### Conveners

#### Cosmography with Gravitational Lensing: Block 1

- Claudio Grillo (University of Milan)
- Mimoza Hafizi ()

### Description

Gravitational lensing has tremendously contributed to our understanding of the Universe in the past thirty years. Progress in this field has been extremely rapid, thanks to major advances in both observation and theory. Several recent studies have shown that gravitational lensing can provide accurate and precise estimates, independent from and complementary to those of other probes, of the Hubble constant and of the geometry of the Universe. The wealth of data from current and future surveys will transform gravitational lensing into a fundamental alternative tool for measuring some of the most relevant cosmological quantities. Analyses will no longer be statistically limited and they might point to exciting new physics. A concerted effort between observers and theorists will be needed to control systematics and reap the rewards from the large gravitational lensing datasets.

The Hubble constant ($H_{0}$) is one of the most important parameters in

cosmology. Its value directly sets the age, the size, and the critical

density of the Universe. Despite the success of the flat $\Lambda$CDM model, the

derived Hubble constant from Planck data under the assumption of a flat

LCDM model has 4.4-$\sigma$ tension with the direct measurements. If this

tension is not due...

Our cosmological discourse is currently dominated by the discrepancy between early and late-time cosmological probes. This tension, if confirmed, can only be resolved by yet unknown physics or by our lack of accounting for systematic uncertainties in the methods. Given the drastic implications of the former, the latter has been of great interest lately. In the context of time-delay strong...

For a flat $\Lambda$CDM (standard) cosmology, a small sample of gravitationally lensed quasars with measured time delays has recently provided a value of the Hubble constant $H_0$ in agreement with data from SNe, but in tension with the Planck flat $\Lambda$CDM result. Identifying biases in some methods may solve this tension, avoiding hasty rejection of the standard cosmological model. As a...

In this talk, I will present my work on cosmography with strong-lensing in galaxy-clusters observed with the Hubble Space Telescope. I will detail some particular aspects of the analysis, in preparation for future surveys like Euclid and CSST.

Strongly lensed supernovae (SNe) are emerging as a new probe of cosmology and SN progenitors. The time delays between the multiple images of a lensed SN can be used to determine the Hubble constant (H0) that sets the expansion rate of the Universe. An independent determination of H0 is important to ascertain the possible need of new physics beyond the standard cosmological model, given the...

Galaxy cluster strong lensing has numerous applications in cosmology. Thanks to the wealth of multi-wavelength observations of clusters using state-of-the-art observatories, such as the Hubble Space Telescope and the Very Large Telescope, this field is providing significant contributions to the understanding of our Universe. One of the main points that are still not fully understood is the...

In the last years, thanks to the increased precision of the measurements of the Hubble constant, H0, some tension has emerged between measurements from local and early-Universe probes. Strong gravitational (SL) lenses with measured time delays between the multiple images are yielding a competitive approach to estimate H0, that is independent and complementary to other techniques. Such studies...

The Advanced LIGO and Advanced Virgo detectors are now observing large numbers of gravitational-wave signals from compact binary coalescences, with 50 entries in the latest transient catalogue GWTC-2. The next detector upgrades will continue bringing rapidly growing event rates and redshift range, so our chances become better both to detect rare astrophysical effects on these novel cosmic...