36 research outputs found
Physics, Astrophysics and Cosmology with Gravitational Waves
Gravitational wave detectors are already operating at interesting sensitivity
levels, and they have an upgrade path that should result in secure detections
by 2014. We review the physics of gravitational waves, how they interact with
detectors (bars and interferometers), and how these detectors operate. We study
the most likely sources of gravitational waves and review the data analysis
methods that are used to extract their signals from detector noise. Then we
consider the consequences of gravitational wave detections and observations for
physics, astrophysics, and cosmology.Comment: 137 pages, 16 figures, Published version
<http://www.livingreviews.org/lrr-2009-2
f(R) theories
Over the past decade, f(R) theories have been extensively studied as one of
the simplest modifications to General Relativity. In this article we review
various applications of f(R) theories to cosmology and gravity - such as
inflation, dark energy, local gravity constraints, cosmological perturbations,
and spherically symmetric solutions in weak and strong gravitational
backgrounds. We present a number of ways to distinguish those theories from
General Relativity observationally and experimentally. We also discuss the
extension to other modified gravity theories such as Brans-Dicke theory and
Gauss-Bonnet gravity, and address models that can satisfy both cosmological and
local gravity constraints.Comment: 156 pages, 14 figures, Invited review article in Living Reviews in
Relativity, Published version, Comments are welcom
Late time behaviors of the expanding universe in the IIB matrix model
Recently we have studied the Lorentzian version of the IIB matrix model as a
nonperturbative formulation of superstring theory. By Monte Carlo simulation,
we have shown that the notion of time ---as well as space---emerges dynamically
from this model, and that we can uniquely extract the real-time dynamics, which
turned out to be rather surprising: after some "critical time", the SO(9)
rotational symmetry of the nine-dimensional space is spontaneously broken down
to SO(3) and the three-dimensional space starts to expand rapidly. In this
paper, we study the same model based on the classical equations of motion,
which are expected to be valid at later times. After providing a general
prescription to solve the equations, we examine a class of solutions, which
correspond to manifestly commutative space. In particular, we find a solution
with an expanding behavior that naturally solves the cosmological constant
problem.Comment: 25 pages, 3 figure
Giant Graviton Oscillators
We study the action of the dilatation operator on restricted Schur
polynomials labeled by Young diagrams with p long columns or p long rows. A new
version of Schur-Weyl duality provides a powerful approach to the computation
and manipulation of the symmetric group operators appearing in the restricted
Schur polynomials. Using this new technology, we are able to evaluate the
action of the one loop dilatation operator. The result has a direct and natural
connection to the Gauss Law constraint for branes with a compact world volume.
We find considerable evidence that the dilatation operator reduces to a
decoupled set of harmonic oscillators. This strongly suggests that
integrability in N=4 super Yang-Mills theory is not just a feature of the
planar limit, but extends to other large N but non-planar limits.Comment: 72 page
Varying constants, Gravitation and Cosmology
Fundamental constants are a cornerstone of our physical laws. Any constant
varying in space and/or time would reflect the existence of an almost massless
field that couples to matter. This will induce a violation of the universality
of free fall. It is thus of utmost importance for our understanding of gravity
and of the domain of validity of general relativity to test for their
constancy. We thus detail the relations between the constants, the tests of the
local position invariance and of the universality of free fall. We then review
the main experimental and observational constraints that have been obtained
from atomic clocks, the Oklo phenomenon, Solar system observations, meteorites
dating, quasar absorption spectra, stellar physics, pulsar timing, the cosmic
microwave background and big bang nucleosynthesis. At each step we describe the
basics of each system, its dependence with respect to the constants, the known
systematic effects and the most recent constraints that have been obtained. We
then describe the main theoretical frameworks in which the low-energy constants
may actually be varying and we focus on the unification mechanisms and the
relations between the variation of different constants. To finish, we discuss
the more speculative possibility of understanding their numerical values and
the apparent fine-tuning that they confront us with.Comment: 145 pages, 10 figures, Review for Living Reviews in Relativit