Talks

This presentation will delve into the intricate dynamics of the Indian Summer Monsoon Rainfall (ISM), focusing on the crucial role of oceanic and land moisture sources. By synthesizing findings from recent studies, we will explore the complex interplay between atmospheric circulation, oceanic processes, and land-surface conditions that shape the variability of the ISMR. We will present evidence highlighting the dominant influence of moisture transported from the western Indian Ocean on the overall ISM rainfall. Additionally, we will discuss the significant contribution of moisture recycling within the Ganges basin to regional precipitation patterns. Our research has also revealed the importance of land-atmosphere interactions, particularly the role of vegetation cover and soil moisture, in modulating the monsoon system. We will demonstrate the role of human water management, such as irrigation, in shaping monsoon rainfall patterns. By understanding these intricate processes, we aim to improve our ability to predict the onset, intensity, and spatial distribution of the ISM, which has profound implications for water resource management, agriculture, and disaster risk reduction in South Asia.

Projected ensemble, formed by the collection of pure states obtained by partial measurement of a quantum many body system and labeled by the measurement outcome provides a means to define a distribution of states in the Hilbert space, thereby going beyond the limitations of density matrices that can describe the unlabeled states. We discuss this and some results in the context of a many body system where conserved charges have local support.
 

In this talk, the moist physical processes associated with extreme precipitation will be discussed and the lack of representation of moist dynamics in numerical model will be emphasized. It will be shown with specific example the current status of forecasting extreme by NWP models and also by data driven models. The talk will throw insights on the gaps that can be addressed for possible improvement of moist dynamics vis-a-vis the fidelity of models in capturing extreme precipitation

In the first part of my talk, I will discuss anomalous subdiffusive phases that appear in clean long-range fermionic lattice systems and their origin. I will then talk about how such a long-range lattice, when subjected to dephasing noise that acts at all lattice sites, shows an interesting crossover from super-diffusive to diffusive transport regime as one tunes the long-range hopping exponent.

In this plenary lecture, I will discuss various aspects of seasonal and decadal monsoon forecasting for the Indian monsoon. In the initial years, the seasonal forecasts for the Indian summer monsoon rainfall (ISMR) are based on statistical methods using predictors representing the monsoon teleconnections. In 2017, the India Meteorological Department (IMD) introduced the statistical ensemble forecasting system, which was used by IMD for operational forecasts. With the rapid advancements in coupled modelling strategies and tools, the seasonal forecasts for monsoon rainfall are now produced using coupled ocean-atmosphere models. In 2021, IMD introduced multi-model ensemble forecasts based on different dynamical models. These models have shown more skill compared to the current statistical models. However, the current seasonal forecast skill is still far below the potential predictability. The ways in which the seasonal forecasts can be further improved will be discussed. Since the monsoon precipitation exhibits significant multi-decadal variability, attempts are being made to predict the decadal variability of the monsoon precipitation. However, recent results suggest that the decadal prediction for south Asian monsoon region is currently not very skilful.

Spontaneous symmetry breaking underpins some of the most important phenomena in condensed matter and statistical physics. A description of direct transitions between symmetry breaking phases in terms of local order parameters is formulated when the symmetry breaking patterns were Landau-compatible i.e. when the unbroken symmetries of one phase is a subset of the other. About twenty years ago, Senthil et al [1] demonstrated that a direct transition between Landau-incompatible symmetry breaking phases was also possible in two-dimensional quantum magnets. Such 'deconfined quantum critical' (DQC) transitions are believed to be exotic and found in interacting quantum systems, often with anomalous symmetries (e.g.: constrained by Lieb-Schultz-Mattis theorems).

In this talk, based on recent work with N. Jones [2], I will demonstrate that such special conditions are unnecessary and Landau-incompatible transitions can be found in a well-known family of classical statistical mechanical models introduced by Jose, Kadanoff, Kirkpatrick and Nelson [3]. All smoking-gun DQC features such as charged defect melting and enhanced symmetries are present and readily understood. I will also show that a closely related family of models also exhibits another unusual critical phenomenon found in quantum systems- 'unnecessary criticality' where a stable critical surface exists within a single phase of matter analogous to the first-order line separating liquid and gases.

[1] SCIENCE, Vol 303, Issue 5663
[2] arXiv: 2404.19009
[3] Phys. Rev. B 16, 1217 (1977)
 

One of the first nontrivial examples of quantum matter to be understood at equilibrium was the behavior of a chain of two-state spins, or qubits, entangled by nearest-neighbor interactions. Hans Bethe’s solution of the ground state in 1931 eventually led to the concept of Yang-Baxter integrability, and the thermodynamics were fully understood in the 1970s. However, the dynamical properties of this spin chain at any nonzero temperature remained perplexing until some unexpected theoretical and experimental progress beginning around 2019. Atomic emulators and quantum computers are beginning to complement solid-state quantum magnetism experiments, and computer scientists, physicists, and mathematicians all have their own reasons to care about the dynamics of simple arrangements of quantum spins. The last part of the talk covers how dynamics of more complicated spin models in higher dimensions are being used to search for emergent gauge fields and other phenomena.

The long-range force between neutrinos is poorly constrained. In the late-time universe, a long-range force that is a few orders of magnitude stronger than gravity can induce Jeans perturbation instability in the non-relativistic cosmic neutrino background, drastically changing its large-scale behavior. In this talk, I will describe how the cosmic neutrino background evolves and forms nonlinear bound states in the presence of a long-range force. I will then discuss the impact of these neutrino bound states on the matter structures in the universe, and the constraints due to the absence of these signals.