Harish-Chandra 研究学院

Abstract We investigate axially symmetric accretion of low-angular-momentum hydrodynamic matter onto a rotating black hole. The gravitational field under consideration is assumed to be described by the pseudo-Newtonian Kerr potential proposed by Artemova et al. (ApJ 461:565, https://doi.org/10.1086/177084 , 1996). A relativistic equation of state that incorporates information about different species is used in this work. Our aim is to construct and solve the hydrodynamical conservation equations governing such a flow and to obtain the corresponding stationary integral solutions. We find that, depending on the values of the initial boundary conditions, the accretion flow may exhibit multitransonic behaviour and a standing shock may form. It is observed that the spin of the black hole influences the transonic properties of the accretion flow. In addition, the composition of the infalling matter determines the thermodynamic characteristics of the flow. In this work, we investigate in detail the interplay between spin and composition in shaping the dynamics of accretion flows and the astrophysics of shock formation.

We show how the 2-Higgs Doublet Model (2HDM) Type-I can explain some excesses recently seen at the Large Hadron Collider (LHC) in γγ and τ+τ− final states in turn matching Large Electron Positron (LEP) data in bb¯ signatures, all anomalies residing around 95 GeV. The explanation to such anomalous data is found in the aforementioned scenario when in inverted mass hierarchy, in two configurations: i) when the lightest CP-even Higgs state is alone capable of reproducing the excesses; ii) when a combination of such a state and the CP-odd Higgs boson is able to do so. To test further this scenario, we present some Benchmark Points (BPs) of it amenable to phenomenological investigation.

We consider the qubit-qutrit model of self-contained quantum refrigerator and observe the quantum Mpemba effect in its cooling. In this system, the qutrit acts as the refrigerator while the qubit is to be cooled. The entire system is coupled to three bosonic heat baths, due to which the dynamics of the system is governed by a Gorini-Kossakowski-Sudarshan-Lindblad master equation. We investigate the Liouvillian that generates the dynamics of the system and find that it has a block diagonal form. The dynamics of each element of the system's density matrix can be determined by solving the dynamical equation of the corresponding block that contains it. We find that the steady state belongs to the block containing only the diagonal elements in the energy basis. We numerically solve for the steady state and investigate the steady-state cooling over a significant region of the parameter space. Moreover, we demonstrate the quantum Mpemba effect in the refrigerator: a Mpemba state obtained by applying a unitary on the equilibrium state of the system reaches the steady state faster than the equilibrium state, despite the Mpemba state being initially farther away from the steady state. The Mpemba state thus leads to an acceleration in cooling of the cold qubit. We also find that both local and global unitaries on the qubit-qutrit system can generate the Mpemba state. Finally, we study the effect of the system-bath couplings on the Mpemba effect.

It is a specific type of quantum correlated state that achieves optimal precision in parameterestimation under unitary encoding. We consider the potential experimental limitation on probe entanglement, and find a relation between achievable precision and initial probe entanglement, in both bipartite and multipartite scenarios. For two-qubit probes, we analytically derive an exact relationship between the entanglement-constrained optimal quantum Fisher information and the limited initial entanglement, measured via both generalized geometric measure and entanglement entropy. We demonstrate that this fundamental relationship persists across the same range of the entanglement measures even when higher-dimensional bipartite probes are considered. Furthermore, we identify the specific states that realize maximum precision in these scenarios. Additionally, by considering the geometric measure of entanglement, we extend our approach to multiqubit probes. We find that in every case, the optimal quantum Fisher information exhibits a universal behavior:a steep increase in the low-entanglement regime, followed by a gradual and nearly-saturated improvement as the probe entanglement approaches values close to those required for achieving the Heisenberg limit.

We investigate localization transitions in interacting Bose-Einstein condensates (BECs) confined in tilted optical lattices, focusing on both the continuum limit accessed via shallow lattice depths and the tight-binding limit realized in the deep lattice regime. Utilizing the Gross-Pitaevskii equation (GPE) and the many-body Bose-Hubbard model, we analyze the scaling behavior of localization indicators, such as the root mean square width and fidelity susceptibility, as a function of the applied tilt. Our results reveal clear signatures of a localization-delocalization transition driven by the linear potential, with scaling properties that characterize criticality even in the presence of interactions within the GPE description. Despite the single-mode nature of the condensate wavefunction, we demonstrate that it can effectively probe quantum criticality. Building on this, we propose the use of interacting BECs in tilted lattices as a platform for quantum critical sensing, where the condensate wavefunction serves both as a sensitive probe of localization and a practical resource for quantum-enhanced metrology. This approach opens new avenues for precision gradient sensing based on localization phenomena in bosonic systems.