3,340 research outputs found
Brans-Dicke Wormhole Revisited
A basic constraint to be satisfied by Brans class I solution for being a
traversible wormhole is derived. It is argued that the solution could be a
wormhole analogue of the Horowitz-Ross naked black hole. It is further
demonstrated that the wormhole is traversible only "in principle", but not in
practice. Using a recently proposed measure of total gravitational energy
inside a static wormhole configuration, it is shown that the wormhole contains
repulsive gravity required for the defocussing of orbits at the throat.Comment: 13 pages, 6 figures, accepted for publication in Class. Quant. Gra
Performance of combined tillage equipment and it’s effect on soil properties
An experiment was conducted to evaluate the performance of a locally manufactured combined tillage implement (moldboard plow + ripper) in one of the fields of the kufa university faculty of agriculture. The experiment was included two factors , the first factor is combing the ripper to mold board plow in five level these are fixing the combined ripper shanks while the shanks points oriented in two different levels with and opposite to the plowing direction , two levels of different ripper depths the same depth and 5 cm above the depth of mold board plow share and the fifth level is control treatment ( mold board plow alone ) .The second factor was the plowing operation speed at five levels (1.4, 2.0 , 3.6 and 4.7) Km.hr ̵ ¹ . the experiment was conducted as a factorial experiment with RCBD , the LSD test at 5 % was used to compare between means .The results of the research were showed that combining the locally manufactured ripper implement to mold board plow resulted in significant increase in the number of soil clods with the desired diameter (5-10 cm ) very low number of soil block with diameter larger than 10 cm , more even soil roughness and the actual productivity has not decreased to the extent that it affects the efficient performance of the tillage process compared to the use at the mold board plow alone
A Nonsingular Brans Wormhole: An Analogue to Naked Black Holes
In a recent paper, we showed the Jordan frame vacuum Brans Class I solution
provided a wormhole analogue to Horowitz-Ross naked black hole in the wormhole
range -3/2<{\omega}<-4/3. Thereafter, the solution has been criticized by some
authors that, because of the presence of singularity in that solution within
this range, a wormhole interpretation of it is untenable. While the criticism
is correct, we show here that (i) a singularity-free wormhole can actually be
obtained from Class I solution by performing a kind of Wick rotation on it,
resulting into what Brans listed as his independent Class II solution (ii) the
Class II solution has all the necessary properties of a regular wormhole in a
revised range -2<{\omega}<-3/2 and finally, (iii) naked black holes, as
described by Horowitz and Ross, are spacetimes where the tidal forces attain
their maxima above the black hole horizon. We show that in the non-singular
Class II spacetime this maxima is attained above the throat and thus can be
treated as a wormhole analogue. Some related issues are also addressed.Comment: 20 pages, 4 figure
Non-factorizable long distance contributions in color suppressed decays of B mesons
, , and decays are
studied. Their amplitude is given by a sum of factorized and non-factorizable
ones. The latter which is estimated by using a hard pion approximation is
rather small in color favored and decays but still
can efficiently interfere with the main amplitude given by the factorization.
In the color suppressed and decays, the
non-factorizable contribution is very important. The sum of the factorized and
non-factorizable amplitudes can reproduce well the existing experimental data
on the branching ratios for the color favored and
and the color suppressed and decays by
taking reasonable values of unknown parameters involved.Comment: 19 pages, Revte
Resonant Two-body D Decays
The contribution of a resonance to is
calculated by applying the soft pion theorem to , and is
found to be about 30% of the measured amplitude and to be larger than the
component of this amplitude. We estimate a 70% contribution to
the total amplitude from a higher resonance. This implies large
deviations from factorization in D decay amplitudes, a lifetime difference
between D^0 and D^+, and an enhancement of mixing due to SU(3)
breaking.Comment: To be published in Physical Review Letters, some corrections,
references update
Anisotropy in the helicity modulus of a 3D XY-model: application to YBCO
We present a Monte Carlo study of the helicity moduli of an anisotropic
classical three-dimensional (3D) XY-model of YBCO in superconducting state. It
is found that both the ab-plane and the c-axis helicity moduli, which are
proportional to the inverse square of the corresponding magnetic field
penetration depth, vary linearly with temperature at low temperatures. The
result for the c-axis helicity modulus is in disagreement with the experiments
on high quality samples of YBCO. Thus we conclude that purely classical phase
fluctuations of the superconducting order parameter cannot account for the
observed c-axis electrodynamics of YBCO.Comment: 7 pages, 1 figur
The S-wave \Lambda\pi phase shift is not large
We study the strong interaction S-wave \Lambda\pi phase shift in the region
of the \Xi mass in the framework of a relativistic chiral unitary approach
based on coupled channels. All parameters have been previously determined in a
fit to strangeness S= -1 S-wave kaon-nucleon data. We find 0^\circ \le \delta_0
\le 1.1^\circ in agreement with previous chiral perturbation theory
calculations (or extensions thereof). We also discuss why a recent coupled
channel K-matrix calculation gives a result for \delta_0 that is negative and
much bigger in magnitude. We argue why that value should not be trusted.Comment: 3 pages, REVTe
D1-brane with Overcritical Electric Field in AdS3 and S-brane
We study aspects of Dirichlet S-branes, which are defined as Dirichlet
boundary condition on a time like embedding of open strings, in general
backgrounds. By applying T-duality along an isometry of the unphysical
dS2-branes in NS-NS supported AdS3-background, we find S0-brane. We also study
the time dependent tachyon condensation on the unstable Dp-brane and interpret
the singular solutions as lower dimensional S(p-1)-brane that couples to real
Ramond-Ramond fields while to imaginary NS-NS modes.Comment: 23 pages, JHEP style, V2: minor changes, typos fixe
s-s*-d-wave superconductor on a square lattice and its BCs phase diagram
We study an extended Hubbard model with on-site repulsion and nearest
neighbors attraction which tries to mimic some of the experimental features of
doped cuprates in the superconducting state. We draw and discuss the phase
diagram as a function of the effective interactions among electrons for a wide
range of doping concentrations. We locate the region which is relevant for the
cuprates setting some constraints on the parameters which may be used in this
kind of effective models. We also study the effects of temperature and
orthorrombicity on the symmetry and magnitude of the gap function, and map the
model onto a simpler linearized hamiltonian, which produces similar phase
diagrams.Comment: 4 pages, 3 figures included. Accepted for publication in Phys. Rev.
Bound States of String Networks and D-branes
We show the existence of non-threshold bound states of (p, q) string networks
and D3-branes, preserving 1/4 of the full type IIB supersymmetry, interpreted
as string networks dissolved in D3-branes. We also write down the expression
for the mass density of the system and discuss the extension of the
construction to other Dp-branes. Differences in our construction of string
networks with the ones interpreted as dyons in N=4 gauge theories are also
pointed out.Comment: 11 pages, latex, minor modifications (version to appear in Phys. Rev.
Lett.
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