91 research outputs found
On systematic and GR effects on muon experiments
We derive in full generality the equations that govern the time dependence of
the energy of the decay electrons in a muon experiment. We
include both electromagnetic and gravitational effects and we estimate possible
systematics on the measurements of , whose experimental
uncertainty will soon reach . In addition to the
standard modulation of when the motion is orthogonal to a
constant magnetic field , with angular frequency , we
study effects due to: (1) a non constant muon factor, in presence of
electric fields , (2) a correction due to a component of the muon velocity
along (the `pitch correction'), (3) corrections to the precession rate due
to fields, (4) non-trivial spacetime metrics. Oscillations along the radial
and vertical directions of the muon lead to oscillations in with
a relative size of order , for the BNL experiment. We then find
a subleading effect in the `pitch' correction, leading to a frequency shift of
and subleading effects of
about due to fields. Finally we show that GR effects are
dominated by the Coriolis force, due to the Earth rotation with angular
frequency , leading to a correction of about . A similar correction might be more appreciable for future
electron experiments, being of order ,
compared to the present experimental uncertainty, , and forecasted to reach soon .Comment: 37 pages, 6 figure
Disantangling the effects of Doppler velocity and primordial non-Gaussianity in galaxy power spectra
We study the detectability of large-scale velocity effects on galaxy
clustering, by simulating galaxy surveys and combining the clustering of
different types of tracers of large-scale structure. We employ a set of
lognormal mocks that simulate a deg near-complete survey up to
, in which each galaxy mock traces the spatial distribution of dark
matter of that mock with a realistic bias prescription. We find that the ratios
of the monopoles of the power spectra of different types of tracers carry most
of the information that can be extracted from a multi-tracer analysis. In
particular, we show that with a multi-tracer technique it will be possible to
detect velocity effects with . Finally, we investigate the
degeneracy of these effects with the (local) non-Gaussianity parameter , and how large-scale velocity contributions could be mistaken for the
signatures of primordial non-Gaussianity.Comment: 17 pages, 25 figure
Gravitational potential evolution in Unified Dark Matter Scalar Field Cosmologies: an analytical approach
We investigate the time evolution of the gravitational potential Phi for a
special class of non-adiabatic Unified Dark matter Models described by scalar
field lagrangians. These models predict the same background evolution as in the
LambdaCDM and possess a non-vanishing speed of sound. We provide a very
accurate approximation of Phi, valid after the recombination epoch, in the form
of a Bessel function of the first kind. This approximation may be useful for a
future deeper analysis of Unified Dark Matter scalar field models.Comment: 5 pages, 6 figure
Generalisation of the Kaiser Rocket effect in general relativity in the wide-angle galaxy 2-point correlation function
We study wide-angle correlations in the galaxy power spectrum in redshift
space, including all general relativistic effects and the Kaiser Rocket effect
in general relativity. We find that the Kaiser Rocket effect becomes important
on large scales and at high redshifts, and leads to new contributions in
wide-angle correlations. We believe this effect might be very important for
future large volume surveys.Comment: 24 pages, 12 figures. Matches published versio
Degeneracy between primordial non-Gaussianity and interaction in the dark sector
If dark energy and dark matter interact via exchange of energy and momentum, then this may affect the galaxy power spectrum on large scales. When this happens, it may be degenerate with the signal from primordial non-Gaussianity via a scale-dependent bias. We consider a class of interacting dark energy models and show that the matter overdensity is scale dependent on large scales. We estimate the effective non-Gaussianity arising from the large-scale effects of interaction in the dark sector. The signal of dark sector interaction can be disentangled from a primordial non-Gaussian signal by measuring the power at two redshifts
Does Quartessence Ease Tensions?
Tensions between cosmic microwave background observations and the growth of
the large-scale structure inferred from late-time probes pose a serious
challenge to the concordance CDM cosmological model. State-of-the-art
data from the Planck satellite predicts a higher rate of structure growth than
what preferred by low-redshift observables. Such tension has hitherto eluded
conclusive explanations in terms of straightforward modifications to
CDM, e.g. the inclusion of massive neutrinos or a dynamical dark
energy component. Here, we investigate models of 'quartessence' -- a single
dark component mimicking both dark matter and dark energy -- whose
non-vanishing sound speed inhibits structure growth at late times on scales
smaller than its corresponding Jeans' length. In principle, this could
reconcile high- and low-redshift observations. We put this hypothesis to test
against temperature and polarisation spectra from the latest Planck release,
SDSS DR12 measurements of baryon acoustic oscillations and redshift-space
distortions, and cosmic shear correlation functions from KiDS. This the first
time that any specific model of quartessence is applied to actual data. We show
that, if we naively apply CDM nonlinear prescription to quartessence,
the combined data sets allow for tight constraints on the model parameters.
Apparently, quartessence alleviates the tension between the total matter
fraction and late-time structure clustering, although in fact the tension is
transferred from the latter to the quartessence sound speed parameter. However,
we found that this strongly depends upon information from nonlinear scales.
Indeed, if we relax this assumption, quartessence models appear still viable.
For this reason, we argue that the nonlinear behaviour of quartessence deserves
further investigation and may lead to a deeper understanding of the physics of
the dark Universe.Comment: 8 pages, 6 figures, 1 table; matching published versio
Unified Dark Matter Scalar Field Models
In this work we analyze and review cosmological models in which the dynamics
of a single scalar field accounts for a unified description of the Dark Matter
and Dark Energy sectors, dubbed Unified Dark Matter (UDM) models. In this
framework, we consider the general Lagrangian of k-essence, which allows to
find solutions around which the scalar field describes the desired mixture of
Dark Matter and Dark Energy. We also discuss static and spherically symmetric
solutions of Einstein's equations for a scalar field with non-canonical kinetic
term, in connection with galactic halo rotation curves.Comment: 57 pages, 6 figures, LaTeX file. Typos corrected; Added References;
Revised according to reviewer's suggestions; Invited Review for the special
issue "Focus Issue on Dark Matter" for Advances in Astronom
How the Scalar Field of Unified Dark Matter Models Can Cluster
We use scalar-field Lagrangians with a non-canonical kinetic term to obtain
unified dark matter models where both the dark matter and the dark energy, the
latter mimicking a cosmological constant, are described by the scalar field
itself. In this framework, we propose a technique to reconstruct models where
the effective speed of sound is small enough that the scalar field can cluster.
These models avoid the strong time evolution of the gravitational potential and
the large Integrated Sachs-Wolfe effect which have been a serious drawback of
previously considered models. Moreover, these unified dark matter scalar field
models can be easily generalized to behave as dark matter plus a dark energy
component behaving like any type of quintessence fluid.Comment: 26 pages, 1 figur
Unified Dark Matter scalar field models with fast transition
We investigate the general properties of Unified Dark Matter (UDM) scalar
field models with Lagrangians with a non-canonical kinetic term, looking
specifically for models that can produce a fast transition between an early
Einstein-de Sitter CDM-like era and a later Dark Energy like phase, similarly
to the barotropic fluid UDM models in JCAP1001(2010)014. However, while the
background evolution can be very similar in the two cases, the perturbations
are naturally adiabatic in fluid models, while in the scalar field case they
are necessarily non-adiabatic. The new approach to building UDM Lagrangians
proposed here allows to escape the common problem of the fine-tuning of the
parameters which plague many UDM models. We analyse the properties of
perturbations in our model, focusing on the the evolution of the effective
speed of sound and that of the Jeans length. With this insight, we can set
theoretical constraints on the parameters of the model, predicting sufficient
conditions for the model to be viable. An interesting feature of our models is
that what can be interpreted as w_{DE} can be <-1 without violating the null
energy conditions.Comment: Slightly revised version accepted for publication in JCAP, with a few
added references; 27 pages, 13 figure
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