Speakers

Invited opening talk: Current problems of ΛCDM on small scales: open star clusters and the absence of halo dynamical friction

Abstract: There are two aspects to the ongoing cosmological paradigm shift: one the one had side one can readily show that dark matter does not exist using tenvts based on Chandrasekhar dynamical friction and other tests. What does not exist cannot be found and that is why dark matter has not been found. On the other hand side, one can test a different gravitational framework for consistency with data and predictions of new phenomena hitherto not known. This has been done using Milgromian gravitation (MOND) with the greatest of success. One such prediction is that the leading tail of an open star cluster needs to have more stars in it than its trailing tail. This has been found to be the case for the nearest open cluster, the Hyades. The newtonian prediction of equal numbers is ruled out by more than 6 sigma confidence. Thus, the observational data compellingly inform us that cold, fuzzy or warm dark matter does not exist, and that MOND describes the observed systems stunningly well.

Title:  Modifying the standard ΛCDM: Non-minimal coupling between the dark matter and k-essence scalar field

Abstract: The ΛCDM model stands out as the most successful framework in describing a multitude of phenomena in the universe at the largest scale. Precise alignment with observations from the cosmic microwave background and supernovae solidifies its credibility. However, as we delve into measuring fundamental constants, such as the Hubble constant, using these observations, a noteworthy discrepancy in values surfaces, prompting an exploration beyond the concordance model of cosmology. Despite its success, ΛCDM is not exempt from inherent challenges involving fine-tuning and cosmological coincidence. To address these issues, one avenue of exploration involves investigating non-gravitational interactions between dark sectors. In this talk, I will delve into the study of non-gravitational interaction between dark matter and a scalar field based on the action principle.

Title:  Nuances of coasting cosmologies

Abstract: Beginning with the fundamentals of FRW cosmologies, we present salient features of coasting cosmological models. Various  formulations of coasting models, including the classic Milne model, are reviewed. The absence of  cosmological problems in the eternal coasting model' is explained in detail. Some of these  problems are not solvable in the presently popular ΛCDM model, even with the widely speculated cosmic inflation'.  The much publicised  `accelerated expansion of the present universe' is argued to be arising from a  model-dependent analysis of SNe data. A model-independent analysis of the same SNe Ia data, which ascribes substantial probability to the deceleration parameter q0 = 0  is discussed. The recent observations of early bright galaxies with JWST requires that galaxy formation has taken place much earlier than expected in the ΛCDM model. Some such objects at reshifts z=10.4^{+0.4}{-0.5} and z=12.4^{+0.1}{-0.3} appear to be  over a million solar masses  and might have built-up their masses in only t < 300— 400$ Myr after the Big Bang. This is quite  unexpected as per  the current understanding of galaxy formation.  On the other hand, in the eternal coasting model, even a universe at redshift z = 12 has ample time (~1070 Myrs) for galaxy formation, which suggests that in the early universe too, data support the eternal coasting model, when compared to the ΛCDM model.

Invited talk:  From stellar systems to the CMB: MOG across 15+ orders of magnitude

Abstract: MOG, John Moffat's modified theory of gravity, has its roots in Einstein's attempt to explore a nonsymmetric theory as a means to unify gravitation with classical electromagnetism. Moffat chose a different route: his NGT, nonsymmetric gravitational theory, introduced an additional antisymmetric contribution to gravitation itself. NGT ran into difficulties, but the concept prevailed: Today, Moffat's STVG (Scalar-Tensor-Vector Gravity), also known by the acronym MOG, is a classical Lagrangian theory of gravitation that extends general relativity with a vector and a scalar field. The result is stronger gravity augmented with a repulsive Yukawa-type force that cancels out the non-Newtonian part at shorter ranges, with a field strength and range that are mass scale dependent, unlike the well-known MOND paradigm which is acceleration scale dependent. MOG works well on all scales: It predicts Newtonian behavior on the scale of solar systems or stellar clusters, accurately predicts galaxy rotation curves, and provides cosmological predictions consistent with the Lambda-CDM model. Challenges include finding more robust solutions of the theory's complex field equations, and obtaining reliable post-Newtonian predictions for precision solar system tests.