Talks

small RNAs are among the main drivers of epigenetic gene regulation. There are three main categories of small RNAs: microRNAs, piRNAs, and endogenous siRNAs. These various small RNA pathways are conserved across most eukaryotes. I will talk about the role of small RNAs in the inheritance of memory of stress using the nematode model, followed by our findings on the role of microRNAs in host-pathogen interaction using the SARS-CoV-2 model. We sequenced small RNAs from SARS-CoV-2-infected cells and identified a miRNA derived from a recently evolved region of the viral genome that targets the 3′UTR of interferon-stimulated genes and represses their expression, thus aiding in host immune evasion. Lastly, I will highlight our group’s new ventures to understand the role of small RNAs in host-parasite interaction using the eukaryotic parasite Toxoplasma as a model.

 The process of translation initiation from an mRNA uses a special tRNA called initiator tRNA (tRNAfMet or i-tRNA). The i-tRNA is aminoacylated with methionine and then formylated with N10-formyl-tetrahydrofolate (N10-fTHF). Both methionine and N10-fTHF are produced via one-carbon metabolism providing a metabolic regulation of mRNA translation. The fidelity of translation initiation by i-tRNA is attributed to the structural features found in its acceptor-, and anticodon-, stems. The extent of i-tRNA formylation regulates its participation exclusively at the step of initiation or also at the step of elongation. Further, the pioneering round of initiation by i-tRNA triggers the final stages of ribosome maturation. In our recent work, use of an anticonvulsant drug, lamotrigine, has provided important insights into the mechanism of the role of IF2 in the process of ribosome maturation.

The good books on GR agree on certain aspects of the theory that we could consider to be its “core” features. Beyond the core, however, we do not know exactly what GR should allow or not allow physically. For example, should we consider spacetimes with closed causal loops as part of physical GR or not? Are spacetimes with certain types of boundaries or singularities part of GR?  Most people expect that the answer to these sorts of questions will be answered by quantum gravity when we have it.  We can start to address them within different quantum gravity approaches even at their current partial state of their development. Within the framework of the path integral for quantum gravity and a Feynmanian heuristic for the recovery of the classical approximation, I will sketch out how answers may arise. I will use the example of causal set quantum gravity but I suggest that the ideas are applicable to other path integral approaches.

Pulsar timing arrays (PTAs) consist of a set of regularly monitored millisecond pulsars with extremely stable rotational periods that are used as precise cosmic clocks. The arrival time of pulses can be altered by the passage of gravitational waves (GWs) between them and the Earth, thus serving as a galaxy-wide GW detector. Evidence for low-frequency (~nHz) gravitational waves has recently been reported for the first time across multiple PTA collaborations, opening a new observational window into the Universe. I will discuss how pulsar observations are used to measure GWs, what we are currently learning by mapping the nanohertz GW sky, and what lies ahead following a first detection.

The AdS/CFT duality has been extremely useful in understanding quantum gravity. Tensor networks are a toy model of holography that have provided valuable lessons that have been imported to AdS/CFT. In particular, random tensor networks have a quantitative connection with fixed-area states in the gravitational path integral. This has allowed for a translation of various tensor network results to gravity that I will discuss, including an understanding of the Renyi entropy, entanglement negativity, entanglement wedges for bulk regions and resolving entropic paradoxes using wormholes.

 In this talk I'll explain how to take a well-defined flat-space limit of brane models of AdS coupled to a non-gravitating bath. In the dual BCFT this amounts to a triple-scaling limit where both the number of boundary degrees of freedom and the boundary coupling are taken to infinity while the BCFT boundary piecewise approaches a lightcone. The resulting construction offers a new approach to study the relation between the flat limit of AdS and Carrollian/Celestial CFT, as well as the potential to carry over ideas from AdS/CFT to flat space. I will discuss some implications for entanglement entropy in flat space, in particular the fact that two different notions of entanglement entropy arise on scri, depending on whether one traces out modes which have left through scri.