97 research outputs found
Structure formation in Multiple Dark Matter cosmologies with long-range scalar interactions
(Abridged) An interaction between Cold Dark Matter (CDM) and a classical
scalar field playing the role of the cosmic dark energy (DE) might provide
long-range dark interactions without conflicting with solar system bounds.
Although presently available observations allow to constrain such interactions
to a few percent of the gravitational strength, some recent studies have shown
that if CDM is composed by two different particle species having opposite
couplings to the DE field, such tight constraints can be considerably relaxed,
allowing for long-range scalar forces of order gravity without significantly
affecting observations both at the background and at the linear perturbations
level. In the present work, we extend the investigation of such Multiple Dark
Matter scenarios to the nonlinear regime of structure formation, by presenting
the first N-body simulations ever performed for these cosmologies. Our results
highlight some characteristic footprints of long-range scalar forces that arise
only in the nonlinear regime for specific models that would be otherwise
practically indistinguishable from the standard LCDM scenario both in the
background and in the growth of linear density perturbations. Among these
effects, the formation of "mirror" cosmic structures in the two CDM species,
the suppression of the nonlinear matter power spectrum at k > 1 h/Mpc, and the
fragmentation of collapsed halos, represent peculiar features that might
provide a direct way to constrain this class of cosmological models.Comment: 11 pages, 4 figures. Submitted to MNRA
Soft Supersymmetry Breaking from Gaugino Condensation
We study the structure of soft breaking terms in the context of a gaugino
condensation scenario. Assuming that the Supergravity Lagrangian is the correct
quantum field theory limit, at some momentum scale , of a more
fundamental one, we demonstrate that the correct result is obtained simply by
substituting, in the tree level Supergravity Lagrangian, (the
gaugino condensate) by its vacuum expectation value . In string
inspired scenarios this implies, in particular, that the scalar masses are
vanishing at the string tree-level and receive a contribution, at the one loop
level, which is proportional to the Green Schwarz coefficient .
Our results do not agree with the ones obtained in the effective Lagrangian
approach. We study in detail the origin of this discrepancy, and we argue that
the use of the supertrace anomaly to determine the effective theory for the
condensate does not fix its gravitational interactions, leaving the soft
breaking terms and the vacua of the theory unspecified.Comment: Latex, 18 pages, 4 postcript figures appended at the end (they can be
inserted in the text using the macro epsf.tex), OUTP-94-16
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
Modified Gravity and Cosmology
In this review we present a thoroughly comprehensive survey of recent work on
modified theories of gravity and their cosmological consequences. Amongst other
things, we cover General Relativity, Scalar-Tensor, Einstein-Aether, and
Bimetric theories, as well as TeVeS, f(R), general higher-order theories,
Horava-Lifschitz gravity, Galileons, Ghost Condensates, and models of extra
dimensions including Kaluza-Klein, Randall-Sundrum, DGP, and higher
co-dimension braneworlds. We also review attempts to construct a Parameterised
Post-Friedmannian formalism, that can be used to constrain deviations from
General Relativity in cosmology, and that is suitable for comparison with data
on the largest scales. These subjects have been intensively studied over the
past decade, largely motivated by rapid progress in the field of observational
cosmology that now allows, for the first time, precision tests of fundamental
physics on the scale of the observable Universe. The purpose of this review is
to provide a reference tool for researchers and students in cosmology and
gravitational physics, as well as a self-contained, comprehensive and
up-to-date introduction to the subject as a whole.Comment: 312 pages, 15 figure
Effective gravitational couplings for cosmological perturbations in the most general scalar-tensor theories with second-order field equations
In the Horndeski's most general scalar-tensor theories the equations of
scalar density perturbations are derived in the presence of non-relativistic
matter minimally coupled to gravity. Under a quasi-static approximation on
sub-horizon scales we obtain the effective gravitational coupling
associated with the growth rate of matter perturbations as well as the
effective gravitational potential relevant to the deviation of
light rays. We then apply our formulas to a number of modified gravitational
models of dark energy--such as those based on f(R) theories, Brans-Dicke
theories, kinetic gravity braidings, covariant Galileons, and field derivative
couplings with the Einstein tensor. Our results are useful to test the
large-distance modification of gravity from the future high-precision
observations of large-scale structure, weak lensing, and cosmic microwave
background.Comment: 12 pages, no figure
Neutrinos
229 pages229 pages229 pagesThe Proceedings of the 2011 workshop on Fundamental Physics at the Intensity Frontier. Science opportunities at the intensity frontier are identified and described in the areas of heavy quarks, charged leptons, neutrinos, proton decay, new light weakly-coupled particles, and nucleons, nuclei, and atoms
- …