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Longitudinal association between smoking abstinence and depression severity in those with baseline current, past, and no history of major depressive episode in an international online tobacco cessation study
Universe Models with a Variable Cosmological "Constant" and a "Big Bounce"
We present a rich class of exact solutions which contains radiation-dominated
and matter-dominated models for the early and late universe. They include a
variable cosmological ``constant'' which is derived from a higher dimension and
manifests itself in spacetime as an energy density for the vacuum. This is in
agreement with observational data and is compatible with extensions of general
relativity to string and membrane theory. Our solutions are also typified by a
non-singular ``big bounce'' (as opposed to a singular big bang), where matter
is created as in inflationary cosmology.Comment: 17 pages, 2 figures, AASTEX. To appear in Ap
A Quasi-Spherical Gravitational Wave Solution in Kaluza-Klein Theory
An exact solution of the source-free Kaluza-Klein field equations is
presented. It is a 5D generalization of the Robinson-Trautman quasi-spherical
gravitational wave with a cosmological constant. The properties of the 5D
solution are briefly described.Comment: 10 pages Latex, Revtex, submitted to GR
What can gauge-gravity duality teach us about condensed matter physics?
I discuss the impact of gauge-gravity duality on our understanding of two
classes of systems: conformal quantum matter and compressible quantum matter.
The first conformal class includes systems, such as the boson Hubbard model
in two spatial dimensions, which display quantum critical points described by
conformal field theories. Questions associated with non-zero temperature
dynamics and transport are difficult to answer using conventional field
theoretic methods. I argue that many of these can be addressed systematically
using gauge-gravity duality, and discuss the prospects for reliable computation
of low frequency correlations.
Compressible quantum matter is characterized by the smooth dependence of the
charge density, associated with a global U(1) symmetry, upon a chemical
potential. Familiar examples are solids, superfluids, and Fermi liquids, but
there are more exotic possibilities involving deconfined phases of gauge fields
in the presence of Fermi surfaces. I survey the compressible systems studied
using gauge-gravity duality, and discuss their relationship to the condensed
matter classification of such states. The gravity methods offer hope of a
deeper understanding of exotic and strongly-coupled compressible quantum
states.Comment: 34 pages, 11 figures + 16 pages of Supplementary Material with 4
figures; to appear in Annual Reviews of Condensed Matter Physics; (v2) add a
figure, and clarifications; (v3) final version; (v4) small correction
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