Exotic atoms at extremely high magnetic fields: the case of neutron star atmosphere

¹ INFN, Sezione di Pavia
² Dipartimento di Fisica, Università degli Studi di Pavia
³ Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Ferrara and INFN, Sezione di Ferrara
⁴ Anton Pannekoek Institute for Astronomy, University of Amsterdam
⁵ INFN - Laboratori Nazionali di Frascati
⁶ National Superconducting Cyclotron Laboratory, Michigan State University and Theoretical Division, Los Alamos National Laboratory
⁷ Dipartimento di Fisica, Università degli Studi Trento and INFN, Trento Institute for Fundamental Physics and Application

^* e-mail: andrea.fontana@pv.infn.it

Published online: 25 June 2018

Abstract

The presence of exotic states of matter in neutron stars (NSs) is currently an open issue in physics. The appearance of muons, kaons, hyperons, and other exotic particles in the inner regions of the NS, favoured by energetic considerations, is considered to be an effective mechanism to soften the equation of state (EoS). In the so-called two-families scenario, the softening of the EoS allows for NSs characterized by very small radii, which become unstable and convert into a quark stars (QSs). In the process of conversion of a NS into a QS material can be ablated by neutrinos from the surface of the star. Not only neutron-rich nuclei, but also more exotic material, such as hypernuclei or deconfined quarks, could be ejected into the atmosphere. In the NS atmosphere, atoms like H, He, and C should exist, and attempts to model the NS thermal emission taking into account their presence, with spectra modified by the extreme magnetic fields, have been done. However, exotic atoms, like muonic hydrogen (p μ⁻) or the so-called Sigmium (Σ⁺ e⁻), could also be present during the conversion process or in its immediate aftermath. At present, analytical expressions of the wave functions and eigenvalues for these atoms have been calculated only for H. In this work, we extend the existing solutions and parametrizations to the exotic atoms (p μ⁻) and (Σ⁺ e⁻), making some predictions on possible transitions. Their detection in the spectra of NS would provide experimental evidence for the existence of hyperons in the interior of these stars.