19,077 research outputs found
Accretion disk reversal and the spin-up/spin-down of accreting pulsars
We numerically investigate the hydrodynamics of accretion disk reversal and
relate our findings to the observed spin-rate changes in the accreting X-ray
pulsar GX~1+4. In this system, which accretes from a slow wind, the accretion
disk contains two dynamically distinct regions. In the inner part viscous
forces are dominant and disk evolution occurs on a viscous timescale. In the
outer part dynamical mixing of material with opposite angular momentum is more
important, and the externally imposed angular momentum reversal timescale
governs the flow. In this outer region the disk is split into concentric rings
of material with opposite senses of rotation that do not mix completely but
instead remain distinct, with a clear gap between them. We thus predict that
torque reversals resulting from accretion disk reversals will be accompanied by
minima in accretion luminosity.Comment: 13 pages, 7 figures, accepted for publication in Ap
PT-Symmetric Quantum Rabi Model
In this work, we explore the PT-symmetric quantum Rabi model (PTQRM), which
describes a PT-symmetric qubit coupled to a quantized light field. By employing
the adiabatic approximation (AA), we are able to solve this model analytically
in the parameter regime of interest and analyze various physical aspects. We
investigate the static and dynamic properties of the model, using both the AA
and numerical diagonalization. Our analysis reveals a multitude of exceptional
points (EPs) that are closely connected with the exactly solvable points in the
Hermitian counterpart of the model. Intriguingly, these EPs vanish and revive
depending on the light-matter coupling strength. Furthermore, we discuss the
time evolution of physical observables under the non-Hermitian Hamiltonian. Our
work extends the theory of PT-symmetry into the full quantum light-matter
interaction regime and provides insights that can be readily enlarged to a
broad class of quantum optical systems.Comment: 6+7 pages, 6+6 figure
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