7,266 research outputs found
A study of global monopole in Lyra geometry
A class of exact static solution around a global monopole resulting from the
breaking of a global S0(3) symmetry is obtained in the context of Lyra
geometry. Our solution is shown to possess an interesting feature like
wormholes space-time. It has been shown that the global monopole exerts no
gravitational force on surrounding non-relativistic matter.Comment: 6 pages, Published in Mod.Phys.Lett.A19:2785-2790,200
Poluklasični gravitacijski efekti blizu kozmičke strune u Lyrinoj geometriji
In recent past, W. A. Hiscock [Phys. Lett. B 188 (1987) 317] studied the semi-classical gravitational effects near cosmic strings. He obtained the vacuum expectation value of the stress-energy tensor of an arbitrary collection of conformal massless free-quantum fields (scalar, spinor and vectors) in the presence of a static, cylindrically symmetric cosmic string. With this stress-energy tensor, we study the semi-classical gravitational effects of a cosmic string in the context of Lyra geometry.Nedavno je W. A. Hiscock [Phys. Lett. B 188 (1987) 317] proučavao poluklasične gravitacijske efekte u blizini kozmičkih struna. Izveo je vakuumsku očekivanu vrijednost za tenzor naprezanja-energije za proizvoljan skup konformnih, bezmasenih i slobodnih kvantnih polja (skalara, spinora i vektora) u prisustvu statičke cilindrično-simetrične kozmičke strune. S tim tenzorom proučavamo poluklasične gravitacijske efekte kozmičke strune u okviru Lyrine geometrije
Proučavanje globalnih struna u Lyrinoj geometriji
An exact solution for the space-time outside the core of a U(1) static global string in Lyra geometry is presented. Our global string is nonsingular at a finite distance from the string core. The gravitational field of the global string is shown to be attractive in nature.Dajemo egzaktno rješenje za prostor-vrijeme izvan sredice mirne globalne U(1) strune u Lyrinoj geometriji. Nalazi se da globalna struna nije singularna na konačnoj daljini od sredice strune. Pokazuje se da je gravitacijsko polje globalne strune privlačno
Vacuumless topological defects in Lyra geometry
Few years ago, Cho and Vilenkin have proposed that topological defects can
arise in symmetry breaking models without having degenerate vacua. These types
of defects are known as vacuumless defects. In the present work, the
gravitational field of a vacuumless global string and global monopole have been
investigated in the context of Lyra geometry. We find the metric of the
vacuumless global string and global monopole in the weak field approximations.
It has been shown that the vacuumless global string can have repulsive whereas
global monopole exerts attractive gravitational effects on a test particle. It
is dissimilar to the case studied in general relativity.Comment: 14 pages, 9 figures. To appear in Astrophys.Space.Sc
Electronic structure, phase stability and chemical bonding in ThAl and ThAlH
We present the results of theoretical investigation on the electronic
structure, bonding nature and ground state properties of ThAl and
ThAlH using generalized-gradient-corrected first-principles
full-potential density-functional calculations. ThAlH has been reported
to violate the "2 \AA rule" of H-H separation in hydrides. From our total
energy as well as force-minimization calculations, we found a shortest H-H
separation of 1.95 {\AA} in accordance with recent high resolution powder
neutron diffraction experiments. When the ThAl matrix is hydrogenated, the
volume expansion is highly anisotropic, which is quite opposite to other
hydrides having the same crystal structure. The bonding nature of these
materials are analyzed from the density of states, crystal-orbital Hamiltonian
population and valence-charge-density analyses. Our calculation predicts
different nature of bonding for the H atoms along and . The strongest
bonding in ThAlH is between Th and H along which form dumb-bell
shaped H-Th-H subunits. Due to this strong covalent interaction there is very
small amount of electrons present between H atoms along which makes
repulsive interaction between the H atoms smaller and this is the precise
reason why the 2 {\AA} rule is violated. The large difference in the
interatomic distances between the interstitial region where one can accommodate
H in the and planes along with the strong covalent interaction
between Th and H are the main reasons for highly anisotropic volume expansion
on hydrogenation of ThAl.Comment: 14 pages, 9 figure
Wilson Expansion of QCD Propagators at Three Loops: Operators of Dimension Two and Three
In this paper we construct the Wilson short distance operator product
expansion for the gluon, quark and ghost propagators in QCD, including
operators of dimension two and three, namely, A^2, m^2, m A^2, \ovl{\psi} \psi
and m^3. We compute analytically the coefficient functions of these operators
at three loops for all three propagators in the general covariant gauge. Our
results, taken in the Landau gauge, should help to improve the accuracy of
extracting the vacuum expectation values of these operators from lattice
simulation of the QCD propagators.Comment: 20 pages, no figure
- …