Tata Institute of Fundamental Research

About: Tata Institute of Fundamental Research is a education organization based out in Mumbai, Maharashtra, India. It is known for research contribution in the topics: Magnetization & Large Hadron Collider. The organization has 7786 authors who have published 21742 publications receiving 622368 citations. The organization is also known as: TIFR.

Estimating the Contribution of Dynamical Ejecta in the Kilonova Associated with GW170817

Abstract: The source of the gravitational-wave (GW) signal GW170817, very likely a binary neutron star merger, was also observed electromagnetically, providing the first multi-messenger observations of this type. The two-week-long electromagnetic (EM) counterpart had a signature indicative of an r-process-induced optical transient known as a kilonova. This Letter examines how the mass of the dynamical ejecta can be estimated without a direct electromagnetic observation of the kilonova, using GW measurements and a phenomenological model calibrated to numerical simulations of mergers with dynamical ejecta. Specifically, we apply the model to the binary masses inferred from the GW measurements, and use the resulting mass of the dynamical ejecta to estimate its contribution (without the effects of wind ejecta) to the corresponding kilonova light curves from various models. The distributions of dynamical ejecta mass range between = - - - M M ej 10 10  3 2 for various equations of state, assuming that the neutron stars are rotating slowly. In addition, we use our estimates of the dynamical ejecta mass and the neutron star merger rates inferred from GW170817 to constrain the contribution of events like this to the r-process element abundance in the Galaxy when ejecta mass from post-merger winds is neglected. We find that if 10% of the matter dynamically ejected from binary neutron star (BNS) mergers is converted to r-process elements, GW170817-like BNS mergers could fully account for the amount of r-process material observed in the Milky Way.

Size-induced structural phase transitions and hyperfine properties of microcrystalline Fe2O3

Abstract: Microcrystalline particles of Fe2O3 having different sizes (varying between 70 and 5 nm) have been synthesised using a novel three-component micro-emulsion technique. A succession of crystal-size-induced structural transitions was observed. While alpha -Fe2O3 was found to nucleate for a particle size above 30 nm, gamma -Fe2O3 was preferentially formed for a size below 30 nm, whereas amorphous Fe2O3 was formed at a particle size of 5 nm. These structural transformations have been related to the increase in the unit-cell volume that occurs as the particle size is decreased. The size dependence of the lattice parameter is shown to arise from a coupling of the surface energy to the dilatational lattice mode. A model Hamiltonian which incorporates this interaction and displays size-induced phase transitions is defined. The Mossbauer hyperfine field in the microcrystalline samples at 4.2 K was found to be substantially smaller than in the 'bulk'. The hyperfine parameters of the amorphous sample were found to be similar to those pertaining to samples prepared by conventional techniques such as melt quenching. A large anisotropy in the ionic vibrational amplitudes was detected in samples with particles smaller than about 10 nm.

Projective planes I

Abstract: Semiadditive rings are defined and their relationship with the projective planes is studied. Free semiadditive rings provide an analogue of the ring of integers and polynomials for the ternary rings. A structure theory for free semiadditive rings is developed. It is shown that each element of a large class of semiadditive rings is obtained from a quotient of a polynomial ring over integers by an additive subgroup, by twisting addition and multiplication. This class includes all planar ternary rings. These methods are being developed to study the well known conjectures that every finite projective plane with no proper subplane is isomorphic to a prime field plane and that the order of a finite projective plane is a power of a prime number. Applications to these problems will be discussed in part II.

Forced fluid dynamics from gravity

Abstract: We generalize the computations of [1] to generate long wavelength, asymptotically locally AdS5 solutions to the Einstein-dilaton system with a slowly varying boundary dilaton field and a weakly curved boundary metric. Upon demanding regularity , our solutions are dual, under the AdS/CFT correspondence, to arbitrary fluid flows in the boundary theory formulated on a weakly curved manifold with a prescribed slowly varying coupling constant. These solutions turn out to be parameterized by four-velocity and temperature fields that are constrained to obey the boundary covariant Navier Stokes equations with a dilaton dependent forcing term. We explicitly evaluate the stress tensor and Lagrangian as a function of the velocity, temperature, coupling constant and curvature fields, to second order in the derivative expansion and demonstrate the Weyl covariance of these expressions. We also construct the event horizon of the dual solutions to second order in the derivative expansion, and use the area form on this event horizon to construct an entropy current for the dual fluid. As a check of our constructions we expand the exactly known solutions for rotating black holes in global AdS5 in a boundary derivative expansion and find perfect agreement with all our results upto second order. We also find other simple solutions of the forced fluid mechanics equations and discuss their bulk interpretation. Our results may aid in determining a bulk dual to forced flows exhibiting steady state turbulence.