5,180 research outputs found
Age determination of the HR8799 planetary system using asteroseismology
Discovery of the first planetary system by direct imaging around HR8799 has
made the age determination of the host star a very important task. This
determination is the key to derive accurate masses of the planets and to study
the dynamical stability of the system. The age of this star has been estimated
using different procedures. In this work we show that some of these procedures
have problems and large uncertainties, and the real age of this star is still
unknown, needing more observational constraints. Therefore, we have developed a
comprehensive modeling of HR8799, and taking advantage of its gamma
Doradus-type pulsations, we have estimated the age of the star using
asteroseismology. The accuracy in the age determination depends on the rotation
velocity of the star, and therefore an accurate value of the inclination angle
is required to solve the problem. Nevertheless, we find that the age estimate
for this star previously published in the literature ([30,160] Myr) is
unlikely, and a more accurate value might be closer to the Gyr. This
determination has deep implications on the value of the mass of the objects
orbiting HR8799. An age around 1 Gyr implies that these objects are
brown dwarfs.Comment: 5 pages, 3 figures, accepted in MNRAS Letter
Solution to the Landau-Zener problem via Susskind-Glogower operators
We show that, by means of a right-unitary transformation, the fully quantized
Landau-Zener Hamiltonian in the weak-coupling regime may be solved by using
known solutions from the standard Landau-Zener problem. In the strong-coupling
regime, where the rotating wave approximation is not valid, we show that the
quantized Landau-Zener Hamiltonian may be diagonalized in the atomic basis by
means of a unitary transformation; hence allowing numerical solutions for the
few photons regime via truncation.Comment: 6 pages, 5 figure
Connecting nth order generalised quantum Rabi models: Emergence of nonlinear spin-boson coupling via spin rotations
We establish an approximate equivalence between a generalised quantum Rabi
model and its nth order counterparts where spin-boson interactions are
nonlinear as they comprise a simultaneous exchange of bosonic excitations.
Although there exists no unitary transformation between these models, we
demonstrate their equivalence to a good approximation in a wide range of
parameters. This shows that nonlinear spin-boson couplings, i.e. nth order
quantum Rabi models, are accessible to quantum systems with only linear
coupling between boson and spin modes by simply adding spin rotations and after
an appropriate transformation. Furthermore, our result prompts novel
approximate analytical solutions to the dynamics of the quantum Rabi model in
the ultrastrong coupling regime improving previous approaches.Comment: 9 pages, 3 figures plus Supplemental Informatio
Propagation and perfect transmission in three-waveguide axially varying couplers
We study a class of three-waveguide axially varying structures whose dynamics
are described by the su(3) algebra. Their analytic propagator can be found
based on the corresponding Lie group generators. In particular, we show that
the field propagator corresponding to three-waveguide structures that have
arbitrarily varying coupling coefficients and identical refractive indices is
associated with the orbital angular momentum algebra. The conditions necessary
to achieve perfect transmission from the first to the last waveguide element
are obtained and particular cases are elucidated analytically.Comment: 5 pages, 4 figure
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