541 research outputs found

### New multicritical matrix models and multicritical 2d CDT

We define multicritical CDT models of 2d quantum gravity and show that they
are a special case of multicritical generalized CDT models obtained from the
new scaling limit, the so-called "classical" scaling limit, of matrix models.
The multicritical behavior agrees with the multicritical behavior of the
so-called branched polymers.Comment: 16 pages, 4 figures. References adde

### Lorentzian and Euclidean Quantum Gravity - Analytical and Numerical Results

We review some recent attempts to extract information about the nature of
quantum gravity, with and without matter, by quantum field theoretical methods.
More specifically, we work within a covariant lattice approach where the
individual space-time geometries are constructed from fundamental simplicial
building blocks, and the path integral over geometries is approximated by
summing over a class of piece-wise linear geometries. This method of
``dynamical triangulations'' is very powerful in 2d, where the regularized
theory can be solved explicitly, and gives us more insights into the quantum
nature of 2d space-time than continuum methods are presently able to provide.
It also allows us to establish an explicit relation between the Lorentzian- and
Euclidean-signature quantum theories. Analogous regularized gravitational
models can be set up in higher dimensions. Some analytic tools exist to study
their state sums, but, unlike in 2d, no complete analytic solutions have yet
been constructed. However, a great advantage of our approach is the fact that
it is well-suited for numerical simulations. In the second part of this review
we describe the relevant Monte Carlo techniques, as well as some of the
physical results that have been obtained from the simulations of Euclidean
gravity. We also explain why the Lorentzian version of dynamical triangulations
is a promising candidate for a non-perturbative theory of quantum gravity.Comment: 69 pages, 16 figures, references adde

### Center Disorder in the 3D Georgi-Glashow Model

We present a number of arguments relating magnetic disorder to center
disorder, in pure Yang-Mills theory in D=3 and D=4 dimensions. In the case of
the D=3 Georgi-Glashow model, we point out that the abelian field distribution
is not adequatedly represented, at very large scales, by that of a monopole
Coulomb gas. The onset of center disorder is associated with the breakdown of
the Coulomb gas approximation; this scale is pushed off to infinity in the
QED_3 limit of the 3D Georgi-Glashow model, but should approach the
color-screening length in the pure Yang-Mills limit.Comment: 22 pages including 3 figures, Latex2

### Scaling with a modified Wilson action which suppresses Z_2 artifacts in SU(2) lattice gauge theories

A modified Wilson action which suppresses plaquettes which take negative
values is used to study the scaling behavior of the string tension. The use of
the \b_E scheme gives good agreement with asymptotic two loop results.Comment: Latex (ps figure appended in the end), 7 page

### A model for emergence of space and time

We study string field theory (third quantization) of the two-dimensional
model of quantum geometry called generalized CDT ("causal dynamical
triangulations"). Like in standard non-critical string theory the so-called
string field Hamiltonian of generalized CDT can be associated with W-algebra
generators through the string mode expansion. This allows us to define an
"absolute" vacuum. "Physical" vacua appear as coherent states created by vertex
operators acting on the absolute vacuum. Each coherent state corresponds to
specific values of the coupling constants of generalized CDT. The cosmological
"time" only exists relatively to a given "physical" vacuum and comes into
existence before space, which is created because the "physical" vacuum is
unstable. Thus each CDT "universe" is created as a "Big Bang" from the absolute
vacuum, its time evolution is governed by the CDT string field Hamiltonian with
given coupling constants, and one can imagine interactions between CDT
universes with different coupling constants ("fourth quantization"

### Scattering amplitudes of regularized bosonic strings

We compute scattering amplitudes of the regularized bosonic Nambu-Goto string
in the mean-field approximation, disregarding fluctuations of the Lagrange
multiplier and an independent metric about their mean values. We use the
previously introduced Lilliputian scaling limit to recover the Regge behavior
of the amplitudes with the usual linear Regge trajectory in space-time
dimensions d>2. We demonstrate a stability of this minimum of the effective
action under fluctuations for d<26.Comment: 11 pages, v2: typos corrected, to appear in PR

### Non-critical string field theory for 2d quantum gravity coupled to (p,q)--conformal fields

We propose a non-critical string field theory for $2d$ quantum gravity
coupled to ($p$,$q$) conformal fields. The Hamiltonian is described by the
generators of the $W_p$ algebra, and the Schwinger-Dyson equation is equivalent
to a vacuum condition imposed on the generators of $W_p$ algebra.Comment: LaTeX, 30 pages, 6 figure

### A modified Friedmann equation

We recently formulated a model of the universe based on an underlying
W3-symmetry. It allows the creation of the universe from nothing and the
creation of baby universes and wormholes for spacetimes of dimension 2, 3, 4, 6
and 10. Here we show that the classical large time and large space limit of
these universes is one of exponential fast expansion without the need of a
cosmological constant. Under a number of simplifying assumptions our model
predicts that w=-1.2 in the case of four-dimensional spacetime. The possibility
of obtaining a w-value less than -1 is linked to the ability of our model to
create baby universes and wormholes.Comment: Clarifying comment on page

### Creating 3, 4, 6 and 10-dimensional spacetime from W3 symmetry

We describe a model where breaking of W3 symmetry will lead to the emergence
of time and subsequently of space. Surprisingly the simplest such models which
lead to higher dimensional spacetimes are based on the four "magical" Jordan
algebras of 3x3 Hermitian matrices with real, complex, quaternion and octonion
entries, respectively. The simplest symmetry breaking leads to universes with
spacetime dimensions 3, 4, 6, and 10

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