24 research outputs found
Vector dark matter, inflation and non-minimal couplings with gravity
We propose a cosmological dark matter production mechanism in the form of a
longitudinal massive vector boson. We build upon the work of Graham et.al.
including non-minimal couplings of the massive vector with gravity, developing
a well motivated set-up from an effective field theory perspective. We
carefully track the dynamics of vector field in passing from inflation to
radiation dominated universe to show that the late time abundance of
longitudinal modes -- excited initially by the quantum fluctuations during
inflation -- can provide the observed dark matter abundance for sufficiently
weak non-minimal coupling and wide range of vector masses . The final abundance of dark
matter depends on two parameter, the vector mass and its non-minimal coupling
with gravity. We discuss experimental venues to probe this framework, including
the production of a stochastic gravitational wave background. The latter is
especially interesting, as the same mechanism that generates dark matter can
potentially lead to the production of gravitational waves in the LISA frequency
band, through the second-order effects of large dark matter iso-curvature
perturbations at small scales. We take a first step in this direction,
identifying the potential information that gravitational wave experiments can
provide on the parameter space of dark matter within this scenario.Comment: 25 pages plus appendices, 9 figures. Links to codes are provided in
the tex
Consistency conditions and primordial black holes in single field inflation
We discuss new consistency relations for single field models of inflation
capable of generating primordial black holes (PBH), and their observational
implications for CMB -space distortions. These inflationary models include
a short period of non-attractor evolution: the scale-dependent profile of
curvature perturbation is characterized by a pronounced dip, followed by a
rapid growth leading to a peak responsible for PBH formation. We investigate
the squeezed and the collapsed limits of three and four point functions of
curvature perturbation around the dip, showing that they satisfy consistency
relations connecting their values to the total amplification of the curvature
spectrum, and to the duration of the non-attractor era. Moreover, the
corresponding non-Gaussian parameters are scale-dependent in proximity of the
dip, with features that again depend on the amplification of the spectrum. For
typical PBH scenarios requiring an order enhancement of the
spectrum from large towards small scales, we generally find values and
in a range of scales that can be probed by CMB -space distortions. Using
these consistency relations, we carefully analyze how the scale-dependence of
non-Gaussian parameters leads to characteristic features in and correlators, providing distinctive
probes of inflationary PBH scenarios that can be tested using well-understood
CMB physics.Comment: 27 Pages + Appendices, 15 Figure
Inflation and Primordial Black Holes
We review conceptual aspects of inflationary scenarios able to produce
primordial black holes, by amplifying the size of curvature fluctuations to the
level required for triggering black hole formation. We identify general
mechanisms to do so, both for single and multiple field inflation. In single
field inflation, the spectrum of curvature fluctuations is enhanced by
pronounced gradients of background quantities controlling the cosmological
dynamics, which can induce brief phases of non--slow-roll inflationary
evolution. In multiple field inflation, the amplification occurs through
appropriate couplings with additional sectors, characterized by tachyonic
instabilities that enhance the size of their fluctuations. As representative
examples, we consider axion inflation, and two-field models of inflation with
rapid turns in field space. We develop our discussion in a pedagogical manner,
by including some of the most relevant calculations, and by guiding the reader
through the existing theoretical literature, emphasizing general themes common
to several models.Comment: 58 Pages, 19 Figures + Appendices, this version: the discussion on
the threshold is clarified with a footnote, an extensive list of references
added, some typos are correcte
New constraints on axion-gauge field dynamics during inflation from and BICEP/Keck data sets
We present new constraints on spectator axion- gauge field
interactions during inflation using the latest (PR4) and BICEP/Keck
2018 data releases. This model can source tensor perturbations from amplified
gauge field fluctuations, driven by an axion rolling for a few e-folds during
inflation. The gravitational waves sourced in this way have a strongly
scale-dependent (and chiral) spectrum, with potentially visible contributions
to large/intermediate scale -modes of the CMB. We first derive theoretical
bounds on the model imposing validity of the perturbative regime and negligible
backreaction of the gauge field on the background dynamics. Then, we determine
bounds from current CMB observations, adopting a frequentist profile likelihood
approach. We study the behaviour of constraints for typical choices of the
model's parameters, analyzing the impact of different dataset combinations. We
find that observational bounds are competitive with theoretical ones and
together they exclude a significant portion of the model's parameter space. We
argue that the parameter space still remains large and interesting for future
CMB experiments targeting large/intermediate scales -modes.Comment: 26 pages + appendix, 11 Figures. Accepted for publication in JCAP.
Updated reference