2,938 research outputs found
A Curvature Principle for the interaction between universes
We propose a Curvature Principle to describe the dynamics of interacting
universes in a multi-universe scenario and show, in the context of a simplified
model, how interaction drives the cosmological constant of one of the universes
toward a vanishingly small value. We also conjecture on how the proposed
Curvature Principle suggests a solution for the entropy paradox of a universe
where the cosmological constant vanishes.Comment: Essay selected for an honorable mention by the Gravity Research
Foundation, 2007. Plain latex, 8 page
String Theory and Cosmology
We discuss the main cosmological implications of considering string-loop
effects and a potential for the dilaton in the lowest order string effective
action. Our framework is based on the effective model arising from regarding
homogeneous and isotropic dilaton, metric and Yang-Mills field configurations.
The issues of inflation, entropy crisis and the Polonyi problem as well as the
problem of the cosmological constant are discussed.Comment: 7 pages, plain Tex, no figure
Generalized Chaplygin Gas Model: Dark Energy - Dark Matter Unification and CMBR Constraints
The generalized Chaplygin gas (GCG) model allows for an unified description
of the recent accelerated expansion of the Universe and the evolution of energy
density perturbations. This dark energy - dark matter unification is achieved
through an exotic background fluid whose equation of state is given by , where is a positive constant and .
Stringent constraints on the model parameters can be obtained from recent WMAP
and BOOMERanG bounds on the locations of the first few peaks and troughs of the
Cosmic Microwave Background Radiation (CMBR) power spectrum as well as SNe Ia
data.Comment: 9 pages, 2 figures; essay selected for an honorable mention by the
Gravity Research Foundation, 200
Adaptive Cluster Expansion for Inferring Boltzmann Machines with Noisy Data
We introduce a procedure to infer the interactions among a set of binary
variables, based on their sampled frequencies and pairwise correlations. The
algorithm builds the clusters of variables contributing most to the entropy of
the inferred Ising model, and rejects the small contributions due to the
sampling noise. Our procedure successfully recovers benchmark Ising models even
at criticality and in the low temperature phase, and is applied to
neurobiological data.Comment: Accepted for publication in Physical Review Letters (2011
Proximal operators for multi-agent path planning
We address the problem of planning collision-free paths for multiple agents
using optimization methods known as proximal algorithms. Recently this approach
was explored in Bento et al. 2013, which demonstrated its ease of
parallelization and decentralization, the speed with which the algorithms
generate good quality solutions, and its ability to incorporate different
proximal operators, each ensuring that paths satisfy a desired property.
Unfortunately, the operators derived only apply to paths in 2D and require that
any intermediate waypoints we might want agents to follow be preassigned to
specific agents, limiting their range of applicability. In this paper we
resolve these limitations. We introduce new operators to deal with agents
moving in arbitrary dimensions that are faster to compute than their 2D
predecessors and we introduce landmarks, space-time positions that are
automatically assigned to the set of agents under different optimality
criteria. Finally, we report the performance of the new operators in several
numerical experiments.Comment: See movie at http://youtu.be/gRnsjd_ocx
Role of Modified Chaplygin Gas as a Dark Energy Model in Collapsing Spherically Symmetric Cloud
In this work, gravitational collapse of a spherical cloud, consists of both
dark matter and dark energy in the form of modified Chaplygin gas is studied.
It is found that dark energy alone in the form of modified Chaplygin gas forms
black hole. Also when both components of the fluid are present then the
collapse favors the formation of black hole in cases the dark energy dominates
over dark matter. The conclusion is totally opposite to the usually known
results.Comment: 7 Latex Pages, RexTex style, No figure
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