Large scale structure of the universe

The majority of bright distant quasars $(z {}^{>}_{\sim} 1)$ may form in massive mergers appearing in compact galaxy groups in/and young clusters. The expected tests are (i) large correlation signal for medium-$z$ QSOs $(1 < z < 2)$ and (ii) direct search for quasar groups (QGs) indicating positions of distant pre-superclusters which later will evolve to the systems like the local Great Attractor or Shapley concentration. We discuss large QGs with more than ten members within regions $\le l_{LS} \sim 100-150 \, h^{-1} Mpc$, tracing the enhanced density regions at $z {}^{<}_{\sim} 2$. These early large scale structures (i) provide a natural way to bias the distribution of Abell clusters, and (ii) suggest that the spectrum of primordial density perturbations is nearly flat at scales encompassing both cluster and GAs, $l = \pi k^{-1} \in(10,100)h^{-1} Mpc: \Delta^{2}_{k} \sim k^{3}P(k) \sim k^{\gamma}, \gamma = 1^{+0.6}_{-0.4}$.

We investigate the process of reionisation in a model in which the dark matter is a warm elementary particle such as a sterile neutrino. We focus on models that are consistent with the dark matter decay interpretation of the recently detected line at 3.5 keV in the X-ray spectra of galaxies and clusters. In warm dark matter models the primordial spectrum of density perturbations has a cut-off on the scale of dwarf galaxies. Structure formation therefore begins later than in the standard cold dark matter (CDM) model and very few objects form below the cut-off mass scale. To calculate the number of ionising photons, we use the Durham semi-analytic model of galaxy formation, GALFORM. We find that even the most extreme 7 keV sterile neutrino we consider is able to reionise the Universe early enough to be compatible with the bounds on the epoch of reionisation from Planck. This, perhaps surprising, result arises from the rapid build-up of high redshift galaxies in the sterile neutrino models which is also reflected in a faster evolution of their far-UV luminosity function between 10 &gt; z &gt; 7 than in CDM. The dominant sources of ionising photons are systematically more massive in the sterile neutrino models than in CDM. As a consistency check on the models, we calculate the present-day luminosity function of satellites of Milky Way-like galaxies. When the satellites recently discovered in the DES survey are taken into account, strong constraints are placed on viable sterile neutrino models.

The redshifted 21‐cm line of distant neutral H atoms provides a probe of the cosmic “dark ages” and the epoch of reionization (“EOR”) which ended them, within the first billion years of cosmic time. The radio continuum produced by this redshifted line can be seen in absorption or emission against the cosmic microwave background (“CMB”) at meterwaves, yielding information about the thermal and ionization history of the universe and the primordial density perturbation spectrum that led to galaxy and large‐scale structure formation. Observing this 21‐cm background is a great challenge, as it is necessary to detect a diffuse signal at a brightness temperature that differs from that of the CMB at millikelvin levels and distinguish this from foreground continuum sources. A new generation of low‐frequency radio arrays is currently under development to search for this background. Accurate theoretical predictions of the spectrum and anisotropy of this background, necessary to guide and interpret future observations, are also quite challenging. Toward this end, it is necessary to model the inhomogeneous reionization of the intergalactic medium and determine the spin temperature of the 21‐cm transition and its variations in time and space as it decouples from the temperature of the CMB. In my talk, I summarized some of the theoretical progress in this area. Here, I will focus on just a few of the predictions for the 21‐cm background from the EOR, based on our newest, large‐scale simulations of patchy reionization. These simulations are the first with enough N‐body particles (from 5 to 29 billion) and radiative transfer rays to resolve the formation of and trace the ionizing radiation from each of the millions of dwarf galaxies believed responsible for reionization, down to 108 M⊙, in a cubic volume large enough (90 and 163 comoving Mpc on a side) to make meaningful statistical predictions of the fluctuating 21‐cm background.

The airborne Na lidar and Christmas Island MF radar were used to measure the spectra of gravity wave density and wind perturbations during ALOHA‐90 on the 25 March mission. Wave activity was especially strong near Christmas Island with measured wind variances between 1000 and almost 1400 (m/s)². The vertical and meridional wave number spectra of horizontal wind perturbations exhibited power law shapes with slopes of −3.17 and −2.22, respectively. The temporal frequency spectrum appeared to be influenced by strong Doppler effects and had a shallow slope near −1. The magnitudes of the spectra were 4.9 × 105 (m/s)²/(cyc/m) at the vertical wave number 2π/(4 km), 8.4 × 106 (m/s)²/(cyc/m) at the meridional wave number 2π/(200 km) and 7 × 105 (m/s)²/(cyc/m) at the temporal frequency 2π/(1 h).

We analytically compute the power spectrum of primordial curvature perturbations in Type III hilltop inflation models under the slow-roll approximation. The model parameters are constrained using current Cosmic Microwave Background (CMB) data. The curvature perturbations that exit the horizon at small scales show sufficiently large amplitudes to produce primordial black holes (PBHs). We then consider the quantum one-loop corrections in these models from both the self-interaction of the inflaton and its interaction with the waterfall field. We show the loop corrections in both cases for 60 e-folds of inflation are negligible, ensuring the tree-level results are reliable within the chosen parameter regime.

On the quasi-de sitter cosmological model of Starobinsky

Effects of features in the inflaton potential on the spectrum and bispectrum of primordial curvature perturbations

Primordial black holes (PBHs) are mainly characterized by their mass function, in which there may be some huge suppression for certain mass spans. If this is the case, the absence of these PBHs will form mass gaps. In this paper, we investigate the PBH mass function with the mass gap. First, to obtain a data-supported PBH mass function with the mass gap for subsolar masses PBHs, we fine-tune the coefficients of a model-independent power spectrum of primordial curvature perturbations. Then we take this unique PBH mass function into consideration and calculate the energy-density spectrum of the stochastic gravitational-wave background from PBH mergers. We find the location of its first peak almost has no relationship with the mass gap and is only determined by the probability distribution of frequencies at which PBH binaries merge. Apart from the first peak, there must be an accompanying smaller trough at a higher frequency resulting from the mass gap. Therefore, the detection of this smaller trough will provide more information about inflation and PBH formation.

The primordial black hole (PBH) is an effective candidate for dark matter. In this work, the PBH abundance $f$ is calculated in peak theory, with one or two perturbations in the inflaton potential. We construct an antisymmetric perturbation that can create a perfect plateau in the inflaton potential, leading inflation to the ultraslow-roll stage. During this stage, the power spectrum of primordial curvature perturbation is remarkably enhanced on small scales, generating abundant PBHs. The PBH abundance $f\ensuremath{\sim}0.1$ can be achieved in one or two typical mass windows at ${10}^{\ensuremath{-}17}\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$, ${10}^{\ensuremath{-}13}\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$, and $30\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$, without spoiling the nearly scale-invariant power spectrum on large scales. For comparison, $f$ is calculated in two approximate methods of peak theory (with different spectral moments) and also in the Press-Schechter theory. It is found that the Press-Schechter theory systematically underestimates $f$ by 2 or 3 orders of magnitude compared with peak theory.

We determine the slope of the power spectrum of the matter perturbations from the Tenerife observations of the cosmic background radiation temperature anisotropies. We compute the projected radiation anisotropy power spectrum measured by this experiment and study its dependence with respect to the slope of the temperature anisotropy spectrum on the sky. We show that Tenerife alone implies the upper bound on the spectral index of $m \le 3$. Stronger conclusions can not be reached due to the small data set. The method proposed can be applied to any small scale experiment. Sampling the same region of the skywith different window functions could probe the slope of the radiation anisotropy power spectrum at different scales and confirm the presence of Doppler peaks.

The cosmological observations of cosmic microwave background and large-scale structure indicate that our universe has a nearly scaling invariant power spectrum of the primordial perturbation. However, the exact origin for this primordial spectrum is still unclear. Here, we propose the Weyl scaling invariant $R^2+R^3$ gravity that gives rise to inflation that is responsible for the primordial perturbation in the early universe. We develop both analytic and numerical treatments on inflationary observables, and find this model gives a distinctive scalar potential that can support two different patterns of inflation. The first one is similar to that occurs in the pure $R^2$ model, but with a wide range of tensor-to-scalar ratio $r$ from $\mathcal O(10^{-4})$ to $\mathcal O(10^{-2})$. The other one is a new situation with not only slow-roll inflation but also a short stage of oscillation-induced accelerating expansion. Both patterns of inflation have viable parameter spaces that can be probed by future experiments on cosmic microwave background and primordial gravitational waves.

We consider cosmological models with a non-scale-invariant spectrum of primordial perturbations and assess whether they represent a viable alternative to the concordance {Lambda}CDM model. We find that in the framework of a model selection analysis, the WMAP and 2dF data do not provide any conclusive evidence in favor of one or the other kind of model. However, when a marginalization over the entire space of nuisance parameters is performed, models with a modified primordial spectrum and {Omega}{sub {Lambda}=}0 are strongly disfavored.

Inflationary cosmology and the scale-invariant spectrum

Supernatural inflation: inflation from supersymmetry with no (very) small parameters

Cosmic microwave background tests of inflation