5 research outputs found
The Effective Field Theory of Large Scale Structures of a Fuzzy Dark Matter Universe
Ultra-light scalar fields and their non-interacting class, the so-called
fuzzy dark matter (FDM), are candidates for dark matter, introduced to solve
the small-scale problems of the standard cold dark matter. In this paper, we
address whether the small-scale effects, specifically the quantum pressure,
could leave sizable imprints on the large-scale statistics of the matter. For
this purpose, We utilize the Effective Field Theory of Large Scale Structures
(EFT of LSS) wherein small-scale physics is integrated and represented on large
scales by only a set of free parameters. These parameters can be determined by
fitting to the cosmological simulations. We use the \textit{Gadget-2} code to
study the evolution of particles in a box of side length
. Fitting EFT predictions to the simulation data, we
determine the value of the speed of sound. We use the suppressed FDM initial
conditions for the FDM case, sufficient to produce accurate -- enough for our
purpose -- results on large scales. We perform three FDM simulations with
different masses and compare their sound speed with the standard cold dark
matter (CDM) simulation. We found that the FDM sound speed is slightly higher
than CDM's. The deviation of the sound speed for FDM from CDM is larger for
lower FDM masses. We conclude that the impact of the FDM is not limited to the
small scales alone, and we can search for them by studying the matter on large
scales. Though it is beyond the observations' scope today, it is possible to
discriminate it with upcoming observations.Comment: 15 pages, 6 figures and 1 tabl
Rare Events Are Nonperturbative: Primordial Black Holes From Heavy-Tailed Distributions
In recent years it has been noted that the perturbative treatment of the
statistics of fluctuations may fail to make correct predictions for the
abundance of primordial black holes (PBHs). Moreover, it has been shown in some
explicit single-field examples that the nonperturbative effects may lead to an
exponential tail for the probability distribution function (PDF) of
fluctuations responsible for PBH formation -- in contrast to the PDF being
Gaussian, as suggested by perturbation theory. In this paper, we advocate that
the so-called formalism can be considered as a simple, yet
effective, tool for the nonperturbative estimate of the tail of the PDF. We
discuss the criteria a model needs to satisfy so that the results of the
classical formalism can be trusted and most possible complications
due to the quantum nature of fluctuations can be avoided. As a proof of
concept, we then apply this method to a simple example and show that the tail
of the PDF can be even {\it heavier} than exponential, leading to a significant
enhancement of the PBH formation probability, compared with the predictions of
the perturbation theory. Our results, along with other related findings,
motivate the invention of new, nonperturbative methods for the problem and open
up new ideas on generating PBHs with notable abundance.Comment: 7 pages, 3 figures, 1 table, V2: matches the published versio
Tail diversity from inflation
The tail of the distribution of primordial fluctuations (corresponding to the
likelihood of realization of large fluctuations) is of interest, from both
theoretical and observational perspectives. In particular, it is relevant for
the accurate evaluation of the primordial black hole (PBH) abundance. In this
paper, we first analyze the non-perturbative formalism as a method
to non-perturbatively estimate the probability distribution function (PDF) of
primordial fluctuations, discuss its underlying assumptions and deal with
several subtleties that may arise as a result of considering large
fluctuations. Next, we employ the method to study several non-attractor
single-field inflationary models as the simplest examples that may lead to the
abundant production of PBHs. We conclude that the Gaussian extrapolation from
linear perturbation theory may fail drastically to predict the likelihood of
large fluctuations. Specifically, we show that a truncation of the tail, a
power-law tail, a double-exponential tail, and a doubly peaked distribution can
all be realized for the curvature perturbation in the single-field
non-attractor models of inflation. We thus show that there is a diverse zoo of
possible tails from inflation so that a model-dependent, non-perturbative study
of the distribution of the primordial fluctuations seems inevitable concerning
PBH abundance.Comment: 25 pages, 12 figures, 3 table
The Effective Field Theory of Large-scale Structures of a Fuzzy Dark Matter Universe
Ultralight scalar fields and their noninteracting class, i.e., the so-called fuzzy dark matter (FDM), are dark matter candidates introduced to solve the small-scale problems of the standard cold dark matter. In this paper, we investigate whether the physics of FDM, particularly the quantum pressure that leads to the suppression of structure formation on small scales, could leave significant imprints on the large-scale statistics of matter fluctuations. For this purpose, we utilize the Effective Field Theory of Large Scale Structures (EFT of LSS), wherein small-scale physics is integrated and represented on large scales by only a set of free parameters. These parameters can be determined by fitting them into the cosmological simulations. By fitting the EFT predictions to the simulation data, we determine the value of the speed of sound as a quantitative measure of how UV physics affects large-scale perturbation. We use the Gadget-2 code to study the evolution of 512 ^3 particles in a box with a side length 250 h ^−1 Mpc. We exploit the suppressed FDM initial power for the FDM universe and perform N -body simulation sufficient to produce accurate—enough for our purpose—results on large scales. In particular, we perform three FDM simulations with different masses and compare their sound speed with the standard cold dark matter (CDM) simulation. We found no difference between the FDM and CDM sound speeds beyond the confidence intervals. However, a consistently increasing trend can be seen in the sound speed for lower masses. This result suggests further investigations using higher-resolution simulations
Multiple Field Ultra Slow Roll Inflation: Primordial Black Holes From Straight Bulk And Distorted Boundary
We study a model of two-field ultra-slow-roll (USR) inflation bounded by a
curve in the field space. Curvature perturbations and non-Gaussianities can be
enhanced both during the USR phase and from the inhomogeneities at the
boundary. We employ the full non-linear formalism to calculate the
probability distribution function (PDF) for curvature perturbation
non-perturbatively and show that the non-linear effects can significantly
enhance the abundance of the primordial black holes (PBHs). For large curvature
perturbations, the PDF has a universal exponential tail, but for the
intermediate values, the PDF -- and, therefore, the abundance of the PBHs --
depend sensitively on the geometry of the boundary.Comment: 7 pages, 5 figure