4,403 research outputs found
Reclaiming our discipline
In this editorial we are taking the opportunity to set out our views on the current legal education and training reforms. In doing so we are perhaps taking a slightly unusual approach for an editorial but the issues currently facing us all as legal academics and educators are, we feel, too important for us to miss this opportunity
Large Scale Inhomogeneities from the QCD Phase Transition
We examine the first-order cosmological QCD phase transition for a large
class of parameter values, previously considered unlikely. We find that the
hadron bubbles can nucleate at very large distance scales, they can grow as
detonations as well as deflagrations, and that the phase transition may be
completed without reheating to the critical temperature. For a subset of the
parameter values studied, the inhomogeneities generated at the QCD phase
transition might have a noticeable effect on nucleosynthesis.Comment: 15 LaTeX pages + 6 PostScript figures appended at the end of the
file, HU-TFT-94-1
Non-Equilibrium Evolution of Scalar Fields in FRW Cosmologies I
We derive the effective equations for the out of equilibrium time evolution
of the order parameter and the fluctuations of a scalar field theory in
spatially flat FRW cosmologies.The calculation is performed both to one-loop
and in a non-perturbative, self-consistent Hartree approximation.The method
consists of evolving an initial functional thermal density matrix in time and
is suitable for studying phase transitions out of equilibrium. The
renormalization aspects are studied in detail and we find that the counterterms
depend on the initial state. We investigate the high temperature expansion and
show that it breaks down at long times. We also obtain the time evolution of
the initial Boltzmann distribution functions, and argue that to one-loop order
or in the Hartree approximation, the time evolved state is a ``squeezed''
state. We illustrate the departure from thermal equilibrium by numerically
studying the case of a free massive scalar field in de Sitter and radiation
dominated cosmologies. It is found that a suitably defined non-equilibrium
entropy per mode increases linearly with comoving time in a de Sitter
cosmology, whereas it is {\it not} a monotonically increasing function in the
radiation dominated case.Comment: 29 pages, revtex 3.0, 11 figures available upon request, PITT-93-6;
LPTHE-93-52; CMU-HEP-93-2
Making predictions in the multiverse
I describe reasons to think we are living in an eternally inflating
multiverse where the observable "constants" of nature vary from place to place.
The major obstacle to making predictions in this context is that we must
regulate the infinities of eternal inflation. I review a number of proposed
regulators, or measures. Recent work has ruled out a number of measures by
showing that they conflict with observation, and focused attention on a few
proposals. Further, several different measures have been shown to be
equivalent. I describe some of the many nontrivial tests these measures will
face as we learn more from theory, experiment, and observation.Comment: 20 pages, 3 figures; invited review for Classical and Quantum
Gravity; v2: references improve
Bubble collisions and measures of the multiverse
To compute the spectrum of bubble collisions seen by an observer in an
eternally-inflating multiverse, one must choose a measure over the diverging
spacetime volume, including choosing an "initial" hypersurface below which
there are no bubble nucleations. Previous calculations focused on the case
where the initial hypersurface is pushed arbitrarily deep into the past.
Interestingly, the observed spectrum depends on the orientation of the initial
hypersurface, however one's ability observe the effect rapidly decreases with
the ratio of inflationary Hubble rates inside and outside one's bubble. We
investigate whether this conclusion might be avoided under more general
circumstances, in particular placing the observer's bubble near the initial
hypersurface. We find that it is not. As a point of reference, a substantial
appendix reviews relevant aspects of the measure problem of eternal inflation.Comment: 24 pages, two figures, plus 16-page appendix with one figure; v2:
minor improvements and clarifications, conclusions unchanged (version to
appear in JCAP
Alternative inflationary scenario due to compact extra dimensions
The main goal of this paper is to give an alternative interpretation of
space-like and time-like extra dimensions as a primary factor for inflation in
the early universe. We introduce the 5-dimensional perfect fluid and compare
the energy-momentum tensor for the bulk scalar field with space-like and
time-like extra dimensions. It is shown, that additional dimensions can imply
to negative pressure in the slow roll regime in the early higher-dimensional
world.Comment: 6 page
Inflation and squeezed quantum states
The inflationary cosmology is analyzed from the point of view of squeezed
quantum states. As noted by Grishchuk and Sidorov, the amplification of quantum
fluctuations into macroscopic perturbations which occurs during cosmic
inflation is a process of quantum squeezing. We carefully develop the squeezed
state formalism and derive the equations that govern the evolution of a
gaussian initial state. We derive the power spectrum of density perturbations
for a simple inflationary model and discuss its features. We conclude that the
squeezed state formalism provides an interesting framework within which to
study the amplification process, but,in disagreement with the claims of
Grishchuk and Sidorov, that it does {\em not} provide us with any new physical
results.Comment: 33 pages, one section added, significant revisions, 6 figures (in
uuencoded file), Imperial/TP/92-93/2
Quantum Rolling Down out of Equilibrium
In a scalar field theory, when the tree level potential admits broken
symmetry ground states, the quantum corrections to the static effective
potential are complex. (The imaginary part is a consequence of an instability
towards phase separation and the static effective potential is not a relevant
quantity for understanding the dynamics). Instead, we study here the equations
of motion obtained from the one loop effective action for slow rollover out of
equilibrium.
We considering the case in which a scalar field theory undergoes a rapid
phase transition from to . We find that, for slow rollover
initial conditions (the field near the maximum of the tree level potential),
the process of phase separation controlled by unstable long-wavelength
fluctuations introduces dramatic corrections to the dynamical evolution of the
field. We find that these effects slow the rollover even furtherComment: 33 pages, Latex,LPTHE-PAR 92-33 PITT 92-0
Measures for a Transdimensional Multiverse
The multiverse/landscape paradigm that has emerged from eternal inflation and
string theory, describes a large-scale multiverse populated by "pocket
universes" which come in a huge variety of different types, including different
dimensionalities. In order to make predictions in the multiverse, we need a
probability measure. In landscapes, the scale factor cutoff measure
has been previously shown to have a number of attractive properties. Here we
consider possible generalizations of this measure to a transdimensional
multiverse. We find that a straightforward extension of scale factor cutoff to
the transdimensional case gives a measure that strongly disfavors large amounts
of slow-roll inflation and predicts low values for the density parameter
, in conflict with observations. A suitable generalization, which
retains all the good properties of the original measure, is the "volume factor"
cutoff, which regularizes the infinite spacetime volume using cutoff surfaces
of constant volume expansion factor.Comment: 30 pages, 1 figure Minor revisions, reference adde
Non-stationary rotating black holes: Entropy and Hawking's radiation
We derive a class of non-stationary embedded rotating black holes and study
the Hawking's radiation effects on these embedded black holes. The surface
gravity, entropy and angular velocity, which are three important properties of
black holes, are presented for each of these embedded black holes.Comment: 36 pages, LaTe
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