Binary neutron star mergers with a crossover to quark mater: Comparing the QHC19 and QHC21 equations of state

Dame In previous work [1] it was shown that a crossover transition from hadronic to quark matter during the merger of neutron stars can lead to interesting observational consequences in the emergent gravitational radiation. In particular, the increased pressure in the crossover density region (2 − 5 times the nuclear saturation density) can lead to an extended duration of high frequency ( ∼ 2 − 3 kHz) gravitational wave emission during the post merger epoch. However, that study was based upon the QHC19 formulation of the crossover equation of state. More recently, the updated QHC21 version has been developed based upon the NICER observations suggesting larger radii for neutron stars. In this talk we will discuss new simulations of neutron-star mergers based upon the QHC21 EoS. In comparison with the previous results we find that the long duration post-merger gravitational-wave emission is even more pronounced in the QHC21 EoS. Prospects for the detection of the GW emission in the spectral density function via current and future GW observatories is discussed. [1] A. Kedia,1 H. I. Kim, I.-S. Suh, and G. J. Mathews, Phys. Rev. D 106, 103027 (2022). Strong electromagnetic and gravitational field physics: From laboratories to early Universe / 106 Electromagnetic memory in arbitrary curved spacetimes IIT BOMBAY 2 IIT Bombay The gravitational memory effect and its electromagnetic (EM) analog are potential probes in the strong gravity regime. In the literature, this effect is derived for static observers at asymptotic infinity. While this is a physically consistent approach, it restricts the spacetime geometries for which one can obtain the EM memory effect. To circumvent this, we evaluate the EM memory effect for comoving observers (defined by the 4-velocity u_{μ}) in arbitrary curved spacetimes. Using the covariant approach, we split Maxwell’s equations into two parts—projected parallel to the 4-velocity u_{μ} and into the 3-space orthogonal to u_{μ}. Further splitting the equations into 1 + 1 + 2-form, we obtain the acceleration vector of the comoving observer located in a two-dimensional (2D) surface orthogonal to the direction of propagation of the EM waves. We refer to this expression as the master equation for the EM memory in an arbitrary curved spacetime. The master equation corresponding to the acceleration of the comoving observer in the 2D surface provides a physical understanding of the contribution to the EM memory. For instance, the leading order contribution only requires information about the total energy density of the EM field, while the subleading contributions contain information about the spacetime geometry and the other components of the energy-momentum tensor of the EM field. To our knowledge, this is the first time a transparent and easily applicable final expression for electromagnetic memory has been derived for a general curved spacetime. We then obtain EM memory for specific spacetime geometries and demonstrate the advantages of our approach. Spectral and temporal properties of accretion flows and jets around compact objects and the