Using Shapefinders, which are ratios of Minkowski functionals, we study the morphology of neutral hydrogen (HI) density fields, simulated using semi-numerical technique (inside-out), at various stages of reionization. Accompanying the Shapefinders, we also employ the 'largest cluster statistic' (LCS), originally proposed in Klypin & Shandarin (1993), to study the percolation in both neutral and ionized hydrogen. We find that the largest ionized region is percolating below the neutral fraction x HI 0.728 (or equivalently z 9). The study of Shapefinders reveals that the largest ionized region starts to become highly filamentary with non-trivial topology near the percolation transition. During the percolation transition, the first two Shapefinders -'thickness' (T ) and 'breadth' (B) -of the largest ionized region do not vary much, while the third Shapefinder -'length' (L) -abruptly increases. Consequently, the largest ionized region tends to be highly filamentary and topologically quite complex. The product of the first two Shapefinders, T ×B, provides a measure of the 'cross-section' of a filament-like ionized region. We find that, near percolation, the value of T × B for the largest ionized region remains stable at ∼ 7 Mpc 2 (in comoving scale) while its length increases with time. Interestingly all large ionized regions have similar cross-sections. However, their length shows a power-law dependence on their volume, L ∝ V 0.72 , at the onset of percolation.

The phantom brane has several important distinctive features: (i) Its equation of state is phantomlike, but there is no future 'big rip' singularity, (ii) the effective cosmological constant on the brane is dynamically screened, because of which the expansion rate is smaller than that in ΛCDM at high redshifts. In this paper, we constrain the Phantom braneworld using distance measures such as Type Ia supernovae (SNeIa), Baryon Acoustic Oscillations (BAO), and the compressed Cosmic Microwave Background (CMB) data. We find that the simplest braneworld models provide a good fit to the data. For instance, BAO +SNeIa data can be accommodated by the braneworld for a large region in parameter space 0 ≤ Ω ℓ < ∼ 0.3 at 1σ. The Hubble parameter can be as high as H0 < ∼ 78 km s −1 Mpc −1 , and the effective equation of state at present can show phantom-like behaviour with w0 < ∼ − 1.2 at 1σ. We note a correlation between H0 and w0, with higher values of H0 leading to a lower, and more phantom-like, value of w0. Inclusion of CMB data provides tighter constraints Ω ℓ < ∼ 0.1. (Here Ω ℓ encodes the ratio of the five and four dimensional Planck mass.) The Hubble parameter in this case is more tightly constrained to H0 < ∼ 71 km s −1 Mpc −1 , and the effective equation of state to w0 < ∼ − 1.1. Interestingly, we find that the universe is allowed be closed or open, with −0.5 < ∼ Ωκ < ∼ 0.5, even on including the compressed CMB data. There appears to be some tension in the low and high z BAO data which may either be resolved by future data, or act as a pointer to interesting new cosmology.

Abstract. We explore the possibility of emergent cosmology using the effective potential formalism. We discover new models of emergent cosmology which satisfy the constraints posed by the cosmic microwave background (CMB). We demonstrate that, within the framework of modified gravity, the emergent scenario can arise in a universe which is spatially open/closed. By contrast, in general relativity (GR) emergent cosmology arises from a spatially closed pasteternal Einstein Static Universe (ESU). In GR the ESU is unstable, which creates fine tuning problems for emergent cosmology. However, modified gravity models including Braneworld models, Loop Quantum Cosmology (LQC) and Asymptotically Free Gravity result in a stable ESU. Consequently, in these models emergent cosmology arises from a larger class of initial conditions including those in which the universe eternally oscillates about the ESU fixed point. We demonstrate that such an oscillating universe is necessarily accompanied by graviton production. For a large region in parameter space graviton production is enhanced through a parametric resonance, casting serious doubts as to whether this emergent scenario can be past-eternal.

Identifying multiply imaged quasars is challenging owing to their low density in the sky and the limited angular resolution of wide-field surveys. We show that multiply imaged quasars can be identified using unresolved light curves, without assuming a light-curve template or any prior information. After describing our method, we show, using simulations, that it can attain high precision and recall when we consider high-quality data with negligible noise well below the variability of the light curves. As the noise level increases to that of the Zwicky Transient Facility telescope, we find that precision can remain close to 100% while recall drops to ∼60%. We also consider some examples from Time Delay Challenge 1 and demonstrate that the time delays can be accurately recovered from the joint light-curve data in realistic observational scenarios. We further demonstrate our method by applying it to publicly available COSMOGRAIL data of the observed lensed quasar SDSS J1226−0006. We identify the system as a lensed quasar based on the unresolved light curve and estimate a time delay in good agreement with the one measured by COSMOGRAIL using the individual image light curves. The technique shows great potential to identify lensed quasars in wide-field imaging surveys, especially the soon-to-be-commissioned Vera Rubin Observatory.

Minkowski functionals and Shapefinders shed light on the connectedness of large-scale structure by determining its topology and morphology. We use a sophisticated code, SURFGEN2, to measure the Minkowski functionals and Shapefinders of individual clusters by modelling cluster surfaces using the Marching Cube 33 triangulation algorithm. In this paper, we study the morphology of simulated neutral hydrogen (HI) density fields using Shapefinders at various stages of reionization from the excursion set approach. Accompanying the Shapefinders, we also employ the 'largest cluster statistic' (LCS) to understand the percolation process. Percolation curves demonstrate that the non-Gaussianity in the HI field increases as reionization progresses. The large clusters in both the HI overdense and underdense excursion sets possess similar values of "thickness" (T ), as well as "breadth" (B), but their third Shapefinder -"length" (L) -becomes almost proportional to their volume. The large clusters in both HI overdense and underdense segments are overwhelmingly filamentary. The 'cross-section' of a filamentary cluster can be estimated using the product of the first two Shapefinders, T × B. Hence the cross sections of the large clusters at the onset of percolation do not vary much with volume and their sizes only differ in terms of their lengths. This feature appears more vividly in HI overdense regions than in underdense regions and is more pronounced at lower redshifts which correspond to an advanced stage of reionization.