5,183 research outputs found
Gravitational Forces on the Branes
We examine the gravitational forces in a brane-world scenario felt by point
particles on two 3-branes bounding a 5-dimensional AdS space with
symmetry. The particles are treated as perturbations on the vacuum metric and
coordinate conditions are chosen so that no brane bending effects occur. We
make an ADM type decomposition of the metric tensor and solve Einstein's
equations to linear order in the static limit. While no stabilization mechanism
is assumed, all the 5D Einstein equations are solved and are seen to have a
consistent solution. We find that Newton's law is reproduced on the Planck
brane at the origin while particles on the TeV brane a distance from the
origin experience an attractive force that has a growing exponential dependence
on the brane position.Comment: Based on a talk given at PASCOS 2004/Pran Nath Fes
Gravitational Forces in the Randall-Sundrum Model with a Scalar Stabilizing Field
We consider the problem of gravitational forces between point particles on
the branes in a five dimensional (5D) Randall-Sundrum model with two branes (at
and ) and symmetry of the fifth dimension. The matter on
the branes is viewed as a perturbation on the vacuum metric and treated to
linear order. In previous work \cite{ad} it was seen that the trace of the
transverse part of the 4D metric on the TeV brane, , contributed a
Newtonian potential enhanced by and thus
produced gross disagreement with experiment. In this work we include a scalar
stabilizing field and solve the coupled Einstein and scalar equations to
leading order for the case where is small and the vacuum
field is a decreasing function of . then grows a mass
factor where however, is suppressed from its natural value,
, by an exponential factor ,
. Thus agreement with experiment depends on the interplay
between the enhancing and decaying exponentials. Current data eliminates a
significant part of the parameter space, and the Randall-Sundrum model will be
sensitive to any improvements on the tests of the Newtonian force law at
smaller distances.Comment: 22 pages, Fig.1 adde
Cosmological frames for theories with absolute parallelism
The vierbein (tetrad) fields for closed and open Friedmann-Robertson-Walker
cosmologies are hard to work out in most of the theories featuring absolute
parallelism. The difficulty is traced in the fact that these theories are not
invariant under local Lorentz transformations of the vierbein. We illustrate
this issue in the framework of f(T) theories and Born-Infeld determinantal
gravity. In particular, we show that the early Universe as described by the
Born-Infeld scheme is singularity free and naturally inflationary as a
consequence of the very nature of Born-Infeld gravitational action.Comment: 8 pages, 1 figure. Talk given at the 8th Alexander Friedmann
International Seminar on Gravitation and Cosmology, Rio de Janeiro, Brazil,
June 2011. Submitted to the Proceeding
Recommended from our members
CO and CI maps of the starburst galaxy M82
The first map of an external galaxy in the 3P₁ - 3P0 fine-structure line of atomic carbon (CI) is presented towards the nucleus of the starbuster M82, and compared with the distinction of the CO J = 4 - 3 molecular emission. The CI traces features that are seen in lower transition CO maps, and shows that CI and the CO are well mixed and have similar spatial distributions. There are small differences between the CO J = 4 - 3 line and lower transition CO data towards the NE part of the molecular ring, where the emission is less prominent. The abundance ratio [CI]/[CO] across M82 is very high, with an average value ~ 0.5 across most of the nucleus, a factor at least 5 times that which is typical of dense molecular cloud cores seen in our own Galaxy. This means that on average, CI is overabundant towards M82. This result can be explained using models which provide enhancements to the CI abundance above normal Interstellar Medium values, a result of a greater cosmic ray flux in M82, or where there is substantial mixing of the gas
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Copyright © 2002, BMJJanusz Jankowski, Roger Jones, Brendan Delaney and John Den
Primordial nucleosynthesis as a probe of fundamental physics parameters
We analyze the effect of variation of fundamental couplings and mass scales
on primordial nucleosynthesis in a systematic way. The first step establishes
the response of primordial element abundances to the variation of a large
number of nuclear physics parameters, including nuclear binding energies. We
find a strong influence of the n-p mass difference (for the 4He abundance), of
the nucleon mass (for deuterium) and of A=3,4,7 binding energies (for 3He, 6Li
and 7Li). A second step relates the nuclear parameters to the parameters of the
Standard Model of particle physics. The deuterium, and, above all, 7Li
abundances depend strongly on the average light quark mass hat{m} \equiv
(m_u+m_d)/2. We calculate the behaviour of abundances when variations of
fundamental parameters obey relations arising from grand unification. We also
discuss the possibility of a substantial shift in the lithium abundance while
the deuterium and 4He abundances are only weakly affected.Comment: v2: 34 pages, 2 figures, typo in last GUT scenario corrected, added
discussion and graph of nonlinear behaviour in GUT scenarios, added short
section discussing binding of dineutron and 8Be, refs added, conclusions
unaltered. Accepted for publication, Phys. Rev.
Sub-millimeter images of a dusty Kuiper belt around eta Corvi
We present sub-millimeter and mid-infrared images of the circumstellar disk
around the nearby F2V star eta Corvi. The disk is resolved at 850um with a size
of ~100AU. At 450um the emission is found to be extended at all position
angles, with significant elongation along a position angle of 130+-10deg; at
the highest resolution (9.3") this emission is resolved into two peaks which
are to within the uncertainties offset symmetrically from the star at 100AU
projected separation. Modeling the appearance of emission from a narrow ring in
the sub-mm images shows the observed structure cannot be caused by an edge-on
or face-on axisymmetric ring; the observations are consistent with a ring of
radius 150+-20AU seen at 45+-25deg inclination. More face-on orientations are
possible if the dust distribution includes two clumps similar to Vega; we show
how such a clumpy structure could arise from the migration over 25Myr of a
Neptune mass planet from 80-105AU. The inner 100AU of the system appears
relatively empty of sub-mm emitting dust, indicating that this region may have
been cleared by the formation of planets, but the disk emission spectrum shows
that IRAS detected an additional hot component with a characteristic
temperature of 370+-60K (implying a distance of 1-2AU). At 11.9um we found the
emission to be unresolved with no background sources which could be
contaminating the fluxes measured by IRAS. The age of this star is estimated to
be ~1Gyr. It is very unusual for such an old main sequence star to exhibit
significant mid-IR emission. The proximity of this source makes it a perfect
candidate for further study from optical to mm wavelengths to determine the
distribution of its dust.Comment: 22 pages, 4 figures. Scheduled for publication in ApJ 10 February
2005 issu
CTS 11.7 GHz isolation data for the calendar year 1978
Monthly and annual percent-of-time data on polarization isolation measured for the CTS spacecraft 11.7 GHz downlink are presented. The relationship between isolation and attenuation and the degree to which isolation can be predicted from attenuation data are discussed
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