40 research outputs found
Vacuum Energy: If Not Now, Then When?
We review the cosmological evidence for a low matter density universe and a
cosmological constant or dynamical vacuum energy and address the cosmolog$
coincidence problem: why is the matter density about one-half the vacuum energy
{\em now}. This is reasonble, following the anthropic argument of Efstathiou
and of Martel, Schapiro & Weinberg.Comment: 4 pages (latex
Solar Core Homology, Solar Neutrinos and Helioseismology
Precise numerical standard solar models (SSMs) now agree with one another and
with helioseismological observations in the convective and outer radiative
zones. Nevertheless these models obscure how luminosity, neutrino production
and g-mode core helioseismology depend on such inputs as opacity and nuclear
cross sections. Although the Sun is not homologous, its inner core by itself is
chemically evolved and almost homologous, because of its compactness, radiative
energy transport, and ppI-dominated luminosity production. We apply
luminosity-fixed homology transformations to the core to estimate theoretical
uncertainties in the SSM and to obtain a broad class of non-SSMs, parametrized
by central temperature and density and purely radiative energy transport in the
core.Comment: 14 pp., jnl.tex macro, minor corrections; accepted by Astrophysical
Journa
Variational Principles for Stellar Structure
The four equations of stellar structure are reformulated as two alternate
pairs of variational principles. Different thermodynamic representations lead
to the same hydromechanical equations, but the thermal equations require, not
the entropy, but the temperature as the thermal field variable. Our treatment
emphasizes the hydrostatic energy and the entropy production rate of luminosity
produced and transported. The conceptual and calculational advantages of
integral over differential formulations of stellar structure are discussed
along with the difficulties in describing stellar chemical evolution by
variational principles.Comment: 28 pages, LaTeX, requires AASTeX, 1 PostScript figure, revisions:
erratum; accepted by Astrophysical Journa