SYMPHY 2019

Abstract: Transient objects, such as supernovae and gamma-ray bursts, represent the most energetic explosions in the Universe. These explosions are linked to end stages of massive stars. However, the specific properties of progenitor stars and the last stages of their stellar evolution, causing the diversity in these objects are not well understood. Study of the explosion ejecta interacting with their surrounding medium is a powerful way to trace back the last stages of evolution history of these progenitors. Another kind of explosive events are electromagnetic (EM) counterparts of gravitational wave (GW) events. While we have so far only one such event, i.e. GW 170817, multi-messenger observations of this event has provided plethora of information, mainly from the explosion ejecta interacting with immediate environments. In this talk, I will review the current understanding in supernovae, gamma-ray bursts and EM counterparts of GW events and discuss the open problems in this field, in view of current state-of-the-art and upcoming observing facilities. I will also talk towards some exotic transients of unknown origin like Fast Radio Bursts etc.

Abstract: What happens when two neutron stars collide? Are these really the sources of most of the gold, platinum, and other heavy elements in the universe? After decades of theoretical speculation, we finally found the answer last August. Advanced gravitational wave detectors - LIGO and Virgo - discovered the coalescence of two neutron stars 130 million light years away from Earth. At nearly the same time, Earth-orbiting satellites saw a flash of high energy radiation from the same direction. What followed was arguably the most frantic period of activity in modern astronomy: with over 3500 individuals from 950 institutes joining forces to pinpoint the source in the sky and uncover it's secrets. But as we celebrated this discovery, we also realised a major problem: the burst of X-rays and gamma-rays was very faint, and our global network of satellites is woefully inadequate to detect future such bursts. Enter Daksha: a proposed mission that will be an order of magnitude more sensitive than the current best satellites in the world. This project, led by IIT Bombay, will revolutionise our understanding of the deaths of stars and the creation of elements in the universe. The project has been rated highly by ISRO and selected for demonstrating a proof-of-concept. I will talk about this mission, and the opportunities for all of you to get involved in it.

Abstract: In this talk, I’ll present some results of tuning material properties through nanotexturing. To mimic various high-performance nanostructures present in nature, we use block copolymer based self-assembly for nanopattern generation. I’ll discuss the applications of block copolymer based nanopatterning scheme for improving the performance of solar cells, self-cleaning superhydrophobic, antifogging and super-transparent structures. Combining self-assembly of block copolymer thin films and plasma-based etching, we developed a new approach for texturing any surfaces over arbitrarily large areas. This process creates densely packed arrays of sub-wavelength size nano-cones, whose tapered profile grades the refractive index transition between air and substrate material. The gradual change in refractive index greatly reduces reflection at the air/substrate interface over a broad wavelength range. Also due to the narrow tip diameter (< 10nm), theses structures show robust superhydrophobic and antifogging property.

Nuclear matter under extreme conditions of temperature or net-baryon density is likely to undergo a transition from hadronic to a deconfined phase of quarks and gluons called Quark-gluon plasma. Such extreme states are believed to have existed in micro-second old universe and inside the core of neutron star. Worldwide, dedicated experimental programmes have been undertaken at various accelerator centres to create and study such states of matter by colliding highly energetic heavy ions. Prominent examples are RHIC-BNL and LHC-CERN. Details of the ongoing experiments, results and future programmes will be discussed.

Light generation and propagation in nanostructured media is a topic of significant implications. When the structure is periodic, or disordered over a periodic template, the transport obeys mesoscopic physics of electrons in conductors. Essentially, the transport is strongly modified by the self-interference of multiply scattered waves, which realizes exotic effects such as Anderson localization. In this talk, I shall first describe the general relevance of mesoscopic optics in a modern context. Thereafter, I shall summarise our recent work on Anderson localization in one-dimensional amplifying and hybrid-plasmonic media, and two-dimensional dielectric media.

Abstract: Alexei Kitaev has recently given a new interpretation to a zero-dimensional solvable model of interacting fermions, now known as Sachdve-Ye-Kitaev (SYK) model, connecting it to non-Fermi liquid metals, thermalization and many-body quantum chaos or information scrambling. The SYK non-Fermi liquid is characterized by an emergent low-energy time reparameterization symmetry, a finite zero-temperature residual entropy and a maximal Lyapunov exponent or scrambling rate with a universal value 2πkBT/ћ that only depends on temperature T. I will discuss a model, that can be realized in a graphene flake connected to leads, exhibiting a dynamical quantum phase transition between a SYK non-Fermi liquid and a slow scrambling Fermi liquid. I will also discuss non-equilibrium dynamics and thermalization after a quench across the non-Fermi liquid-Fermi liquid transition.

Abstract: Discovery of dark energy has changed our understanding of the future of our universe. In this talk I shall describe the story of our future.

Abstract:Can an atomically thin mechanical oscillator push, pull and change properties of another one, which is ten-thousand times heavier than it? In this talk, we will explore this question with a series of recent experiments we have performed with suspended graphene resonators, strongly coupled to a large area and heavy, Silicon Nitride resonator. In particular, we find that graphene amplifies motion of the heavier oscillator in excess of 40 dB. Thermo-mechanical squeezing of graphene’s motional state results in a detection sensitivity that can resolve a displacement down to 3.4 femto-meters integrated over a second. We also find the back-action force of graphene to be significant, changing inherent response of the large area oscillator and inducing a giant Duffing nonlinearity. The nonlinearity is manifested in the form of a phase coherent phononic-frequency comb, carrying unique signatures of the underlying physics of instability and multi-mode phonon lasing.

Abstract: The runaway success of the Standard Model of particle physics has largely been due to a succession of beautiful experiments carried out at colliding-beam machines, or colliders. The most important of them, the LHC at CERN, has been running since 2009 and it discovered the Higgs boson in 2012. However, the LHC now faces a midlife crisis, since the last seven years have been singularly barren of new discoveries. Particle physicists are, therefore, already planning for the next generation of colliders, of even higher energy, which may lead us to a deeper understanding of Nature than the Standard Model affords. This talk will carry out a broad survey of some of these plans and the issues involved.

Abstract: Phase transitions are ubiquitous in active and living matter and the physics of these phenomena is of fundamental interest. The control of phase transitions may serve as a unique probe: (i) in living systems, mechanisms encoding the control of such transitions may be used a window to understand evolutionary dynamics/constraints and (ii) in synthetic systems, they point to design principles to engineer novel phenomena.

After discussing this viewpoint briefly, I will present two mechanisms that lead to the phase separation of active agents (i) Flow-Induced Phase Separation (FIPS) in self-propelled particle populations, which we explore using a synthetic system of active particles and (ii) Motility-Induced Phase Separation (MIPS) a complementary mechanism to FIPS which I will discuss in the context of fruiting body formation in Myxococcus Xanthus, a soil bacterium.