Abstract
Future observations of continuous gravitational waves from single neutron stars, apart from their monumental astrophysical significance, could also shed light on fundamental physics and exotic particle states. One such avenue is based on the fact that magnetic fields cause deformations of a neutron star, which results in a magnetic-field-induced quadrupole ellipticity. If the magnetic and rotation axes are different, this quadrupole ellipticity may generate continuous gravitational waves which may last decades, and may be observable in current or future detectors. Light, milli-magnetic monopoles, if they exist, could be pair-produced non-perturbatively in the extreme magnetic fields of neutron stars, such as magnetars. This non-perturbative production furnishes a new, direct dissipative mechanism for the neutron star magnetic fields. Through their consequent effect on the magnetic-field-induced quadrupole ellipticity, they may then potentially leave imprints in the early stage continuous gravitational wave emissions. We speculate on this possibility in the present study, by considering some of the relevant physics and taking a very simplified toy model of a magnetar as the prototypical system. Preliminary indications are that new-born millisecond magnetars could be promising candidates to look for such imprints. Deviations from conventional evolution, and comparatively abrupt features in the early stage gravitational waveforms, distinct from other astrophysical contributions, could be distinguishable signatures for these exotic monopole states.
Highlights
Recent observation of gravitational waves (GWs) by the LIGO-VIRGO collaboration [1,2] has ushered in a new era of multimessenger astronomy
II we briefly review the relevant, well-known theoretical underpinnings behind the generation of continuous gravitational waves, from single neutron stars, and outline how magnetic fields may generically lead to mass quadrupole moments
Exotic particle states beyond the Standard Model have the potential to leave their imprints on these waveforms
Summary
Recent observation of gravitational waves (GWs) by the LIGO-VIRGO collaboration [1,2] has ushered in a new era of multimessenger astronomy. Similar bounds have been placed on light milli-electrically charged particles [55], for which the relevant pair-production and astrophysical considerations are very different from MMMs. If MMMs exist, they may be nonperturbatively pair produced [56,57], via Schwinger pair production, in the extreme magnetic fields of a neutron star, such as a magnetar [58,59]. The modified magnetic field evolution in turn may affect the time evolution of the quadrupole ellipticity, assuming the concerned neutron star crustal strains are below the breaking limit [60,61] This opens up an avenue for probing these exotic states by their imprints on the gravitational waves emitted. There, we highlight some of the shortcomings of the study, along with a few future directions
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