1,286,753 research outputs found
One Loop Graviton Self-Energy In A Locally De Sitter Background
The graviton tadpole has recently been computed at two loops in a locally de
Sitter background. We apply intermediate results of this work to exhibit the
graviton self-energy at one loop. This quantity is interesting both to check
the accuracy of the first calculation and to understand the relaxation effect
it reveals. In the former context we show that the self-energy obeys the
appropriate Ward identity. We also show that its flat space limit agrees with
the flat space result obtained by Capper in what should be the same gauge.Comment: 35 pages, plain TeX, 4 Postscript files, uses psfig.sty, revised June
1996 for publication in Physical Review
Presupernova evolution of accreting white dwarfs with rotation
We discuss the effects of rotation on the evolution of accreting
carbon-oxygen white dwarfs, with the emphasis on possible consequences in Type
Ia supernova (SN Ia) progenitors. Starting with a slowly rotating white dwarf,
we simulate the accretion of matter and angular momentum from a quasi-Keplerian
accretion disk. The role of the various rotationally induced hydrodynamic
instabilities for the transport of angular momentum inside the white dwarf is
investigated. We find that the dynamical shear instability is the most
important one in the highly degenerate core. Our results imply that accreting
white dwarfs rotate differentially throughout,with a shear rate close to the
threshold value for the onset of the dynamical shear instability. As the latter
depends on the temperature of the white dwarf, the thermal evolution of the
white dwarf core is found to be relevant for the angular momentum
redistribution. As found previously, significant rotation is shown to lead to
carbon ignition masses well above 1.4 Msun. Our models suggest a wide range of
white dwarf explosion masses, which could be responsible for some aspects of
the diversity observed in SNe Ia. We analyze the potential role of the bar-mode
and the r-mode instability in rapidly rotating white dwarfs, which may impose
angular momentum loss by gravitational wave radiation. We discuss the
consequences of the resulting spin-down for the fate of the white dwarf, and
the possibility to detect the emitted gravitational waves at frequencies of 0.1
>... 1.0 Hz in nearby galaxies with LISA. Possible implications of fast and
differentially rotating white dwarf cores for the flame propagation in
exploding white dwarfs are also briefly discussed.Comment: 22 pages, 16 figures, Accepted to A&
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