cortex. To summarise, nicotine dependence was associated with greater behavioural valuation of cigarettes and brain activity during cigarette decisions. When purchasing cigarettes and vouchers, reward and decisionârelated brain regions were activated in both groups. For the first time, we identified value signals for cigarettes in the brain
Bumpy black holes from spontaneous Lorentz violation
We consider black holes in Lorentz violating theories of massive gravity. We
argue that in these theories black hole solutions are no longer universal and
exhibit a large number of hairs. If they exist, these hairs probe the
singularity inside the black hole providing a window into quantum gravity. The
existence of these hairs can be tested by future gravitational wave
observatories. We generically expect that the effects we discuss will be larger
for the more massive black holes. In the simplest models the strength of the
hairs is controlled by the same parameter that sets the mass of the graviton
(tensor modes). Then the upper limit on this mass coming from the inferred
gravitational radiation emitted by binary pulsars implies that hairs are likely
to be suppressed for almost the entire mass range of the super-massive black
holes in the centers of galaxies.Comment: 40 pages, 4 figure
Rotating Resonator-Oscillator Experiments to Test Lorentz Invariance in Electrodynamics
In this work we outline the two most commonly used test theories (RMS and
SME) for testing Local Lorentz Invariance (LLI) of the photon. Then we develop
the general framework of applying these test theories to resonator experiments
with an emphasis on rotating experiments in the laboratory. We compare the
inherent sensitivity factors of common experiments and propose some new
configurations. Finally we apply the test theories to the rotating cryogenic
experiment at the University of Western Australia, which recently set new
limits in both the RMS and SME frameworks [hep-ph/0506074].Comment: Submitted to Lecture Notes in Physics, 36 pages, minor modifications,
updated list of reference
Tensor-scalar gravity and binary-pulsar experiments
Some recently discovered nonperturbative strong-field effects in
tensor-scalar theories of gravitation are interpreted as a scalar analog of
ferromagnetism: "spontaneous scalarization". This phenomenon leads to very
significant deviations from general relativity in conditions involving strong
gravitational fields, notably binary-pulsar experiments. Contrary to
solar-system experiments, these deviations do not necessarily vanish when the
weak-field scalar coupling tends to zero. We compute the scalar "form factors"
measuring these deviations, and notably a parameter entering the pulsar timing
observable gamma through scalar-field-induced variations of the inertia moment
of the pulsar. An exploratory investigation of the confrontation between
tensor-scalar theories and binary-pulsar experiments shows that nonperturbative
scalar field effects are already very tightly constrained by published data on
three binary-pulsar systems. We contrast the probing power of pulsar
experiments with that of solar-system ones by plotting the regions they exclude
in a generic two-dimensional plane of tensor-scalar theories.Comment: 35 pages, REVTeX 3.0, uses epsf.tex to include 9 Postscript figure
STATIONARY SOLUTIONS IN BRANS-DICKE STOCHASTIC INFLATIONARY COSMOLOGY
In Brans-Dicke theory the Universe becomes divided after inflation into many
exponentially large domains with different values of the effective
gravitational constant. Such a process can be described by diffusion equations
for the probability of finding a certain value of the inflaton and dilaton
fields in a physical volume of the Universe. For a typical chaotic inflation
potential, the solutions for the probability distribution never become
stationary but grow forever towards larger values of the fields. We show here
that a non-minimal conformal coupling of the inflaton to the curvature scalar,
as well as radiative corrections to the effective potential, may provide a
dynamical cutoff and generate stationary solutions. We also analyze the
possibility of large nonperturbative jumps of the fluctuating inflaton scalar
field, which was recently revealed in the context of the Einstein theory. We
find that in the Brans--Dicke theory the amplitude of such jumps is strongly
suppressed.Comment: 19 pages, LaTe
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