1,385 research outputs found
Self-Calibration of Cluster Dark Energy Studies: Observable-Mass Distribution
The exponential sensitivity of cluster number counts to the properties of the
dark energy implies a comparable sensitivity to not only the mean but also the
actual_distribution_ of an observable mass proxy given the true cluster mass.
For example a 25% scatter in mass can provide a ~50% change in the number
counts at z~2 for the upcoming SPT survey. Uncertainty in the scatter of this
amount would degrade dark energy constraints to uninteresting levels. Given the
shape of the actual mass function, the properties of the distribution may be
internally monitored by the shape of the_observable_ mass function. An
arbitrary evolution of the scatter of a mass-independent Gaussian distribution
may be self-calibrated to allow a measurement of the dark energy equation of
state of Delta w ~0.1. External constraints on the mass_variance_ of the
distribution that are more accurate than Delta var < 0.01 at z~1 can further
improve constraints by up to a factor of 2. More generally, cluster counts and
their sample variance measured as a function of the observable provide internal
consistency checks on the assumed form of the observable-mass distribution that
will protect against misinterpretation of the dark energy constraints.Comment: 6 pages, 6 figures, submitted to PR
A Testable Solution of the Cosmological Constant and Coincidence Problems
We present a new solution to the cosmological constant (CC) and coincidence
problems in which the observed value of the CC, , is linked to other
observable properties of the universe. This is achieved by promoting the CC
from a parameter which must to specified, to a field which can take many
possible values. The observed value of Lambda ~ 1/(9.3 Gyrs)^2\Lambda$-values
and does not rely on anthropic selection effects. Our model includes no
unnatural small parameters and does not require the introduction of new
dynamical scalar fields or modifications to general relativity, and it can be
tested by astronomical observations in the near future.Comment: 31 pages, 4 figures; v2: version accepted by Phys. Rev.
Particle-wave duality: a dichotomy between symmetry and asymmetry
Symmetry plays a central role in many areas of modern physics. Here we show
that it also underpins the dual particle and wave nature of quantum systems. We
begin by noting that a classical point particle breaks translational symmetry
whereas a wave with uniform amplitude does not. This provides a basis for
associating particle nature with asymmetry and wave nature with symmetry. We
derive expressions for the maximum amount of classical information we can have
about the symmetry and asymmetry of a quantum system with respect to an
arbitrary group. We find that the sum of the information about the symmetry
(wave nature) and the asymmetry (particle nature) is bounded by log(D) where D
is the dimension of the Hilbert space. The combination of multiple systems is
shown to exhibit greater symmetry and thus more wavelike character. In
particular, a class of entangled systems is shown to be capable of exhibiting
wave-like symmetry as a whole while exhibiting particle-like asymmetry
internally. We also show that superdense coding can be viewed as being
essentially an interference phenomenon involving wave-like symmetry with
respect to the group of Pauli operators.Comment: 20 pages, 3 figure
Parametrized post-Newtonian virial theorem
Using the parametrized post-Newtonian equations of hydrodynamics, we derive
the tensor form of the parametrized post-Newtonian virial theorem.Comment: 10 pages, submitted to CQ
Einstein static universes are unstable in generic f(R) models
We study Einstein static universes in the context of generic f(R) models. It
is shown that Einstein static solutions exist for a wide variety of modified
gravity models sourced by a barotropic perfect fluid with equation of state
w=p/rho, but these solutions are always unstable to either homogeneous or
inhomogeneous perturbations. Our general results are in agreement with specific
models investigated in that past. We also discuss how our techniques can be
applied to other scenarios in f(R) gravity.Comment: 7 pages, 2 figures. Minor corrections. Minor changes and references
added to match version accepted by Phys. Rev.
Born-Infeld type Gravity
Generalizations of gravitational Born-Infeld type lagrangians are
investigated. Phenomenological constraints (reduction to Einstein-Hilbert
action for small curvature, spin two ghost freedom and absence of Coulomb like
Schwarschild singularity) select one effective lagrangian whose dynamics is
dictated by the tensors g_{\mu\nu} and R_{\mu\nu\rho\sigma}(not R_{\mu\nu} or
the scalar R).Comment: 7 pages, 3 figures, revte
A Way to Dynamically Overcome the Cosmological Constant Problem
The Cosmological Constant problem can be solved once we require that the full
standard Einstein Hilbert lagrangian, gravity plus matter, is multiplied by a
total derivative. We analyze such a picture writing the total derivative as the
covariant gradient of a new vector field (b_mu). The dynamics of this b_mu
field can play a key role in the explanation of the present cosmological
acceleration of the Universe.Comment: 5 page
Numerical search for a fundamental theory
We propose a numerical test of fundamental physics based on the complexity
measure of a general set of functions, which is directly related to the
Kolmogorov (or algorithmic) complexity studied in mathematics and computer
science. The analysis can be carried out for any scientific experiment and
might lead to a better understanding of the underlying theory. From a
cosmological perspective, the anthropic description of fundamental constants
can be explicitly tested by our procedure. We perform a simple numerical search
by analyzing two fundamental constants: the weak coupling constant and the
Weinberg angle, and find that their values are rather atypical.Comment: 6 pages, 3 figures, RevTeX, expansion and clarification, references
adde
A tensor instability in the Eddington inspired Born-Infeld Theory of Gravity
In this paper we consider an extension to Eddington's proposal for the
gravitational action. We study tensor perturbations of a homogeneous and
isotropic space-time in the Eddington regime, where modifications to Einstein
gravity are strong. We find that the tensor mode is linearly unstable deep in
the Eddington regime and discuss its cosmological implications.Comment: 5 pages, approved by Phys. Rev. D, additional references and minor
modification
On the penetration of meridional circulation below the solar convection zone
Meridional flows with velocities of a few meters per second are observed in
the uppermost regions of the solar convection zone. The amplitude and pattern
of the flows deeper in the solar interior, in particular near the top of the
radiative region, are of crucial importance to a wide range of solar
magnetohydrodynamical processes. In this paper, we provide a systematic study
of the penetration of large-scale meridional flows from the convection zone
into the radiative zone. In particular, we study the effects of the assumed
boundary conditions applied at the convective-radiative interface on the deeper
flows. Using simplified analytical models in conjunction with more complete
numerical methods, we show that penetration of the convectively-driven
meridional flows into the deeper interior is not necessarily limited to a
shallow Ekman depth but can penetrate much deeper, depending on how the
convective-radiative interface flows are modeled.Comment: 13 pages, 5 figures. Subitted to Ap
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