380 research outputs found
A generalized lens equation for light deflection in weak gravitational fields
A generalized lens equation for weak gravitational fields in Schwarzschild
metric and valid for finite distances of source and observer from the light
deflecting body is suggested. The magnitude of neglected terms in the
generalized lens equation is estimated to be smaller than or equal to 15 Pi/4
(m/d')^2, where m is the Schwarzschild radius of massive body and d' is
Chandrasekhar's impact parameter. The main applications of this generalized
lens equation are extreme astrometrical configurations, where 'Standard
post-Newtonian approach' as well as 'Classical lens equation' cannot be
applied. It is shown that in the appropriate limits the proposed lens equation
yields the known post-Newtonian terms, 'enhanced' post-post-Newtonian terms and
the Classical lens equation, thus provides a link between these both essential
approaches for determining the light deflection.Comment: 11 pages, 3 figure
Probing the strange quark condensate by di-electrons from phi meson decays in heavy-ion collisions at SIS energies
QCD sum rules predict that the change of the strange quark condensate in hadron matter at finite baryon density causes a shift of the peak
position of the di-electron spectra from meson decays. Due to the
expansion of hadron matter in heavy-ion collisions, the peak suffers a
smearing governed by the interval of density in the expanding fireball, which
appears as effective broadening of the di-electron spectrum in the
region. The emerging broadening is sensitive to the in-medium change of . This allows to probe directly in-medium modifications of
via di-electron spectra in heavy-ion collisions at SIS energies with HADES
Evaluation of QCD sum rules for light vector mesons at finite density and temperature
QCD sum rules are evaluated at finite nucleon densities and temperatures to
determine the change of mass parameters for the lightest vector mesons ,
and in a strongly interacting medium. For conditions relevant
for the starting experiments at HADES we find that the in-medium mass shifts of
the and mesons are governed, within the Borel QCD sum rule
approach, by the density and temperature dependence of the four-quark
condensate. In particular, the variation of the strength of the density
dependence of the four-quark condensate reflects directly the decreasing mass
of the meson and can lead to a change of the sign of the meson
mass shift as a function of the density. In contrast, the in-medium mass of the
meson is directly related to the chiral strange quark condensate which
seems correspondingly accessible
Numerical versus analytical accuracy of the formulas for light propagation
Numerical integration of the differential equations of light propagation in
the Schwarzschild metric shows that in some situations relevant for practical
observations the well-known post-Newtonian solution for light propagation has
an error up to 16 microarcsecond. The aim of this work is to demonstrate this
fact, identify the reason for this error and to derive an analytical formula
accurate at the level of 1 microarcsecond as needed for high-accuracy
astrometric projects (e.g., Gaia).
An analytical post-post-Newtonian solution for the light propagation for both
Cauchy and boundary problems is given for the Schwarzschild metric augmented by
the PPN and post-linear parameters , and . Using
analytical upper estimates of each term we investigate which
post-post-Newtonian terms may play a role for an observer in the solar system
at the level of 1 microarcsecond and conclude that only one post-post-Newtonian
term remains important for this numerical accuracy. In this way, an analytical
solution for the boundary problem for light propagation is derived. That
solution contains terms of both post-Newtonian and post-post-Newtonian order,
but is valid for the given numerical level of 1 microarcsecond. The derived
analytical solution has been verified using the results of a high-accuracy
numerical integration of differential equations of light propagation and found
to be correct at the level well below 1 microarcsecond for arbitrary observer
situated within the solar system. Furthermore, the origin of the
post-post-Newtonian terms relevant for the microarcsecond accuracy is
elucidated. We demonstrate that these terms result from an inadequate choice of
the impact parameter in the standard post-Newtonian formulas
Freeze Out Process with In-Medium Nucleon Mass
We investigate the kinetic freeze out scenario of a nucleon gas through a
finite layer. The in-medium mass modification of nucleons and it's impact on
the freeze out process is studied. A considerable modification of the
thermodynamical parameters temperature, flow-velocity, energy density and
particle density has been found in comparison with evaluations which use a
constant vacuum nucleon mass.Comment: 6 pages, 4 figures, Proceeding of the Conference "Quark Matter 2005",
4th - 9th August 2005, Budapest/Hungar
Pion Mass Shift and the Kinetic Freeze Out Process
The kinetic Freeze Out process of a pion gas through a finite layer with
time-like normal is considered. The pion gas is described by a Boltzmann gas
with elastic collisions among the pions. Within this model, the impact of the
in-medium pion mass modification on the Freeze Out process is studied. A
marginal change of the Freeze Out variables temperature and flow velocity and
an insignificant modification of the frozen out particle distribution function
has been found.Comment: European Physical Journal A (2009), in pres
Evidence for In-Medium Changes of Four-Quark Condensates
Utilizing the QCD sum rule approach to the behavior of the omega meson in
nuclear matter we derive evidence for in-medium changes of particular
four-quark condensates from the recent CB-TAPS experiment for the reaction
gamma + A -> A' + omega (-> pi0 gamma) with A = Nb and LH2.Comment: Submitted to Phys. Rev. Lett., 4 page
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