5,275 research outputs found
A Braneworld Universe From Colliding Bubbles
Much work has been devoted to the phenomenology and cosmology of the
so-called braneworld universe, where our (3+1)-dimensional universe lies on a
brane surrounded by a (4+1)-dimensional bulk spacetime that is essentially
empty except for a negative cosmological constant and the various modes
associated with gravity. For such a braneworld cosmology, the difficulty of
justifying some preferred initial conditions inevitably arises. The various
proposals for inflation restricted to the brane only partially explain the
homogeneity and isotropy of the resulting braneworld universe because the
homogeneity and isotropy of the bulk must be assumed. We propose a mechanism by
which a brane surrounded by AdS space arises naturally so that the homogeneity
and isotropy of both the brane and the bulk are guaranteed. We postulate an
initial false vacuum phase of (4+1)-dimensional Minkowski or de Sitter space
subsequently decaying to a true vacuum of anti-de Sitter space, assumed
discretely degenerate. This decay takes place through bubble nucleation. When
two bubbles of the true AdS vacuum collide, a brane (or domain wall) inevitably
forms between the two AdS phases. We live on this brane. The SO(3,1) symmetry
of the collision geometry ensures the three-dimensional spatial homogeneity and
isotropy of the universe on the brane as well as of the bulk. In the
semi-classical limit, this symmetry is exact. We sketch how the leading quantum
corrections translate into cosmological perturbations.Comment: 15 pages Latex (seven ps figures). Minor revisions, references added
and figures improve
Separation Distribution of Vacuum Bubbles in de Sitter Space
We compute the probability distribution of the invariant separation between
nucleation centers of colliding true vacuum bubbles arising from the decay of a
false de Sitter space vacuum. We find that even in the limit of a very small
nucleation rate per unit Hubble volume the production of widely separated
bubble pairs is suppressed. This distribution is of particular relevance for
the recently proposed ``colliding bubble braneworld'' scenario, in which the
value of Omega_k (the contribution of negative spatial curvature to the
cosmological density parameter) is determined by the invariant separation of
the colliding bubble pair. We also consider the probability of a collision with
a `third' bubble.Comment: 15 pages REVTEX, 2 Postscript figure
General Solutions for Tunneling of Scalar Fields with Quartic Potentials in de Sitter Space
The tunneling rates for scalar fields with quartic potentials in de Sitter
space in the limit of no gravitational back reaction are calculated numerically
and the results are fitted by analytic formulae.Comment: (Contours in Figure 1 corrected, two-dimensional fitting coefficient
corrected, references added.), 16 pages, KUNS 124
Metallic Ferromagnetism in the Kondo Lattice
Metallic magnetism is both ancient and modern, occurring in such familiar
settings as the lodestone in compass needles and the hard drive in computers.
Surprisingly, a rigorous theoretical basis for metallic ferromagnetism is still
largely missing. The Stoner approach perturbatively treates Coulomb
interactions when the latter need to be large, while the Nagaoka approach
incorporates thermodynamically negligible electrons into a half-filled band.
Here, we show that the ferromagnetic order of the Kondo lattice is amenable to
an asymptotically exact analysis over a range of interaction parameters. In
this ferromagnetic phase, the conduction electrons and local moments are
strongly coupled but the Fermi surface does not enclose the latter (i.e. it is
small). Moreover, non-Fermi liquid behavior appears over a range of frequencies
and temperatures. Our results provide the basis to understand some
long-standing puzzles in the ferromagnetic heavy fermion metals, and raises the
prospect for a new class of ferromagnetic quantum phase transitions.Comment: 21 pages, 9 figures, including Supporting Informatio
General Solutions for Tunneling of Scalar Fields with Quartic Potentials
For the theory of a single scalar field with a quartic potential
, we find semi-analytic expressions for the Euclidean action in
both four and three dimensions. The action in four dimensions determines the
quantum tunneling rate at zero temperature from a false vacuum state to the
true vacuum state; similarly, the action in three dimensions determines the
thermal tunneling rate for a finite temperature theory. We show that for all
quartic potentials, the action can be obtained from a one parameter family of
instanton solutions corresponding to a one parameter family of differential
equations. We find the solutions numerically and use polynomial fitting
formulae to obtain expressions for the Euclidean action. These results allow
one to calculate tunneling rates for the entire possible range of quartic
potentials, from the thin-wall (nearly degenerate) limit to the opposite limit
of vanishing barrier height. We also present a similar calculation for
potentials containing terms, which arise in the
one-loop approximation to the effective potential in electroweak theory.Comment: 17 pages, 6 figures not included but available upon request, UM AC
93-
Hard Art of the Universe Creation
We develop a stochastic approach to the theory of tunneling with the baby
universe formation. This method is applied also to the theory of creation of
the universe in a laboratory.Comment: 20 page
Extended Inflation from Strings
We study the possibility of extended inflation in the effective theory of
gravity from strings compactified to four dimensions and find that it strongly
depends on the mechanism of supersymmetry breaking. We consider a general class
of string--inspired models which are good candidates for successful extended
inflation. In particular, the --problem of ordinary extended inflation
is automatically solved by the production of only very small bubbles until the
end of inflation. We find that the inflaton field could belong either to the
untwisted or to the twisted massless sectors of the string spectrum, depending
on the supersymmetry breaking superpotential.Comment: 18p
Smooth Non-Abelian Bosonization
We present an extension of ``smooth bosonization'' to the non-Abelian case.
We construct an enlarged theory containing both bosonic and fermionic fields
which exhibits a local chiral gauge symmetry. A gauge fixing function depending
on one real parameter allows us to interpolate smoothly between a purely
fermionic and a purely bosonic representation. The procedure is, in the special
case of bosonization, complementary to the approach based on duality.Comment: LaTeX, 13 pages, CERN--TH-7347/9
Quantum State During and after -Symmetric Bubble Nucleation with Gravitaional Effects
We extend our previous analysis of the quantum state during and after
-symmetric bubble nucleation to the case including gravitational effects.
We find that there exists a simple relationship between the case with and
without gravitational effects. In a special case of a conformally coupled
scalar field which is massless except on the bubble wall, the state is found to
be conformally equivalent to the case without gravity.Comment: 31 pages plain Tex file, uuencoded postscript figure file is
available from [email protected] upon request, KUNS126
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