719 research outputs found
Quantum Criticality and Yang-Mills Gauge Theory
We present a family of nonrelativistic Yang-Mills gauge theories in D+1
dimensions whose free-field limit exhibits quantum critical behavior with
gapless excitations and dynamical critical exponent z=2. The ground state
wavefunction is intimately related to the partition function of relativistic
Yang-Mills in D dimensions. The gauge couplings exhibit logarithmic scaling and
asymptotic freedom in the upper critical spacetime dimension, equal to 4+1. The
theories can be deformed in the infrared by a relevant operator that restores
Poincare invariance as an accidental symmetry. In the large-N limit, our
nonrelativistic gauge theories can be expected to have weakly curved gravity
duals.Comment: 10 page
Casimir Effect Between World-Branes in Heterotic M-Theory
We study a non-supersymmetric compactification of
M-theory on , related to the supersymmetric theory by
a chirality flip at one of the boundaries. This system represents an M-theory
analog of the D-brane anti-D-brane systems of string theory. Alternatively,
this compactification can be viewed as a model of supersymmetry breaking in the
``brane-world'' approach to phenomenology. We calculate the Casimir energy of
the system at large separations, and show that there is an attractive Casimir
force between the and boundary. We predict that a tachyonic
instability develops at separations of order the Planck scale, and discuss the
possibility that the M-theory fivebrane might appear as a topological defect
supported by the system. Finally, we analyze the eventual
fate of the configuration, in the semiclassical approximation at large
separations: the two ends of the world annihilate by nucleating wormholes
between the two boundaries.Comment: 26 pp, 3 figures, harvmac (b); v2: typos correcte
Eleven-Dimensional Supergravity on a Manifold with Boundary
In this paper, we present a systematic analysis of eleven-dimensional
supergravity on a manifold with boundary, which is believed to be relevant to
the strong coupling limit of the heterotic string. Gauge and
gravitational anomalies enter at a very early stage, and require a refinement
of the standard Green-Schwarz mechanism for their cancellation. This uniquely
determines the gauge group to be a copy of for each boundary component,
fixes the gauge coupling constant in terms of the gravitational constant, and
leads to several striking new tests of the hypothesis that there is a
consistent quantum -theory with eleven-dimensional supergravity as its low
energy limit.Comment: 28 pages, no figures; harvma
A Worldsheet Description of Large N_c Quantum Field Theory
The N_c to infinity limit of a matrix quantum field theory is equivalent to
summing only planar Feynman diagrams. The possibility of interpreting this sum
as some kind world-sheet theory has been in the air ever since 't Hooft's
original paper. We establish here just such a world sheet description for a
scalar quantum field with interaction term g\Tr\phi^3, and we indicate how the
approach might be extended to more general field theories.Comment: 16 pages, 3 figures, latex, typos corrected, references added,
interpretation of ghost determinant clarifie
Hidden Lorentz symmetry of the HoĆavaâLifshitz gravity
In this Letter it is shown that the HoĆavaâLifshitz gravity theory admits Lorentz symmetry preserving preferred global time foliation of the spacetime
On the motion of particles in covariant Horava-Lifshitz gravity and the meaning of the A-field
We studied the low energy motion of particles in the general covariant
version of Horava-Lifshitz gravity proposed by Horava and Melby-Thompson. Using
a scalar field coupled to gravity according to the minimal substitution recipe
proposed by da Silva and taking the geometrical optics limit, we could write an
effective relativistic metric for a general solution. As a result, we
discovered that the equivalence principle is not in general recovered at low
energies, unless the spatial Laplacian of A vanishes. Finally, we analyzed the
motion on the spherical symmetric solution proposed by Horava and
Melby-Thompson, where we could find its effective line element and compute
spin-0 geodesics. Using standard methods we have shown that such an effective
metric cannot reproduce Newton's gravity law even in the weak gravitational
field approximation.Comment: New result about equivalence principle added, improved discussion and
typos corrected. Version to appear in Phys. Lett.
Deconstructing de Sitter
Semiclassical gravity predicts that de Sitter space has a finite entropy. We suggest a picture for Euclidean de Sitter space in string theory, and use the AdS/CFT correspondence to argue that de Sitter entropy can be understood as the number of degrees of freedom in a quantum mechanical dual
Non-conventional cosmology from a brane-universe
We consider ``brane-universes'', where matter is confined to four-dimensional
hypersurfaces (three-branes) whereas one extra compact dimension is felt by
gravity only. We show that the cosmology of such branes is definitely different
from standard cosmology and identify the reasons behind this difference. We
give a new class of exact solutions with a constant five-dimensional radius and
cosmologically evolving brane. We discuss various consequences.Comment: 22 pages, Latex; minor addition
Designing Cyclic Universe Models
Recent advances in understanding the propagation of perturbations through the
transition from big crunch to big bang (esp. Tolley et al. hep-th/0306109) make
it possible for the first time to consider the full set of phenomenological
constraints on the scalar field potential in cyclic models of the universe. We
show that cyclic models require a comparable degree of tuning to that needed
for inflationary models. The constraints are reduced to a set of simple design
rules including "fast-roll" parameters analogous to the "slow-roll" parameters
in inflation.Comment: 4 pages, 2 figures. Minor typos and figure correcte
Universal description of viscoelasticity with foliation preserving diffeomorphisms
A universal description is proposed for generic viscoelastic systems with a
single relaxation time. Foliation preserving diffeomorphisms are introduced as
an underlying symmetry which naturally interpolates between the two extreme
limits of elasticity and fluidity. The symmetry is found to be powerful enough
to determine the dynamics in the first order of strains.Comment: 12 pages, 6 figures, v2:minor changes, v3:clarification adde
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