3,084,327 research outputs found
Effective energy-momentum tensor of strong-field QED with unstable vacuum
We study the influence of a vacuum instability on the effective
energy-momentum tensor (EMT) of QED, in the presence of a quasiconstant
external electric field, by means of the relevant Green functions. In the case
when the initial vacuum, |0,in>, differs essentially from the final vacuum,
|0,out>, we find explicitly and compared both the vacuum average value of EMT,
, and the matrix element, . In
the course of the calculation we solve the problem of the special divergences
connected with infinite time T of acting of the constant electric field. The
EMT of pair created by an electric field from the initial vacuum is presented.
The relations of the obtained expressions to the Euler-Heisenberg's effective
action are established.Comment: 8 pages, 1 figure, Talk given at "QFEXT'05", the 7-th workshop on
quantum field theory under the influence of external conditions, Barcelona,
Spain, Sept. 5-9, 2005; minor misprints correcte
Precise Formulation of Neutrino Oscillation in the Earth
We give a perturbation theory of neutrino oscillation in the Earth. The
perturbation theory is valid for neutrinos with energy E \gsim 0.5 GeV. It is
formulated using trajectory dependent average potential. Non-adiabatic
contributions are included as the first order effects in the perturbation
theory. We analyze neutrino oscillation with standard matter effect and with
non-standard matter effect. In a three flavor analysis we show that the
perturbation theory gives a precise description of neutrino conversion in the
Earth. Effect of the Earth matter is substantially simplified in this
formulation.Comment: References added, 21 pages, 10 figures, version to appear in PR
On the global visibility of singularity in quasi-spherical collapse
We analyze here the issue of local versus the global visibility of a
singularity that forms in gravitational collapse of a dust cloud, which has
important implications for the weak and strong versions of the cosmic
censorship hypothesis. We find conditions as to when a singularity will be only
locally naked, rather than being globally visible, thus preseving the weak
censorship hypothesis. The conditions for formation of a black hole or naked
singularity in the Szekeres quasi-spherical collapse models are worked out. The
causal behaviour of the singularity curve is studied by examining the outgoing
radial null geodesics, and the final outcome of collapse is related to the
nature of the regular initial data specified on an initial hypersurface from
which the collapse evolves. An interesting feature that emerges is the
singularity in Szekeres spacetimes can be ``directionally naked''.Comment: Latex file, 32 pages, 12 postscript figures. To appear in the Journal
of General Relativity and Gravitatio
Necessary and sufficient condition for hydrostatic equilibrium in general relativity
We present explicit examples to show that the `compatibility criterion' is
capable of providing a {\em necessary} and {\em sufficient} condition for any
regular configuration to be compatible with the state of hydrostatic
equilibrium. This conclusion is drawn on the basis of the finding that the
relation gives the necessary and sufficient condition for dynamical
stability of equilibrium configurations only when the compatibility criterion
for these configurations is appropriately satisfied. In this regard, we
construct an appropriate sequence composed of core-envelope models on the basis
of compatibility criterion, such that each member of this sequence satisfies
the extreme case of causality condition at the centre. The maximum
stable value of (which occurs for the model corresponding to
the maximum value of mass in the mass-radius relation) and the corresponding
central value of the local adiabatic index, , of
this model are found fully consistent with those of the corresponding {\em
absolute} values, , and ,
which impose strong constraints on these parameters of such models. In addition
to this example, we also study dynamical stability of pure adiabatic polytropic
configurations on the basis of variational method for the choice of the `trial
function', , as well as the mass-central density relation,
since the compatibility criterion is appropriately satisfied for these models.
The results of this example provide additional proof in favour of the statement
regarding compatibility criterion mentioned above.Comment: 31 pages (double-spaced) revtex style, 1 figure in `ps' forma
Solar neutrinos and 1-3 leptonic mixing
Effects of the 1-3 leptonic mixing on the solar neutrino observables are
studied and the signatures of non-zero are identified. For this
we have re-derived the formula for -survival probability including all
relevant corrections and constructed the iso-contours of observables in the
plane. Analysis of the solar neutrino
data gives (90% C.L.) for
eV. The combination of the ratio CC/NC at
SNO and gallium production rate selects
(). The global fit of all oscillation data leads to zero best value of
. The sensitivity ( error) of future solar
neutrino studies to can be improved down to 0.01 - 0.02 by
precise measurements of the pp-neutrino flux and the CC/NC ratio as well as
spectrum distortion at high ( MeV) energies. Combination of experimental
results sensitive to the low and high energy parts of the solar neutrino
spectrum resolves the degeneracy of angles and .
Comparison of as well as measured in
the solar neutrinos and in the reactor/accelerator experiments may reveal new
effects which can not be seen otherwise.Comment: 36 pages, latex, 10 figures. Analysis and figures are updated with
new (salt phase II) SNO results, several clarifications added, typos
correcte
Unified Angular Momentum of Dyons
Unified quaternionic angular momentum for the fields of dyons and
gravito-dyons has been developed and the commutation relations for dynamical
variables are obtained in compact and consistent manner. Demonstrating the
quaternion forms of unified fields of dyons (electromagnetic fields) and
gravito-dyons (gravito-Heavisidian fields of linear gravity), corresponding
quantum equations are reformulated in compact, simpler and manifestly covariant
way
Energy-momentum tensor in thermal strong-field QED with unstable vacuum
The mean value of the one-loop energy-momentum tensor in thermal QED with
electric-like background that creates particles from vacuum is calculated. The
problem differes essentially from calculations of effective actions (similar to
that of Heisenberg--Euler) in backgrounds that do not violate the stability of
vacuum. The role of a constant electric background in the violation of both the
stability of vacuum and the thermal character of particle distribution is
investigated. Restrictions on the electric field and its duration under which
one can neglect the back-reaction of created particles are established.Comment: 7 pages, Talk presented at Workshop "Quantum Field Theory under the
Influence of External Conditions", Leipzig, September 17-21, 2007;
introduction extended, version accepted for publication in J.Phys.
- …