286 research outputs found
Large-k Limit of Multi-Point Propagators in the RG Formalism
Renormalized versions of cosmological perturbation theory have been very
successful in recent years in describing the evolution of structure formation
in the weakly non-linear regime. The concept of multi-point propagators has
been introduced as a tool to quantify the relation between the initial matter
distribution and the final one and to push the validity of the approaches to
smaller scales. We generalize the n-point propagators that have been considered
until now to include a new class of multi-point propagators that are relevant
in the framework of the renormalization group formalism. The large-k results
obtained for this general class of multi-point propagators match the results
obtained earlier both in the case of Gaussian and non-Gaussian initial
conditions. We discuss how the large-k results can be used to improve on the
accuracy of the calculations of the power spectrum and bispectrum in the
presence of initial non-Gaussianities.Comment: 30 page
Dark Energy Condensation
The two most popular candidates for dark energy, i.e. a cosmological constant
and quintessence, are very difficult to distinguish observationally, mostly
because the quintessence field does not have sizable fluctuations. We study a
scalar field model for dark energy in which the scalar field is invariant under
reflection symmetry, phi -> -phi. Under general assumptions, there is a phase
transition at late times (z < 0.5). Before the phase transition, the field
behaves as a cosmological constant. After the phase transition, a
time-dependent scalar condensate forms, the field couples with dark matter and
develops sizable perturbations tracking those of dark matter. The background
cosmological evolution is in agreement with existing observations, but might be
distinguished from that of a cosmological constant by future Supernovae
surveys. The growth of cosmological perturbations carries the imprint of the
phase transition, however a non-linear approach has to be developed in order to
study it quantitatively.Comment: 6 pages, 7 figures. References added. Discussion on the early
evolution of the field added. Matches the version to appear on PR
Non-linear Power Spectrum including Massive Neutrinos: the Time-RG Flow Approach
Future large scale structure observations are expected to be sensitive to
small neutrino masses, of the order of 0.05 eV or more. However, forecasts are
based on the assumption that by the time at which these datasets will be
available, the non-linear spectrum in presence of neutrino mass will be
predicted with an accuracy at least equal to the neutrino mass effect itself,
i.e. about 3%. Motivated by these considerations, we present the computation of
the non-linear power spectrum of LambdaCDM models in the presence of massive
neutrinos using the Renormalization Group time-flow approach, which amounts to
a resummation of perturbative corrections to the matter power spectrum to all
orders. We compare our results with those obtained with other methods, i.e.
linear theory, one-loop perturbation theory and N-body simulations and show
that the time-RG method improves the one-loop method in fitting the N-body
data, especially in determining the suppression of the matter power spectrum
when neutrino are massive with respect to the linear power spectrum.Comment: 8 pages, 11 figure
A Comment on the Path Integral Approach to Cosmological Perturbation Theory
It is pointed out that the exact renormalization group approach to
cosmological perturbation theory, proposed in Matarrese and Pietroni, JCAP 0706
(2007) 026, arXiv:astro-ph/0703563 and arXiv:astro-ph/0702653, constitutes a
misnomer. Rather, having instructively cast this classical problem into path
integral form, the evolution equation then derived comes about as a special
case of considering how the generating functional responds to variations of the
primordial power spectrum.Comment: 2 pages, v2: refs added, published in JCA
Dark Matter Relic Abundance and Scalar-Tensor Dark Energy
Scalar-tensor theories of gravity provide a consistent framework to
accommodate an ultra-light quintessence scalar field. While the equivalence
principle is respected by construction, deviations from General Relativity and
standard cosmology may show up at nucleosynthesis, CMB, and solar system tests
of gravity. After imposing all the bounds coming from these observations, we
consider the expansion rate of the universe at WIMP decoupling, showing that it
can lead to an enhancement of the dark matter relic density up to few orders of
magnitude with respect to the standard case. This effect can have an impact on
supersymmetric candidates for dark matter.Comment: 12 pages, 13 figures; V2: references added, matches published versio
Non-linear matter power spectrum from Time Renormalisation Group: efficient computation and comparison with one-loop
We address the issue of computing the non-linear matter power spectrum on
mildly non-linear scales with efficient semi-analytic methods. We implemented
M. Pietroni's Time Renormalization Group (TRG) method and its Dynamical 1-Loop
(D1L) limit in a numerical module for the new Boltzmann code CLASS. Our
publicly released module is valid for LCDM models, and optimized in such a way
to run in less than a minute for D1L, or in one hour (divided by number of
nodes) for TRG. A careful comparison of the D1L, TRG and Standard 1-Loop
approaches reveals that results depend crucially on the assumed initial
bispectrum at high redshift. When starting from a common assumption, the three
methods give roughly the same results, showing that the partial resumation of
diagrams beyond one loop in the TRG method improves one-loop results by a
negligible amount. A comparison with highly accurate simulations by M. Sato &
T. Matsubara shows that all three methods tend to over-predict non-linear
corrections by the same amount on small wavelengths. Percent precision is
achieved until k~0.2 h/Mpc for z>2, or until k~0.14 h/Mpc at z=1.Comment: 24 pages, 7 figures, revised title and conclusions, version accepted
in JCAP, code available at http://class-code.ne
Dynamical Relaxation of the Dark Matter to Baryon Ratio
A scalar field interacting differently with dark matter and baryons may
explain why their ratio is of order unity today. We provide three working
examples, checking them against the observations of CMB, Large Scale Structure,
supernovae Ia, and post-newtonian tests of gravity. Such a scenario could make
life much easier for supersymmetric dark matter candidates.Comment: 7 pages, 5 .eps figures. Discussion of the approach of the field to
the fixed point added. Figures modified accordingly. Conclusions unchanged.
Version to be published on Phys Rev.
Constraints on modified gravity from the BOSS galaxy survey
We develop a pipeline to set new constraints on scale-independent modified
gravity, from the galaxy power spectrum in redshift space of BOSS DR12. The
latter is modelled using the effective field theory of large-scale structure up
to 1-loop order in perturbation theory. We test our pipeline on synthetic and
simulated data, to assess systematic biases on the inferred cosmological
parameters due to marginalization and theoretical errors, and we apply it to
the normal branch of the DGP model with a CDM background. We observe
biased posteriors due to the strong degeneracy between the nDGP parameter
and the primordial amplitude of fluctuations . Fixing
the latter to the Planck central value, we obtain
at 95 C.L. We also discuss a procedure to alleviate the prior dependence of
this bound.Comment: 27 pages, 9 figure
On the Physical Significance of Infra-red Corrections to Inflationary Observables
Inflationary observables, like the power spectrum, computed at one- and
higher-order loop level seem to be plagued by large infra-red corrections. In
this short note, we point out that these large infra-red corrections appear
only in quantities which are not directly observable. This is in agreement with
general expectations concerning infra-red effects.Comment: 11 pages; LateX file; 5 figures. Some coefficients in Eq.(A6)
corrected; References adde
Hard Non-commutative Loops Resummation
The non-commutative version of the euclidean theory is
considered. By using Wilsonian flow equations the ultraviolet renormalizability
can be proved to all orders in perturbation theory. On the other hand, the
infrared sector cannot be treated perturbatively and requires a resummation of
the leading divergencies in the two-point function. This is analogous to what
is done in the Hard Thermal Loops resummation of finite temperature field
theory. Next-to-leading order corrections to the self-energy are computed,
resulting in contributions in the massless case, and
in the massive one.Comment: 4 pages, 3 figures. The resummation procedure is now discussed also
at finite ultraviolet cut-off. Minor changes in abstract and references.
Final version to be published in Physical Review Letter
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