1,957 research outputs found
Gravitational Wave Emission by Cataclysmic Variables: numerical models of semi-detached binaries
Gravitational wave emission is considered to be the driving force for the
evolution of short-period cataclysmic binary stars, making them a potential
test for the validity of General Relativity. In spite of continuous refinements
of the physical description, a 10% mismatch exists between the theoretical
minimum period ( min) and the short-period cut-off
( min) observed in the period distribution for
cataclysmic variable binaries. A possible explanation for this mismatch was
associated with the use of the Roche model. We here present a systematic
comparison between self-consistent, numerically constructed sequences of
hydrostatic models of binary stars and Roche models of semi-detached binaries.
On the basis of our approach, we also derive a value for the minimum period of
cataclysmic variable binaries. The results obtained through the comparison
indicate that the Roche model is indeed very good, with deviations from the
numerical solution which are of a few percent at most. Our results therefore
suggest that additional sources of angular momentum loss or alternative
explanations need to be considered in order to justify the mismatch.Comment: 7pages, 4figures. To appear in MNRA
Phase Structure of Thermal QED Based on the Hard Thermal Loop Improved Ladder Dyson-Schwinger Equation --a "Gauge Invariant" Solution--
Based on the hard-thermal-loop resummed improved ladder Dyson-Schwinger
quation for the fermion mass function, we study how we can get the gauge
invariant solution in the sense it satisfies the Ward identity. Properties of
the ``gauge-invariant'' solutions are discussed.Comment: 3figures, Proceedins of SCGT06 (Nagoya University, Japan, November
2006
Chiral Phase Transitions in QED at Finite Temperature: Dyson-Schwinger Equation Analysis in the Real Time Hard-Thermal-Loop Approximation
In order for clarifying what are the essential thermal effects that govern
the chiral phase transition at finite temperature, we investigate, in the
real-time thermal QED, the consequences of the Hard-Thermal-Loop (HTL) resummed
Dyson-Schwinger equation for the physical fermion mass function .
Since is the mass function of an ``unstable'' quasi-particle in
thermal field theories, it necessarily has non-trivial imaginary parts together
with non-trivial wave function renormalization constants. In the present
analysis we correctly respect this fact, and study, in the ladder
approximation, the effect of HTL resummed gauge boson propagator. Our results
with the use of numerical analysis, show the two facts; i) The chiral phase
transition is of second order, since the fermion mass is dynamically generated
at a critical value of the temperature , or at the critical coupling
constant , without any discontinuity, and ii) the critical
temperature at fixed value of is significantly lower than the
previous results, namely the restoration of chiral symmetry occurs at lower
temperature than previously expected. The second fact shows the importance of
correctly taking the essential thermal effect into the analysis of chiral phase
transition, which are, in the previous analyses, neglected due to the
inappropriate approximations. The procedure how to maximally respect the gauge
invariance in the present approximation, is also discussed.Comment: Revtex4 with 6 figures, 11 page
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