41,261 research outputs found
Unveiling the Dynamics of the Universe
We explore the dynamics and evolution of the Universe at early and late
times, focusing on both dark energy and extended gravity models and their
astrophysical and cosmological consequences. Modified theories of gravity not
only provide an alternative explanation for the recent expansion history of the
universe, but they also offer a paradigm fundamentally distinct from the
simplest dark energy models of cosmic acceleration. In this review, we perform
a detailed theoretical and phenomenological analysis of different modified
gravity models and investigate their consistency. We also consider the
cosmological implications of well motivated physical models of the early
universe with a particular emphasis on inflation and topological defects.
Astrophysical and cosmological tests over a wide range of scales, from the
solar system to the observable horizon, severely restrict the allowed models of
the Universe. Here, we review several observational probes -- including
gravitational lensing, galaxy clusters, cosmic microwave background temperature
and polarization, supernova and baryon acoustic oscillations measurements --
and their relevance in constraining our cosmological description of the
Universe.Comment: 94 pages, 14 figures. Review paper accepted for publication in a
Special Issue of Symmetry. "Symmetry: Feature Papers 2016". V2: Matches
published version, now 79 pages (new format
Galaxy alignments: An overview
The alignments between galaxies, their underlying matter structures, and the
cosmic web constitute vital ingredients for a comprehensive understanding of
gravity, the nature of matter, and structure formation in the Universe. We
provide an overview on the state of the art in the study of these alignment
processes and their observational signatures, aimed at a non-specialist
audience. The development of the field over the past one hundred years is
briefly reviewed. We also discuss the impact of galaxy alignments on
measurements of weak gravitational lensing, and discuss avenues for making
theoretical and observational progress over the coming decade.Comment: 43 pages excl. references, 16 figures; minor changes to match version
published in Space Science Reviews; part of a topical volume on galaxy
alignments, with companion papers at arXiv:1504.05546 and arXiv:1504.0546
COrE (Cosmic Origins Explorer) A White Paper
COrE (Cosmic Origins Explorer) is a fourth-generation full-sky,
microwave-band satellite recently proposed to ESA within Cosmic Vision
2015-2025. COrE will provide maps of the microwave sky in polarization and
temperature in 15 frequency bands, ranging from 45 GHz to 795 GHz, with an
angular resolution ranging from 23 arcmin (45 GHz) and 1.3 arcmin (795 GHz) and
sensitivities roughly 10 to 30 times better than PLANCK (depending on the
frequency channel). The COrE mission will lead to breakthrough science in a
wide range of areas, ranging from primordial cosmology to galactic and
extragalactic science. COrE is designed to detect the primordial gravitational
waves generated during the epoch of cosmic inflation at more than
for . It will also measure the CMB gravitational lensing
deflection power spectrum to the cosmic variance limit on all linear scales,
allowing us to probe absolute neutrino masses better than laboratory
experiments and down to plausible values suggested by the neutrino oscillation
data. COrE will also search for primordial non-Gaussianity with significant
improvements over Planck in its ability to constrain the shape (and amplitude)
of non-Gaussianity. In the areas of galactic and extragalactic science, in its
highest frequency channels COrE will provide maps of the galactic polarized
dust emission allowing us to map the galactic magnetic field in areas of
diffuse emission not otherwise accessible to probe the initial conditions for
star formation. COrE will also map the galactic synchrotron emission thirty
times better than PLANCK. This White Paper reviews the COrE science program,
our simulations on foreground subtraction, and the proposed instrumental
configuration.Comment: 90 pages Latex 15 figures (revised 28 April 2011, references added,
minor errors corrected
Dark neutrino interactions make gravitational waves blue
New interactions of neutrinos can stop them from free streaming in the early
Universe even after the weak decoupling epoch. This results in the enhancement
of the primordial gravitational wave amplitude on small scales compared to the
standard CDM prediction. In this paper we calculate the effect of dark
matter neutrino interactions in CMB tensor -modes spectrum. We show that the
effect of new neutrino interactions generates a scale or dependent
imprint in the CMB -modes power spectrum at . In the event
that primordial -modes are detected by future experiments, a departure from
scale invariance, with a blue spectrum, may not necessarily mean failure of
simple inflationary models but instead may be a sign of non-standard
interactions of relativistic particles. New interactions of neutrinos also
induce a phase shift in the CMB B-mode power spectrum which cannot be mimicked
by simple modifications of the primordial tensor power spectrum. There is rich
information hidden in the CMB -modes spectrum beyond just the tensor to
scalar ratio.Comment: 31 pages, 10 figures. Version published in Phys. Rev.
Gamma-ray Line from Nambu-Goldstone Dark Matter in a Scale Invariant Extension of the Standard Model
A recently proposed scale invariant extension of the standard model is
modified such that it includes a Dark Matter candidate which can annihilate
into gamma-rays. For that a non-zero hypercharge is assigned to
the fermions in a QCD-like hidden sector. The Nambu-Goldstone bosons, that
arise due to dynamical chiral symmetry breaking in the hidden sector, are cold
Dark Matter candidates, and the extension allows them to annihilate into two
photons, producing a gamma-ray line spectrum. We find that the gamma-ray line
energy must be between 0.7 TeV and 0.9 TeV with the velocity-averaged
annihilation cross section cm^3/s for . With a
non-zero hypercharge , the hidden sector is no longer completely dark and
can be directly probed by collider experiments.Comment: 21 Pages, 8 Figures. Typos corrected, references added, the section
about the properties of the dark matter in our model is extended. Result and
conclusion unchanged. To appear in JHE
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