15 research outputs found
Finite-temperature scalar fields and the cosmological constant in an Einstein universe
We study the back reaction effect of massless minimally coupled scalar field
at finite temperatures in the background of Einstein universe. Substituting for
the vacuum expectation value of the components of the energy-momentum tensor on
the RHS of the Einstein equation, we deduce a relationship between the radius
of the universe and its temperature. This relationship exhibit a maximum
temperature, below the Planck scale, at which the system changes its behaviour
drastically. The results are compared with the case of a conformally coupled
field. An investigation into the values of the cosmological constant exhibit a
remarkable difference between the conformally coupled case and the minimally
coupled one.Comment: 7 pages, 2 figure
Squeezed States in the de Sitter Vacuum
We discuss the treatment of squeezed states as excitations in the Euclidean
vacuum of de Sitter space. A comparison with the treatment of these states as
candidate no-particle states, or alpha-vacua, shows important differences
already in the free theory. At the interacting level alpha-vacua are
inconsistent, but squeezed state excitations seem perfectly acceptable. Indeed,
matrix elements can be renormalized in the excited states using precisely the
standard local counterterms of the Euclidean vacuum. Implications for
inflationary scenarios in cosmology are discussed.Comment: 15 pages, no figures. One new citation in version 3; no other change
Bose-Einstein condensation for interacting scalar fields in curved spacetime
We consider the model of self-interacting complex scalar fields with a rigid
gauge invariance under an arbitrary gauge group . In order to analyze the
phenomenon of Bose-Einstein condensation finite temperature and the possibility
of a finite background charge is included. Different approaches to derive the
relevant high-temperature behaviour of the theory are presented.Comment: 28 pages, LaTe
A comment on multiple vacua, particle production and the time dependent AdS/CFT correspondence
We give an explicit formulation of the time dependent AdS/CFT correspondence
when there are multiple vacua present in Lorentzian signature. By computing
sample two point functions we show how different amplitudes are related by
cosmological particle production. We illustrate our methods in two example
spacetimes: (a) a ``bubble of nothing'' in AdS space, and (b) an asymptotically
locally AdS spacetime with a bubble of nothing on the boundary. In both cases
the alpha vacua of de Sitter space make an interesting appearance.Comment: 9 page
Nitrogen fixation by groundnut and velvet bean and residual benefit to a subsequent maize crop
Topological Inflation
We consider the possibility that higher-curvature corrections could drive
inflation after the compactification to four dimensions. Assuming that the
low-energy limit of the fundamental theory is eleven-dimensional supergravity
to the lowest order, including curvature corrections and taking the descent
from eleven dimensions to four via an intermediate five-dimensional theory, as
favored by recent considerations of unification at some scale around GeV, we may obtain a simple model of inflation in four dimensions. The
effective degrees of freedom are two scalar fields and the metric. The scalars
arise as the large five-dimensional modulus and the self-interacting conformal
mode of the metric. The effective potential has a local maximum in addition to
the more usual minimum. However, the potential is quite flat at the top, and
admits topological inflation. We show that the model can resolve cosmological
problems and provide a mechanism for structure formation with very little fine
tuning.Comment: 25 pages, latex, 2 eps figures, minor changes, accepted for
publication in Phys. Rev.